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Discussion Starter · #1 ·
This is a revised compilation of a monstrous thread from this board on the subject of C4 build levels. While lots of good information resides there, it is a tough read. To facilitate better use of the captured information, and to more easily respond to quite a few requests, we are rearranging the info to create summaries and brief discussions organized by sub-topic. Plus, we've incorporated some info from other threads on the C4 forum to try and keep this as the authoritative thread.
The posters are quite experienced builders who have learned their C4 tricks the hard way: they have tried them out. This is an international group with GregAust (GA) from Australia, Mario Van Wiechen (MVW) from Canada and 89Coupe (89C) Winsoreight (W<IMG SRC="/phpBB/images/smiles/icon_cool.gif"> TimR (TR) TurboJoe (TJ) and several others, all from the US. 89C pulled apart a Performance Automatics Super Stock C4 and let us know what he found.
Clearly the C4 is a very stout unit that our panel has made live over hundreds of passes, behind ultra-high power BBFs (even a high power 2.3 turbo) deep into the 8 second ET range. So buckle up, here is a mountain of info on the C4.

Section Title
1 Introduction
2 Tranny Identification
3 Build levels
4 Input shafts
5 Case differences, C5 details
6 Oiling mods, line pressure
7 Valve bodies, shift modifications
8 Servos and the 2-3 flare
9 Servo modifications
10 Planetaries
11 Sealing rings
12 Bands
13 Clutch types
14 Adding clutches
15 4, 5 and 7 clutch drums
16 Drilling drums, aligning steels
17 Do you need to weld forward drums?
18 How to weld forward drums
19 Stator support bushing
20 End play
21 Clutch clearances
22 Roller thrust conversion

1 - Introduction
Most of the builders describe their trannys as nothing too tricky. Several use stock H or R servos, many do no welding on the forward drum, some even use run of the mill clutches. Most seem to agree though that starting with the later, 26 spline input shaft factory unit (26 on the converter end and 24 on the forward clutch housing end) a good hard shift engagement, an extra clutch in each pack, careful attention to clutch pack clearances and use of the best parts available will result in a VERY stout little tranny. Many more details and opinions to come, but first, what have you got?

2 - Identifying the tranny
Lots of confusion exists here, but there is the early C4, with its .788" 24 spline input shaft. This tranny is inappropriate for all but the mild small block. The pan fill case, introduced in ’65 is considered stronger than the case fill. The later C4 introduced in ’70 with its .839" 26 spline input shaft is considered the heavy duty unit and is the choice of the builders on this site. This basic HD C4 was again redesigned in 1982 with a convertor clutch (that locks up), a deeper bell housing, a unique valve body, a number of other different internals and named the C5. The C5’s superior oiling circuit includes a number of small differences from the C4 making it the preferred setup of the three as you can replace the C5 convertor, bell and valve body with standard C4 units and have a super duty C4. All three versions can be either case-fill or pan fill.
Of course there are a couple bastard versions you may run across. The ‘65-’66 “green dot” shift pattern valve body versions are in a ton of Mustangs. A good upgrade is to retrofit a ‘67-’69 valve body to those units. A rarer one is the ’70 26 spline version which was a one-year deal. Both ends of the input shaft have 26 splines which was changed to 26 on the converter end and 24 on the forward clutch housing end for all subsequent years.
So the various versions-
C4 - 64-83
· Case fill 24x24 spline {C4 to C9}
· Case fill 26x26 spline {D0}
· Case fill 26x24 spline {D1 to D9, & E1SP)
· Pan fill 24x24 spline {C5 to C9}
· Pan fill 26x26 spline {D0}
· Pan fill 26x24 spline {D1 to D9}
· C5 - 82-86
· Case fill {E2AP only)
· Pan fill {E2TP only}
Bellhousings of course come in several versions. Case fills come with bells that bolt to the pump while pan fills come with bells that bolt to the case. C5 bells are deeper than either of the C4 versions. Most of the time, the case fills use the 157 tooth flywheel and the pan fills use the 164 tooth, but there are exceptions. The best tip I've seen to ID them is to measure the depth. If the depth is 5 7/8" it is a small bell 157t, if it is 6 1/4 is regular bell 164t and if it is 7" it is a c5 bell 164t.

3 - Build level suggestions
What would I want to do to a C4 to get it to propel my dedicated 2500lb bracket car with a 250 HP carbureted motor to the lowest E.T.s? 89C - 250HP in 2500# car only requires a good working V-8 C-4 which would work great stock or with a shift kit. No other mods needed. RC – How to squeeze some ET by modding his C4? 89C - A full manual valve body is going to bump up the line pressure considerably, which takes power from the engine to do. No need to spend a lot of money on a trans that will already hold up to 250HP. The governor assembly doesn't add significant weight to the reciprocating assembly and doesn't use any power. About the only way you will reduce parasitic drag in the C-4 is to completely convert it to a full roller, which is expensive for the small ET gain and not needed unless you plan on having 600+HP.
JJ - On a mild, say 350HP, or under application would a good rebuild using 5 Red Eagle or similar clutches in the forward pack and 4 in the high/reverse pack be OK?
W8 – Yes, for a mild motor that would hold up fine.

