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Discussion Starter · #1 ·
Things have been alittle quiet here lately....so lets hear some opinions on WHY the C4 still has its old issue, namely hi/reverse pack wear.
Comparing it with a glide, the hi gear change works the same for both transmissions...namely band release/clutch applied to do the change, so there is a timing issue there I guess...but they both have it.
People have messed with H and R and A and B...and all sorts of servo's to try and help with this problem, but there doesn't appear to be any hard and fast rules as far as a specific servo to use and there is certainly no "golden" fix....as far as servo's go.
Then we have the clutch pack clearance debate, some use "minimull" clearance, the 0.005" per plate "rule", others use more. There have been posts regarding opening up aftermarket C4's and finding quite large clearances in the hi/rev pack.

There are two things that stand out in my mind after reading of peoples experiences/problems in this area -

#1. Faced with reasonable HP (say 500-600), a C4 that is sealed and clearanced well, will hold up fine and function with minimull wear.

#2. Faced with a challenge (say 800+ hp), its a whole different story. Whilst "some" will last a "reasonable" time (nodoubt the better prepared ones), its generally not a long time between freshens.

I think there is nodoubt that pack clearance is a major player in the longevity of a C4....but why? Compared with a glide which runs WAY more clearance in the packs (typically around 0.015" PER PLATE), line pressures are similar and a C4 seems to have way more pump volume than the glide?!?

So a C4 is way tighter, which means more drag and more heat generated as a result.

Ok, lets hear some opinions on why there is an issue here...sure we have a obvious plate diameter difference but the basic functions appear identical? Or are we expecting too much from the little C4? Theories? Ideas?
 

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If we look at what is turning in a particular gear that will shed some light on the subject.
Second gear for instance.

In second gear the forward clutch and front band are applied.
The intermediate drum is held stationary.

The direct fibre clutches are splined to the forward drum and turn as fast as it does. Which is very close to engine rpm.

As the shift into third takes place the band must release and the clutches apply.
Remember, the fibres are doing engine rpm, the steels are at a stand still.

Zooooooooooooooom. Instant wear.




<font size=-1>[ This Message was edited by: Stuart1 on 8/3/06 2:18am ]</font>
 

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Discussion Starter · #3 ·
Stuart, yep I can see what your saying and that is surely what causes the wear....but a glide (for example) is also working exactly the same.

It brings acouple of thoughts to mind though... - the higher the rpm the engine is doing when the change occurs the harder its going to be to lock that clutch up ... - a tight converter is also going to put more potential load on the pack as it won't absorb the speed/load change as well as a loose converter?

What about plate diameter? Large plates are going to be travelling faster in the area of the friction material....the C4's smaller plates will be moving slower....that should be a help rather than a hindrance - though I guess the actual force on the plates themselves will be much greater (given the same conditions)?

They re-line bands with kevlar....why not frictions?
 

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I have seen kevlar frictions somewhere for transmissions. Just a side point though,did a 9" LSD centre with alto kevlar frictions and went through 3 sets in a few weeks. They just stripped the lining off.
 

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Discussion Starter · #5 ·
Hi Greg, did it look worn off or did it come "unstuck"?
I think I may have found a place that does kelar for C4's, I tried ringing them today but only got an answering machine....will keep you posted.

I see they do kevlar for Lenco's....so it must hold up ok.

<font size=-1>[ This Message was edited by: cmf60 on 8/3/06 2:39pm ]</font>
 

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It was worn away,waffle pattern was worn off. I set it up once and a diff guy did it twice. It now has some good 2nd hand clutches and its good. Maybe different with transmissions but.
 

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Discussion Starter · #7 ·
I wonder if it had a compatability problem with the fluid perhaps?
When I had the pressure issue with my C4 some time ago and toasted every band and friction....the only one that survived was the kevlar.

If I do find some frictions, I will definitely try them and see what happens. It may help, it may not - but the should handle the punishment better surely?
Like Stuart points out, its gotta grab the steels that are at rest, running tight clearances will mean the piston doesn't have to shift very far to do this but that in itself generates heat and drag. Those issues must be present all thru 1st and 2nd gears as well. Does this friction/heat effect the 2/3 shift?
Does anyone know the maximum line pressure you can run with these trans'....or the max. that has been used?
 

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I just replaces my forward drum. I have cracked it.
I inspected my Rev/High frictions to see if they needed to be freshened.
I was pleased to find them in almost new condition. Now this Rev/High drum is from Broader Performance and has 6 frictions in it. I am using standard Alto's.
I was also surprised at the condition of the forward drum frictions. I had 5 smooth standard Alto's in it when it broke. All the frictions showed ware. As i recall when i measured the friction thickness they had worn about .015 I had not ecpected that. Could not be more than 30 passes on them. I have replaced the forward drum with a Broader Performance high strength setup with 6 frictions.
I am no where near a guru on these tranny's but seems what i found is unusual?
 

