T-90 rebuild help

Thunderbird712 · Post by **Thunderbird712** » Thu Dec 17, 2015 4:44 pm

I am getting close to finishing the rebuild of my T-90 out of my M38A1 and have a question. I have been using the T-90 rebuild guide at willytech.com which says that the rear main shaft bearing has to be pressed on. When I go to slide my bearing on it slides right up to the spacer. I am using the original main shaft and a new bearing. I only saw a repair and rebuild standard diameter for the pilot end of the main shaft in the TM. If the bearing doesn't press on does this mean the main shaft is worn to much?

oilleaker1 · Post by **oilleaker1** » Thu Dec 17, 2015 6:00 pm

It doesn't press on. Yours is normal. All mine are this way. John

Bretto · Post by **Bretto** » Thu Dec 17, 2015 9:37 pm

X2
Mine didn't exactly slip on and off but I didn't need a press. Just a few taps and it was on. To get it off, I used the 1st/rev gear as a slide hammer to knock it off.

Post by **wesk** » Thu Dec 17, 2015 11:25 pm

I think where Rick's guide says press fit (AKA Interference fit) there is actually a location fit only. I do not think a free sliding inner race on the main shaft is the norm. It may be the norm for heavily worn main shafts.

For the bearing to perform it's job both the inner and outer races are not suppose to move on the edge fitted to. IE outer race must not move in the retainer and inner race must not move on or relative to the shaft. Just the rollers within the races are suppose to spin. A location fit assures the inner race will not rotate about the main shaft but instead will rotate with it always. This fit requires mild tapping to slide the bearing in place on the shaft. This fit also is required on the outer race as you should have to tap it into the bearing adapter.

If you have a sliding fit the inner race will be free to rotate around the shaft. This will wear the shaft even more. This phenomena will be even worse when the tranny lube is cold.

Thunderbird712 · Post by **Thunderbird712** » Fri Dec 18, 2015 12:53 pm

Thanks for the replies. I am glad I asked because I got scope locked on the fit between the bearing and shaft and don't think of the fit between the bearing and the adaptor. The new bearing doesn't need to be tapped in to that either. I have another parts transmission and will take a look at that shaft and adaptor. If there is any doubt I will just buy replacements. Again thanks for the help.

Thunderbird712 · Post by **Thunderbird712** » Fri Dec 18, 2015 3:39 pm

Just as a follow up I pulled the main shaft and bearing adaptor out of a second tranny I had. The bearing end is not as worn and would require the bearing to be pressed on as well as tapped into the adaptor. However the pilot end of the shaft measures out to 0.7625 and according to the manual the tolerance is 0.7627 to 0.7632. So since I dont want to half a** anything and have issues with the pilot bushing later I got to purchase a new shaft. I am glad this came up because I missed on my other main shaft pilot end measured out to only 0.7610.