Lubing caliper pistons, red rubber grease or brake fluid?

[TroubledSoul]

Going to put new pads on the 330i tonight, one is not working as well as the other as the car pulls to one side under braking. I may end up replacing the calipers, but first I'm trying the new pads and I will lube the pistons before pushing them back in.

Is there a danger of contaminating the brake fluid if I lube the piston with RRG? Should I use brake fluid?

[E-bmw]

Use the grease, the grease will be "outside" of the seal so will not contaminate anything.

[TroubledSoul]

Might be being thick here, but wouldn't it be inside the seal if I grease the exposed piston then wind it back in?

[finlo]

No, the seal will scrape off excess grease as it retracts.

[TroubledSoul]

Ah OK, makes sense. Cheers guys.

[The Wookie]

It wont make any difference, it's just as likely to free it off pushing it back and applying the brakes (being careful not to pop the pistons) a few times. You'll be better off replacing the slider pins as a first effort, it's more likely to be your issue. If not then the calipers aren't hard to rebuild if you can get hold of a seal kit and have access to an air compressor.

[TroubledSoul]

The Wookie said:

It wont make any difference, it's just as likely to free it off pushing it back and applying the brakes (being careful not to pop the pistons) a few times. You'll be better off replacing the slider pins as a first effort, it's more likely to be your issue. If not then the calipers aren't hard to rebuild if you can get hold of a seal kit and have access to an air compressor.

Was going to give them a decent checkover while I do it all

[The Wookie]

TroubledSoul said:

Was going to give them a decent checkover while I do it all

Good stuff, make sure to check them for play as well as just making sure they slide. Even a small amount of play can cause them to stick when the brakes are applied!

[TroubledSoul]

Will do. It's going to be a day of fun. New pads all round, checking each caliper and also swapping out the steering rack for a remanufactured item to eliminate a small bit of play in the middle.