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Discussion Starter #1 (Edited)
Sometime in the beginning of this year, I missed a 1-2 shift during a warm up at the track. The end result of the blotched shift was that my toploader wouldn’t downshift into second gear. I continued to race the car for several more weeks while I gathered parts and waited for the day that the tranny gave out or a race was canceled. The toploader held up admirably and stayed together until I was ready to tear it down one rainy day. Since the wife was also out of town, I couldn't think of a better time to remove the toploader from my car in order to make the necessary repairs and to finish its “big block” conversion.

This article details swapping the output shaft for the heavy duty 31 spline Ford offering. The following procedures are recommended only for those who are familiar with these transmissions and are willing to assume such risk. If you are interested specific information on swapping an input shaft in a toploader, I suggest the following link: http://www.fordmuscle.com/forums/transmission-articles/482359-toploader-input-shaft-replacement.html

Here is a picture of all the parts needed to convert a small block output shaft toploader into a big block spec 31 spline output shaft transmission:



Shown above are the 31 spline output (main) shaft, the special tailhousing, larger tailhousing bushing, larger tranny-to-driveshaft seal and a 31 spline yoke (which is the same as a C6 yoke.) These parts are specific to this conversion and must be specified as being for a 31 spline, big block transmission. Also shown is an 11/16” core plug and a gasket set, both of which are common to all toploaders. This collection is the minimal amount of parts required for the conversion. Should your transmission have other mechanical issues, you will probably need additional repair parts. Luckily the popularity of the toploader has gained the attention of the aftermarket and 100% of the parts have been reproduced and are readily available through various sources.

Here is a comparison of a stock 24” long, 28 spline output shaft and the new 24” long, 31 spline shaft:



From the bearing boss back, the 31 spline output shaft (shown on the bottom) is quite a bit larger in diameter. Although I used a new reproduction output shaft, an original 31 spline Ford shaft of the correct length would work just as well for the conversion.

The larger diameter output shaft requires a larger diameter tailhousing and related parts (shown above.) Here are some comparison photos of my stock 14” 28 spline Mustang tailhousing and the new 14” 31 spline tailhousing:







The 14” 31 spline tailhousing shown has 3 different bolt patterns which allows it to be used with virtually any shifter combination that was made to fit most 64-69’ Mustang, Cougar, Falcon, Fairlane, Cyclone, Ranchero, and Torino cars. Although this tailhousing is new, used original big block 31 spline tailhousings are available from time to time in online auctions. Be forewarned that used big block tailhousings are rare, and they are not much cheaper than a new reproduction (which comes with a warranty.) The universal tailhousing shown above is only available through David Kee and it allowed me to keep my aft mounted shifter and rods, whereas original units mount the shifter much more forward. It appears to be a well made, quality piece.

Alternately, a machine shop (or even David Kee) may be able to bore your tailhousing to accept the larger bushing and rear seal. Thanks to FM member Cain for doing the research.

In order to install a replacement output shaft in a toploader, you will have to practically disassemble the transmission. To do this you will need a few tools and particularly a good pair of heavy duty C-clip removing pliers:



First I drain the fluid out of the toploader. Most, but not all, toploaders have a drain plug on the bottom:



Remove the 10 top cover bolts. Next, remove the 5 bolts that retain the tailhousing and then remove the speedometer gear C-clip and then the gear:





Roll the transmission on its top and drive the cluster gear shaft out of the main case.
CAUTION, once you have done this, you are literally at the point of no return:



The transmission gets put back on its bottom so that the 4 bolts that retain the front snout can be removed. Then the snout and the input shaft can be pulled straight out the front of the transmission:



Several small roller bearings may have fallen to the bottom of the case. If you have a magnet, you can catch them now or wait until you get to the bottom of the case in the next few steps.

Next I remove the shift forks. In order to do that, you must first loosen up the Allen screws that are ran into them. Both forks and the heads of the Allen screws can be seen in the following photo:



Using a boxed end wrench on the end of the Allen wrench will give you added leverage to remove the screws.



Perhaps the most misunderstood part of the toploader have to do with the shift rails. There are 3 rails, an interlock pin, several springs, and different detents available depending on the year of manufacture. Each item needs to be carefully removed and identified to its specific location. Here is a picture of these parts:



Note that I laid them out in the order that they were installed in the transmission, from top to bottom. Most of these springs and detents are removed through the top of the case (just behind the 3-4 shift fork) with the use of a long skinny magnetic retriever:



Early model toploaders (like shown above) use a blocking screw and in later models the detents are held in place by a tall spring:



An additional spring and detent is removed from the side of the case, near the shift forks:



The shift rods themselves were individually pried out of the case. Note that to remove the 3-4 shift rod, you must remove the small 11/16” core plug from the front of the transmission. Used a center punch to make a hole in the plug so that it will be easier to pry it out:



The 1-2 shift rod gets pushed out the rear of the main case. You will not be able to remove the reverse shift rod until the output assembly and the cluster gear are removed from the case.

