Can axle flange thickness affect brake rotor/caliper alignment?

Situation:
I just swapped a set of rear LT1 brakes onto my '84 drum brake axle. When I was pulling the brakes off the donor car, I noticed that the axle flanges were a not as thick as the ones on my car, but it didn't really register at the time.

Now that I have the brakes on my axle (the axle is still out of the car), the inside pad seems to be hitting the rotor pretty hard with the wheels on, like making the whole unit really hard to push around the yard. Way harder than it was with the old drums. I have to turn each wheel by hand. I'm getting a narrow contact path on the inside of the rotor where the pad is hitting and it's knocking off the surface rust. Do I have anything to worry about, or am I just being paranoid? Anyone had a situation like this?

 

Shims are sometimes required to center the carrier over the rotor (that wouldn't seem to be the case here, however):

https://www.thirdgen.org/forums/atta...s-89-shims.jpg

JamesC

 

Okay, so check the sliding assembly and possibly break it loose or lube it. I'm assuming there's a limit to how far they will float, so hopefully I'll be within that range. If I'm not, I'll probably have to remove some material. If it comes to that, would it be better to remove it from the caliper or the mounting bracket?

 

okay, i just took a closer look, and the rotor is actually contacting the caliper. If i'm thinking logically, this means the caliper needs to move in toward the axle a bit. The span in the caliper that the rotor sits in is .935", and the rotor is .795". That translates into either removing .070" (starting at half the difference and moving gradually up from there as needed) from the mounting flange, or adding a .070" spacer behind the rotor. any suggestions as to which road i should take?

JamesC, this seems to be a similar situatiuon to your own spacing issues, only in the other direction. Do you know if they make wheel spacers (for behind the rotor) as fine as i need?

 

Shoot Ed Miller (ebmiller) a PM. He should be able to advise you on the best method.

JamesC

 

it was getting dark out with the first one, sorry. since the rotor is hitting the inside of the carrier and the carrier can't be shimmed inward, i should shim the rotor outward, right? where might i find such shims? is it something i can get from GM?

 

And therein lies the problem, I guess. The shim(s) are typically put between the axel flange and backing plate (as seen in the link above) to push the carrier outward. You apparently have the opposite problem.

In answer to your question, I ordered the four shims, two approx. .62 and two approx. 1.18 mm, from AndyZ28 at http://www.andyz28.com/ Whether these would be useful to you or not, I have no idea.

JamesC

 

No, I think I'm gonna end up machining some material off the mounting bracket unless someone can tell me why that would be a bad idea.

 

Which disc backing plate are you using, the 3rd steel one or 4th gen cast plate? Just curious...


Can you post pics of the rotor or the part number you used (if new)? Reason I ask this is that there are two different rear rotors for 4th gens, and although they are very close in size, they are just different enough to cause this issue. There are early and late rotors for those setups. I'm ataching pics of both types so you can see the difference, one type has a casting with a rounded or tapered hat with a 6.0" flange ID, the other has more of a square hat and will fit over drum axles perfectly and has a 6.25" flange ID. You obviously need to move the flange out somehow but your solution may be as simple as a rotor change.

Hope this helps.

 

originally I had the rotors with the rounded hat (second pic). When i took them to have them turned, the shop said that there wasn't enough meat left on them, so I had to buy a new pair. The new ones are the same as the first pic.

I'm using the 4th gen cast plate. I took it over to my local machine shop after much measuring and had them remove 0.065" from the carrier mounting flange. putting everything together with the new rotors and the shaved plate, the rotors now clear the carrier by about 0.140"

The arrow shows where I had material removed.

now all i have to worry about is parking brake cables