Rear vibration ...need help,suggestions

[Fitz]

Originally Posted by Hart_Rod

So I started looking at the hub where the wheels go on the axle. With the car on jack stands and running you can see wheel hub is off centered which is causing the up and down bounce. It appears that my Billet Specialty wheels aren't centering up when I bolt them on. home from work today I'll take it for a test drive and see if anything changes.

There isn't any way that a 'lug centric' wheel can do what you describe if you are using the correct lugnuts. They should have a tapered face which engages the matching taper surrounding the hole in the wheel. I run Billet Specialties SLC 65's and they use the lugs shown in the photo. If the lugs are correct and correctly installed you have a bad axle. It isn't drive shaft or rotor hat or any of the rest of the stuff that has been suggested here. Either the tire on that side is not round, the axle was drilled for the studs off center, the studs are not pressed into the axle straight or the axle itself is bent. Swap that wheel from one side to the other and see what you get. If it still seems to move, the tire is out of round. If it turns true, it is your axle.

[72MARIO]

Did you fix this problem yet ?

[Hart_Rod]

Originally Posted by Fitz

There isn't any way that a 'lug centric' wheel can do what you describe if you are using the correct lugnuts. They should have a tapered face which engages the matching taper surrounding the hole in the wheel. I run Billet Specialties SLC 65's and they use the lugs shown in the photo. If the lugs are correct and correctly installed you have a bad axle. It isn't drive shaft or rotor hat or any of the rest of the stuff that has been suggested here. Either the tire on that side is not round, the axle was drilled for the studs off center, the studs are not pressed into the axle straight or the axle itself is bent. Swap that wheel from one side to the other and see what you get. If it still seems to move, the tire is out of round. If it turns true, it is your axle.

Fitz - I hear what you are saying, but it's doing it on both sides and with 2 completely different set of wheels. I've used press in studs and now have screw in studs. I have the correct tapered face lug nuts, but I think I may purchase some new ones just to eliminate that as a possibility. I thought I was a pretty good trouble shooter and could diagnose mechanical problems, but I'm at a loss......

Originally Posted by 72MARIO

Did you fix this problem yet ?

Nope, I've been sick for the last few weeks and haven't really felt like messing with it. I put my big tires back on it and have just been driving it.

[tsetsaf]

Can you physically see a hop in the wheel if you sit it on jackstands and run at idle? Maybe the bead is not set right on the tires. Just went through this with mine and it ended up being a bad wheel balance. I had to literally stand there while the machine ran to ensure a good balance. All is good now.

[68 short step]

rob, I had almost the same problem, I chased it and chased it, like you did. what it turned out to be was the rear axle didn't have enough limited slip additive, so I added one bottle of the additive, and it fixed the problem...so if you're running straight 80/90, with a posi unit, be sure to add the additive , and enough of it...
hope this fixes your problem, and for sure let us know when you do solve it.

[Hart_Rod]

Originally Posted by tsetsaf

Can you physically see a hop in the wheel if you sit it on jackstands and run at idle? Maybe the bead is not set right on the tires. Just went through this with mine and it ended up being a bad wheel balance. I had to literally stand there while the machine ran to ensure a good balance. All is good now.

You can see it go up and down. I need to borrow a mich to check out the runout of the wheel itself while its running.

Originally Posted by 68 short step

rob, I had almost the same problem, I chased it and chased it, like you did. what it turned out to be was the rear axle didn't have enough limited slip additive, so I added one bottle of the additive, and it fixed the problem...so if you're running straight 80/90, with a posi unit, be sure to add the additive , and enough of it...
hope this fixes your problem, and for sure let us know when you do solve it.

Can you describe what you were seeing? I added one bottle of additive (8 OZs??). Should it have more?

[72MARIO]

The shop that rebuilt my differential said to use 2 bottles of Fords additive. The say it better than AC delco stuff

[chevy2tom]

Ship it to me with a gas card, I don't care how long it takes I'll figure it out! Lol.
Good luck

[chevy2tom]

Does it happen after the rear brakes get warmed up ? Sticking caliper/warped rotor? Emergency brake hanging up?
Axle bearing?

[Hart_Rod]

Originally Posted by 72MARIO

The shop that rebuilt my differential said to use 2 bottles of Fords additive. The say it better than AC delco stuff

Where do you pick that up at? I used some stuff I got from the parts store, K&W LSA.

Originally Posted by chevy2tom

Ship it to me with a gas card, I don't care how long it takes I'll figure it out! Lol.
Good luck

I'm would gladly do that if I you could guarantee a fix...

Originally Posted by chevy2tom

Does it happen after the rear brakes get warmed up ? Sticking caliper/warped rotor? Emergency brake hanging up?
Axle bearing?

No, it does it as soon as you start driving it. Calipers are good, I swapped in some new rotors, bearings are new......

I spent 15 years flying military helicopters and you become very attuned to every sound and vibration.....maybe it's in my head and I'm overthinking it.....

[davischevy]

Nope, I've been sick for the last few weeks and haven't really felt like messing with it. I put my big tires back on it and have just been driving it.

Does it hop with these tires?

[72MARIO]

Any ford dealership should stock it. Its 6$ CDN. I had problems with the CRseal posi additive. As soon as the truck got warm it would bind up going around corners. The ford additive solved that problem.

[Hart_Rod]

Originally Posted by davischevy

Nope, I've been sick for the last few weeks and haven't really felt like messing with it. I put my big tires back on it and have just been driving it.

Does it hop with these tires?

It does it with both sets of wheels and tires.

Originally Posted by 72MARIO

Any ford dealership should stock it. Its 6$ CDN. I had problems with the CRseal posi additive. As soon as the truck got warm it would bind up going around corners. The ford additive solved that problem.

I'll see what I can find. This is what I put in when I changed the axles out (7 oz):

http://shop.advanceautoparts.com/p/k...ive#fragment-1