Brake Piston w/Grease

[Roger S.]

This morning I removed the rear calipers and upon disassembly I found the area between the front of the piston and the grease seal was packed with grease, dry hard grease. Also in the bottom of each recess for the pistons was a brownish slime. What does grease and DOT3 brake fluid make? The calipers are VBP units but the pistons and seals were standard issue GM items. VBP o-ring pistons are going back in.
Anyway, does anyone out there put grease around the front side of the piston before installing the dust seal?
Roger

[Joe L.]

Re: Brake Piston w/Grease

Roger------

I don't know of any reason to put grease anywhere near a brake caliper piston. In fact, all of the rubber parts of a brake system are incompatible with petroleum-based grease (or, any petroleum-based product, for that matter) of any kind.

[Ed Jennings]

Re: Brake Piston w/Grease

I suspect the "grease" is really a sludge of leaking brake fluid and rust/corrosion from the piston.

[Terry F.]

Re: Brake Piston w/Grease

If it is grease it would have to be silicone grease. It might serve some function but I really don't know for sure. It may make the area less likely to get moisture into it preventing future sealing problems. That would be a guess. I bet it is just sludge. The brown stuff is rust that probably settle into the bottom of the caliper from your brake lines....good ol' rust.

I wonder why they use an o-ring instead of a quad seal?

Regards, Terry

[Duke W.]

Re: Brake Piston w/Grease

I believe there is such a thing as "brake grease" that is glycol mixed with a soap to give a grease-like consistency. It it NOT a petroleum based grease and is compatible with conventional glycol brake fluids and brake system rubber parts.

I have seen recommendations in shop manuals to use such grease to assemble brake hydraulic components, and I think some OE component manufacturers may use it, but I have never found any in an auto parts store or anywhere else for than matter.

Once installed on an operating system the soap in the grease will probably disperse as small solid particles and I think they may be one reason why brake fluid on many new cars turns dark fairly fast and the remants of this grease may be part of the sludge that you can find in old brake systems.

If you flush your brake system at regular intervals, most remants of this soap will likely be purged after several system flushes.

Duke

[Wayne K.]

Re: Brake Piston w/Grease

Duke,

I too remember "brake grease". When I had English cars the Girling (spelling) brake seal kits came with a tube of assembling brake grease.

Wayne