GM 12 bolt axles off-center for rear disc brake kit

[JustJohn]

I hope someone can point me in the right direction.



I thought my brake kit was spaced wrong for caliper alignment but I had only checked one side. It turns out the other side if off in the opposite direction. The brake rotor is just touching the inside of the caliper on the driver side and just touching the caliper on the outside on the passenger side.

SSBC has actually been very responsive but I just discovered my issue today.

Digging into this I think my carrier is off center because of how it was shimmed when it was put back in???

Will I be able to just pull the carrier and adjust the spacing over with shim packs???

[pist0lpete]

Don't touch the carrier it is shimmed for proper gear mesh. I would see what ssbc says my guess is they will want you to shim the caliper bracket. You might check your axle end play as well. Should be 0.005 to 0.025" range if memory serves correctly

[bryant]

on gm 12 bolts their are 3 different series carriers. a 2 series, 3 series, and 4 series. i have seen people try shimming to make of for running the wrong series ring gear on the wrong series carrier.
it is possible that is your problem.
pull the diff cover and look at the shims on each side of the carrier. they should look to the be the same thickness. if they are obviously different thicknesses then thats what is going on.

[JustJohn]

I'll take a look at this tonight. The dust has settled somewhat and I do have some options without going into a whole new rear end. It has clearly been rebuilt as there is not enough end play on the axles to even warrant measuring - I'd have to pull out my magnetic base and indicator because it's not enough to check with just a scale.

on gm 12 bolts their are 3 different series carriers. a 2 series, 3 series, and 4 series. i have seen people try shimming to make of for running the wrong series ring gear on the wrong series carrier.
it is possible that is your problem.
pull the diff cover and look at the shims on each side of the carrier. they should look to the be the same thickness. if they are obviously different thicknesses then thats what is going on.

[JustJohn]

I can do this on one side. The other side would have to be shimmed under the rotor as the caliper cannot move any further inboard. That was the main reason for the mild state of panic but SSBC is going to machine a caliper for me and I separately found the remaining pieces I need to make everything fit.

Don't touch the carrier it is shimmed for proper gear mesh. I would see what ssbc says my guess is they will want you to shim the caliper bracket. You might check your axle end play as well. Should be 0.005 to 0.025" range if memory serves correctly

[SRGN]

If the axle flange to housing flange is diferent from side to side, the carrier location/setup has nothing to do with it. You might want to make sure the axle bearing is pressed fully into the axle tube on both sides. This can cause one axle to protrude further than the other. The axles may also be slightly different lengths. Since it's only a c-clip rear, try swapping axles left to right. While the axles are out, look for burrs on the surface that is in contact with the inner bearing race.

[JustJohn]

If the axle flange to housing flange is diferent from side to side, the carrier location/setup has nothing to do with it. You might want to make sure the axle bearing is pressed fully into the axle tube on both sides. This can cause one axle to protrude further than the other. The axles may also be slightly different lengths. Since it's only a c-clip rear, try swapping axles left to right. While the axles are out, look for burrs on the surface that is in contact with the inner bearing race.

Did all that. Axles are the same length. Someone else mentioned that the diff may have been rebuilt with the wrong series carrier for the housing. Likely that is the issue. SSBC has been really fast and efficient with helping me clearance everything to fit. That's where I am now. I can live with safe and functional until I really pull things apart this winter.

[bryant]

i looked further into the differences in the carriers and they are greater than the shims allow space to make up the difference with. ive still seen it done. the results are bad. the gears should be noisy if this is the case.
did you ever figure out the exact difference on each side?

[JustJohn]

It's about 2mm. I know what gear whine sounds like but I don't really have any discernible noise from the rear. It actually seems very smooth and has so little end play at the axles that I'd have to get out my magnetic base and dial to measure it (I'd eyeball 1/16" with a scale).

Plans are to pull it apart for a posi carrier over the winter so this isn't a long term solution. I'll get to the bottom of what really happened then I'm sure.

[pist0lpete]

Who build the axle? Is it original GM stuff? Have the ends been changed?

[JustJohn]

Who build the axle? Is it original GM stuff? Have the ends been changed?

No idea. The car was an older restoration (loosely used) when I bought it. I have a few receipts for engine work and paint but nothing for the diff.

[bryant]

2mm is barely any thing when it comes to axles and brakes. that is .078. i wonder if a ring gear spacer was used in the diff. that could throw things off far enough to move the cross shaft off that much. anyways im glad to hear that ssbc was very helpful and got you taken care of.