T84 Transmission Improvements/Repairs

[OZM29C]

Thought that I would capture some of the improvements and repairs that I made to my Weasel's T84 Transmission in this separate post to facilitate an easier search for future restorers. The ideas and repairs methods that I have put forward here are in an advisory capacity and should by no means influence you on what you consider is best method for your restoration.

Lets start with the transmission mainshaft. The case hardening on the ground bearing surface of the shaft where it runs in the pilot rollers of the main drive gear had badly de laminated. In view of the low miles (1194Miles) on this transmission I can only guess that this was a manufacturing problem right from the start. Replacement shafts were available out of the USA but the exchange rate and overseas shipping costs made for a very expensive repair. For $18AUD I purchased a hardened steel collar (an inner bearing race) https://us.misumi-ec.com/vona2/detail/221005155573/?HissuCode=IRT1216  ,machined the mainshaft down to an interference fit size which allowed the steel collar to be press fitted onto the mainshaft. As added security, I used a Loctite super bearing mount compound. To date the repair has been very successful.

[OZM29C]

The Cluster gear in my transmission needed to be replaced. Although the Weasel T84 transmission does share some commonality with the MB/GPW Jeep transmission, the cluster gear is not one of them. The Weasel cluster gear is longer that the Jeep cluster gear when they are sat side by side. See photo. Weasel cluster gear is on the left of the photo. MB/GPW Cluster gears are a good substitute and are still readily available nowadays but a small modification is needed to make them work in a weasel transmission. In my case I machined a thicker thrust washer but I have heard that you can add an extra MB/GPW Jeep thrust washer to make them work as well. All I know is that by machining a new thrust washer, I could get the correct end thrust clearance.

[OZM29C]

The main bearing retainer cap seal is not the best of design so I decided to modify this assembly to prevent the possibility of oil leaking from the front of the transmission into the bell housing.

I silver brazed a steel collar into the inside of the bearing cap and then machined the cap to accept a standard off the shelf oil seal. I can't offer any updates on how this modification is going but in theory 😀 it should work.

[OZM29C]

Finding replacement OEM cork seals for the transmission selector shafts nowadays is a challenge. If found, time has not been too kind to them. I found a Viton O ring that made for a good seal on both the selector shaft and the transmission housing. Coupled with a machined to size Nylon retainer that is secured in position with the selector arm, this makes for a suitable replacement seal.

[OZM29C]

When rebuilding my weasel transmission, I had to replace the output shaft drive seal. I could not find an OEM seal at the time but nowadays I believe that they are available in the USA. With the exchange rate and overseas shipping costs to consider, I decided to fit an off the shelf, local supplied generic metric Viton seal. I bored the end cap out to suit the new seal. The last two photos show the OEM seal that I removed.

[OZM29C]

Another recommendation made to me was to fit High Capacity Bearings. Unfortunately I didn't record the bearing size and codes for future reference. For the small extra cost involved and knowing how hard a T84 transmission works in a Weasel i though that this was a worthwhile improvement. In the photo you can see some of the replacement parts that were sourced from my local Studebaker Parts dealer here in OZ.

[OZM29C]

Finally to compliment all of this work, I filled the transmission with an oil that was recommended by Penrite Australia.

https://penriteoil.com.au/products/categories/veteran-vintage-classic/geartransmission-oils/transoil-sae-90

I am sure that there are suitable compatible oils available overseas.

Transoil 90 is premium non EP, API GL-1 rated SAE 90 gear oil designed specifically for use in veteran, vintage and Edwardian gearbox, transaxles and selected spur and bevel type rear axles. It does not contain any aggressive load carrying additives that may cause corrosion damage to ferrous and non ferrous metal types used in these types of vehicles.

Application

Transoil 90 suitable for use in manual transmissions and transaxles in veteran, vintage & Edwardian vehicles.

Transoil 90 is used primarily as a gearbox oil in medium to large veteran and Edwardian cars. Also used in gearbox applications in vintage and pre war cars. It may also be used as a rear axle oil in many light cars or voiturettes. This oil is compatible with leather and synthetic rubber seals.

DO NOT use in axles fitted with any sort of hypoid gears.

[Patrick Tipton]

Great information John!

In the US, Tractor Supply sells 90wt GL1 as "Ford Tractor Transmission Fluid".  Works great and is about $40 for 2 gallons.

In addition to the possibility of the front bearing holder leaking, many don't squeeze the front bearing/snap ring tightly enough to secure the front bearing - I have seen jeep T84's where the front bearing spins in the case.  If you have a lathe, you can take about 10 thou off the face of that bearing retainer.  This causes it to squeeze tighter on the bearing snap ring.  It makes the input shaft noticeably more stable.

All syncronizers are not created equally.  Check the syncro sleeve as I have seen several that were not hardened and they fail very quickly.  If a file will cut it, the sleeve is too soft.  Also, the syncro dogs have been manufactured in many different lengths from about .750 up to about .820.  First, they all need to be the same size. In my experience, the best shifting transmission have dogs that are in the .760 range.  Much shorter and the transmission will grind downshifting from 3rd (not such a problem in the Weasel but...) and much longer the dog can pop out of the syncro and jam the entire operation.  Weasel transmissions are easy to remove compared to the jeep, but still not something you want to have to do many times.

There should be next to no axial play in the syncro, 2nd gear stack - so forward- back on the shaft.  I am looking for less than .003.  Peter Debella has special shims (fluted) - in a pack with a .010, .001 and .002.  The combination of new syncro hubs and 2nd gear will often leave in excess of .010 play - enough to cause the transmission to jump out of 2nd gear upon sudden deceleration or going down a hill. The shims go next to the syncro by the snap ring.

2nd gear should be rebushed and the reamed to a snug fit - again...we are looking for nearly no radial play.  There should be no rocking, but the gear should rotate freely.

I am about to make a video on rebuilding the T84 - the jeep will be first, but I will do a Weasel one as well.

Cheers.