Once the shift rails, springs, and detents are removed from the transmission, we will need to push the output shaft off to one side of the case in order to remove the forks. I tend to remove the large C-clip found on the outside of the bearing and push the whole output shaft assembly further into the main case. Once the bearing is completely inside, the whole assembly can be pushed to the side, which allows both forks to be removed:



Once both forks have been removed, reinstall the output shaft assembly bearing back into the main case as it originally was and then reinstall the outer C-clip. Next remove the C-clip that holds the bearing on the shaft. Set the main case on its nose and, using a block of wood and a heavy hammer, carefully drive the mainshaft through the bearing:



Once the bearing has been removed from the shaft, the mainshaft assembly can removed from the top of the case—thus the source of the name “toploader.”



You can now reach in and remove the cluster gear and all its needle roller bearings:





The main shaft will need stripped of its gears, spacers, and synchronizers. The C-clip pliers will come in very handy as there are several C-clips found on the mainshaft:







When I remove these parts, I lay them in an orderly fashion to speed up reassembly:



If you are replacing only the mainshaft gears, blocking rings, or synchronizers, you will not need to remove the reverse shift rod and gear from the case:



If you do remove the reverse gear, expect to find more needle roller bearings.

Here is a stripped case:



Reassembly is the reverse of assembly (don’t you hate seeing that?) Rather than go through all the individual steps in reverse I will highlight them, and offer a few helpful suggestions for reassembly.

First make sure that all parts have been cleaned and blown dry of solvent. Needle roller bearings are installed by first putting a layer of axle grease in the gear’s bore, and then individually installing the needles in the bore:



Reinstall the reverse gear/fork assembly. Next install the counter gear and its thrust washers, using a layer of grease on the thrust washers to hold them in place. It is best to install a dummy shaft in the counter gear to keep the needle bearings in place. A dummy shaft is a rod that the length of the counter gear and has a diameter that is large enough to keep the needle bearings in place. It will be removed later when the transmission is further reassembled. My dummy shaft is a piece of PVC pipe:



Reassemble the mainshaft (minus the rear bearing) while lubricating each contact surface with an oil based gear lube, then reinstall the mainshaft through the top of the case.

Reinstall the shift forks, shift rods and detents. Use a long magnetic retriever to drop the springs/detents in and a screwdriver to hold them in place while installing the shift rods. Tighten the shift fork screw with the Allen wrench.

To install the rear bearing, I use a small piece of metal pipe as a slide-hammer type driver. I found that the new 32 spline input shaft was clearanced enough so that the bearing fit on nicely without being driven.



The input shaft will need to have its roller bearings installed. Again, apply some heavy axle grease in the gear’s bore and then install the rollers:



The input shaft then gets reinstalled into the front of the case:



The counter shaft is installed next. It is easier to do this by rolling the tranny over so that it is almost resting on its top, like in this photo:



With a screwdriver or other suitable tool, align the thrust washer and the inside of the counter gear so that the countershaft can be pushed gently through from the rear of the case:





In the process the dummy shaft will be pushed out the front of the case:



Once the countershaft is through the counter gear, you will need to seat it with a hammer. It should be installed 1/16” below the rear of the case surface:



To drive the 11/16” plug in the front of the case, first install it convexed, then use a flat drift punch to flatten it:



Apply a light coating of silicone sealant over the plug and then smooth it out with a razor blade. Also put a coating over the front of the countershaft:



The input shaft snout gets installed with the drain "track" facing down so that it matches the hole in the case:
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I apply a touch of silicone sealant to the gasket. Because the bolts pass into the case (are not blind), I apply Teflon based thread sealer to the bolt threads.

Be sure to install the speedometer gear before buttoning up the rear of the transmission:



Notice the location of the ball bearing. Some early transmissions used a clip instead to help align the speedometer gear.
Next install the bushing in the tailshaft housing. For this I used WD 40 on the mating surfaces and a seal driver:



The rear seal also gets installed with a driver or a large socket:



Both the bushing and the seal should have a light coating of grease put on them before attaching the tailhousing to the main case.

When installing the tailhousing, put a little silicone sealant on its gasket. Also put a little Teflon based thread sealant on the 5 bolts that hold the housing to the case.

