Hayes HFX-9 Pistons - Clarification Needed

stevieboy

The inside piston on my front caliper doesnt push out at the same speed as the opposing one, does this sound like a simple case of strip, clean and re-bleed? It's currently making caliper alignment a major pain. Once the pads are set its fine, but the disk nearly always is touching the caliper body.

Dr Nosh

First action to carry out B4 making any cap/caliper adjustments is to ensure that :
1. Check bolts holding the rotor to the hub are tight. Usually torx fitting. If any are loose remove, clean, re-fit with threadlok and tighten.
2. Check the actual disc rotor runs true. Fit a stiff piece of wire to a fork leg against the rotor and spin the wheel. This will show any out of true running. (Bit like checking if a wheel is buckled).
You might be lucky if a few skilfully applied taps with a light soft mallet can true up the rotor. Or else replace.
3. Check the 'centering' of the caliper body to the rotor You might need to shim it to achieve this. (Thin specific thickness washers between the fork leg fixing and the caliper body mount).
4. Now start to make pad adjustments, bleeding etc.

stevieboy

The caliper's are on post mounts so getting them centred is not a problem, the disc is true so looks like it's time to clean and re-bleed.

Dr Nosh

OK, so now asuming that disc rotor is running true and that the caliper body is central over the rotor.

I'm not familiar with this particular disc brake type.

Is there a moving piston on both sides? Then bleed and adjust each side.
Is there a moving piston on one side? Adjust the non moving side so that the pad just 'kisses' the rotor and the wheel can spin freely. Bleed, then adjust the moving side, once again so the pad just 'kisses' the rotor and the wheel can spin freely.

If the piston (s) are still moving unequally, then a further strip down will be necessary to ensure that there is no dirt infront/behind any O rings preventing smooth movement of the pistons.

stevieboy

They are twin piston calipers (one each side).

I suspect that a clean re-bleed will sort it as brake performance is fine, just a bugger to centre! After a years (ab)use these things are bound to happen, my girlfriends barely used Kula's brakes (same) are spot on still and centre easily.