Giant/MPH disc brake problem

roobarb

Recently I tried to replace the rear pads on my Giant Terrago. I have replaced both front and rear without difficulty in past so I thought nice quick job.
Pads were fitted as per instructions but the rotor wouldn't fit between them when I tried to replace the wheel.
So I tried loosening the cylinder adjuster on the brake lever to give maximum space between the calipers. Now I have always found the adjuster stiff and so I used 2 slips of wood to give a little mechanical advantage.

Now not only does the rotor not want to slip in but the cylinder wheel doesn't want to stiff in either direction.

Well have I completly buggered it up?
Is it a job for the LBS or is there anything else I should try?
I have thought about draining the brake but don't have a "bleeder" as illustrated in manufactorers instructions.

Any help would be appreciated

Bikedevil

My mate had a similar problem to his with Giant MPH's when he replaced the pads, best thing that comes to mind is to remove the pads, try and wind off the cylinder adjustment as much as you can and see whether or not the piston are sitting properly/flush with the caliper, if not (as i suspect is the case, very very very very gently try to persuade them back in.

If its not expanded pistons then either go to your LBS or give the Distributor for Giant a call and speak to their Tech Department

TurboMonkey

Ive had this exact problem before, remove the pads and prize the cylinders apart with a flat head screwdriver or something similar, probably worth re-bleeding the brakes while you are at it.

S_J_P

Those cylinder-adjusters are always playing up on MPH brakes! You can try getting some penetrating-oil (WD40, GT85 or the like) between the adjuster knurled wheel and the cylinder body, but you're unlikely to free them up if they're already seized.

As the Giant MPH3 is a closed system, your only real option is to remove the wheel and pads, then slacken the reservoir/lever clamp bolts and rotate so that the bleed-nipple is uppermost.

Remove the bleed nipple from the reservoir. Make sure you put plenty of rags around the cylinder, and then prize the pistons back into their housings. This should be pretty easy, as there's no pressure in the system. You only want to press the cylinders back just enough to obtain clearance for the disc rotor, as you can't compensate for excess fluid loss using the adjusters! Replace the bleed nipple (not too tightly as theres a compression washer to seal it which is fragile). Clean-up the spilled fluid thoroughly!

Put the new pads in, and refit the wheel (it should fit okay now). Pull the brake lever repeatedly. At this stage you may find that the lever moves all the way to the bar as there isn't sufficient fluid in the system, you can try using the lever-reach adjustment (grub screw) to compensate for some of the deficiency. Usually, you'd just wind the adjuster in, but yours is seized, so you'll have to remove the bleed-nipple again and try to get some fluid inside. A bleed-kit would be very useful for this stage!! Remember to relocate & tighten the reservoir/level clamp again!

If you can't/don't want to get the official bleed-kit (which should have come with the bike) then any suitably sized clear hose and syringe will suffice. It's worth investing in, as spongy brakes really aren't worth saving a few quid for!!

Good luck!

roobarb

Cheers S_J_P that seems to have worked.

Got a bleed kit gratis from LBS. The mechanic also sold me a small quantity of brake fluid if needed (in a syringe!)
Didn't need either in the end thanks to your instructions but good to have them on standby if I needed to bleed the system.

I managed to get the cylinder adjuster wheel moving with WD40 and "gentle" persuasion!

Thanks again!

S_J_P

Glad to be of help, and even more glad that you've got the problem sorted!