Differential issue...

[| 1990 ZR-1 |]

Well Gentlemen, here I am again seeking help with the beast. I've had a great time for the past 3 months with the car since I repalced all the injectors, brakes, and replaced/fixed the FX3 system. Now I have an issue with the rear diff. The car is MY 90 with 34k original miles.

Two weeks ago, I noticed the driver rear wheel visually looked out of allignment. Upon closer inspection, it had a pretty big negative camber, and the toe was pointing in. A couple of days prior, I hauled about 300lbs in the trunk area, which I didn't think was a big deal, but it sure enough caused some kind of damage. The car drove fine with the exception of very slight vibration at about 40 mph. At first I thought maybe one of the busings wore off or expolded, or some suspenssion part either broke or bent, but after jacking the car up and inspecting all the components underneath, I didn't see anything out of ordinary. I dropped the car off with my local mecahnic, and he said that something in the differential broke and is causing the wheel to get out of allighment. He said he would not take it apart and suggested we replace the whole rear diff, which looks like an expensive option.

My questions are:
Has anyone else experienced anythign like this and could tell me which part would be a suspect? I searched the tech forum, but didnt' see anything.

Should I take the car from my macahnic and take the diff appart to see if i can fix it?

I've never removed diffs before, but am pretty handy. How complicated is it, and would I need any special tools? I do have the service manual that I will reference to, but if anyone has step by step instructions they could reference, I'd appreciate it.

Last but not least, I keep reading about the 4.10 gear upgrade. How envolved and costly is this upgrade? If it's too much money, I'd rather just replace the broken part, and put her back together.

As always, thanks in advance!


-Gary

[Ccmano]

Originally Posted by Dynomite

Hold on.....I think the camber adjusting cam moved on you. Loosen the nut (center of photo) and rotate the cam to get the camber you desire

If something let loose in differential, you would hear it and that has nothing to do with camber. You have a short shaft between differential and wheel bearing as you can see on differential side in photo.

No way that's internal to the differential! Either a suspension issue or a wheel bearing (even that would be a stretch). Your mechanic is either clueless, doesn't communicate well, or is flat trying to rip you off.
H

[| 1990 ZR-1 |]

Thanks guys. I'm really hoping this is the case. This guy came highly recomended by my neighbor who's a car enthusiast, but is not a technical at all.

Here's another thing. This mecahnic installed my new tires and did a 4 wheel alignment about a month ago. I bet they didn't tighten somethign up properly, and with the additional weight I had in the trunk, somehtign gave and shifted. It just sounds wierd that a diff would go on a 34k mi car. I don't drag race it, or abuse it, or launch it severaly. Just spirited driving on weekends. I'll call him tomorrow. I just wish there was a knowlagble corvette mechanic around here.

[PhillipsLT5]

Try VBP align recomendations, works for me
http://www.vbandp.com/
Dynomite your info is GREAT!!!!!!!
4.10's are the way to go, really push you back in seat, instant improvement

[ZR1Vette]

Sound like the boys have the issue ID'd, but just 'to cover' everything inspect the leaf spring and make sure is was not fractured etc. with the additional weight.

[Z51JEFF]

For starters Id find a new mechanic.Id go with the camber adjustment moving.

[| 1990 ZR-1 |]

Quick update. I had a chance to pick up the car from the mechanic this week, and jack it up and inspect it myself. I did not see any bent parts, and I also do not see anything visibly wrong with the diff. The mechanic claimed that the half shaft where it connects to the the diff was loose, but I pulled on it in every which direction by hand and also with a crowbar and it didn't budge. I did notice, however, that the yoke is presssed into the diff about an 1/8 of an inchwhen compared to the passanger side and caused the big spacer with rounded edges rub against the diff housing. I also noticed a little bit of diff fluid on that side, but not enough where it dripped on the floor. I started to inspect the trailing rod bushigs, and noticed that the all have small cracks on them and one on the lower rod connecting to the spidle had a huge crack in it. I removed the lower dog bone and noticecd that the bushing is not centered and looks severily deformed. I ordered a new set of 8 bushings and will repalce them on both sides. I just hope this has not caused any issues with the seal in the diff since the half shaft is pushing into the diff.

I really think that my issue lies in those 21 year old, blown trailing rod bushings. I belive when i had the additional 400lbs loaded in the trunk that day, the extra weight did it. If this is the case, I'm going to take those old busings to my mechanic and will put him to shame, since he's suppose to be the pro, but I, a none mechanic just a handy person, used my brian and figured this out within the 15 minutes I had the wheel off.

