T90 Reverse Idler Shaft Tear Down Controversy

[BobM]

I am right in the middle of the T90 trans on my CJ3A. I have it torn down inspected and parts ordered. I used the Service Manual for Universal Jeep Vehicles as a guide. It was fairly straight forward nothing unusual. A LOT of water damage.

The service manual page 168, indicates you "remove the reverse idler shaft by driving it into the case with a brass drift" A procedure I followed right down to the brass drift. I had no trouble. I drove the shaft out by completely driving it into the case and, removing it. All seems good.

As I was looking for parts on the WWW, I noticed a tear down article on the CJ web page. The writers stated to NEVER drive the reverse idler shaft into the case as it will damage the case and will not come out that way? I just did that and it seemed to work fine. Is the service manual incorrect? I wonder if I damaged the case? I then read in more than one forum about persons having a very difficult time getting the reverse shaft out. All kinds of ideas on how to perform this difficult task. All focused on getting the shaft out via the outside of the case. I had zero trouble driving it into the case with a brass drift per the manual. What gives here? Can anyone shed a little light?

[oldtime]

BobM. for what it's worth it's certainly true that one should never drive a T98 or a T18 reverse gear shaft into the case.

[BobM]

I am at a loss! Maybe the writers got mixed up with the model. Right now I am at a loss. Either the manual is wrong or, the web page instruction for the T90 on the CJ3A page is misquoted.

[athawk11]

I have always followed the advice laid out in Rick Stivers T90 rebuild guide.  He too was pretty adamant that the idler shaft should be driven out the back of the case.

http://www.willystech.com/wt/T90RebuildGuide/T90rebuild.htm

[BobM]

I have always followed the advice laid out in Rick Stivers T90 rebuild guide.� He too was pretty adamant that the idler shaft should be driven out the back of the case.

http://www.willystech.com/wt/T90RebuildGuide/T90rebuild.htm

I was reading Ricks guide where I found the info. He is clear about driving it to the outside of the case. I can only say, I followed the manual, drove to the INSIDE and it worked quite well as far as I can tell. The shaft came out fairly easy to the INSIDE of the case as the manual indicates it should be done. Maybe it can be done either way? It would be great if someone could clarify this.

[BobM]

I do know that the manual has been wrong before. Specifically the process for rebuilding the water pump. I believe more than one person has ruined a pulley taking a pump apart per the manual.

I hope someone can shed a little light. What can happen when you drive a T90 rev idler into the case?

[athawk11]

Well, I can confirm that the internet is riddled with stories pointing out the mistakes in the service manuals, and some other printed Willys materials.

The boys knew how to do it back then, but the editor's translation leaves us wondering if they were smoking something potent.

My understanding is the hole on the back of the transmission is a few thousandths of an inch smaller than the internal hole, but I didn't ever try to measure it.� My guess is the tolerance between the case and the shaft isn't as tight...or perhaps is more tight than it might have been at some point.

[oldtime]

The Universal Service Manual (USM) is correct on this matter.
There is no problem with driving the T90 reverse idler shaft into the case.
In fact it's safer than using a long drift at angle to drive the reverse shaft out from the case as is required in some other Borg Warner transmissions.
If not careful when driving a shaft out away from the case, one runs the risk of case bore damage.

Some Borg Warner transmissions use a slightly tapered reverse idler shaft.
The T90 and very similar T86AA transmissions have a reverse idle shaft with zero taper, so no problem is encountered when driving it into the case so long as the end is not mashed.
The T90 reverse idler shaft is a medium press fit and held in position via the lock plate.

I've rebuilt my share of BW T90's and have always driven the reverse idlers into the case and have never encountered any problems doing so.

That said...
All Borg Warner transmission countershafts must be driven out toward the rear of the case because the countershaft bore is always tapered to provide a tight seal up front.

[BobM]

Thanks a ton! I was sweating it. I thought I may have split the bore inside the case. The shaft was tight but, nothing serious. Maybe a tad tighter than the counter shaft. Once it cleared the case front it was fairly easy to tap it the rest of the way into the case and remove it.

There are a lot of guys trying to push it through from inside the case, with all kinds of ways. I wonder if Rick could update the instructions. They are very good. I had not seen them. I was using the manual. I have the box torn down and parts just arrived. Now that I have read Rick's guide, I am finding it an excellent guide.