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I have a rear caliper (just one) where the hole of the piston adjusting screw, and the screw itself, is reasonably corroded. How would one go about removing the corrosion? WOuld i just chuck some WD40 in and let it sit? Does it communicate with the brake fluid from this hole, and will it affect the chemistry of hte brake fluid???

Also, how does one go about removing pistons on front calipers without it being connected to the car?

WD40 should be fine on the bolt.

To get the piston out use compressed air to push. I wrap a rag around the nozzle of an air gun then blow the air in the hole the brake line would normally connect to. Make sure you put a bit of wood to stop the piston popping completely out and shooting across your workshop.

Video here http://www.youtube.com/watch?v=mE-qitXDbuM&feature=related

How about if it's the front brake's piston I need to get out?

The above method is for a front caliper.

Rear piston screw - I agree that WD40 is your answer. It won't remove the corrosion, but it will soak into it and loosen it up allowing you to turn the screw and retract the piston. If there's still lots of corrosion product remaining, then you could try soaking in phosphoric acid based "rust remover" (Coke or Pepsi is a backyard chemist's alternative to the commercial stuff).

Front pistons - do you want to remove the piston completely or just compress it into the caliper? If the latter, I use a G-clamp with a piece of wood on the face of the piston. Just tighten up the clamp and the piston compresses into the caliper. But if you want to remove the piston completely, then it sounds like fattima has got some good advice there.

I want to get it out to replace the piston seal and the dust boot. If I don't have access to compressed air is there another way?

you can remove the caliper and take it to the local brake repairer. An examination of the bore is essential- if it is scored it is likely to leak again anyway. If you are disconnecting brake lines then air into the system also means that they will need to be bled. One thing bush mechanics did was to pinch the lines with say a vyce grip to reduce the air getting into the lines- check others to see if this is dodgy advice. A Haynes manual should also give some advice on these matters.

these calipers are actually off the car (NA8 calipers going on NA6), and my workshop manual says that vice grip will do the job.

Mr Morlock wrote:you can remove the caliper and take it to the local brake repairer. An examination of the bore is essential- if it is scored it is likely to leak again anyway. If you are disconnecting brake lines then air into the system also means that they will need to be bled. One thing bush mechanics did was to pinch the lines with say a vyce grip to reduce the air getting into the lines- check others to see if this is dodgy advice. A Haynes manual should also give some advice on these matters.

You can actually buy brake line clamps designed to pinch the rubber hose without damaging it.

The idea is you pinch the line and then remove it from the caliper and do your job. The idea of pinching the brake line is that you wont allow the entire system to drain so the bleeding process is much easier.

Personally I would just bleed your brakes properly anyway. Its not very expensive and its easy enough to do.

Should there be fluid in the piston adjusting screw hole, or should it be dry??

My mechanic said it should eb dry, but in the 4 calipers that have been through my hands so far, none of them have been...?

Anyone know. Or has anyone noticed fluid in the hole for the screw (in the rear caliper) when they were changing pads or something?

mitch_f1 wrote:Anyone know. Or has anyone noticed fluid in the hole for the screw (in the rear caliper) when they were changing pads or something?

Pretty sure when I did mine last year they had no fluid in there.

Looking at the workshop manual explosion for the rear caliper, it shows a seal between the piston and the adjusting screw, so that would suggest a) it shouldnt have fluid in there, and b) if it does then the seal is worn..

Neithe rof the workshop manuals i have explained that at all, so thanks

cool, cheers for that