I've never encountered a situation where I had to put sealer on a gasket to keep brake fluid under control. So, I'm wondering if anyone here has experience. We all know what the stuff does to paint. What sealer did you use? My Treadle-Vac was mounted on a little more angle than it was intended for. It seems that the gasket alone doesn't seal up enough and I'm getting a leak at the lowest corner. It looked like they may have used hardening Permatex when they put it together originally, the cover was a bitch to get off. I have several sealers in stock. I can always get more. I have: VersaChem Type 3 aviation sealer, Permatex Ultra black and Right Stuff, and good old Gasgacinch. Any experience sealing brake fluid?
It looks like its designed to take a gasket. Dont use sealer make a gasket from cork or sheet rubber.
A nice gasket came in the rebuild kit. I trued up the surfaces and assembled it as directed but it leaked at the corner circled in the photo. Nothing unusual there, no dings or corrosion, the cover is flat. I did a retorque of the screws in the car, but it didn't improve. I want to just glue it down forever. If I have to take it out again, I'll probably change the whole brake pedal/MC system to something more modern, but I really want to give it a chance.
if it might be leaking around the screw head, you could put a gasket under the screw head. I've never tried to seal a gasket against brake fluid. How about you do some experiments? put some sealer on something, let it dry, drip some brake fluid on it, see what happens, over a few days
This may or may not help, but I have seen paper gaskets used on the master cylinder caps on early '60's Chevy pickups.
If it's leaking around the bolt head I'd find some small copper washers to put under the heads. Copper washers are used under the brake hose connections on disc brake calipers and look at the pressure they take. ..
Copper washers are a good idea, but I'd be sure to anneal them first so they are as soft as possible. Along those lines.... you might try to make a washer out of coiled solder. Just a thought...
Copper washers only work when you can get the fitting really tight. Since there's a paper gasket under the plate that he wants to put the washer on top of, I doubt he could get the screw tight enough for the copper washer to seal. I'd suggest a paper washer.
I don’t think that the leak is from the screws but since it’s such a bitch to get the unit in and out I won’t be taking any chances. I have quite a selection of fiber (and other) washers available since my ex-wife was the sales manager for a self-sealing screw manufacturer. I often made prototypes for them. She laughingly referred to herself as the “Screw Lady”. Driving home from visiting my Mom last night I got to thinking, just what is brake fluid anyway? It has to have a high resistance to compression, some lubrication properties, it has to have stable viscosity, it can’t freeze, it can’t be corrosive to metal or “rubber”. It’s a miracle substance that’s been around a very long time. What is it?
Amazing stuff, and one helluva paint stripper….. Good idea, I have some 1/16” rubber sheet somewhere I think.
I had the same issue on a MK II. I went with a little thicker gasket and dipped the screw threads in aviation sealant. I don't know which choice stopped it. Yeah, that angle thing on those makes as much sense as it doesn't. That whole system works on fluid displacement to make pressure, and as the reservoir refills it counts on a good edge seal. It also has to have a remote (sort of) vent that a lotta builders fill in. Wrong move. Good luck, let us know...
One off topic tip for the Treadle-vac is to put a small pipe plug or plug valve at the bottom of the vacuum piston canister. When these units fail, brake fluid leaves the master cylinder and runs into a the vacuum canister undetected. Pulling the plug every year or so gives an indication if this has started to happen.
Wonder if Hylomar will seal brake fluid? It's helped me out in some unique situations where a normal sealer wouldn't work well in. Wouldn't be surprised, it's some amazing stuff.
My experiences are that DOT 5 will eat rubber. DOT 3 is recommended for use in TO bearings where o-rings may be negatively effected by the former. My M/C in my roadster has a remote reservoir lid and it does have a rubber gasket that seals the lid tight. It has been on there for years with no leaks. I run DOT 3. I would imagine that you could use a rubber gasket on that lid as well.
My master cyl has been in place for 22 years and as of a month ago when I changed & flushed the system , the DOT 5 hadnt harmed the gasket ? Loktite 545 is recommended for use with brake fluid .
@2OLD2FAST I mentioned it because I had a failure in a hydraulic T/O bearing, the manufacturer (McLeod) said the use of DOT 5 voids the warranty. I assumed it ate the o-rings but in truth, I have no idea why. I just know they said don't and I didn't...the second time. This is from their tech sheet; I copied and pasted. Fill the master cylinder with DOT 3 or DOT4 brake fluid. DO NOT USE SILICONE BASED FLUID or DOT 5 FLUID!! Use of silicone fluid will damage the O-rings resulting in leaks and or damage to the assembly.
Don't over fill it. There needs to be an air space above the fluid so it can return when you let off the pedal. The fill cap, or tube in your case must be vented, too. A tiny hole at the top of the tube or dip stick will do it. The fluid will also expand when it gets hot and there must be a vent and enough space above the fluid for it to do so.
The cap actually has a breather hole in it and it’s clear. I used Permatex #1, a brown, hardening sealer. After it dried, I set the unit up at the angle required and filled it with fluid. Two days later it was still dry on the outside so I put it back in the truck. So far so good.
ALL brake seals, and OEM rubber brake lines are made if the same material regardless of the fluid. The ONLY issue is if you switch fluids because the seals absorb a tiny amount of fluid and the fluids do not mix so you get contamination. The idea that DOT 5 rots seals is a myth that keeps getting repeated over and over again, regardless of what it says on data sheets. There are other technical reasons why some glycol or silicone fluids may be preferable for your application but rubber compatibility isnt one.
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