nate14

Hello all, I'm having troubles installing a rear 8 inch avid BB7 on my .243 racing frame. It should be a quick bolt onto the rear IS frame mount, but I'm having clearance issues. Basically, when I slide the caliper over the rotor, the bracket (the bit which is bolted into the caliper body, and which in turn bolts onto the bike's disc tabs) touches both the disc on one side and the frame's mounting tabs on the other.

The frame is designed to accomodate an 8 inch rotor, and the bracket is definitely the rear bracket. Additionally, the frame is not bent (the droupouts are about 1/4" steel, so it's not exactly fragile). I contacted the frame manufacturer, and they said they hadn't heard of such clearance issues before with these particular brakes. The caliper can only be oriented one way as far as I can tell, so that isn't the problem. Is it possible that the bracket is just a bit too fat, and I'll have to grind its profile down a couple millimeters?

Has anyone else had this problem and solved it? Am I missing something totally obvious? Thanks in advance for any help!

Old_Fart

Is this the bracket you have?

Adapter on the BikeParts web site

nate14

Yes, that is the adapter I have...you can sort of see in that pic that the holes for mounting the adapter onto the IS mounts are fairly pronounced on the far side. That's the portion that is giving me clearance troubles. It seems weird--these are pretty standard brakes, and the frame is designed for this rotor size.

That's why I'm thinking I may be doing something wrong...

ISeeDeadHuffies

So if I understand correctly the adaptor hits the rotor when it is bolted onto the frame? Is there extra thick paint on the I.S. tabs? Could be a factory error, the I.S. mount is to close to frame centerline. Maybe the hub is not asembled correctly.

ISeeDeadHuffies

Also install the adaptor to the frame, then the caliper to the adaptor.

tool boy

I've run into tight mounting on a couple of bikes. I have filed the adapter to make it work but you need to be careful to not file at an angle. Slow and steady.

nate14

Now that I think about it, the disc mount holes were not faced when the rest of the frame was prepped, so paint buildup might account for the snug fit. I might do a little poor man's facing with a pen knife to see if that helps. It probably won't solve the problem completely, but will reduce the amount of adaptor which needs to be filed down!

As for the wheel, it is a Shimano LX ISO 6 bolt on a singletrack which came off of a Kona Coiler Deluxe. It's an okay wheel, and I assume the dishing was accurate straight from the wheel-building machine (though that might be a bad assumption to make in the bike industry)...who knows though, maybe the hub was built a bit off-center? I will definitely check that as well!