4 - Input shafts
Early transmissions used a 24-spline input shaft that is smaller and weaker than the 26. The early 24 spline input shafts have a diameter of .788" and the 26 spline shafts are .839". The 24 spline shaft trannies can be upgraded to a 26 by swapping the stator support and the hi/reverse and the forward drum. There's a how to at GA - It is said that the factory 26 spline input shaft will take up to 600 hp. TR - Use of an after market hardened input shaft is only needed for the very high powered cars and heavy trucks. Up to 450 HP is fine for the stock one, above that it would be good insurance. 89C - Very few factory C-4 input shafts are hardened and seems that only the original C-4s that had the "R" servos had them (all mine came from trucks with yoke that bolts on tail shaft and 4WD C-4s with transfer cases bolted on where tail shaft goes.) If you can scratch the input shaft, then it isn't hardened. I have tweaked the splines and shafts of the non hardend inputs but not the hardened ones. (Once I found out they do exist from the factory.)

5 - Case differences, C5 details
GA - There is no real problem with the early cases, it all depends on the final use. The early case has the bell housing retained by the same bolts that hold the front pump in where the later ones have a larger flange on the case to allow the bell housing to be fitted separately and this is considered to be stronger. JS - The bells that bolt to the case were a heavy duty version. GH - I run the C5 case. Those cases have larger circuits through them and hence more volume. W8 - The C5 case is better because of its oil circuit improvements but is as strong as the older cases, but I have never heard of any problems with the strength of the main case. GA - The way to pick a c5 from the outside is the 2.5” deep pan, the fine threaded front band adjuster, the large 1/4" thread on the cooler fittings and the E2 casting code.
Inside, the #9 thrust washer has the normal 2 locate tangs but also has 2 cutouts to line up with a 9/64" lube hole drilled through the case to meet up with the cooler return passage. The cooler return passage is 13/64" which is larger than a c4’s 5/32". The rear roller clutch spring retainer has the wafer springs clipped to it instead of being loose like a c4. The front pump has no check ball in the stator support cooler passage and this passage is drilled to 1/4" vs. the c4’s 3/16" and the C4 has a check ball fitted. The sun gear where it fits into the front and rear planetaries has 4 lube holes in each end at .094" while the c4 has 3 holes each end at .040". The forward hub has 5 clutches. It has a different bevel plate in the bottom of the clutch pack which is .310"overall with a .110" step versus the c4 bevel plate’s .265" with a .125"step. The hi/rev hub has 4 .078" clutches and all .090" steels with a dished cushion plate on top. Both the fwd + hi/rev clutches have thin .140" pressure plates. The hi/rev hub has the circlip grooved machined higher also as has been mentioned before that the c5 hub has the capacity for more clutches. The top edge of the groove is down 1.020" where a c4 is down 1.082". This trans is a case fill type and the input shaft has a recess about half way along it and it seems to be hardened.

6 – C4 Oiling mods, line pressure
GA - Remove the check ball from the stator support for increased cooler flow. MVW - More oil volume is good, deeper pan with filter extension of some kind.
89C - How are you modifying the C-4 cases? I haven't modified a C-4 case and haven't had any problems other than spinning the #9 thrust washer.
GH - My transmission runs about 215-217 psi line pressure. (MVW's C4 runs 200) I go in and put a small radius around the openings for feed from the oil pump as they are razor sharp from machining and this seems to help. 1FP - The easiest way to increase the pressure is to install a manual valve body or you can increase the relief valve spring tension and that should help too. Remember of course if it was leaking before at lower pressures it will begin to leak even more with added pressure. DR - I have had several C4s that have spun the tangs off of the #9 thrust washer (the one behind the one way clutch that seats to the case) I noticed the C5 case has an extra lube hole in the thrust washer and of course a matching hole in the case. The return lube circuit from the cooler is the feed hole for this circuit and is larger. I have added this circuit to the C4 cases and have eliminated problems with knocking the tangs off the thrust washer. GA – To improve oiling to the #9 thrust washer, drill through the back of the case into the rear oil cooler return line passage to pick up direct lubrication for that thrust washer and drill the washer to match. Drill this passage to 3/16" to open it up slightly from 5/32". The hole in the case for the cooler fitting is quite a restriction so opening it up should improve flow slightly. GA - One of the C4's I rebuilt had this mod done already. I didn't realize that was the same as a c5. Jay – If you do the #9 roller bearing upgrade mentioned below in section 22, this oil circuit mod is probably not needed. You might drill the existing feed hole to .125" diameter. Then, because the cage assembly is slightly closer to the case with the #9 kit , grind an oil channel about .020-.030 deep to help get the extra lube past the cage. This will help feed the #9 bearing, sprag and help the cooler flow circuit. Good for off road and abnormal street driving in warm climates. W8 - I prefer the heavy duty C4 case (bell to case-dipstick in pan). I believe that they are stronger overall. I have just been modifying my C4 cases for better flow. GA - I have noticed that some of the earlier 26 spline type front planetaries don’t have a lube hole in the planetary case that the later ones have. This is in the area of the front thrust washer drilled through to the center of the case. It would be easy to drill and may be worth drilling if it's not there already.

