Hi all,
the rear brake of my 1993 ultra classic keeps braking even when i lift my foot off the pedal. This happened when i installed new brake pads. I reinstalled the old ones and the brake releases fine, as before..any thoughts?

Stavros

 

If it does it all the time (Hot or Cold) could be the caliper needs to be rebuilt. If it only does after riding a while (hot) there could be moisture in the brake fluid or even air.. Try a good brake flush first, if that doesn't work then you'll have to rebuild the caliper.. Doubt it the Master Cylinder.

 

It does it either hot or cold with the new pads. It never does it with the old ones, thats why im confused

 

Make sure the MC is an overfilled. Also take a c-clamp and push the Piston all the way back in then recheck the whole system after checking the fluid level again..

 

Thanks, will do that. If that doenst work i guess i need to rebuild the caliper. Would that require to take out the rear wheel?

 

Shouldn't..

 

I would Say!!! I('m wondering just How folks get a rear Wheel Off/On, without removing the Caliper First???? Maybe I'm just Uncoordinated???

 

Have a look at the piston(s) in the caliper. As the pad wears more is showing. Has the bit sticking out now corroded such that when you pushed it/them back they now stick?

Can the caliper move freely on the pins if singled sided piston.

 

I don't remove the caliper when I take the rear wheel off. Why would you have to?

Guessing here. If the caliper is not sliding properly on the pins, that might be causing the problem. New pads too thick? Are they OEM pads or aftermarket? I wouldn't think an over filled master cylinder would do that, but I'd check that anyway.

 

Problem could be either the master cylinder plunger sticking forward in the pressed inwards position, or the rear brake caliper piston binding /guide pins binding on up on the sleeves.

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So on that note since you can remove the rear brake caliper from the bracket (don't have to remove the rear wheel). Would first work the pads outward to slightly compress the piston, then remove bolts 7 so you can lift the caliper up off the rotor and bracket. From here, make sure to make sure that the pins are not binding in the sleeves (6), they can move freely in the sleeves, then remove the pads to press the piston all the way in to make sure that is not binding (should be able to push the piston in by hand).
As for greasing the rod pins to bushings, the piston to pad backer and other metal to metal areas (never grease the pad face or rotor), or anywhere near the seals, do not use a petroleum grease, but a silicone grease only. The petroleum grease anywhere near the rubber parts will cause them to swell, and can cause binding problems.

As for brake fluid, the spec calls out for both front and back to use Dot 5, and if you are looking at the fluid and is its not purple, it needs to be power flushed with new replacement fluid. Hence fluid should be changed about every 2 years on the bike, to keep the moisture out of it that it will pull from the air, which can cause the aluminum inner surfaces to rust, and cause the rubber seals to deteriorate over just normal wear isntead.

If problem is the front master cylinder the problem, pretty easy to pick that one up with a vacuum bleeder when you go to bleed the brakes.
The way that the cylinder works, is when you come off the pedal, part 31 has to retract back past the fill line port in the housing piece (forward piece on 35), so the pressure on the line is pushed back up to the reserve tank. So if you go to power bleed the caliper via vacuum pump on the bleeder at the caliper, and you can not get the fluid to flow through the caliper from the reserve tank to power bleed, then plunger is stuck forward, and blocking the port in the housing up to the reserve tank/not allowing the brake line to relieve it built up pressure.
Note. 31 and 33 is just ball in cup, so pedal can come back with 33 in tow, while 31 can be stuck forward in the housing piece.

Simply, if the brake fluid has not been changed in say 10 years on the bike, I would plan on both rebuilding not only the brake caliper, but the master cylinder as well.
As for kits, would wait to pull the rear caliper apart to see if you really need the piston or not/if the caliper piston channel is pitted and can not be saved, or if you just need the rubber parts alone at a reduced cost.

Hell, if the caliper is not leaking now, may not even need the new rubber parts, but pull the seals to clean and give then a good silicone greasing before reinstalling them so they are not binding up on the cleaned surfaces when they are reinstalled.
Note, use a Q tip on the cylinder surfaces to mirror clean them up of any rubber that may have bound to the surface metals. If you see that you have crystalized crap in the fluid system from the brake fluid never begin power flushed/wrong fluid being added to the system, than all that needs to be cleaned out of the system before hand, the system allowed to dry, then you can reassembly the silicone greased (dielectric grease) parts, and power bleed the system to get the air out of it.

Last one, if the rear tire was removed, then go back and double check to make sure you have the axle shims in the correct locations. The caliper float on the two pins, but if the axle shims are wrong, it will kick the rotor off so it not centered in the caliper.
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