Slide the case over the output shaft and install the 5 bolts so that they are just snug, and then back them off a turn. Install the yoke fully onto output shaft before final torquing the bolts. This helps to align the tailhousing properly in relationship to the output shaft:



Testing the transmission by shifting through the gears:



You will find that two bolts of the top cover are longer than the other 8. Install the longer bolts here:



As far as lube preferences go, the toploader experts suggest staying away from synthetic lubricants as they tend to hinder the function of the brass blocking rings (which need to have some “grab” for the transmission to shift properly.) Therefore it is best to stick with a conventional 85-90wt lube or in extreme situations, a 90-140wt.

Also, if you are using a Hurst Competition Plus type shifter, you might consider freshening it up at this time in order to get better shifts. For details of how to clean it up, I suggest the following tech article: http://www.fordmuscle.com/forums/transmission-articles/487409-servicing-hurst-shifter.html

Conclusion:
All in all, my big block conversion was a huge success. The new aftermarket parts that I purchased from both David Kee at David Kee Toploader Transmissions, Inc. and from <cite></cite>Mark at Toploader Heaven <cite> </cite>fit great and no modification were needed. Not only did I make my toploader much stronger, during the rebuild I also replaced several other parts that were showing wear from weekly abuse at the track. Happily, the transmission shifts like a dream on the street and I have confidence that it will hold up for many more 6400rpm floorboard shifts at the track.

 

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Discussion Starter #3 (Edited)
Here are a few more pictures (and some comments) that wouldn't fit in the opening article due to space constraints.

Output shaft comparison:



Length in the above pic is an optical illusion as they are both the same.

Serious neck down shown on the 28 spline shaft below:



More tailhousing shots:



The bushing from a 28 spine toploader easily fits inside the installed bushing of the 31 spline toploader:



Difference is also seen in the seals:



The David Kee unit includes a breather that is not found on an original. Also it includes the early arm casting which could be removed if desired. Luckily it doesn't offer any interference with the driveshaft tunnel in the 65/66 chassis:



The transmission is much heavier after the installation fo the big block specific parts. The aftermarket tailhousing casting vs the C4 original:





For my application, I like the improved transmission mount pad on the new tailhousing. I used the outermost holes which should help to better support my drivetrain from rotating at the track:





I am not sure that the C4 tailhousing casting has enough meat to be bored out for the bushing and yet remain strong. It necks down quite a bit in the critical area. I do believe that only the C7 and up castings are healthy enough to allow for a bushing bore job though:





The 31 spline yoke is a billet piece. I learned my lesson about using a plain steel piece last year as I twisted the interior splines:



The removeable caps make it easy to swap yokes in a pinch:

 

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The 31 spline yoke is a billet piece. I learned my lesson about using a plain steel piece last year as I twiste the interior splines:



The removeable caps make it easy to swap yokes in a pinch:

Dennis,who makes that yoke and (if you don't mind) what did it cost you?It would sure make my back and forth tko/t5 swaps easier!
 

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Discussion Starter #5
Dennis,who makes that yoke and (if you don't mind) what did it cost you?It would sure make my back and forth tko/t5 swaps easier!
These yokes are made by Victory and being billet are a little pricy--expect to pay around $200 each for these--still cheaper than what Mark Williams gets for his. Mine came from Moneymaker Racing.
 

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Nice write up Dennis. I found that I couldn't get my tailhousing machined for the larger bushing and seal locally for less than $200. I made a few calls and found out that Dan Williams does the machine work for a much more reasonable $75. I had him do mine and it turned out great. He bored my tailhousing, installed the bushing and seal, and added a breather. I shipped my tailhousing to him on Monday and I had it back on Friday. Dan Williams Toploader Transmissions
 

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Very nice Dennis, GREAT write up and Pics, the mystery surrounding the Toploader. Can I just send you mine?
 

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Nice job there. Reminds me of all those I use to build way back when. It wasn't uncommon to go through 4 - 6 a weekend. Only part I hated was those C-clips or as I called them Jesus clips since if they slipped off the pliers they not only went flying and you had to duck saying the J word but the pliers would leave a nice blood blister in your palm.
 

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Discussion Starter #10
Nice job there. Reminds me of all those I use to build way back when. It wasn't uncommon to go through 4 - 6 a weekend. Only part I hated was those C-clips or as I called them Jesus clips since if they slipped off the pliers they not only went flying and you had to duck saying the J word but the pliers would leave a nice blood blister in your palm.
LOL--Yeah, those clips can be horrible to deal with. I've certainly had my share of sore fingers and hands at there expense.
 
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