7 - Valve bodies, shift modifications
PH - I was checking out and saw a lot of Transgo shift kits some for around $15 and others around $80. What’s the difference? J6 - Some of the shift kits are just to correct valve body problems, others are performance driven to give you firmer shifts. Ideally just run a manual pattern aftermarket valve body, it is the way to go if you can, but you will have to shift every gear. Also Transgo has a manual conversion kit, that makes your VB a full manual, but for the money I'd get a reverse pattern full manual valve body.
GA - A good valve body helps the trans live. I have used the Transgo stage 2 kits. There are some mods in the article posted that also work well. I use those mods. RC – There are three different versions you can do in Greg’s valve body piece on the Burly4x4 site. I’d do those instead of buying B&M or TransGo kits. J67 - In doing these mods, are you changing the shift points at all? GA - No, it just changes the firmness of the shifts. TR - I only use good manual valve bodies and trans brakes for my modified trans builds. I think there is no comparison in the shift quality of a manual valve body versus a shift kit or stock builds. Mine all shift hard and firm with no slip. MVW – I use valve body gaskets for better sealing and that has helped several different bodies seal better. Use them even with full manual valve bodies. 89C – PA said they use gaskets in the valve body separator plate too for the full manual reverse pattern bodies but not in the trans brake valve bodies with billet transfer plate. I match the passages to the separator plate or make them slightly larger just in case. J6 - Friend of mine got a PA Reverse Manual and it was cut out of a chunk of aluminum, but his was a custom order with engine braking in 2nd and 3rd. Just got my in and it is the standard unit, with engine braking in 1st only. I was surprised that it wasn’t cut out of a chunk of aluminum, but is a modified original valve body. MVW - Got my trans brake valve body this week. The billet bottom half of the VB is an interesting piece. Yesterday my curiosity got the best of me and I took it apart. Not too many valves working anymore, the separator plate has only 1/3 of the holes of a stocker and the billet plate had minimal fluid passages. The separator plate does have some very tiny holes in it but the metering holes seem to be quite big. Most of their valves are still in but most seem locked into place.
Pressure regulator spring is very stiff. I am guessing line pressure is going to be 220-250. Valve that sits beside pressure regulator is missing and the hole blocked at the outside of the VB. Man does the tranny shift nice now. Instant shifts that push me back into the seat every time. Even on a test drive to check stuff the 1-2 was a head bobber at 2500 RPM.

8 – Servo choices and the 2-3 flare
There are a few different opinions on the subject, although there is a bit of convergence on the issue around stock R and H servos. GA – I like the R servos. MVW - I like the R servos but have used H's with good success. I spoke to Epping and they use stock servos with the letter machined off. They said the servo makes no difference in their trannies. J6 - I get my H servos from the local trans parts house. Cost me a whopping $15. GH – I use the H model servo because it gives very solid shifts. It is the largest factory unit, highly desirable and plentiful. W8 - I use an H servo with the outer seal removed and 3 flats ground on the surface and I plug the hole in the case. (More detail on this mod down below under servo mod.) 89C - I never modified any servos, never needed to. An "H" or "R" servo with a Kevlar rigid or flex band has always been more than enough for the 9 second big blocks and small blocks my trannies have been behind. The weakness isn't in the apply area. It's in the release area and until very recently where somebody here posted the apply and release areas of different letter servos, I saw why the "H" allowed a small flare up from 2-3 shift and the "R" didn't. The "R" has a smaller release area that fills quicker thus allowing fluid to pass to the direct clutches quicker to prevent the flare up. "R" servo has a smaller apply area but that is insignificant seeing that properly setup the 1-2 shift and 1st/2nd gears don't have problems. It's the 2-3 shift that causes the wear on the direct clutches and making 3rd shift harder and quicker is what makes the C-4 live. 89C - The 2-3 flare can be from one or all in combination of: A loose intermediate band adjustment, loose direct drum clutch pack clearances, a servo with a large release area, low line pressure, a slow reacting valve in the VB. An "R" servo with the smallest release area, 1 full turn out from snug on the band adjustment, and .006-.010" clearance per clutch in the direct drum will basically eliminate the flare-up. Higher pressure also helps greatly. If the clutches are glazed at all, that will cause slippage when the clutches are trying to apply too.
'A' 2.825" apply 3.785" release
'B' 2.710" apply 3.785" release
‘C’ 3.120” apply 3.785" release
'H' 2.960" apply 3.785" release
'K' 2.375" apply 3.355" release
'N' 2.560" apply 3.785" release
'O' 2.460” apply 3.785” release
'R' 2.820" apply 3.265" release
'W' 2.375" apply 3.300" release
'Z' 2.500" apply 3.335" release

