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The T90/D18 in my 1952 M38A1 is "tired." I say that in the fact that the transmission pops out of second gear, it is difficult to shift into first gear when decelerating ( to a creeping speed-not fast). Additionally when I got the jeep the tail shaft for the transfer case was not shimmed well leading to too much play in the output shaft. The yoke sealing surfaces appeared to be worn.

I am getting to the point where I want to do something. I have a spare T90/D18 that I got in a package of parts a while ago...the condition is unknown to me. The combo did have adapter Offenhauser bellhousing for a SBC the transfer had an overdrive (I forget if it was a Husky or Warn)-- the overdrive has been removed and I have a replacement gear for the x-fer.

I am thinking I will removed the current tranny/xfer combo and install the spare. However before I do so does anyone know of a good guide/resource to inspect the transmission with a shift tower removed? This way I can could possibly verify the work 2nd gear/1st synchro currently in the jeep and also pass a read face test before I put in the unknown transmission.

I see there are rebuild guides but I am just looking for an inspection guide from the top. I may take my time and rebuild the original combo from the jeep as time permits...and possibly even add an warn overdrive...I think I have one with the right amount of teeth on the main gear.

Any advise, insight, or pointing me towards good T90 resources is appreciated

mcj115 wrote:...it is difficult to shift into first gear when decelerating ( to a creeping speed-not fast).

Might want to review the Army operating instructions manual?
First gear in the T90 isn't synchronized.
Having to come to a complete stop (or pretty near it) to engage 1st is normal.
Double-clutching is an option, but you'll likely be going so slow anyway that a stop or near stop is preferred to grinding it in.

There's several excellent interweb guides for rebuilding the T90 and D18.
Novak comes to mind here:
https://www.novak-adapt.com/knowledge/t ... 0-rebuild/

and here: https://www.novak-adapt.com/knowledge/t ... uild-guide

The Army manuals include detailed inspection and specs for the internals of both.
The manuals are free using the "downloads" button above.

Good luck!

Hello MCJ115 ___________? (Note: Our web site has a signature element you can load that will sign each of your posts automatically so when someone wants to help you they can address you by at least your first name.)

As Ron D. mentioned already there is a ton of extremely detailed inspection and repair data already published by Spicer, the Military and Willys/Kaiser factory. There are also two good sources for a blow by blow from Novak Enterprises and there are excellent video and written tutorials by Rick Stivers out there.

Rick Stiver's T90 Video: https://www.youtube.com/watch?v=D3sxwkqkpJA
Rick Stivers T90 written: https://www.cj3apage.com/index/Tech_Tip ... ebuild.htm

Rick Stiver's D-18 Video: https://www.youtube.com/watch?v=3-2TgW2hE_w Part 1. https://www.youtube.com/watch?v=vW60pnl43Dk Part 2
Rick Stiver's D-18 written: https://www.cj3apage.com/index/Tech_Tip ... ebuild.htm

The TM's you are going to need are: TM 9-8014, TM 9-8015-1 (covers clutch), TM 9-8015-2 Chassis & running gear,

Since you appear to be quite unfamiliar with the T90/D18 combo I suggest you invest in some reading and viewing research efforts before you consider inserting a used, unknown condition pair in your current jeep which you said appears tired because it is hard to shift in 1st while still rolling! Which is a common trait for any manual trans with a very low geared first gear which is not synchronized at all as is reverse. Only 2nd and third use a synchro.

The CJ3B page offers a very helpful guide: https://cj3b.info/Tech/T90.html

and this WillysTech Page is darn good: https://www.willystech.com/faqs/Breakou ... e.html#SXO