Caliper grease

[944cabby]

Can anyone tell me what's the type of grease used on caliper pistons.
In the last repair kit that i bought there was a small sachet to lube up the piston before fitting which resembled vaseline.
Looks like i've got some sticking pistons again so i want to tackle all four corners and may need some of this grease - is it a special type or will high temp grease do?

 

[millview]

Bad idea to use HMP grease as it will contaminate fluid.[] and everything else.
I think proper stuff is called Optimoly, available from your OPC on (I think) part no. 000 043 020 00. But it's not cheap, I seem to remember it's about £15! But it does go a loooong way[8|]

 

[944cabby]

Thanks Millview,
Would something like "copper-ease" which i've used previously on the back of the brake pads be unsuitable for the pistons?

 

[924nutter]

If you have the four pot alloy calipers, corrosion can build up under the staineless steel wear plates and cause the plates to grip the brake-pads quite tightly. The was an article in Post or Porker and 811 Wrold, but the jist is that you remove each caliper and remove the screw holding the wear plates in, clean out the corrosion and rebuild with new plates and screw. Brake fluid is just as good as the special grease, and certainly it is a method I have used when I rebuilt the calipers on my 924. The retraction of the piston relies on the distortion of the square caliper seal returning to shape as the brakes are released, and assuming your car is around 1990 then these seals are 17 years old and probaly a lot harder than when they were new, consequently they do not retract the piston as well.
As a "get you through the mot without a lot of dimantling," you could try removing one pad and inserting a stout spring in its place, one stiff enough to push the piston back, then lubricate the piston well with brake-fluid and pump the pedal. This will articulate the piston back and forth in the caliper and free it off quite well temporarily, giving you the chance to remedy it properly at your leisure. This has proved to be very effective on a binding calliper on my 924 turbo.