9 - Servo modification discussion
MVW – I do not like the servo mod where the small sealing ring is taken out. The only C-4's I see that take 2nd gear band out have this mod and I believe it is hard on high gear also. My thought is if the small sealing ring is removed on the servo piston and some oil transfer slots cut the pressures on both sides of the piston will be the same. The problem with that is if the valve body does the same thing as a stock one when the tranny goes to high gear the apply pressure on the servo piston is not released. This means the only thing moving the piston up and disengaging the band is the spring. I have never seen this tech tip come with the advice to use a heavier spring. Using an H servo for an example there is a 4.4 square inch area difference between the two seal areas. If line pressure was 150 PSI, with both seals in use there is 660 lbs of force pushing the piston up the bore. The band disengages quickly and the pressure gets to the direct clutch quicker and with less lag. There is an 8 sec Fairmont running here that has the servo mod done and the band lasts about 10 runs. While I only run high 10's I have never killed a band. I believe Dynamic has a valve body that releases the 2nd gear pressure when high gear comes on. I spoke to them at Epping and they use stock servos with the letter machined off and he said the servo makes no difference in their trannies.
This is my theory and I am sticking to it. Poke enough holes in it and I will try the mod late in the year just to prove my point only with an A servo so I do not waste my good servos. W8 - I think it depends on the valve body too. I do the mod only on the C4's I build with manual valve bodies. I have been using TCI or ATI valve bodies and all of them want you to do this mod. I have not had a broken band yet. I Have a C4 in a friends 67 mustang with a 429 running 10's and in 4 seasons he has not broken a band. Same with the others I have done. I have seen some of the stock bands come apart though, with runaway line pressure. I am using Kevlar bands and they seem to hold up well. TR - I have used the servo mod on many of my builds with only one that ever gave me any trouble and I think that the cover is flexing on that one so I plan to build a girdle for it and see if that will help.

10 - Planetaries
MV - I use the stock planetaries and they seem to hold up fine. QM - I've run a stock planet for almost 10 years with over 700 HP N/A and a bottle to boot. GA - I rebuild the front planetaries using parts from the rear planets as per the article in the archives. 89C – My PS Super Comp has the 6 gear planetary set. SC - I destroyed a planetary last fall. It was a stock unit. I presume that it was weak to start with as nobody has any issues with these at the 600-700 hp range. PA recommends their 6 gear set above 700 hp. I went with a rollerized 3 gear set. That said, when the planetary broke, it wreaked havoc inside the tranny with all the shrapnel pieces floating around. GA - I went with the PA 6 gear power planet based on their success.

11 - Teflon vs. cast sealing rings
One of the builders likes the teflon sealing rings, but that doesn't seem too universal. GA - I personally use the steel sealing rings but some guys do prefer the Teflon. 89C - The teflon rings won't wear out as quickly as the iron rings and will seal better but if you are still using the governor it really won't matter. Either will be fine. By the way, the teflon rings are narrower than the actual grooves on the governor. TR - I have used only cast seal rings like stock with very good luck, but feel that there is some merit to the Teflon ones and some day will try them myself. MVW – I have used both with good success. Mine has both and my brother’s tranny has all teflon. Controlling endplay seems more important that ring type. GH - I get the Teflon seals for forward and direct from H&R Transmissions in Indy.

12 – Bands
GA – I use Kevlar bands. W8 - I use Kevlar bands. GH - Use Kevlar bands. JS - My thoughts on killing bands is the use of the "Flex-Band" not the servos or the servo mods mentioned above. I have never killed a band when using or re-using the rigid front bands. 89C - I have never had or seen a flex band break but I went with the rigid band for peace of mind. PA said they prefer the intermediate Kevlar lined flex band instead of the "rigid" intermediate Kevlar lined band because it can wrap around the drum easier therefore having better and more surface contact with drum. The rigid band needs time to seat in and wear to the contours of the drum before they become better than the flex band but most racers don't have extra time to wear the rigid bands in before the race so they aren't used. In a street car, they become better as they get more wear for increased contact surface

13 - Clutch manufacturers
89C - I like Kolene steels and Blue clutches for the harder shifts and less slippage. GH - I run Alto race clutches and Kolene steels. 89C - PA said the red Alto and Blue Raybestos clutches are just personal preferences and that's why they offer both but they both work as good as the other so you can pay more for the blue clutches or less for the red clutches and have the same performance either way. TR – The need for high dollar clutches and bands is debatable. I have used new rebuilder kits for most of my builds with no problems mostly Raybestos, Borg-Warner and others. GA -My parts guy is using Borg Warners with up to 800 hp and they work fine. I'm using them in the forward clutch on my B.B C4 but using the Alto's in the direct.

