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Do you lubricate the wheel brake cylinder pistons when you put them together with a special kind of grease, or put them together dry?
My Dad way back when told me never to use grease in the brake system components. So I never have. But have always had corrosion where the piston meets cylinder wall. I am replacing the wheel cylinders today.

Your dad was correct. The only protection against rust to the cylinder wall between the top of the piston and the boot is a good fresh tight fitting boot and 24 month flushing of the DOT 3 fluid to remove all moisture laden DOT 3 from the cylinders.

This 24 month flush schedule is the most overlooked preventative maintenance procedure in all brake systems.

I found a frozen piston on the right front yesterday. All four cylinders have been on the jeep since restoration 5yrs ago. I always flushed system annually. What made the piston freeze was a hole in the boot. The left rear also had a hole in it. But it didn't get corroded to freeze up. But did see evidence of a slight leak. I don't know if I accidently caused it when I installed them back then or if the shoe rubbed it. Anyway they are getting replaced.

I agree, the brake system is probably the most important item that gets neglected.

Put silicone grease inside the boot on top of piston when you re-assemble. Some rebuild kits come with it. John

You do not want to contaminate a DOT 3 brake system with silicon grease. That grease comes in some kits so the boot can be lubed where it has the shoe end or pushrod passing though it. It's not meant to be used inside the wheel cylinder.

Wes, just the hole in the boot or also inside the boot to act as a moisture barrier? I had a new master cylinder that came that way. I didn't lube the piston with it. I also used silicone brake fluid. John

Hello John,

Sounds a lot better than "on top of the piston".

Most of us are using DOT 3 or 4. I never cared for MV brakes serviced with DOT 5 silicon during my 22 years on active duty and I still don't use it in any of my stuff. The arguments for and against are endless. So I just try to remind folks what chemicals they should not mix with whichever fluid they are using. Silicon & petroleum based lubes should be kept away from DOT 3 & 4 Glycol brake fluids and Glycol and petroleum lubes should be kept away from DOT 5 silicon fluids. I am talking lube locations that have a possibility of allowing the lube to mix or contaminate the system's fluid. The best choice for lubing cylinder boots in DOT 3 & 4 systems is the DOT 3 & 4 brake fluid itself. As for moving metal parts the preferred lubes for reducing friction yet have no tendency to melt and run at high temps are the dry film lubes like moly and graphite based lubes.

Thanks Wes. I use silicone in my restored projects only because it won't eat the paint off like Dot 3. They say it fails in a high heat situation sooner than standard Dot 3. I actually prefer Dot 3 and I seem to get a harder petal, and don't notice expansion of the fluid back into the master cylinder like I have with silicone. You get all that nice paint and work done and it seems even with all new lines, it leaks until several tightenings and checks. By then as it runs down and along everything, Bye bye paint with Dot 3. John