Front brake jamming

[DUBDUB]

Hi people. I have recently been having problems with my brakes jamming on making my bike (87 GSXR250) unmovable and will definately not get a vin with them. I tried cleaning the whole system out and putting new brake fluid in (dot 4) and then bled them even after the bubbles had stopped flowing but once I ride the bike the lever slowly starts to get harder and harder to pull in untill the brakes make the bike come to a stop, at this stage I have to bleed the pressure out of them. Anyone have any ideas on whats wrong and how to fix this problem? Cheers

[riffer]

When you say you cleaned the system do you just mean you changed the brake fluid, or did you pull off the calipers, push out the pistons and clean and lube the pistons and seals?

I've done this recently for the first time, and I was really surprised at how easy it is to do this.

It sounds like the pistons are binding in the calipers.

[imdying]

I would check the lever to master piston clearance first. There should be free play there. Failing that, I too would strip the calipers as my next move.

In fact, I would strip the calipers anyway. Every 6 months with a toothbrush and hot soapy water (after pumping the pistons out a goodly amount), every 2-3 years for a full overhaul. It's cheap, dead easy, and makes a surprising difference to lever feel.

[DUBDUB]

I stripped both calipers down and put them and the pistons in a parts cleaner at work then used brake cleaner and an air gun to make sure there was no shit in there. I washed the seals out with soapy water but they werent too dirty in the first place. I then put some hydraulic lube on the seals and put the calipers back together and the pistons were moving but I did have to use a tiny bit of force to push them in. By binding do you mean that the pistons would not move at all? Thats what my old calipers did and would a set of new seals fix this?

[slimjim]

when you stripped them, did you keep the pistons and brake cal's as a Pair,? as they sometimes prefer to bed themselves to each caliper, but with that degree of cleaning new seal's would have been healther to fit

[DUBDUB]

Yes I made sure that I put the piston and seals where they came from. The disks are also straight.

[imdying]

when you stripped them, did you keep the pistons and brake cal's as a Pair,? as they sometimes prefer to bed themselves to each caliper, but with that degree of cleaning new seal's would have been healther to fit

No, you can interchange them till they're blue in the face, the pistons won't bed to the bore of a caliper.

The seals are a square section o-ring. The skew when the brakes go on, and revert back to square when the brakes come off, which helps the pistons come back. New seals obviously work better.

I'm guessing that by hydraulic lube, you mean rubber grease that is specifically compatible with the rubber used in brakes? If not, then you've contaminated the seals, and they've swelled up, causing the brakes to jam on. Hydraulic lube as used on things like rams etc is definitely not suitable. If you've cleaned the seals in anything like kero, that will have rooted them too. CRC will root them also, anything petroleum based in fact.

I would check the lever to master piston clearance first. There should be free play there.

Without seeing them, I can only guess, but contamination isn't uncommon. Check your master cylinder piston clearance though, that's the number one cause of binding brakes.

[dickytoo]

i've had this problem before and it could be dirt in the master cylinder. if the return hole is blocked, there is no way for the pressure in the lines to be released and the brakes will stay on even if you release the brake lever.

in the old fashioned cylinders with the built in reservoir, you can see this with the top off. you should be able to see two holes at the bottom of the reservoir. i think the smaller one is the return one. make sure it's not blocked.

on the new fangled master cylinders with the detached master cylinder, it's harder to see.

[imdying]

i've had this problem before and it could be dirt in the master cylinder. if the return hole is blocked, there is no way for the pressure in the lines to be released and the brakes will stay on even if you release the brake lever.

Yep, that's a definite possibility as well.

[DUBDUB]

Ok then ill take a look at that tomorrow night and will post how it goes.

[scumdog]

A mate of mine had similar problem on his old school Bonnie, turned out the rubber hose had a flap of rubber inside it ( manufacturing fault we suspect) it that was acting like a one-way valve, might pay to check that too.

[imdying]

A mate of mine had similar problem on his old school Bonnie, turned out the rubber hose had a flap of rubber inside it ( manufacturing fault we suspect) it that was acting like a one-way valve, might pay to check that too.

Getting a little bit more obscure, but a possibility also.

[F5 Dave]

If the brakes are dragging then callipers are suspect.

But if they are locking on then as stated above it is master cylinder. Take the lever off when it binds on & it will release. Some cheapo aftermarket or incorrect levers will cause this. As will bad adjustment. Also clean out the vent in the MC & check that the rubber top isn’t split.

[idb]

If I was trying to fault-find this I would probably consider doing it this way.
Remove the master unit from the bars but leave it connected to the hose (to protect the paint work), disconnect the hose at the master cylinder (wrap it up in rags while doing it to stop the fluid squirting everywhere).
If this releases the brakes then that would suggest that the problem is in the master cylinder. If not, the problem is further down.

[marty]

i once had a corolla that had a clutch that would be fine for about 10 changes, then the clutch would slip badly. leave it a while, and it would be fine again.

after pulling the whole system apart about 10 times, replacing the seals, fluid etc etc, and just as i was about to pull the clutch plate, i obtained an illustrated parts manual.

imagine how much i laughed when i saw that the seals (which were cup seals) had been installed by the previous owner/mechanic sdrawkcab! i didn't even think about it, and just replaced the seals, copying the originals. this meant that pressure would slowly build up, until the clutch was held in.

sounds very similar to what you have. check the seals are orientated correctly. they should be quite difficult to get in, as the cups need to be concave to the fluid side