14 - Adding clutches
GA - I use 5 forward + 5 hi/rev clutches. W8 - I am now using 5 clutches in the hi/rev drum using the lower plate from a forward drum and the smooth red clutches. I use 6 clutches in the forward drum by having the snap ring groove widened higher. Performance also has a kit to do something similar. TR - I use as many as 11 clutches in my C4 transmissions and I do this by using thinned stock steels. I take large batches of them to a machine shop that can surface grind them with a magnetic chuck surface grinder and have them take them down to .061-.065 and then use smooth surface forward clutches that are .061 thick in both clutch packs, final clearance is set at .020-.025 in both packs and this is done by machining the stock pressure plate down to a thickness that gives this much clearance. Don't worry about it being too thin as there are stock ones that are listed at only .141 thick. You can make them pretty thin without trouble. I usually don't need to take them down that far, usually about .160 or so, but be sure to check yours before you machine it unless you have lots of spares. Gregaust and others here have suggested that you can also machine just the edge of the pressure plate to create a lip for the snap ring to set in and I think this would work well. Just watch out for clearances of the assemblies when this is done. And a word of caution I do not believe it is a good idea to machine the snap ring land higher in the drum because you may raise the pressure plate out of the locate lands in the outer perimeter of the drum and this will allow it to turn in the drum and not drive the drum as it is supposed to along with the steels in the pack. GA - On the subject of the 6 clutch fwd hub you need to be careful with the inner hub length for the clutches to engage. I haven't actually measured but more than 5 plates with stock thickness steels would go close to running off the edge of the inner teeth for the clutches. Here is a link to a place here in Australia that has a long skirt hub to overcome this prob. 89C - I used to machine down some high/direct pistons (exactly the thickness of 1 friction and one steel removed from piston) to fit 1 extra clutch. I then used the curved pressure plate from forward clutch turned upside down (has thin outer edge which a snap ring barely fits into when used as top pressure plate) and used as a pressure plate to add 1 more clutch for 6 total with ease. I also used that curved plate on the forward clutch pack as a pressure plate for 6 clutches there too. PA says if you use the thinner forward smooth clutches in high drum, it will slip more before lockup and will not shift as hard or quick. The grooves in the direct clutches are like tire tread and give the fluid a place to go when the clutches are applied. The smooth clutches work good in forward drum because they are applied from the start and thus don't need the quick fluid evacuating grooves. However, when 3rd is engaged, the clutches need to get rid of the fluid between the clutches as quick as possible. The grooved clutches are there for that reason which is why I don’t use forward clutches in the high drum. RC - Maybe, maybe not TR has done this successfully and the Alto power pack uses 6 smooth Red Eagles. Additionally, all the Red Eagles are smooth irrespective of which drum they are for.
Ford Papa - If you have an extra 4 clutch drum take the stepped pressure plate from the bottom of the forward clutch hub and use it as the top pressure plate in the direct clutch like Windsor Eight does since the step is only approx .125". It’s thinner so you can get 5 clutches in the standard 4clutch drum. Other times I have used two steels together as a pressure plate to get clearance. It just depends on the frictions, steels and snap rings you have. It works and is easy.

15 – 4, 5 and 7 clutch drums
Forward clutch drums
GA – The C5 forward hub has 5 clutches. It has a different bevel plate in the bottom of the clutch pack which is .310"overall with a .110" step. Papa - The five clutch drums are hard to find, but I do have one that came out of a c-4 with a yoke on the tranny, likely a truck application. MVW - I always looked harder for pan fill cores which tend to be out of heavier vehicles so maybe I take 5 clutch drums a bit for granted. Comparison pictures at
Direct clutch drums (The direct clutch is the same as the high/reverse clutch. It is the drum towards the front pump.)
GA – The C5 direct drum has the capacity for more clutches because the circlip groove is machined higher. The top edge of the groove is down 1.020" giving .065” more room than a C4 direct. MVW - I never really thought about it, I just have some 5 clutch drums and I use them. I have one I bought from PA, I needed a drum and clutches so I bought a direct drum kit from them. Came with 5 blue clutches in it. When I rebuilt it I grabbed a stack of 5 Alto Red Eagle smooth clutches from a kit I had. I also grabbed 5 kolene steels and my pressure plate which is a thinner one (possibly a .140” C5 pressure plate.) I put it together using the snap ring that had come out. Clearance was .050 with a .065 ring so I put an .080 ring in and I was done. GA - We have lots of pan fill c4's here but they still only come with 4 direct clutches...Very interesting. You learn something new every day. 89C - I don't use the deeper C-5 clutch drum. If I had, then I could fit 7 in the direct with no problem but 6 is enough using the regular waffle clutches and standard thickness steels. RC – By the way, Alto sells 6 disk “power pack” kits for the reverse/high drum. The kit is part number 025755 and contains the frictions, steels, a thin pressure plate and the selective snap rings.
7 clutch direct drums
89C - That Pro Trans drum I put in Gotcubes’ C4 is a 7 clutch aluminum drum that uses the larger AOD steels and AOD Red Alto frictions. This drum is much lighter than stock and shows very high quality machining. The AOD cluch direct drum has a larger O.D. and must use an intermediate flex band because of the larger diameter. The rigid intermediate band won't work. The drum was $550 but well worth it. Turbojoe turned me on to Pro Trans and their tech is great. They make the aluminum drum for JPT and they do other parts that the big name C4 builders and shops sell. Thanks Joe for telling me about Pro Trans.

