I've finally got round to replacing the rear left brake calliper that had a problem with the slide pin sticking. The replacement is a second hand calliper that was said to be in good condition but has sat around in my garage for about a year waiting to be done. The piston turned in nicely and it bled easily but the brake stuck on. I took it off and wound it in again but the same thing happened the second time.

Have I done something wrong? Is it something that is likely to bed in or am I going to have to pay for it to be refurbished?

I had the same problem a few weeks ago - took it to a mechanic who put more oil round the piston and it was as good as new (passed mot a few days later)

Only cost me £20 but maybe I was just lucky that that was all it needed

Freeing off handbrake linkage parts with oil is fine but never put mineral oil (which includes WD40 or similar) anywhere near brake hydraulic rubber parts.

Freeing callipers off with WD40 may appear to work in the short term but it actually even a tiny amount of mineral oil hardens the rubber destroying the elasticity of the seal. It is the elasticity of the seal which acts as as a return spring to pull the calliper piston back a fraction of a mm to give a working clearance between pad and disc.

In normal application of the brake the piston doesn’t slide in the seal but stretches the seal slightly, when the brake pressure is released the piston is pulled back.
Only when the clearance between pad disc reaches the limit of the elastic movement of the seal will the piston slide in the seal and take up wear.
Effectively the inner seal acts as a ratchet type self adjusting mechanism.


WD40 is not a silicone lubricant it mainly consists of white spirit, gas oil/kerosene & mineral oil.

[Edited on 22/9/13 by britishtrident]

I've had a play with it this afternoon and found that the brake pad on the piston side is sticking in the slide. Levering it back and putting a bit of grease on it freed it up so that the pad could be moved by hand but after reapplying the brake it is sticking again. Now I know where the problem it's, I can take it off and clean it up properly.