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I thought the same thing about the fluid compatability.The diff guy had only used these for a short while so i guess he wont be using them again,pity i had to find out the hard way but i thought being alto that they would be fine but oh well...
 

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Discussion Starter · #11 ·
Forthman - the "problem" seems to be related to how much HP you're trying to put through theses things. A well sealed trans with a reasonable amount of HP seem to hang in there, but it appears that relatively tight pack clearance is needed to achieve this.
I'm guessing ...that in your case there was a slight "issue" in there somewhere. As soon as there is alittle wear on the frictions, the problem accelerates and the pack is gone in no time.

30 passes...great (!) ....I got 6 passes out of my first effort but it did have a major leak that didn't show when we air tested at assembly.
Am using a home done hi/rev drum with six alto reds.
 

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Have been thinking about this but I have never been into a glide so I am going off the top of my head.
Going by pictures the glide servo is a lot smaller than a C-4 servo especially in respoect to release size. The C-4 uses a lot more fluid to the servo than the glide does making the band adjustment critical.
Since a glide uses much larger clutches a hard shift will not be as important.
The tiny C-4 clutchs are the issue with a C-4, besides the Super Stock racers using 904's which have a larger clutch than a C-4 (and they expect to do a lot of maintanence) no one expects as much of a tranny as we do with a C-4.
 

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Ok here's one,what about the shaft of the servo leakage? What about cutting a groove in the shaft and fitting some o'rings like where the sonnax servo has teflon? seals.

Could losing some pressure from the release side of the servo while in 3rd gear contribute to clutch wear?

There was a mention on here a while ago where one of the guys ran his PA i think trans up on stands and the wheels stopped momentarily on the 2-3 shift.So obviously there wont be a flare here but the tie up on the shift would be hard on the clutches?????

<font size=-1>[ This Message was edited by: gregaust on 8/4/06 6:35pm ]</font>
 

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Discussion Starter · #14 ·
(SORRY...this is fairly long winded...)

Am pleased you guys brougt up the servo. The glide servo is indeed ALOT smaller than the C4 and from memory, I am pretty sure the apply and release are both the same size. There is alot of debate regarding all these different sized servo's and band holding power verses release area etc etc....but the old glide seems to get by with something alot smaller and equal sized???

Can I just get back to afew basics here, if only to refresh my own mind (and perhaps others)....I have not really had trans thoughts in my head for awhile so please correct any slip-ups. I have looked back through some drawings I did whilst working out how a braked VB functions, the servo apply pressure is on in all forward gears and the release pressure is also on in all gears except 2nd, so the release pressure being the greater force (because of the piston area) holds the servo "off".
Now I am not trying to bore you all too much, but I also found some working figures that I did on R and H servos based on piston [email protected]

R----1670lbs release pressure
1250lbs apply pressure

H----2250lbs release pressure
1374lbs apply pressure

To try and relate this to the 2/3 shift, the release pressure comes on which has a differential of 420lbs for the R and 876lbs for the H (forgetting the spring). Ok....so the H has twice the force to push the fluid out of the apply side BUT it must pump 35% more fluid than the R to move the piston 1/2" (65cc verses 87cc).
So which servo is faster?? I buggered if I know, its been some time since i was at school but perhaps someone who knows the calculations could work out how long it would take. On the apply side the H would only hold 4cc more than the R...for the same 1/2" travel. I am kinda thinking the H might have the advantage speed wise by the look of the figures.


Lets move on to what Greg mentions "trans up on stands and the wheels stopped momentarily on the 2-3 shift".
Does that mean the hi/rev pack has engaged but the int. band is still applied...if the band had released, the trans should still be rotating (albeit in 1st for a split secound)....or am I looking at it wrong ?? If that is infact the case, the servo may have a bigger influence on things than I thought??

As for my opinion on the servo shaft seals, that shaft is running directly through the servo release area....most of the time (except 2nd) the pressure should be equal. When the release pressure is removed and you have leakage past the shaft, it may slow the band apply slightly as it has to "dump" any leakage as well. When release pressure is reapplied, pressure will be higher on the apply side as the fluid gets pushed out....if any of this higher pressure bleeds past the shaft, it should help the release rather than hinder it.
So IMHO its possibly not really necessary except maybe on the 1/2 shift.

Ok, this has already got WAY longer than I anticipated, so we will see what folk's think of this lot and perhaps someone can calculate which servo has the fastest release?

My latest question....do you guys agree/think the band should release before the clutch is applied?? (may explain why a glide has such a small servo and runs large(ish) pack clearances?)
 

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CMF, release side of 2nd gear servo only has pressure in high gear and when tranny brake is on if so equipped. Remember release side is basically connected directly to direct clutch piston.