16 - Drilling the drums
W8 - I drill holes in the outside of the hi/rev drum to stop too much fluid from building up. GA – I drill both the hi/rev and low drum. The holes in the direct drum are evenly spaced, 4 holes at 5/16" in the outside circumference to help evacuate the fluid. Those holes are in the center of where the clutches ride. Measure down the inside of the drum to the approximate center of where the clutches run and mark the outside. It works out pretty much the center. TJ – Align the missing teeth on the steels and put the gaps over where you drill the holes to make oil galleys that allow the fluid to exit the drum as the piston applies. QM - I always lined them up thinking it was to exhaust fluid.

17 - Do you need to weld the forward drum jellybean holes? Some do weld them up while others don’t. Clearly there is disagreement over whether this is necessary.
W8 - I weld up the 3 peanut holes in the forward drum. GA- The weak link is the forward drum jelly bean holes. I weld them. TR- I think it is a good idea to weld or braze the kidney shaped holes in the forward clutch hub to prevent them from breaking out as this is a known weak spot. If nothing else, welding them up tightens the splines up on the input shaft, eliminating any wobble at all.
MVW – I’ve never welded my forward drums. I have never broken one but having said that it will let go on the first pass of the year. (Note: the drum lasted fine after 140 passes.) 89C - I just disassembled my Performance Automatics (PA) Super Comp C-4 and the kidney holes in the forward drum are still there: no welding of any kind on the forward drum. PA says welding or brazing in the kidney shaped holes on the forward drum is only necessary if planning on making over 1000HP and I myself have never stripped out the splines or broken a forward drum even with 1.32 60ft times and I wasn't even close to making 1000HP. TR - I am surprised at the info you shared about PA saying that the kidney holes don't need to be welded I always thought that was a weak point. 89C - There are too many people running 8s with unwelded drums to think the drums are a weak link. A high mileage drum with a lot of wear in the spline area would cause a problem but not a closely inspected drum with nice tight fitting input shaft. I have seen worn out forward drums that I wouldn't use and I carefully inspect the ones I do use along with "feeling" the spline clearance using the input shaft. MVW – The last parts tranny I pulled apart had the drum broken though along with being the most burnt up C-4 I had ever seen.

18 - Forward drum welding how-to
Some weld, while some of the builders braze the holes shut. Each seems to have advantages. The "King of the Cs" article in the Sept 88 Hot Rod says, "the C4 clutch drums tend to crack through their center jelly-bean holes, so they should be MIG welded shut. Welding heat also tends to reduce the i.d. of the center hole in the drum, yielding the added benefit of a tighter fitting and more positively retained input shaft." At least one of the builders, maybe Dynamic brazes theirs. W8-I mig weld them slowly, a little at a time cooling the drum down after every little bit so it doesn't get overheated. Just make sure you drill the lube hole through It is the hole in one of the peanut holes and you will cover it when you weld it up. Just drill it through the same size as the original hole or slightly larger. I also drill a corresponding hole in the thrust washer and chamfer it with a large drill bit. Alternatively, you can make a groove under the thrust washer to one of the holes already in the thrust washer. GA - I mig weld the jelly bean holes in the forward hub. Here's a little tip to help. Make sure to soak the hub in some solvent and get it nice and clean before welding. Soaking in a solvent removes all traces of oil, which is required for a good weld. On the oil hole, I like to redrill the hole then die grind a small groove under the thrust washer to link up with the original hole in the thrust washer.

19 - Stator support bushing
JS - Since the early 80's, I have always used the C6 pump bushing in the C4/C5 pumps with no problems. 89C - I compared the C-6 pump to converter bearing to the C-4 bearing and the C-6 is nearly twice as wide and I guess I will use them from now on instead of the C-4 bushings. Better wear and stability.

