Differential Stuck? Car Glued to Floor....

[ConchZ]

Here's a weird one. I finished up my gas tank, and took the car down off the jack stands. Fired it up, put it in gear, and it wouldn't move, either in forward or reverse. It felt like I had forgotten to remove the wheel chocks, it was that stuck. I got out and looked around it and under it and saw nothing, so I got back in and put it in reverse and gently gave it enough gas that it chirped the left rear tire. I heard a slight popping sound from the right rear. Car wouldn't move, though. Shut it down and jacked it back up. Spun all four wheels by hand, they moved easily. Put it back down, started it and it drove fine. Jacked it back up and could see nothing unusual, so I took it out and drove it hard, trying to stress it. Nothing unusual was noticed.

My differential is original, with 102k miles. I replaced all the U-joints last fall, along with new mount bushings plus the front mount that Dave made. This was in an attempt to solve a clunk that occurs whenever you let out the clutch with the car in gear. The clunk is still there, and I decided it is due to play in the differential. I can grab the right half shaft and rotate it maybe up to a quarter of an inch either direction, and when it does engage inside the diff, I hear the clunk noise. The left half shaft does not have much play in it.

I'm not sure if the play and the strange sticking behavior I got after lowering the car off the stands are both related. I may be asking about two different things, so I'll clarify the questions:

1) What could have caused the sticking behavior?

2) Should I be concerned about the play in the differential? Would you trust it on a 500 mile round trip? The PO says the clunk was there for the 20 years and 30k miles he had the car, so I wasn't worried until the above sticking problem happened.

There are no other noises or odd behavior in the driveline. I don't think the sticking was from sticking brakes, as I really don't think those rear brakes are strong enough to hold the car in place against the engine like it did. The front brakes might be strong enough, but they are completely brand new. When I did the fronts, I adjusted the backs and cleaned them up a bit. They seemed fine. It's a 73, with a completely stock driveline, except for those Spicer U-joints.

Thanks for any help!

Edited April 25, 2011 by ConchZ

[SteveJ]

Did you have your emergency brake lever pulled up? If so, the shoes are stuck to the drum. Search for that to find solutions.

[ConchZ]

I did put the E-brake on before putting it on jack stands, as its just a habit when I jack up the car. My E-brake is not very strong, even when fully engaged...so it wouldn't normally hold the car that tight against the engine, though. I suppose that the suspension being in full droop for two weeks could have pulled the cable further than usual, causing the shoes to get stuck on the drum, and then when I set the car down, found it was stuck and then jacked it back up the shoes came unstuck, thus allowing me to turn both rear wheels by hand while it was on the jack. That's an interesting chain of events, though. I guess I shouldn't put the brake on before jacking up the back end? There's no need to do it, I know.

Any thoughts about the play in the diff?

[SteveJ]

Play in the differential - Check U-joints. Check all of the bolts for the U-joints. If the play is inside, drain the oil and search for metal.

[5thhorsemann]

That is not a u-joint, You need to check your pinion gear and ring gear out.

[ConchZ]

I'm pretty sure it isn't a u-joint, too. As I said, I replaced them all. Plus, if you grab the shaft inboard of the inner most joint and twist it, you can clearly tell the play is coming from inside the diff. I know next to nothing about diffs. I could drain it and take the cover off, but unless I see something obviously broken, I doubt I could tell what was wrong with it. My long term plan for the car is to swap the stock diff for a lower geared one and swap in a 5 speed, but I wanted to put all that off until next winter. Since it's been clunking for years(two years with me, and 20 with the PO), I was hoping to just enjoy driving it for the next 6 months. I do want to take one 500 mile trip in it this summer, though. I hate to risk having a broken diff on that trip.

[5thhorsemann]

Now I am TOTALLY speaking out of my league when it comes to this style jackpot, and admit that I have never gone this deep into a Z R/P set up. There are 2 things that are usually the culprit in play in a diff. (bad parts excluded) your ring gear is adjusted too far outboard, or your pinion is too far forward in the housing. The ring gear is the easiest to adjust (in MOST) rears, the bearings can adjust left or right independently. The pinion usually requires shimming.

I am probably at least somewhat WRONG when it comes to these rears, and I hope someone chimes in to educate us on this.

My point is, I'm thinking you can take it to a transmission shop and have it adjusted. And I will be watching this thread to learn my new thing for today.:bulb:

[jmortensen]

Sounds to me like you're blaming the weird issue you have and the clunk on the diff. Diff clunk is almost never the result of the differential. Search "diff clunk" and you'll see people replacing diffs and having the exact same noise, etc.

I would expect your initial problem to be something with the ebrake. I have a friend who owned a Fiat Spyder back in the 80s and it chipped a tooth on the ring gear and he managed to the the pinion locked together with the ring and it locked the diff solid but I've never heard of another instance like that before or since, and I've had a decent amount of exposure to different differential problems. You can always pull it and check, but I just really doubt that what was going on had anything to do with the differential.

[black gold man]

Did you pull the drums and look. This past summer my rear locked up on my 78.

The liner crumbled

off the brake shoe i thought rear end until i took the drum off.

Once i saw an article it was a review on a new 1978 z . One of the complaints was that clunking noise.

[ConchZ]

After replacing everything else around the diff, and noticing the play in the diff, I'm pretty sure the clunk is coming from the diff. The key evidence for me is that I can reproduce the clunk by turning the half shaft by hand. I watch it move and it doesn't clunk until it engages inside the diff. As for the sticking problem, I figured it might be related, but I don't know enough about diffs to say. I suppose I could have had a locked up brake, then lost a shoe when I jacked it up, but before I spun it by hand, or the ebrake magically released when I jacked it back up. I just thought it was more likely that the diff got screwed up by having the half shafts hanging unevenly because the left side had a tire on, but the right side did not. I figured maybe it realigned itself when I took the weight back off of it as I jacked it up. There's probably going to be an interesting end to this story.

[jmortensen]

I've posted here and at Hybrid Z about testing backlash from the wheel or from the driveshaft. Short version is you can't. Suffice it to say that I think it is unlikely (but not impossible) that your problem is the diff. I do think it is impossible to turn the halfshaft and find out anything meaningful about what is going on inside the diff, unless you feel broken spider gears or something horrendously wrong.

Here is one of those previous threads. Looks like the problem in this case was a transmission mount: http://forums.hybridz.org/index.php/topic/91146-drivetrain-clunkingim-going-to-need-some-help/

Good luck finding your clunk.

Edited April 26, 2011 by jmortensen

[Bonzi Lon]

If your 73 is like mine it should have a magnetic drain plug. Might drain it into an aluminum pan then search further in the oil with a magnet for any other bits. It will only cost a refill to see if there are chunks in the soup.

Bonzi Lon