8.8 Rebuild Nightmare - Deceleration Clunk

RufusT · Dec 31, 2015

Hello Everyone!

I have a 1994 Mustang GT with Automatic Transmission. This is my dream car and I love it. However, I love what I want to do with it more! That said, While I am not a paid mechanic, I have built a chopper, maintained and upgraded a Jeep and now moved to my Mustang. I decided I wanted to upgrade the rear gears from 2.73 to 3.73 earlier this year. For my birthday, I received a set of Ford Racing Gears. Following the instructions at CJPonyParts, I conducted the upgrade. In an effort to make my life easy, I had installed a Yukon Gears Crush Sleeve Eliminator... numerous times... to get the preload right. When it was 22 inch pounds, I installed the carrier and set backlash at .009 - then put it all back together, included a little of 2 quarts of Royal Purple (expensive stuff, but if you are doing it, so it right, right?).

I drove it for about 30 miles to get the initial break-in started. Toward the end of that stretch, I started to feel a weird deceleration clunk. I drove the car another 250 miles, figuring the clunk was a bad u-joint or loose control arm. this was a total of about 4 days. It got progressively worse, so I pulled it into the garage and verified that the pinion was loose and the clunk as the pinion settling down on deceleration, only to go back up on acceleration. So... I got to take it all apart again....

I finished the second rebuild today. I spent 2 days trying to get the crush sleeve eliminator to allow for any bearing preload. I couldn't get any preload at all - even with ZERO shims. I could get the pinion nut tight, with no movement, but could not get any preload. I thought the bearings may have been ruined by the modest about of driving I had done, so I replaced them and this time, installed with a crush sleeve instead of the eliminator. Crushing that thing is not easy, but I was able to get it to preload the bearings to 26 inch pounds. As the pinion preload was a little more than the last time, my backlash was a little out of line, so I got the fun of redoing the shims in the carrier. This time, backlash measurement was an average of .0875 (measured in four places). I recognize this is a little tight, but figured it would loosen up a little over time... so I put it all back together and took it for a drive...

I have put about 10 miles on it, just around town... and the deceleration clunk is there. There is not a sound with it (yet), which is how it was originally before I drove the additional miles.

I had my measurements checked by a friend to confirm the pinion preload and carrier backlash, as it thought I had done that wrong... I'm a little lost of how this pinion could be loose, after all the parts being installed to spec.

Does anyone have any idea how this could happen, or what I need to look for that would cause this problem? Any input is appreciated.

Thanks,
RufusT

OLD H2S · Jan 1, 2016

Right off the bat wild guess I think the outer bearing races for the pinion are not seated and every time you tighten your numbers look good but upon driving the input forces move the outer races a little and pre load drops to zero, confirmed by your after check. If you have the first crush sleave measure it and this plus a .002 shim should be the starting point for the Yukon shim set up, and it should come up loose on the pre load. Since the pinion nut is torque to yeild type, use one of the old ones over and over till you get everything fixed and then go to a new one for the last set up. I have had this problem using crush sleeves and had to keep tightening weekly till the races seated and the gears quit whining .Could be some junk behind the race or it is canted and raising a burr as it gets closer to seating. At this point do not keep buying new parts to put in it, do not worry about damaging a bearing, at worst they will growl but not be too harsh till they are replaced if they have to. DO NOT USE AN IMPACT GUN. even at a low setting it will indent a race.
How can I help? here is a picture of my drivers side axle shaft today, so I am right there with you brother changing my gear set to 3:73. I have the same Yukon shim set to try out. I will report back what I find out, got to wait for the axles to get here so no instant information till No.47 is back on the road. Any way you look at it you're going to learn a lot and be good at Ford 8.8 rear ends by the time this saga ends. We have all been there with install that went bad, really makes you hate the car. It just sucks that you have to become an expert at everything you touch. OldFart out.

96blak54 · Jan 1, 2016

Excellent tech!

RufusT · Jan 2, 2016

OldH2S - Thank you for your reply! I was just telling a friend of mine that the only thing I could imagine to be the problem at this point is the races, as they are the only component I have not completely replaced. In my mind, if the races are not set completely against the housing one of them is mis-formed in some way, the bearings would gain preload, then lose it when torque is added and everything lines up correctly... I was debating if I wanted to run down that path with my third tear down and now it seems, since you also came to the same conclusion, that I am not crazy for my thought process. Looks like I know what I am doing to this thing next!

OLD H2S · Jan 2, 2016

Lets us know what happens.

lwarrior1016 · Jan 2, 2016

I agree with the problem being related to a bearing race. I always seat my races with a punch or a brass drift and a good solid hammer. When I load my bearings I do it with the pinion installed and the carrier, no axels. Just a quick question, [MENTION=20556]RufusT[/MENTION] did you replace the pinion bearings and not install new races? That in itself could be a problem. There are 2 or 3 different bearing/race set ups and if the are mix matched they will not work correctly.

RufusT · Jan 4, 2016

OK - A quick update..

I bought new races for the car and began tearing it down for the third time. When I got to the driveshaft to disconnect it, there is no play in the driveshaft/pinion area. I can't move it - even with a pry bar... So I am thinking that my issue is not in the rear end. I am expecting that the rear end is ok, but that the issue is somewhere else in the driveline. In fact, I followed the driveshaft to where it connects to the automatic AODE and there seems to be quite a bit of play on that end of the drive shaft - is this normal?

My current thought is that whatever problem exists is my own doing. I did not completely remove the driveshaft when I did the rear end, opting to move it up and out of the way. Perhaps, during the repair, something got messed up at the tranny area? or possibly the speedo gear that was installed is not installed right, causing some kind of issue there? I don't really know for sure, but the rear end may not be the culprit after all....

As for the races that are in the rear end, I replaced them during my first rebuild, with the install kit from USA Standard. All of the bearings were replaced on the initial rebuild, but when I had the loose pinion situation come up, I had chose to replace the bearings to eliminate them as a possible issue. I didn't think the races would have had issues that would not be visible at the time. I had not considered that they may not have been seated or could have had a manufacturer defect when I did the second rebuild.

That said, my current issue is a low speed deceleration weight transfer that seems to happen in tandem with the downshift from 2nd to 1st. no real sounds (yet) as it doesn't seem to have impacted the rear end (yet). I think it is the same issue that was there before, which ultimately caused the rear end to fail... I may end up taking it to a shop, but I really don't like paying for labor if I can do it myself.

Any input is always appreciated. Thanks guys!

RufusT