I'll keep you guys posted once the poly bushings are installed.

[lbszr]

Originally Posted by | 1990 ZR-1 |

Quick update. I had a chance to pick up the car from the mechanic this week, and jack it up and inspect it myself. I did not see any bent parts, and I also do not see anything visibly wrong with the diff. The mechanic claimed that the half shaft where it connects to the the diff was loose, but I pulled on it in every which direction by hand and also with a crowbar and it didn't budge. I did notice, however, that the yoke is presssed into the diff about an 1/8 of an inchwhen compared to the passanger side and caused the big spacer with rounded edges rub against the diff housing. I also noticed a little bit of diff fluid on that side, but not enough where it dripped on the floor. I started to inspect the trailing rod bushigs, and noticed that the all have small cracks on them and one on the lower rod connecting to the spidle had a huge crack in it. I removed the lower dog bone and noticecd that the bushing is not centered and looks severily deformed. I ordered a new set of 8 bushings and will repalce them on both sides. I just hope this has not caused any issues with the seal in the diff since the half shaft is pushing into the diff.

I really think that my issue lies in those 21 year old, blown trailing rod bushings. I belive when i had the additional 400lbs loaded in the trunk that day, the extra weight did it. If this is the case, I'm going to take those old busings to my mechanic and will put him to shame, since he's suppose to be the pro, but I, a none mechanic just a handy person, used my brian and figured this out within the 15 minutes I had the wheel off.

I'll keep you guys posted once the poly bushings are installed.

From your description, I would investgate the diff more, as the mechanic described the problem. Because the half shaft does more than just transfer torque. It acts as a fixed link that controls camber, the lower camber rod is the adjustable one. If the halfshaft could be shortened, it would make negative camber, which is what would happen also if the yoke was pushed in the diff. What you found actually backs up the mechanics findings. If the halfshaft has trully pushed in the diff, then that would affect camber and also toe. A lot of force is pushing inward or outward on the halfshaft normally, depends on what type of driving is taking place and if something broke at the halfshaft yoke while in a hard turn....it could be an exciting ride!

If the yoke is pushed in the diff, there might not be enough adjustment in the camber rod to make for it.

The yoke should have .0045 in. +- .004 in. end play. It seems like if part of the yoke is wearing into the housing, the clearance would be a lot more, unless it was set wrong at the factory.

[| 1990 ZR-1 |]

Originally Posted by lbszr

From your description, I would investgate the diff more, as the mechanic described the problem. Because the half shaft does more than just transfer torque. It acts as a fixed link that controls camber, the lower camber rod is the adjustable one. If the halfshaft could be shortened, it would make negative camber, which is what would happen also if the yoke was pushed in the diff. What you found actually backs up the mechanics findings. If the halfshaft has trully pushed in the diff, then that would affect camber and also toe. A lot of force is pushing inward or outward on the halfshaft normally, depends on what type of driving is taking place and if something broke at the halfshaft yoke while in a hard turn....it could be an exciting ride!

If the yoke is pushed in the diff, there might not be enough adjustment in the camber rod to make for it.

The yoke should have .0045 in. +- .004 in. end play. It seems like if part of the yoke is wearing into the housing, the clearance would be a lot more, unless it was set wrong at the factory.

Thanks for this. It makes perfect sense, and it was the answer I was afraid of getting.

How hard is it to remove the diff without a porper lift?

Once the diff is off, is it posible to just replace broken ande worn out parts? Or would you suggest replacing the whole diff with a new one?

Last but not least. What is the best source for diff parts?


Thanks!

[lbszr]

Originally Posted by | 1990 ZR-1 |

Thanks for this. It makes perfect sense, and it was the answer I was afraid of getting.

How hard is it to remove the diff without a porper lift?

Once the diff is off, is it posible to just replace broken and worn out parts? Or would you suggest replacing the whole diff with a new one?

Last but not least. What is the best source for diff parts?


Thanks!

I still would want to verify play in the yoke before tearing into it. Did you check with the wheel on at the 12 and 6 position, with the spring connected to the knuckle it might be hard to move and it might take another person to watch the yoke.

If you still don't feel any play, could try disconnecting the spring from that knuckle and try again, if you haven't already.

Not for this rearend, but gm 12 and 10 bolt, I've bought parts from http://www.drivetrainspecialists.com/