Need Help - Center front/Rear brake piston binding...
 

Argh - not one problem since I picked up this bike in 1996... this week I have new tires put on and now the brakes are binding - totally locking up both front and back after a few miles of riding.

I think I've narrowed it down to the foot pedal as the centre front calliper pistons won't slide back in if I extend them. I've bled the foot pedal circuit and ran new fluid through, including opening the orifice bolt etc to bleed the PVC and 2ndary side etc

Anyone got any suggestions? Am I right in thinking I should be able to press the piston back into the calliper easily (I can with the outside two on the front lever circuit).

I guess I should take it out for a ride and not use the foot pedal at all - see if it works?

It sounds like the piston is not returning, personally I’d remove the caliper get it it on a bench and check that the pistons move freely, usually a light sanding with some fine wet and dry will solve it.

The piston isn't stuck, if I loosen the center bleed valve I can push it in easily. Also I can move it if I loosen the banjo on the foot master cylinder, which makes me think it's the return port on the foot master which is the problem?

Hi, could be you could try this, might as well do the front brake at the same time.
Stand the bike upright, take the tops off the rear and front brake res , get some zip tie's put it around the front brake lever and pull the lever slightly through the free play (only a slight application of the brake) tie off the lever in that position and leave it four a few hours, do the same for the rear brake, hopefully over time this will release air through the res mechanism , and make sure the fluid isn't over filled, put covers back on and see if your brake is any better

I would be a little nervous to ride it at all in this condition, but did you try not using the rear brake pedal. It seems strange that you would have this problem just from changing the tires unless someone depressed/squeezed levers while you were away from the bike. I've seen a wheel bearing problem after a change but never this - Hope you find out what it is.

Just spent a few more hours on the bike - I think I found a chip of varnish in the return hole of the pedal master cylinder. Most likely the mechanic stomped on the rear brake during his "test ride" - I hardly (if ever) use it thanks to the linked system so maybe he just dislodged some crud.

So far all looks good, but I've only driven 2 miles exclusively on the front brake (all worked fine) and 2 miles on the back.

Let's hope that's it - I ordered a front and rear master cylinder rebuild kit, after 22 years, they are probably overdue (as was the 22yr old brake fluid.

Who knows, I might do the clutch as well IF I can find a kit for it.

Brake system is simple. If you can easily return the pistons back, then there is no other culprit than the master cylinder.
I just rebuitd my brakes and it is an 1988. Even though the pistons were retracting, the amount of corrosion inside came visible after taken out.
Get new seals for the calipers and a master cylinder rebuilt kit as mentioned.
Clean EVERYTHING!!!!!

I agree Red Baron - I was wary for two decades to touch it as many people told me "it's impossible to bleed properly", "you'll never get it to balance again" etc - yet, I've had the master cylinders off, empty and it took me a few minutes to bleed on my own, just by using a piece of wood to depress the foot pedal while opening and closing the bleed valve on the other side of the bike.

I may tear down the callipers next - my bike has pretty much dry summer miles only for the last 15 years so it's not in bad condition other than scrapes from moving it across the ocean twice.

I'm more interested in resolving a rough idle - probably the fact I've cleared the clogged slow jets a dozen times, they are probably scored...