Help! C3 noob with rear end problems!

[Oldschool64]

Hey guys, I hope that I am posting this in the right place. I just replaced all 4 u joints on the halfshafts of my 68 and noticed a tight spot during rotation of the wheels with the trailing arms supported to relieve the extreme angles of the axles. I took it for a spin hoping that some exercise would fix the problem. NOT! It feels like the rear of the car is wobbling as it drives down the road. Not much noise is heard either. Also too much wobbling to be attributed to bad tires or rotor runout. Any suggestions? Thanks.

 

[Vettehead Mikey]

I'd look for a binding u-joint. It's easy enough for one of the needle bearings to fall in sideways during assembly.

 

[Oldschool64]

I'd look for a binding u-joint. It's easy enough for one of the needle bearings to fall in sideways during assembly.

Thanks Vettehead Mikey, but that was the first thing I checked. All u joints had smooth operation with no binding or grinding. I will admit that there are certain other areas that need addressing ie, bad tires and check rotors but I didn't think it would be this extreme. It feels like driving with a flat tire.

 

[Vettehead Mikey]

If you disconnect the half shaft from the wheel bearing assembly, does the wheel spin smoothly?

 

[Oldschool64]

If you disconnect the half shaft from the wheel bearing assembly, does the wheel spin smoothly?

Yes it does on both sides. I disconnected both halfshafts to try to isolate the problem. The binding seems to be in the rear end. I need to drop the driveshaft to be certain though. I will let you know when I do. The 4spd trans shifts thru the gears pretty well so I doubt it is the culprit.

 

[GTR1999]

I agree with Mike, check the obvious first. Good to know you blocked up the IRS so it wasn't hanging. I had a customer crack a posi case I 1/2 with the shaft hanging down on a lift while putting it in gear.

Now 68 diffs has their issues. The posi case was the left over design from 1965 and prone to cracks. The spiders were weaker then the later ones but overall not too bad of a unit.

As Mike mentioned jack it up and make sure there is no issue with the rear bearings. Check the end play in the diff axles and then if the driveshaft is disconnected spin it. It should be smooth.

If I can help let me know.

 

[Oldschool64]

I agree with Mike, check the obvious first. Good to know you blocked up the IRS so it wasn't hanging. I had a customer crack a posi case I 1/2 with the shaft hanging down on a lift while putting it in gear.

Now 68 diffs has their issues. The posi case was the left over design from 1965 and prone to cracks. The spiders were weaker then the later ones but overall not too bad of a unit.

As Mike mentioned jack it up and make sure there is no issue with the rear bearings. Check the end play in the diff axles and then if the driveshaft is disconnected spin it. It should be smooth.

If I can help let me know.

Thanks GTR1999, I have read many of your posts and know that you will be able to assist in this matter as is the case with many others on this forum. I will keep you informed as I go. At the rate that I am going at the end of a planned 2 - 3 yr. resto there will probably be an additional 20k spent. But I plan on passing it to one of my sons when I'm gone. Lol.

 

[GTR1999]

Thanks GTR1999, I have read many of your posts and know that you will be able to assist in this matter as is the case with many others on this forum. I will keep you informed as I go. At the rate that I am going at the end of a planned 2 - 3 yr. resto there will probably be an additional 20k spent. But I plan on passing it to one of my sons when I'm gone. Lol.

I'll be happy to offer any assistance I can. Feel free to email any questions. gtrvette1999@gmail.com

 

[Oldschool64]

Update to rear end problems

I'll be happy to offer any assistance I can. Feel free to email any questions. gtrvette1999@gmail.com

After isolating the rear end and finding that there was definitely a tight spot in the diff. I did a little more searching in the forum and found someone else who had this problem. The answer was to add the GM special additive and do some figure 8s in a nearby parking lot. This did the trick for me so now it's on to electrical issues. Thanks to all who helped with advice. Happy motoring!

 

[Vettehead Mikey]

Something's not right.

The additive is to help with excessively sticky positraction clutch plates. The problem would not be evident with a car up on a lift while rotating the diff or wheels manually. It would also not be evident while driving in a straight line.

 

[Oldschool64]

Something's not right.

The additive is to help with excessively sticky positraction clutch plates. The problem would not be evident with a car up on a lift while rotating the diff or wheels manually. It would also not be evident while driving in a straight line.

Not sure what was going on with it. It's still not perfect but with old tires and possible balance issues that have not been addressed I can't expect it to be. All I know is the more it is driven the better it gets. My plans are to do a frame off resto which will mean repairing and replacement of just about everything. For now just looking to get it more road worthy for some summer cruising around town.

 

[Oldschool64]

Something's not right.

The additive is to help with excessively sticky positraction clutch plates. The problem would not be evident with a car up on a lift while rotating the diff or wheels manually. It would also not be evident while driving in a straight line.

Thanks Mikey, I agree that something isn't right with it too. I will probably try my hand at rebuilding the unit but upon inspection it seems like a bigger deal to remove because of how it mounts to the crossmember/frame. Also considering just buying a rebuilt unit but can't see the fun in that. Thanks again and I will post pics whenever I look inside.