I'm in the midst of upgrading my '89 M6 coupe to the J55 brakes, and I'm replacing the old brake lines with SS while I'm at it.

I've run into a problem with the J55 brackets. The right front bracket is just fine, bolts up perfectly. The left front, however, has bolt holes that are too small for the OE bolts. Using undersized bolts is probably not a good idea with the aluminum steering knuckle.

I first ordered the pair of A1 Cardone re-manufactured calipers from RockAuto, and the front right was correct, the front right was wrong. I sent it back to Rockauto for a full refund. No problem. Then, I thought I'd try ordering just the front right caliper and bracket from Parts Geek (also A1 Cardone) so that Rockauto didn't just send back the same part I just returned.

The bracket from Parts Geek has the same problem! Bolt holes are too small. What's up with this? Does anyone have any experience with this problem?

I've also run into problems with the calipers, where threads are too weak to torque the banjo bolts to the required 30 ft-lbs. I stripped out one of the calipers trying to torque it to spec., which of course makes it un-returnable. So now I'm trying to find the most economical way to put steel insert into the stripped caliper, and I might also do it for the other one while I'm at it.

The banjo bolts that come with the SS brake lines are M10X1, but inserts are a little hard to find in that size. I think M10x1.5 might be the way to go, but then I'll need to get different banjo bolts to match. They seem to be available from Summit. Lot's of trouble and additional expenses for what should be a bolt-on upgrade!

Anyone have experience with stripped-out calipers?

 

I'm no expert but it sounds like you received the j55 bracket from a cobra mustang which uses m12 bolts, corvette uses m14. If that is the case you could always have a machine shop drill them to m14

 

That's precisely what has happened to you, you've received FOMOCO product and there's no real easy way to get the vendor to rectify it. You could hold on to yours until someone you speak to at the vendor has a correct in hand then originate a swap or as mentioned have a machine shop change the fit of what you've received. You DO NOT want to attempt this yourself unless you've got the proper tools and equipment.

The casting information on the FOMOCO product and the GM product is identical.

 

Ah! Thanks, Barbedwire and WVZR-1. That's kind of what I suspected, though I didn't know specifically about the Mustang.

It's a little crazy that I got the wrong bracket twice in a row, from two different places. I will say that Rockauto was very good about the return; they paid the return shipping and made it very simple. Parts Geek is making me pay the return shipping, and they will at their discretion also charge me a 15% restocking fee. It doesn't matter if it was their mistake. Rockauto was also cheaper, I only went to the other place to avoid having them send me the same part back again. Maybe a bad decision.

I actually went to a local machine shop today to ask about getting the bracket drilled out, but the place I went doesn't do that kind of work. They did have a couple of ideas of who might, but they said it's kind of hard these days to find a machine shop that does that kind of work. I have no intention of doing it myself.

Thanks again for the help.

 

I've no idea what you paid but rather than return I'd resell it to a FOMOCO guy, an eBay with you posting the casting number and the M12 thread would confirm for the FOMOCO guys. Check yourself first for a similar eBay offering and then just duplicate it. I know someone that can do it correctly but he stays busy and if he would you would need to ship but USPS would be cheap. Confirm there's no other issues with bracket first though if interested.

Does your local school district have a vocational program? Check with the machine shop instructor.

 

Anyone who reads this thread should get on the forum and buy used J55 GM parts. I did and I had zero issues with installation. I used a soft wire brush wheel on a angle grinder and cleaned them up to a brilliant shine. You can paint them or whatever ! I did take the rotors to a shop and they turned them ever so much to ensure no issues with the surface. Cost $15. It breaks my heart hearing the OP dealing with a mistake by a vendor. We have all been there and it sucks.