S80 T90 ?

[71mtnscout]

Now that the goat is running pretty good, will be replacing the spring bushings this weekend, I have a trans question. The t90 likes to pop out in 2nd gear on decelleration only? You can hold it in gear without issue, it will sometimes kick a bit, but not often. It also grinds a bit on upshift. I havent opened it up but would like some opinions on what the problem is.

 

[Robert Kenney]

The t90 is a great trans but it has a few week links. There is a sliding hub that either gives you 2nd or 3rd which is a locking of the input and output shafts. It is actuated by a fork that can be bent and not completely engaging the teeth on 2nd. The hub or in more common terminology the clutch and the actual second gear have small teeth that mesh with each other and 3rd gears. The teeth get chipped and worn down to short to engage properly so they buck out of mesh. Second is the most common because of people shifting these dinosaurs like sports cars.

The grinding is common also as the teeth, which should have a nice 45/side lead in chamfer get worn round and or flattened so they can't engage the syncro ring properly. There in lies your grinding when you shift. Also the brass syncro ring wears and cannot grip and synchronize well any more.



I replaces the clutch I think and second gear because I had a new one and the syncros in my t90 . It never popped out og rear but it ground some when down shifting. Now it is great.


Pictures on 2nd gear tooth damage. The pollished tapered surface is where the syncro ring rides and has to grip to syncronize the tro shaft speed differencials. The shiny surface needs to be deglazed with 200/400 grit wet dry paper if reused. I expect to see the same in your gear box. Sorry I can't find the other parts. Must have hid them away for some reason.

 

[71mtnscout]

So 2nd gear is the one that takes the abuse? I've been looking into a rebuild kit for it and I would guess the ones that come with a new 2nd gear would be the one I should get. I have a jy trans/t-case sitting on the floor, guess I'll go through that one and trade. An IH t90 is a t90 right? It came out of an 80, so it should be the same trans....am I on the right track?

 

[Robert Kenney]

The second gear and the clutch hub both get beat up the same especialy when the syncros lose effectivness. Take the top off and you can do a fair amount of inspecting so you can get what you need.

Bearing and seal kit should be east enough for Jeff to get but hard parts like gears won't be so easy. The t90 under went a syncro redo some time during prior to 65. The rings for one version are hard to find. Sorry but I don't have my info with me. Hope another member will pipe in. I remember the Scout gear boxes had differences from the Jeep ones