Output Shaft Play? AODE

RufusT · Jan 6, 2016

Hello Again Everyone!

I noticed quite a bit of play where my driveshaft connects to the output shaft of the transmission on my 1994GT (automatic/AODE). I can move the shaft noticeably, though I didn't measure it.

Is this connection supposed to have a noticeable amount of play in it, or should it be reasonably stiff? I am trying to figure out if this could be the source of a forward "bump"/Weight Transfer when the car is downshifting from 2nd to 1st.

Any input would be appreciated.

Thanks,
RufusT

RufusT · Jan 8, 2016

I climbed up under the car again and it seems like I only have significant play that goes up/down. This leads me to consider that the ujoint is going out. However, when I put the car in neutral and turned the driveshaft enough to move the ujoint 90 degrees, the play was still only up/down primarily with very little side to side movement. I likely will be removing the driveshaft and replacing the ujoints this weekend, just to eliminate them as possible failure points.

Outside of that, does anyone have any other ideas of any other things to look at?

RufusT

lwarrior1016 · Jan 8, 2016

Is there any way you can have someone video this while you move it? I would like to see how much play there is.

RufusT · Jan 11, 2016

I tried to get a video, but it didn't turn out very well. I had a buddy come by and take a loo at it. He said that he thinks the tailshaft bushing is likely going to need replaced in the future, but that the play that is there shouldn't cause the issues I have relative to the weight transfer during downshift. More likely, the bushing will eventually cause a vibration. This leads me back around to thinking that it has to be something in the rear end of the car, from when I re-geared.

My current thought is that the pinion depth may not be correct. I was reading on some of the various forums and got to reading how the pinion pulls forward slightly when force is applied. While this is not hugely significant in most instances, it is possible that it could cause an issue where there is a "settling" that happens when the car is slowing down and the shift happens. I will be taking it all apart again soon.

lwarrior1016 · Jan 11, 2016

RufusT said:
I tried to get a video, but it didn't turn out very well. I had a buddy come by and take a loo at it. He said that he thinks the tailshaft bushing is likely going to need replaced in the future, but that the play that is there shouldn't cause the issues I have relative to the weight transfer during downshift. More likely, the bushing will eventually cause a vibration. This leads me back around to thinking that it has to be something in the rear end of the car, from when I re-geared.

My current thought is that the pinion depth may not be correct. I was reading on some of the various forums and got to reading how the pinion pulls forward slightly when force is applied. While this is not hugely significant in most instances, it is possible that it could cause an issue where there is a "settling" that happens when the car is slowing down and the shift happens. I will be taking it all apart again soon.

When you rebuilt the rear end, did you use all new bearings and races? Did you preload the pinion bearings, and use a good dial type torque wrench to verify the preload is within spec? Also, did you run a contact pattern on the gears?

RufusT · Jan 12, 2016

I did use new bearings and torqued to spec. I even bought a new in-lb torque wrench to eliminate that from consideration. The contact pattern looked pretty good, when compared to the pictures in the manual that came with the bearings. I read an article that discusses ways to extrapolate the necessary pinion shim, using measurements of the old and new pinion heads, relative to the MHD... So I am going to take the rear apart (again) in order to evaluate the pinion depth in this manner. I also found some information on ways to confirm that the carrier shims are correct. I am thinking they may be a little tighter than they should be, based on some things I have been reading. It could be either of these things being off - or it could be something completely different....

lwarrior1016 · Jan 12, 2016

Carrier shims adjust the backlash, you measure that with a dial indicator. Get one with a magnetic base and put the dial on one tooth and move the ring gear just enough to see the amount of play between the teeth. Now, all that being said, Have you checked all your mounting points and bushings for the rear end? What about the transmission and engine mounts?

RufusT · Jan 26, 2016

Here's an update: I rebuilt the rear end for the third time. This time, I made some measurements of the old ring/pinion and compared to the new ring/pinion, which turned out to be essentially identical in their depths. This meant that the shim needed for the carrier and pinion should be the same. I put the same total shim amounts in place on the new ring/pinion and measured backlash to be at .0012 which is a little loose but still within range. The contact patterns looked appropriate based on my limited experience (a little toward the front/center and both were nearly mirror images of each other). Since it all looked good, I put it back together.

I have been driving it for just over a week this way, so I jacked up the rear and checked for play in the rear end flange. It is still solid and does not move in any direction at the bell housing. This leads me to believe that my rear end rebuild was completed and is working within spec.

That said, I have noticed a few other things. In all of this, I had not really been very observant of my shifts up from 1st to 2nd, as they are happening during acceleration and are less noticeable... The more I paid attention, the more I realized that my shifts INTO 2nd are just as hard as my downshifts OUT of 2nd. Shifts into and out of the other gears seem to be fine. This has me considering that my issue could be in the transmission. I've read a few posts that indicate the 1-2 accumulator spring could be the issue and most of the direction seems to be that I should look into a shift kit.

Will a shift kit make the shifts in all gears stiff and hard like I am getting now? Am I possibly way off on this? Any thoughts?

R

RufusT · Feb 1, 2016

I jacked it up again this weekend and confirmed there is no play in the rear flange. The rear end is quiet and does not make any accel/decal noises, so I believe the rear end to be working as expected.

That said, it occurred to me that the noticeable shift could be related to the rear gearing. As the driveshaft is spinning faster to turn the wheels and my understanding is that the computer shifts based on driveshaft rotations, it would stand to reason that the upshift and downshift are happening at a different speed. I would think the faster turning of the driveshaft would result in an earlier upshift and a later down shift. As such, it could be that this change in shifting points could cause the problem - I would think...

This has me considering saving for a Moates Quarterhorse and associated software to tune/tweak the shift points.

Any input?

R