Resolved 1g big brake rotors not seating

[talonDSMerr]

I purchased 3000gt SL dual piston brakes for my 91 talon awhile ago and just recently got to installing them. I bought 94 awd talon rotors to go with the dual-pot calipers and the swap went without much snags until the entire assembly was put back together, brake system bled, and wheel lugs torqued down.

Backing out of the driveway to test the brakes, the car initially rolled back until the brakes seemed to engage themselves with no pedal pressure applied. I removed the wheels and it looks as if the rotors are not seating correctly onto the hub, causing the rotor to push against the pads at a certain point in the revolution. The rotors even scrape the caliper brackets at that point.

I checked with a straight edge to see if the rotors were warped but they weren't. The only possibility I can think of is the rotors not seating correctly onto the hub. I inspected the face of the hub and there isn't any clump of rust or anything there that would cause this.

Has anybody else run into this problem? Is there anything I may be missing?

 

[NOSLO2PT0]

You have to pump the pedal up a few times to get the pressure built back up in the calipers. That pressure, along with the actual rim of the car, is what keeps the rotor in place when you first install it. After a while, the rust/corrosion buildup will keep the rotor stuck to the hub.

 

[talonDSMerr]

Just went out and tried that but the rotor still rubs against the pads and bracket after I put the wheel lug nuts back on. When the lugs aren't fully tightened, the rotor doesn't rub anymore at that spot..

The rotor actually has scratch marks on it from scraping against the caliper bracket.

 

[steve]

There have been issues in the past with rotors not having the required chamfer on the inside where they sit on the hub and so they don't sit flat on the hub.

 

[talonDSMerr]

It seems like that might be whats happening. I'll try cleaning the hub face tomorrow to see if that works, if not, I'm going to warranty out new rotors.

What did people in the past do to fix this issue with incorrect chamfer?

 

[steve]

What did people in the past do to fix this issue with incorrect chamfer?

They either took them back or used a die grinder.

Tomorrow just look at the inside edge of the rotor where the center hub pokes through. If it's not beveled or have a radius then that could be the problem.

Here's an old thread and a note about 2G hubs.

http://www.dsmtuners.com/forums/handling-tech/186613-help-front-rotor-issue.html

 

[talonDSMerr]

That sounds exactly like the problem I've run into. I'll have a look and compare the new rotors to the stock ones I took off tomorrow and see if that is whats causing the rotor not to sit flat on the hub.

If it turns out that this radius is the problem, I plan on taking a die grinder to the hub and grinding the radius down so the rotor will fit. The only concern I have is if it will affect lining the rotor up hub-centrically.

Thanks a lot for pointing me in the right direction Steve Your advice is much appreciated.

 

[steve]

Don't open the center up just clearance the inner lip to fit.

 

[talonDSMerr]

Do you mean grinding the lip on the rotor? I was thinking about grinding the chamfer on the hub down to match whatever chamfer there may be on the rotor.

 

[steve]

Grind on the rotor not the hub.

You can wire brush the hub to clean it off but make the rotor fit the hub not the other way around.

 

[talonDSMerr]

Okay, I'll get to that tomorrow and hopefully return with some good news. Is there any reason for grinding the rotor over the hub?

 

[steve]

Sure, the rotor should have fit in the first place. They are expendable and easy to replace, changing the hub on a 1G means tearing the front wheel bearings apart, pressing the hub out, and replacing all the seals.

 

[talonDSMerr]

Ah, gotcha. That makes perfect sense.

I took the new rotors off and compared them to my old stock ones and the radius you previously mentioned seemed to be very close if not identical between the two rotors. HOWEVER, there was another "lip" on the new rotor that wasn't present on the old around the inside edge of the rotor. I'll try to get a picture:

On this picture, the lip I'm talking about is the one that appears where the "S" is in the word "Steep" and goes all the way around the inside of the rotor. For some reason, it's been preventing the rotor from seating onto the hub and after grinding it all the way around, I put antisieze on the inside of the rotor and placed it onto the hub. I torqued it down with my lugs and the anitisieze smears from the rotor onto the hub face, meaning the rotor is now flush with the hub.

I'm off to get my rotors replaced because the other ones got scored by the caliper bracket, but its great knowing what the problem is! Thanks again Steve