Rear Wheel Wobble

[Ol' Drippy]

I am having a problem with my 94 C1500 2wd truck that I need help with. It has the stock rear end and everything worked fine when it had the original drum brakes and open carrier (3.42). I swapped in a used posi out of a caprice cop car and at the same time welded some brackets on the axle flanges to add disc brakes. Once I put everything back together, I found that both rear wheels wobble back and forth, one worse than the other. I thought my axles might be bent so I replaced them with new axles but the wobble it still there. I also had the rear wheels checked and they aren't bent. The carrier bearings and axle bearings are also new. At this point I am thinking that maybe something is wrong in the posi? It doesn't make any unusual noises. Any ideas?

[made2drag]

Originally Posted by Ol' Drippy

I am having a problem with my 94 C1500 2wd truck that I need help with. It has the stock rear end and everything worked fine when it had the original drum brakes and open carrier (3.42). I swapped in a used posi out of a caprice cop car and at the same time welded some brackets on the axle flanges to add disc brakes. Once I put everything back together, I found that both rear wheels wobble back and forth, one worse than the other. I thought my axles might be bent so I replaced them with new axles but the wobble it still there. I also had the rear wheels checked and they aren't bent. The carrier bearings and axle bearings are also new. At this point I am thinking that maybe something is wrong in the posi? It doesn't make any unusual noises. Any ideas?

Could be the pinion backlash causing a pinion vibration?

[kwmech]

What do you mean really when you say 'wobble back and forth'? in and out end play? Tires off the ground, do the wheels spin true? Is this a 10 bolt or a 14 bolt. Disc brake rotors not sitting flush on the axle flange? Brake pedal pulsing?

[mongocanfly]

what KW asked....if its the tire/rim wobbling, are the rims seated over the axle hub correctly? there are hub centric rims and lug centric rims...

[Richard]

Definitely check your wheel hub assembly, mounting as the last two posts indicated. Bet it has something to do with the disk brake swap and/or your wheels.

[Ol' Drippy]

I did not remove the pinion gear for this swap, I kept the 3.42 gears. It is a 10 bolt 8.5 in rear end. When I say wobble I mean with the rear end jacked up and the wheels spinning the wheels wobble back and forth as if the axle flange was bent. You can see the disc brakes wobbling along with the wheels but strangely the brake pedal doesn't pulse. In fact the truck drives fine, I only realized the wheels were doing this when someone on the road honked at me and told me.
The wheels are lug centric, I have never heard of a hubcentric solid rear axle? The wheels are torqued correctly and again they didn't have any problem before I swapped the diff and brakes.

[mongocanfly]

I dont think the diff is your issue....it sounds more like maybe your rotor isnt seated on the axle flange...especially if it's both wheels...some pics may help...a video would be even better...
With the wheel off and If your seeing the rotor wobble I'd start there...take the rotor off and put the wheel back on and spin it and see if it still wobbles...
Do you have a dial Indicator?

[Ol' Drippy]

I pulled off the rotors that were on it for about 3 months and did find that the mounting flange was a little uneven just using a straight edge. So I put brand new rotors on it (I am using caprice cop car rear rotors with the stud holes drilled out a little bit) and no change. I am sure the rotor is seated correctly.

[mongocanfly]

Just for fuzzies, take all the brake stuff off and bolt the wheel back on the axle ,do the spin test and see If you still got a wobble...
That will help eliminate one part of it
It would be highly unlikely that the posi unit is causing a wobble that you could see...
That why I'm thinking it has something to do with the brake setup

[Ol' Drippy]

mongocanfly you were right! The rotors are not sitting flush to the axle flange. It looks like they are seated and they fit most of the way over the hub but I looked a little closer and discovered the bore hole on the rotors is just slightly too small. I bolted the wheels straight to the axles and no more wobble! Now I guess I just need to take the rotors to a machine shop and have them opened up a little bit. Thanks for the help.

[mongocanfly]

Glad you found it..,!!

[Richard]

Great! Lots of good tips at this forum. Since you know how to change the axles out. I would maybe consider machining the hub on the axles as opposed to the rotors. That way you do not have to visit a machine shop on the next brake job.