Front Brake Problem

[Jim R]

I have 3 complete sets of OEM calipers. All rebuilt with new seals etc. 2 by me. 1 by a bike shop. They all do the same thing.

[Nessism]

Have you tried new brake pads in that one side? Are the sliding pins greased and does the caliper slide easily back and forth on the hanger bracket? Sometimes the plastic collar around the pins swells up and causes binding too. Another thing is to confirm you used OEM caliper seals, not aftermarket?

One thing to consider is to put some miles on the bike and make sure the pads are seating properly. You can even drag the brakes under power to burnish in the pads quickly. Just give the brakes time to cool off.

[rustybronco]

I haven't read through the complete thread, but have you tried changing the caliper support brackets? The brakes on my '80 850 will pump up and I am almost 100% certain it's because the bore in the bracket is to large for the slide pins-allowing the caliper to cock and the rotor to push the pistons back further than they normally would be.

[Jim R]

Thanks for all of the effort and advice. I have 2 or 3 things to try when the weather allows.

[Grimly]

Worn pin mount holes in the brackets are a common problem. They allow the caliper to tilt and jam slightly - a giveaway is the slanted wear on the pads. If you haven't replaced the mount brackets, examine them closely for wear in the holes. As a guide, the amount of permissible clearance is only enough to allow the slightest of wobble - they can't be too tight, or it becomes problematical the other way, but since we're talking about 30+ year old brackets here you're unlikely to find any as-new ones, but you can find some very good, low mileage ones that will do fine.
As the miles totted up on mine, I became plagued with caliper sticking problems and it took a bit of sorting out. Mine are fine now, but I see no end to the inherent design flaw causing the same problem to recur eventually.
When they're sorted out properly with modern pad material, these are actually half-decent brakes, but it takes very little neglect or wear to let them backslide into being horrible brakes of the 80s.

[bwringer]

Worn pin mount holes in the brackets are a common problem. They allow the caliper to tilt and jam slightly - a giveaway is the slanted wear on the pads. If you haven't replaced the mount brackets, examine them closely for wear in the holes. As a guide, the amount of permissible clearance is only enough to allow the slightest of wobble - they can't be too tight, or it becomes problematical the other way, but since we're talking about 30+ year old brackets here you're unlikely to find any as-new ones, but you can find some very good, low mileage ones that will do fine.
As the miles totted up on mine, I became plagued with caliper sticking problems and it took a bit of sorting out. Mine are fine now, but I see no end to the inherent design flaw causing the same problem to recur eventually.
When they're sorted out properly with modern pad material, these are actually half-decent brakes, but it takes very little neglect or wear to let them backslide into being horrible brakes of the 80s.

Agreed on all points. At around 110,000 miles I installed brackets and pins from a much lower-mileage bike and it helped quite a bit. In my case, they weren't binding, but they were actually rattling a good bit over bumps.

They're still a looser fit than needed, so you end up with angled pad wear and rattling calipers. I think if you have a good machine shop around, you could also have the brackets drilled and sleeved for a nice not-so-sloppy fit.

As Grimly stated, GS brakes work much better than you'd think when they're sorted out.

[Lorenzo]

You said you replaced everything, with new parts, from master cylinder to caliper;

that includes the brake lines? I had the same problem on the RG, with one line swelling under braking;

you also said, you bled the system in any conceivable way, even pneumatically;

have you tried vacuum bleeding it?

I have done it with off the shelf tools, and it came out quite tight and firm.

[silverhorse47]

Is the rotor worn equally from the centre, or worn more on one side only?

S.