Sticking Brakes

[jimmyg]

I have an R90s that appears to not release the front brakes after application. I pull the lever and release but the front wheel is very hard to spin. I've checked the caliper adjustments, etc.

The wheel will spin but it is very hard to do so after applying the brakes

thanks,

jimmyg

[Kurt in S.A.]

How old are the brake lines? Original rubber lines can break down internally and balloon when being pressurized but not release the pressure to the caliper. Also, what brings the piston back after actuation is the square o-ring inside the caliper. It could be cut or binding, not pulling the piston away from the disk.

Also, when's the last time you bled the brakes? Could be the return hole in the master cylinder is plugged, not allowing the fluid to return.

Kurt in S.A.

[jagarra]

Have you had the necessity to adjust the cable at the M/C end, there is an adjustment gap that has to be maintained in order to insure the return hole does not get covered. Replacing the original lines with a set from Spieglers would be a good idea, if not already done.

A partially blocked return hole can leads to major problems. After I adjusted the rear brake linkage on my R1100RS, I burnt up the rear brake, caliper and rotor.

[jimmyg]

How old are the brake lines? Original rubber lines can break down internally and balloon when being pressurized but not release the pressure to the caliper. Also, what brings the piston back after actuation is the square o-ring inside the caliper. It could be cut or binding, not pulling the piston away from the disk.

Also, when's the last time you bled the brakes? Could be the return hole in the master cylinder is plugged, not allowing the fluid to return.

Kurt in S.A.

Hi Kurt, the brakes lines are braided stainless steel and maybe about 10 years old.
The brakes were bled earlier this year when I rebuilt the master cylinder. I'll check on the master cylinder hole (that could be plugged) as suggested.

thanks,

jimmyg

[jimmyg]

Have you had the necessity to adjust the cable at the M/C end, there is an adjustment gap that has to be maintained in order to insure the return hole does not get covered. Replacing the original lines with a set from Spieglers would be a good idea, if not already done.

A partially blocked return hole can leads to major problems. After I adjusted the rear brake linkage on my R1100RS, I burnt up the rear brake, caliper and rotor.

the cable adjustment at the m/c is correct as determined by using the gap tool in the stock toolkit. I have braided stainless steel lines on the bike. To my knowledge, the calipers have never been opened so I'll pop the pistons out and have a look.

thanks,

jimmyg

[jagarra]

Opening the M/C may cause you to end up replacing the seals. They may have softened a bit due to age and they are a bugger to get back in. I used some .002 shim stock rolled up stuck into the bore, then i can slip the piston with the seals in without catching the edge.

[barryh]

I used to have that problem until I learnt to lubricate the caliper pistons with red rubber grease, Deformation of the seal is designed to withdraw the piston when the brakes are released but it can't do that unless the piston is free to move. I've just been out to the garage and given the font wheel a spin by hand. It took 25 secs to come to a stop. That's what you are aiming for and it is achievable with clean lubricated pistons.

[jimmyg]

Barry, thanks for the excellent pictorial.

jimmyg

[tsa]

I went through this a couple of years ago - in my case the chrome of the ATE caliper pistons was badly pitted in the area where the seal is supposes to, eh, seal. Replacement pistons were necessary, and of course meticulous cleaning and greasing of the caliper seals when reassembling.

In hindsight, dismantling and cleaning the calipers is something that should be done routinely every five years or so, at least if riding on salty winter roads.

[barryh]

Jimmy,

If you get down close and look at the brake pads while applying the brake you should be able to see the pads move into contact with the disc, then when you release the brake the pads should move back again. They don't move much but there should be a visible gap between pad and disc when they pull back. If you are not seeing this happen and the problem is not in the hydraulics then it will be stiction in the caliper piston. Some times you can free them up by removing the caliper and exercising the the piston in and out a few times to get it moving. Pump it out with the brake lever and then force it back in again with a G Cramp or with a proper retraction tool.