Another thing to throw into the hydraulic theory, With orifices and torturous passages for fluid to go thru the servo or clutch will not have line pressurer while applying. There will be a pressure drop until the piston stops moving. Less fluid required compared to more force, still do not have an answer.

My brothers car with a H servo, 2700 Lbs and 600 HP is more prone to 2-3 flare then my R servo, 3100 Lbs and 525ish HP.

Glides band wraps around a much larger drum but may be narrower, surface area would come into play.

I can feel my brain working again, this is good.

_________________


<font size=-1>[ This Message was edited by: Mario428 on 8/5/06 12:32am ]</font>
 

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Discussion Starter · #16 ·
Hi Mario. I have been back thru my flow diagrams I had done of both a PA braked VB and PA manual VB's looking for an error in my flow paths....I was 99.9% sure that release pressure is on in all gears except 2nd. I kept looking....then it dawned on me that is indeed the case, because servo apply pressure is "on" in all forward gears...therefore release must be on as well in 1st or the band would apply. Thats on the PA bodies, haven't looked at any others.

The supply passages....just some thoughts on the subject.
I did some fiddling with a broken pump some time ago with the intention of increasing the flow potential to the rev/hi clutch. I drilled the passage as large as I could go up the pump support housing..which is smaller than its supply gallery coming thru the pump housing. Whilst I was doing that I thought about air that is trapped between the feed hole to the hi/rev and the end of the pump support housing, acting as an accumulator. I thought it was probably a good idea to thread and plug that channel next to the supply hole.
Whilst messing with the hi/rev drum one day, I was looking into enlarging the feed holes....which I ended up doing. But looking on the inside of the drum and the angle these holes must be drilled on (unless you have a VERY small right angle drive), I thought, this doesn't look great. The holes are angled towards the inner seal as it the only way they can be drilled BUT the area (and angle to turn) the fluid must do to push the piston is crazy. There is relief machining done under the feed holes but its still tight in there and the fluid must turn near 180 degrees. I think this can't promote fast clutch application, so I measured where the inner seal sits on the piston at rest and where it would sit if all the frictions were worn out. I then cut a large bevel on the area that was left over to try and give the fluid a much easier path to the rear of the piston. This is untried in operation and I hope it hasn't weakened the piston too much in its "neck" to base area. Time will tell!!
I think any de-burring or "common sense" enlarging of feeds must help the operation of the trans and that probably includes servo rod sealing rings.

Can I just touch on your servo experience for a minute....what exactly is the flair?? Looking at the trans' operation I feel (but don't know for sure) that it is most likely caused by band releasing before the pack engages....so the trans thinks its in 1st again, albeit for a split secound. If the pack engaged first would it not struggle against the band or even lock the trans for a split secound ....like Greg mentions??
Am I thinking this thru right????

If so, the R may indeed be slightly slower than the H. All things being equal (unlikely I know), if your brothers is more prone to flair with the H then it may be kicking the band off faster than yours. With the pack clearances you run ( I suspect they may be alittle tighter than the 0.005" "rule"??) , the line pressure, R servo, pump volume etc etc....you may have the actual timing of the shift near perfect....for YOUR setup. I say that because you read of others peoples trans' responding to, say, an H servo...and getting rid of their flair. It is possibly just improving the shift timing in their setup?
 

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What is the volume the the pump can output at a given rpm?
All this talk of pressure and no mention of volume.
High pressure and low volume would cause delay in action of servo and clutch engage as they need "x" volume to get there job done.
Increasing flow volume will decrease pressure without pump increasing output.
A given shift takes "X" volume.
So to understand what time it would take to perform that action would require the volume needed to be know for that action and the pumps volume over time.
Hope that makes sense.
 

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I remember seeing somewhere that some manual valvebodies work as you say Chris with pressure on all the time.I can't remember if it was c4 or c6.
 

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Discussion Starter · #19 ·
I touched on that in the previous post ....87cc for the H servo and 65cc for the for a R servo, thats to release 0.5" . To apply an H 0.5" takes 44cc and an R takes 40cc.
I had worked out the amount required to apply the hi/rev pack but can't work out where I've put that. I do remember its not much if your running tight clearances.
I have no idea what a C4 puts out volume wise, but its substantially larger physically than a glide.
Given that the variables are going to be the same for both servo's (meaning pump volume/pressure and galley restriction's) it shouldn'y be to hard to work out which one is the fastest acting.
 

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Discussion Starter · #20 ·
After alittle digging the only pump output data I can find is for a glide....1.5US gal/min and I have no idea at what revs this is at. Say a C4 is doing 2 US gal/min = 7600cc/min = 126cc/sec. At that rate it would take 0.7 sec to fully release an H servo.
There are lots of "variables" here though...like the area of pressurised fluid available, actual flow rate etc.
It is a point worth further investigation though.
 
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