theyellowone wrote
From what I remember, the rear pads have a locateing lug on them. Ensure this lug is fitted between the appropriate slots in the brake piston. (should be done when winding back the piston)
The handbrake rotates the piston via cables, thats why the piston should be locked into the pads.
No, the slots in the piston are only there so that you can wind it back down. It
MUST be free to rotate, or the self-adjustment won't work. Think about it, if the pistons must be wound down to fit new, wider (unworn) pads, then as the pads wear the pistons MUST be rotating to take up the slack (by winding themselves up the internal threaded rod). A little lubrication between pad and piston is appropriate.
The handbrake cable pulls on a bellcrank at the caliper, which pushes against this rod, which enters the caliper cylinder cavity through a hydraulic seal. The portion of this rod inside the cylinder is threaded and the brake piston is screwed on to it.
When the handbrake is off, the rod is withdrawn, at its rest position, and hydraulic pressure on the piston, through normal brake pedal application, lifts the piston up the rod as the brakes are applied. The rod is held back (by an outside spring, I think) so that it doesn't impede full brake application, but the piston is encouraged to rotate a little with each application. As the pads wear very little, the movements up the thread are tiny, just enough to keep the handbrake adjustment within spec. The piston/rod screw thread is lubricated by brake fluid, so the piston should wind up the thread rather than lift the rod against the resistance of the seal and spring.
When you put new pads on the pistons can be a long way out of adjustment and need a lot of resetting, by much pumping of the brake pedal with the handbrake off (and wheels chocked of course). If this isn't working, then it's likely that the pistons have seized onto the threaded rod and aren't adjusting themselves at all.
FReidiboy, did you screw the pistons in as far as they would go, until you met resistance and they would screw down no further?
If so, it is likely that the pistons have jammed onto the end of the thread. Get the calipers dismounted again and unscrew the pistons enough that they are free (or as free as they get). Now try again.
If the pistons are jammed on the handbrake rods, they can't go in far enough to make the pads grip the disk. Brake pedal pressure is lifting both piston and handbrake rod, and they will only go so far. This will also be why the handbrake isn't working - it too can't move the pads far enough to press on the disks.
Lift the rear of the car onto axle stands (after chocking the fronts, of course), get a mate to sit in the drivers seat (engine running, you need vacuum assistance for the servo), spin a rear wheel and get the mate to apply the brake. If the wheel doesn't stop instantly then the brake isn't being applied to that wheel. Try again with the handbrake, repeat for the other side. The ONLY thing I can think of that would stop the rears applying in the conditions you describe is jammed handbrake adjusters.
This affects the front brakes as well, as the rears are only working against the springs in the handbrake mechanism and it is easier to bend these (and the linkages etc) than it is to apply full braking force to the front disks. So the brakes are enfeebled all round.
Unless you have been very unlucky, you should be able to release the pistons from the handbrake adjusters yourself. In the very worst case this might mean taking the calipers off and apart, requiring replacement seals and proper bleeding once reassembled, but I'd expect that all you need to do is free up the pistons on the adjusters by unscrewing them a bit.
Fingers crossed for you . . .
How do I know all this? I spent many hours of fun and frolic underneath a Mk.2 Golf GTI which had a similar, but less sophisticated, handbrake mechanism, and jammed adjusters were common.
