There is a binding situation in my rear, each one full roatation of the wheel. The wheels turn freely when raised off of the ground, except for one small spot where they feel like they are binding. It happens at exactly the same spot in the rotation. I have had the rear axles apart, rechecked the u-joints, brakes, half shafts, drive shaft, etc., they all check out fine, also, the rear was rebuilt. It almost feels like somothing is out of round.... any ideas?
Thanks!

 

You may want to try the same experiment with the rear compressed a bit and see if you have the same issue or not. With the rear in the air the suspension and axles may be stressed beyond normal, the angle is too severe and this may cause some binding in the u-joints.

If ther binding is still there, you likely have other issues.
Good luck

 

 

It's binding when you jack the rear of the car up? This is normal if you are leaving the TA hanging. Jack the TA up and try.

 

What you feel is your u-joints as you rotate them thru their full rotation. If the trailing arm were raise a little the binding would go away. You are ok!
Bernie

 

I agree with the others that you will get binding when you jack the rear of the car up and the trailing arms are hanging down. The trick would be to put a small jack under each TA and jack them up so that they are almost level. Once level, do your test. I would bet that your resistance is gone.

Gary

 

Yep.... Scared myself once with the same thing!

 

Thanks to all for their replies. This test has already been performed, we jacked up the TA's to reduce the angle, thinking that the U-joints angle's were excessive. We even removed the half shafts one at a time to see if it was in one side or the other. The binding persists, but only at one spot in the 360* of rotation. Any other ideas? Could the new Posi unit contribute to this?

 

Darn, sorry that didn't cure the problem, BTW was the clutch pack replaced in the diff? The only other idea I can think of is binding clutches, why just in one spot is beyond me, but maybe adding some GM friction modifier to the diff and going through the process of running the car in say 15-20 figure 8's in a parking lot may help free up binding clutches, this is such a common problem that it would be a reasonable next step to take without costing much money or time to see if it cures the problem.

 

It seems like great minds think alike! This is our next planned step, to drain the rear and install new fluid and new additive, then try some road time to see if it works itself out. I have heard that the GM brand (from the dealer) additive is superior to the stuff that you get in the auto parts store. Is there any merit to this?

 

Yes, stay with the GM additive it is far superior. As to getting some road time in, it is really important to go through a series of opposing turns, the figure eights work well for this, as the load changes from side to side the clutch pacs open release and close again, allowing the additive to really work its way in between them and freeing things up. It sounds silly but this should be routine regimine for these cars if you do a lot of straight line driving, the binding can come back, a few figure 8's and you're back in business.

Good luck

 

Help me out here. I am having trouble understanding how the posi clutches can cause a binding if both rear wheels are off the ground.

With both rear wheels off the gound, you have to support both trailing arms so that the half-shaft u-joints are not in a bind. My understanding is that you have done this and there is still a binding in one spot.

You mentioned that you replaced the ring gear carrier. That sends up a flag for me. Here are a couple of questions I have.

First, did you put the old ring gear back on the new carrier?

When setting the backlash, did you use the same side shims from the original carrier? Did the backlash checkout 360 degrees?

Before you installed the ring gear on the carrier, did you put the carrier in the housing and check the runout on the ring gear flange?

I have seen more than one carrier have a warped ring gear flange. That caused a loss of backlash in just one spot. We put the carrier in a lathe and machined the warped spot out of the flange. Reinstalled and everything was right with the world.

Hope that I am wrong here and way off base but with both wheels off the ground, trailing arms supported with 1/2 shafts level, I don't see how the posi clutches can cause a binding.

If someone can educate me on how this could happen, my mind is a sponge waiting for wisdom :-)

Bob

 

Hi Bob,

New gears, posi unit, bearings, etc. rebuilt by my mechanic who has been doing this for decades on race cars, Chevy's, Bmw's, you name it. The warped ring gear flange makes sense, seeing as how the binding happens at the same spot in each rotation. I'll pass this on to him and see what he thinks.
Thanks.

 

OK, I stopped in at the shop this morning and spoke with my mechanic, he informs me that all new parts were installed, including the ring gear flange.
Any other ideas? Could the new flange be defective, or is that unlikely?

 

In his second post he stated they removed the halfshaft. That eliminates the diffrential.

 

Thanks for your feedback.
Apparently my statement was misleading, I apologize.
The half shafts were removed one at a time to try and isolate the source of the binding. We eliminated the half shafts as a source through this process. This still leaves us with a problem in the rear itself.

Still fishin' for a solution.....

 

Parking brakes or rotor runout.

 

Hate to say it, but you may want to get some miles on it and "break it in" a bit and then repeat your tests. You've done a lot of checking and it seems as you've ruled out most of the likely causes. Who knows, it just may need to be driven a bit, it may be worth a shot particularly if the binding is not excessive.

Good luck

 

I just got the car back from the shop a few minutes ago, so far all seems to be good. I'll get some driving time on it this weekend and see how it feels.
Thanks to all for your support.

 

note: ring gear flange is part of the posi case and is not replacable,you would have to face it in a lathe or replace it. They all have some varience in them so just how much makes a difference. If the pinion is too deep in the ring gear it could bind but you would hear a howl in the diff. Does it sound ok driving?

Here are a couple of cases. 1 is 3 series the other is 4 series. The flange is where the ring gear is bolted to.