T90 Rebuild

Hi everyone,
I’m getting ready to rebuild my T90 transmission and would like some input. This is from a 56 cj5. It will be mated to a Chevy Bellhousing and v6. I plan on getting adapter and longer input shaft from Novak. Please take a look at these photos of gears and synchros. To me the gears look good. I definitely plan to replace all the bearings and synchros, but don’t know if I need a kit or just certain parts. I will be tearing down soon and can take more detailed photos.
Cameron

 

When i drained the case, more water than gear lube came out. There is a little bit of rust, but I think I can clean that off. I'm not sure about the lower gears.

 

Welcome from Michigan, that trans doesn't look too bad. I can't see the brass on the synchronizers too well but if the points are sharp use it. I would replace the bearings and the shafts just because you are in there now. The cluster gear shaft goes out the back of the case and back in from the back, make sure to put sealer on the shaft in the front of the case, I had mine start leaking and had to pull the trans back out to fix it. The T 90 is as simple as transmissions get so you should not have any problems. Good Luck.

 

Thanks Rick.

 

If you had water in the trans and it set for a while, expect rusy parts down low. Gear oil floats on top of the water, and enough water will overflow all the gear oil out the vent in the transfer case. Count on the transfer case having rust too as they share the oil. If the trans/tc were run with water, it will look like a milkshake in there.
As far as syncros go, check the tapered part that mates on the adjoining gear's taper. There should be a gap (.030?) between the syncro and gear where those finer teeth are.
Since it was full of water, you should pull it all apart and inspect everything. Replace only what is needed.
-Donny

 

Here are the parts from inside the transmission. Good news is, no rust in lower part of transmission. The bad news is the first gear counter shaft. It looks like someone was shifting into first from a roll and forcing it into gear. Should I be concerned about the banged up teeth?
Thanks for your expertise.
Cameron

 

Assuming you have not driven this transmission? I'd put it together and run it. You'll need new blocking rings. There are no broken teeth, and I kinda think the original cluster gear will be as strong as the modern import replacement parts. IMO that's abuse or ignorance - suspect you will not abuse it in this way. I understand these transmissions wear out the bushing inside of 2nd gear, and then they come out of gear when decellerating in 2nd. Hard to predict that if you have not driven it. Ridges on the input shaft synchro surface are surprising. That's 3rd and there's not much asked of that hub - upshift only and never very much speed difference.

Others with more experience of T-90s may know better.

 

I have not driven this transmission. It came to me as a roller with no motor. I'm wondering if someone like to drive with hand on gear shifter. Would that put downward pressure on the shift fork and then the syncro causing those grooves? Will this amount of wear cause issues?
Cameron

 

You are replacing the input shaft with the long shaft for a GM conversion? Then the condition of the input shaft does not matter.

 

Sorry, I was referring to the wear on the clutch sleeve. Still learning names for all the parts. Yes, this will have new input shaft. I filed all of the rough edges off the countershaft gear that is a little beat up and the rough edges on the sliding gear.

 

Wear from a driver keeping their hand on the gearshift shows up more on the actual shift forks attached to the top housing. The gear and 2/3 sleeve are pretty well hardened. The heavy wear on the countershaft is from someone that constantly tried the grab 1st gear while still rolling. They needed to learn to double-clutch.
You might get by assembling all your parts using fresh bearings.
-Donny

 

Just a comment - you don't have to double clutch to drive one of these Jeeps. Around town, if you are moving at all, you can slip the clutch a bit and start off in second. No need to drop into first unless you are fully stopped. If you are fully stopped, push in the clutch, give it a few seconds to let the gears stop spinning, and shift. No clash.

If you can double clutch, so much the better, but I would not bother around town. Before invention of the syncromesh transmission, drivers would routinely match speeds to shift gears, without gear clash. Something you can achieve with a bit of practice.

 

I used to do this with my father n law’s 1970 beetle. Getting in tune with your vehicle

 

Donny, if this was yours and it was going behind 170 hp v6, would you spend the money on the hardened counter shaft?

 

Your father-in-law's '70 beetle was full synchromesh, so it would easily downshift to first while still moving. If I were building a T90 to go behind a V6, I would use the best parts available- no Omix stuff at all. I built my T90 years ago to go behind my 215 Buick V8, and never touched it again with 20 years of abuse.
-Donny

 

Hard to teach modern drivers to not drag it into low as if there was a synchro. cant teach my 45 yo daughter. Starting off in second is equally foreign to them.

 

The '70 beetle had problems with the syncros, thus the need to double clutch.
Thanks for your help.
Cameron

 

None of my children know how to drive a manual gear box. I hope to teach them with the Jeep. It’s hard to find cars or trucks offered with a manual transmission these days.