GPZ 500s FRONT BREAK

[taz408]

Hello mechanical genii. The front brake on the GPZ 500S is constantly on (had a ride round the drive for 5 mins at very low speeds, didn't use the front brake once and now it's as hot as my pants ).

Could someone very clearly explain, or by use of a picture with some helpful colouring - tell me which bit I need to fiddle with, and in what way to make it so it's not permanently on.

Thanks in advance,

Tom

EDIT: Picture of the actual brake, incoming

[Kickstart]

Hi

Assuming it is a single disk GPZ (the ones with twin front disks use different calipers, but are also pretty rare in the UK).

The caliper on the GPZ front brake is a twin piston sliding caliper. By this I mean there are 2 pistons in the caliper that push on the brake pad(s), and these are operated by hydraulic pressure provided by the master cylinder when you yank on the lever. As it is a sliding caliper it only pushes onto one pad, while the other pad is secured to the caliper ; as the pistons push on one pad the whole caliper slides slightly to one side to push the other pad onto the disk.

There are 2 main reasons for the brakes to stick on with a caliper like this. Either the pistons stick or the whole caliper sticks on the pins it slides on.

For the first you need to take the caliper off, take the pads out pump the pistons out a touch and clean them up with brake cleaner and an old tooth brush, push the pistons back in, put the pads back in and put the caliper back on. This might well not be sufficient in which case you need to pump both pistons fully out (fluid will go everywhere), clean them thoroughly, take the seals out of the caliper and clean up behind them thoroughly (tends to be a build up of white powdery stuff), replace the seals (preferably with new replacements) having lubed them with fresh brake fluid, put the piston back in (make sure they go in straight), put the pads back in and put the caliper back on the bike, then bleed the brakes.

In the 2nd case, take the caliper off and pads out, then take the main body of the caliper off the metal bracket it slides on. If they are sticking this might be a pig to do. Clean up the pins, lube with something rubber safe, reassemble and put back on the bike.

All the best

Keith
____________________
Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[ERM1710]

A picture of the culprit!

[taz408]

Thank you for the reply...

Holy shit

[Rogerborg]

It sounds trickier than it is. They're really very mechanically simple, just take it steadily, and take pictures if you think you need reminding where everything goes back on - there tends to be little clips and such tucked away that will escape at the first opportunity.

Oh, and brake fluid is pretty unpleasant stuff. It'll ruin paint and isn't much fun if you get it in your eyes, so if you do take the pistons out, have your fluid capture system (basin) in place good and early.
____________________
Biking is 1/20th as dangerous as horse riding.
GONE: HN125-8, LF-250B, GPz 305, GPZ 500S, Burgman 400 // RIDING: F650GS (800 twin), Royal Enfield Bullet Electra 500 AVL, Ninja 250R because racebike

[Dazbo666]

Mr Haynes would be a big help
or as a last resort, me, if you're anywhere near.

Also, the GPZ benefits a great deal with replacing that original brake line with a braided one... I fitted Goodridge hose with stainless banjos to mine
____________________
1st bike (Sept'06 - May'10) : 1991 GPZ500S / Current bike (since Nov 2009) : 2003 Suzuki Bandit 600N
Word of the day : DILLIGAF

[taz408]

Thanks for your help guys, we'll take it step at a time

[dextersaurus]

As above. the pins do tend to seize. just need to split them down and clean them up

A +1 for stainless hoses too. improve brake power tenfold, it's amazing what they can do

Dunc

[duncanpage]

I had the same problem with my GPZ.

Turned out the winter build-up had got into the seals around the brake pistons and seized them on.
It wasn't fun riding down the road and suddenly finding your front brake wont disengage.

Undo the bolts securing the brake piston, carefully remove the brake pads and if you are up to it, pop out the pistons (being careful to catch the brake fluid)
Use some very very fine wet and dry to clean off any rust from the pistons, clean out any dirt from inside the caliper and refit it all with new brake fluid and preferably new piston seals.

www.wemoto.com do a service kit for them. It's unlikely you'll need new pistons, just the rubber seals and fresh brake pads should be all that's needed.
Depending on how long the brakes were seized for, you'll probably need new pads as too much heat build up will glaze the pads and they'll not work properly again.