20 - Endplay
GH - Make sure you set the clutch clearances to factory clearances. MVW - Keep tranny endplay to a minimum, especially with iron sealing rings but helps all around. JS - I think a killer of the C4 and other transmissions is not paying attention to the clutch pack and endplay clearances. Most home builders don't take time to acquire a selection of selective snap rings and selective thrust washer combos since they might build one or two C4's before getting frustrated and buying one from a company. Get the selective thrust washers and snap rings at any transmission parts house. I use Recon or Transtar. I still have my old Peterson Publishing Auto Repair book that was released back in the 70's and reference it quite often for specs on endplay and clutch packs. W8 - Clearances are very important and that is where most people fail. I also found an H gauge to be a very handy tool for checking the end clearances. It will help keep you out of trouble. I build transmissions everyday but just for everyday vehicles.

21 - Clutch clearances
89C - One of the most important things is to allow .005" clearance for each friction clutch for minimum piston movement and quicker engagement. 5 frictions should have .025" and 7 should have .035" like in my reverse/high packs which I have been calling "direct clutches" for obvious reasons. However PA told me .010" clearance per clutch in the drums will causes the least "drag" and will ET better but wear quicker and require more regular freshening. Said if running .005" clearance per clutch, you will lose a tenth or two depending on how many clutches are being used. MVW - The tight clearance on the direct clutch causes drag in first gear in particular. Remember that in first gear the clutches in the direct drum are spinning the opposite way that the steels are. Tighter clearances mean more friction and drag. Clearances become a guessing game between ET and clutch life.

22 - Roller thrust bearing conversion
GregAust posted a thread on the roller conversion
This process eliminates the thrust washers in four positions in the C4 by replacing the thrust washers with Chevy Turbo Hydro 350 bearings. Since the thrust bearings are .140” thick and the thrust bushings .070”, you need to do some simple machine work to the tranny internals. Essentially you cut recesses in some of the hard parts to maintain the same overall length of the gear train. This set of instructions, shows the elimination of four of the stock thrusts, which is sort of stage 1. A few have machined the front of the forward drum to put a smaller thrust bearing in the #3 position. You can also add a different sized thrust bearing in the very important #9 position with a kit Jay from Broader Performance developed and they are at That is a bit more complex setup and we salute Jay for coming up with a solution. Do that and you are sort of at stage 2 rollerizing the C4.
Keeping in mind that the gear train is thrust rearward under acceleration, the key locations are those under load. Some go so far as to replace ALL the thrusts including those not really under acceleration load, such as the #1 and #10 which would qualify as stage 3 I think. So, choose your plan of attack. Thrust bushing/bearing diagram at
GA – The roller bearings will obviously free up a bit of power but a bigger advantage is there will be less contamination of the oil from the wearing of the stock thrusts. I build mine with roller thrusts as per TimR's info. The #9 roller bearing mod also solves the problem that 89coupe mentioned a while ago. He was shearing the tangs from the stock #9 thrust washers when on the gas.
TR - Interesting note in the April 2002 issue of Muscle Mustangs and Fast Fords. In the PA C4 build up article they show at least 2 more places to put bearings in the trans other than the places I do. It looks like they are all the TH350 bearings, so I will have to give it a try. 89C – The PA Super Comp has roller thrust bearings all over. Hell, even the front pump has a roller needle bearing set behind the front pump instead of a selective plastic thrust washer. My front pump has the roller thrust on #1 and therefore I have no way to control the endplay. I guess you're supposed to know exactly what the #1 thrust washer thickness is for optimum endplay before you have the front pump machined for the roller. That way you can get it dead on by just measuring #1 roller thrust thickness and cutting the receiver groove for the roller accordingly. Then endplay will not change and will always be right as long as the other regular thrust washers are not excessively wearing.
W8 – Hey, 89C you can shim the Torrington bearings. They make different thickness flat steel shims. GA - You could try a bearing place for a shim for #1 if you need it. Try Torrington, part# TRA-3446. This is a .030 steel shim that is the same diameters as the T350 bearing. I am able to buy here .020" + .030" shims to go behind the #1 plastic thrust to get correct clearances. You could use them if needed to. With careful machining hopefully you'd get by without any shims. 89C - I wonder why PA chose to use a roller there. I have never seen a #1 plastic thrust washer even slightly worn in any way. #1 isn't under stress and just takes up clearance for proper endplay to keep the assembly from walking, under power everything is thrust rearward.
TR - has the TH350 roller bearings on the web site with part number 47692 for $5.67. I noticed on the JPT C4 they machine the back of the rear planet for the bearing instead of the ring gear. 89C - My PA C4 has the ring gear machined for the roller bearing instead of the backside of the rear planetary. It also has a roller bearing behind the ring gear against the reverse band drum. GA - Check out the mighty mouse article and the light-o-matic article above for the rear #9 roller. It looks like they machine the inner race for the roller clutch to make room for the bearing. Machining the trans case isn’t necessary. There's also the roller for behind the park gear in the #10 spot. The bearing from a c6 fwd hub is the correct size for the #10. Photo at RC – Jay at Broader Performance as the #9 kit for $55 and it includes a machined inner roller clutch race, a thrust bearing and the required spacers. GA - The roller bearing from a C6 is in the #3 position and sits in the backside of the fwd hub and the front planetaries run against. All c6's have them. It is used in the C4 #10 position where the park gear is up against the rear of the case. It is also the one some are using in the C4 #3 spot over the jelly bean holes too. The bearing measures 2.105" x 1.365" x.140". RC - It is part of a C6 thrust bearing kit on bulkpart with the number 26669A. That kit includes the other C6 thrust bearing (almost the same size as the TH350 bearing, I used it in the front of the rear planetary) and the kit goes for $10. You might do better buying the C6 #3 thrusts solo at a local trans parts place.

