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Installing GM input shaft in T-90

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ThrottleUp View Drop Down
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    Posted: 25 May 2022 at 2:00am
When installing a 1 1/8' diameter and longer input shaft into a T-90 (to accommodate installing a Buick 231 V-6), must the tranny be pulled to do the installation or can it be done from the top through the cut-out in the floorboard?

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Oldpappy Quote  Post ReplyReply Direct Link To This Post Posted: 25 May 2022 at 12:31pm
First, you don't want a "GM" input shaft for a T90, and you couldn't get one anyway since they never made them.

If you don't have the shaft and want a good used one I have a few good ones, and other parts needed for the V6 conversion, such as adaptors and bell housings. I would sell any of this stuff for what I have in it. 

If you want to shop around and buy a new one you want the long input shaft as used in the Willys 6 Cyl trucks and wagons.

You have to pull the transmission to replace the input shaft. I cannot imagine doing this with the transmission in the vehicle. 

It is possible to switch the shaft without complete disassembly of the transmission, but it is tricky. 

The input shaft mates with and supports the main shaft. The drive gear of the input shaft is filled with roller bearings which will fall out when the shaft is separated, and you must make sure none are left in the case to cause further damage. I stuff a rag in around where the shafts join, dab globs of chassis grease on the rag and put in a couple of strong magnets to help catch the roller bearings. I count how many are collected this way, add that to how many remained in the cup of the shaft. If any are missing they will have to be fished out of the case. VERY important that all of them are accounted for.  

The T90 is a simple transmission and such an operation is a good time to simply tear it completely down and replace any damaged gears, install new synchronizers and bearings. Then you have a rebuilt transmission. It is really just a little more trouble than trying to simply swap the input shaft. 


Edited by Oldpappy - 25 May 2022 at 7:03pm
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oldtime View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote oldtime Quote  Post ReplyReply Direct Link To This Post Posted: 25 May 2022 at 12:56pm
What pappy said X2. At a minimum you must separate the transmission from the engine.
The input shaft is properly referred to as the transmissions “main drive gear” (mdg).
Currently building my final F-134 powered 3B .
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SE Kansas 46 CJ-2A Quote  Post ReplyReply Direct Link To This Post Posted: 25 May 2022 at 12:58pm
What oldtime said X2...that makes X4 for what old pappy said.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Fltfndr Quote  Post ReplyReply Direct Link To This Post Posted: 25 May 2022 at 1:19pm
I believe it is a 906203 shaft.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote oldtime Quote  Post ReplyReply Direct Link To This Post Posted: 25 May 2022 at 1:33pm
906203 is for the M715 Borg Warner T98
Make it mdg #640248 for 1-1/8 T90-J
Currently building my final F-134 powered 3B .
T98-A Rock Crawler using exclusive factory parts and Approved Special Equipment from the Willys Motors era (1953-1963)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Oldpappy Quote  Post ReplyReply Direct Link To This Post Posted: 25 May 2022 at 2:41pm
Get a OEM shaft, don't buy the OMIX-ADA crap a lot of suppliers sell. You only want to do this once....
If you can't get there in a Jeep you don't need to be there!
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