Free play in the differential

[Mheinle]

Hey all,
I figured I would send this out to people smarter than me to get some advise or thoughts on a issue I am hearing. I recently replaced my front control arms as well as shocks and springs all around. This resolved a click sound I was hearing when I would stop as there was play in the control arms. I now am hearing a clang sound when I begin accelerating, specifically as I release the clutch. I was not sure of where the sound was coming from and was thinking I introduced different suspension issue. Placing the car on stands I turned the drive shaft and it seemed as though there was some excessive play in the diff. Basically, I would turn the shaft clockwise and hear it is engage with the diff gears after a half inch or so, then the same when reversing the direction. The sound was not the same as when I was driving so I fired the car up and had my wife put it in gear and let out the clutch reproducing the clang, she would shift to reverse let out the clutch and clang. So I know the sound is not suspension and I am fairly certain that play I mentioned is the source of the sound, it just sounds different when the engine is turning the shaft vs. my hand. Is there any thoughts on how I can adjust out the play or what parts might be the issue? The diff is a black box of mystery for me, I have never looked in one or messed with one at all.

Any advise or thoughts are appreciated as always!

[18Fiatsandcounting]

A clang sounds more metallic, whereas differential issues are more of a clunk. Could the issue be the center driveshaft support? Or the bearing associated with it? These are at the rear of the short driveshaft, right in front of the forward U-joint.

I wouldn't mess with the differential unless there is no other option. It's a pretty specialized skill with special tools required. But, a half inch of driveshaft rotation before the differential engages is not terrible. Maybe a tad loose, but I don't think it would cause an issue. If you do need a new differential, I'd look for a good used rear axle/differential.

-Bryan

[Mheinle]

I did try to pay attention to the u-joint while testing by hand it did not seem to be an issue, but removing the shaft would probably be the best way to check. I did not check the carrier bearing, so maybe I need to check that. The issue really sounds like it is coming from the diff but I may definitely could be wrong. The noise does not impact performance (not that is performs great), but it is definitely concerning. I am planning an engine rebuild in the fall/winter so that will be my best opportunity to really look over the u-joint. That said I will put her back up and take a closer look again.

Thank you! I really appreciate the feedback and thoughts, as the great G.I Joe said "knowing is half the battle."

[ORFORD2004]

You can remove the driveshaft and see if you see play in the pinion gear.
For the backlash, you will have to remove the cover and use a dial indicator to check the play. And you will be able to inspect the gear

[Mheinle]

Hey guys,
I went under the car again today and did some more wiggling and banging. The center support does not seem too bad, if I push up on the shaft near the support it moves about 1/4 inch or so. I don't know what is acceptable for that center support and bearing though. I rotated the shaft forward and back and I think 1/2 inch is too generous, it is maybe 1/4 to 1/2 inch. If I smack the shaft I hear the clank sound or at least it is a similar sound. I am wondering, is it possible that when I change direction the first moment of acceleration causes the rear portion of the shaft to buck a little causing the sound? Would that be U-joints? At higher speeds the car drives pretty smooth, but maybe a u-joint could still be failing? I am tempted to grab a drive shaft rebuild kit from AR, I have never pulled the drive shaft from the fiat, other cars yes Fiat no. How bad is it?

Thanks again!

[ORFORD2004]

How bad is it

Easy

[Mheinle]

How bad is it

Easy

Your over whelming evidence of the ease of the shaft removal has me convinced. I will order the parts, I figure this car is 40 years old and virtually everything on it needs replacing. I am sure I will have questions along the way with the shaft, but it will be a few weeks before I can get around to the rebuild.

Thanks!

[ORFORD2004]

The worst part is changing the universal joint. Paint parts to be sure to reinstall at the same position.

[Mheinle]

Yeah I need to go grab a paint pen. I have read many post indicating the importance of maintaining the balance. The u joint replacement does not look too hard and I see the diff side of the shaft is just four bolts. I need to research the guibo side a center support.

[18Fiatsandcounting]

I scribe the rear driveshaft flange and the input flange to the differential so that I put them back in the same orientation. Not sure it's strictly necessary, but might help with keeping things balanced as well.

The front section of the driveshaft slides out of the guibo on a splined shaft. The carrier bearing in the middle can be tricky, mainly in terms of removing that nut. It can be on there pretty tight.

-Bryan

[Mheinle]

Thanks all,
I was able to rebuild the shaft which seems to have resolved the clank/clunk sound. Unfortunately, I made two errors that are causing a headache.
1. I did not mark the sleeve when removing the front shaft yoke. The manual says there are marks to align it but I don't see any.
2. I marked everything else, but while working most of the marks scraped off.

This has resulted in the shaft not being well balanced, at least it does not feel balanced at 80MPH. I am trying to figure out out how to re-align things, but I fear a shop is the way to go.

Thank you to 18fiatsandcounting for all of the help on the side!