Methods to protect wheel cylinders?

[HWooldridge]

I'm rebuilding the brakes on my M37 for the second time in about 10 years. In both instances, all four wheel cylinders slowly froze over time and braking power gradually got worse. When I pulled them, it was obvious that the rubber end caps had trapped moisture and created considerable corrosion that eventually stuck the pistons. The interiors of the cylinders behind the fluid seals were in good shape so the corrosion stayed in front of the pistons. I don't typically drive in water but the truck doesn't get driven much and I expect this is condensation. I am using DOT 5 brake fluid in the system.

Does anyone have a trick(s) to prevent this situation? I was considering punching a small hole in the bottom of the cover but that obviously creates a place where grit can enter. Is it worth packing the end caps with silicone or some other material?

Thanks, Hollis W

[Gordon Maney]

I'm rebuilding the brakes on my M37 for the second time in about 10 years. In both instances, all four wheel cylinders slowly froze over time and braking power gradually got worse. When I pulled them, it was obvious that the rubber end caps had trapped moisture and created considerable corrosion that eventually stuck the pistons. The interiors of the cylinders behind the fluid seals were in good shape so the corrosion stayed in front of the pistons. I don't typically drive in water but the truck doesn't get driven much and I expect this is condensation. I am using DOT 5 brake fluid in the system.

Does anyone have a trick(s) to prevent this situation? I was considering punching a small hole in the bottom of the cover but that obviously creates a place where grit can enter. Is it worth packing the end caps with silicone or some other material?

Thanks, Hollis W

You are not in a humid region, right?

[HWooldridge]

Well, we aren't as powder dry as north or west Texas and it rarely gets above 60% RH but we can get some real soppy dews when it's cool.

Today, it's going to hit 96F and the RH is 56%; we haven't had any appreciable rain in 7 months.

[Desoto61]

I wouldn't pack anything, since it all needs to move and the silicon might pop the seal off if it were packed tight. I would think a light coating of the DOT5 fluid on the other side of the seal might be sufficient. I'd be worried about contamination with anything else. DOT5 doesn't absorb moisture, so as long as it doesn't dry up it should continue to provide a protective layer. A thicker product would probably last longer, just need to make sure it's compatible with the DOT5.

Another option is to have them sleeved. Most of the places that rebuild them do so by lining them with a non-corrosive sleeve (stainless or brass I think). That should help eliminate corrosion issues as long as the piston isn't a dissimilar matieral (galvanic corrosion). Expensive but should be a long-term fix.

[HWooldridge]

I wouldn't pack anything, since it all needs to move and the silicon might pop the seal off if it were packed tight. I would think a light coating of the DOT5 fluid on the other side of the seal might be sufficient. I'd be worried about contamination with anything else. DOT5 doesn't absorb moisture, so as long as it doesn't dry up it should continue to provide a protective layer. A thicker product would probably last longer, just need to make sure it's compatible with the DOT5.

Another option is to have them sleeved. Most of the places that rebuild them do so by lining them with a non-corrosive sleeve (stainless or brass I think). That should help eliminate corrosion issues as long as the piston isn't a dissimilar matieral (galvanic corrosion). Expensive but should be a long-term fix.

Sleeving sounds like a great idea I never considered. I work in a production machine shop and will talk to the chief toolmaker about it - I also have some old wheel cylinders he can practice on. We also have a Sunnen hone so I can get the bores to size and good finish.

[Gordon Maney]

Remember you have a stepped bore, that complicates the honing.

I have used these people: http://www.whitepost.com/brakeform.html

[HWooldridge]

Remember you have a stepped bore, that complicates the honing.

I have used these people: http://www.whitepost.com/brakeform.html

Thanks for the link, Gordon - I'll send them a note about quoting my cylinders.

[Doc Dave]

I used Apple Hydraulics recently and they did a very nice job. They may be less expensive than White Post, who I am sure also does good work.
I had the pistons in my rear wheel cylinders freeze up, and what i discovered was that these cylinders had dissimilar metals in them, the pistons were aluminum in the iron cylinders. The front cylinders had the older steel pistons and those were fine.

http://www.applehydraulics.com/brakes.htm

[El Muerto]

A light wipe of syl-glide sillicone grease inside the end caps and on the outside of the piston ends will keep it healthy. Dont pack it but a complete coating will do it.

My '60 GMC 930 had it bad..dot3 in there messing things up too..its all rebuilt with dot5 now...aaaahh...relief..

I agree on the galvanic action of dissimillar metals..keeping oxygen away will help.

[Matthew Welcher PWA]

Great tip on the Sil-Glide, I have never used it in the wheel cylinders but will give it a try. Thank you.

[Greg Coffin]

I've started using Red Rubber Grease on my wheel cylinders and so far it seems to work well. It is formulated to be used specifically with brake systems, and won't hurt rubber seals like petroleum products. Don't confuse it with red wheel bearing grease, they are completely different.

It's used quite a lot in Europe and Australia, and was used in the States decades ago, but not much any more. I had to order a can from England off of Ebay, but I recently found some domestically on Amazon.