T-86 Guts In A T-90a-1 Case?

Hi, I am now in the process of rebuilding my T90-A. It is fully disassembled and the top is finished. I started to look at the gears and comparing them to new ones to assess what to purchase, besides the obvious kit and noticed that in all the exploded views and replacement parts offered the reverse gear is straight. Mine is as shown. Is this normal or a contraption? Pros, cons?

 

I’m no expert on these, but I’m thinking your guts have been swapped from a t86.

 

Take a picture of the main shaft. A T-86 main shaft has splines that spiral. A T-90 main shaft has splines that are straight. A T-86 has a first and reverse that are helical (slanted) - as shown above - and a T-90 has straight-cut gears. Helical gears are quieter.

A common repair for a T-86 is to replace all the gears with T-90 gears. Inner dimensions of the case are the same for both, but the gear sets are not compatible between - no mixing allowed. Possible someone took your T-86 gears and put them in a T-90 case, so it would work with a T-90 to GM adapter? More pictures needed.

 

This.

 

T-86 gears, no doubt. What's wrong with the transmission? Unless I had a broken gear or other major issue, I'd clean it all and put it back. No functional difference between a T-86 and a T-90. Why did you conclude it's a T-90A? Which engine?

Here's a T-90:



Note the straight splines on the mainshaft and the straight-cut sliding gear. Lots of pictures of T-90s online if you want to look for yourself.

Re which engine, that looks like a F134 bell. It's clearly not a 225 V6 bell. Thinking about it, I'd guess you could combine a T-90A input shaft and case with T-86 mainshaft and gears, and it would fit and function just like a T-90A. Looks like that's what you have.

 

Timgr, I think I messed up my reply by inserting the pic in your comment. Here is the picture again. And I think ITLKSEZ is right, it looks like somebody gutted my T90 and dropped a T86 in it. I will repair that one, I see no point in going back to the original.

 

Yep. Not much else to say here. T-90 case with T-86 gears.

Back when it was done, it likely made economic sense. Today, T-86 gears are basically not available, unless you find a good T-86 donor transmission. New T-90 gears are widely available. Behind a F134, either will last a long time and provide the same service.

 

And yes, it is an F134. Sr, you have a keen eye!
Now the question is: which rebuilt kit should I get? I was dumb enough to dump all the needle rollers so I cannot check dimensions.

 

Well, the input and output bearings have to be the same, or the swap would not work. Also, the input shaft pocket bearings should be the same, otherwise the T-90A input shaft would not be compatible with the T-86 mainshaft. There is no short F134-type input shaft specifically for the T-86, so that has to be T-90. You or someone should check the Jeep PNs and compare. The rest has to be T-86, and again, the resellers may be selling the same parts for either transmission. That would be telling.

 

What has happened is as Tim and others have said. T-86 guts in a T-90A-1 case. That is not an oddity as much as putting the T-90A-1 input on the T-86AA gears and using it with the F134 engine.

 

It’s been a lot of years since I was inside these transmissions, but if my memory serves me, I think the bearings are all the same. PM @oldtime for specifics. I’ve done the swap in the reverse order before (t-90 gears in t-86 case) after I blew the teeth out of the 86, but it’s been nearly 30 years.

Personally, judging by the looks of that one (rust, chipped teeth on input gear, mix-n-match...), I wouldn’t waste my time on it. T-90s are still out there for cheap. I’ll bet Donny has a pile of them.

 

Yeah, lesson learned I expect. I put old parts in baggies, mark with a Sharpie, and toss all the marked discards into a box in the corner of the garage. Stays there until I get annoyed months later and throw it out or move what I want to save to the junk bin.

 

X2

 

Pheeewww! I was losing my mind looking for the posts! Thanks Focker!

 

I have 2 or 3 T90's, but they all have had water in them, and look as bad or worse than Alex's. I've never done a T90 gears on a T86 case, or vise-versa. Is the input shaft length unique to only the T90? If thats a T90 input shaft in Alex's case, is the countershaft gear T90 or T86?
Thinking a little more about this, didn't Jeep use a T86 in the F134 Jeepsters? Maybe all Alex's guts came from a Jeepster.
I don't like the look of 3rd gear, and also the nose of the mainshaft where the rollers ride at the input shaft, as pictured in post #5.
Alex, count the teeth on the input shaft as there are two versions, 16 tooth and 18 tooth. The tooth count has to match the corresponding countershaft gear.
-Donny