23 - C4 websites and links
exploded view

comprehensive parts list

GregAust's rollerizing thread

illustrated C4 build and the GregAust valve body instructions Thanks to CWToyota, well done!

Online tranny parts at great prices including Turbo 350 front pump bearings (thrust bearings) C6 thrust bearings, pump bushings ATSG C4/5 manual, rebuild kits, parts - . listing of a Haynes C4 Manual

Early c4 24 spline to late c4 26 spline input shaft conversion

General info and identification

bellhousing application chart C4/C5

C4 numbers and nomenclature

C4 Build page

Chris Kelly's tranny page with links

RCode's photo pages with the JPT article, GA's stator mod photo the case oil mod photo and the thrust bearing diagram with notations or

<font size=-1>[ This Message was edited by: R Code on 3/11/06 11:15am ]</font>

<font size=-1>[ This Message was edited by: admin on 8/17/06 11:59pm ]</font>

1,250 Posts
Good job R Code, about as summarised as it could get without dropping a lot of good thoughts.
Used some of that stuff myself this year and my tranny along with my brothers had no problems this season. 140 runs on mine, 110 on Brothers. My brother did break the low-reverse band on the last days racing. Still have not done the autopsy, just pushed the car out of its pit spot and raced the ass off it.

Picture of the tranny for the 8 sec Zephyr, that is me kneeling talking to another local Ford racer, car owner in white t-shirt. Driver nowhere in sight. lol
Tightened up some clearances up on the clutches for them. Was still working the last time I talked to them with 20 runs on it, they were getting 8-15 runs per rebuild.
Funny thing is my brother and I would refuse to do this level of work to our cars at the track. If we break, put it on the trailer and fix it where it will stay fixed. This rebuild happened waiting for the Sat gamblers race to start. Brother is putting a 440 Mopar together further down the pits.

<font size=-1>[ This Message was edited by: Mario428 on 1/7/03 5:07am ]</font>

<font size=-1>[ This Message was edited by: Mario428 on 1/7/03 5:12am ]</font>

1,943 Posts
I agree with qtrmiler.....About the only work I ever did at the track was adjust the valves, air the tires and maybe adjust the shocks, other than that, on the trailer.

1,745 Posts
R Code, Thanks for taking the time and effort to condense all of that info.
I recently built up my first C4 using a lot of the mods in the archives. I even did the roller mods. I have done a shake down run and everything is working well, so far. I can't wait until spring and the racing season.

1,904 Posts
Gotta comment on that photo. All the trans work going on and not one "pink shirt"on anyone of those guys. I can get a t-shirt pink from trans fluid just checking the level. Ha.

Good editing on the monster post. Good job.

945 Posts
Great work R Code. I had read those threads over and over to find the info I needed. I just wish you'd done it acouple of months ago.

1,250 Posts
Greg you should have seen the selection of parts he hauled out for me and Freddy to look at. There was clutches everywhere, the ground was the only storage left.
These guys have so much tranny trouble they seem to be able to do it without getting dirty. The driver did get involved in the removal. I just jumped in for the rebuild, do not mind doing that. I will not work on my own car be dammed if I will dive under anyone else's.
Thanks to the scholl of hard knocks and the help from you guys and the "monster C-4 thread" I have become the C-4 goto guy around here.

9,251 Posts
Thanks a ton, R Code. This is real good, hard work. The only thing I'd like to know that wasn't stated is where/what size/how many holes to put in the drum(s).

165 Posts
Very nice job Rcode. info is all great I just hope that it will always be here for all to use, no matter what form it is in long or short. It is great to know that many are benefitting from the work you and others have done.

739 Posts
Discussion Starter · #18 ·
The new line is in there. You and the other contributors really did the work. I was just a facilitator. Thanks to you, Kent and Windsor8, TimR, Mario...
I do have a newfound respect for technical writers and their editors.
Hey Mario, I had you pictured as a wiry Italiano. That pic doesn't match my guess. You look nothing like your posts.
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