Self-correcting master cylinder leak?

[joshs1ofakindxj]

Installed a remote brake fluid reservoir today and made a pressure bleeder from a weed sprayer.

That old DOT 5 brake fluid that came out was nasty. I used a gallon of DOT 3 today flushing and filling.

I bled the airpack then went to the rears and finally the front. I kept pumping the sprayed up a few times every time I moved to another wheel.

When i got to the last wheel I noticed a lot of brake fluid was falling down near the master cylinder.

I checked it out and there was a ton of fluid coming out of the boot on the front.

I released the pressure in the sprayer and the leak stopped.

I gave the brake pedal a few pumps and no leak.

I pressurized the sprayer again, with not as much pressure, and finished bleeding the front without any issues.

I got in the truck, started it up, and the pedal is hard and still no leaks.

I cautiously pulled out of the barn and drove back and forth on the level ground testing the brakes and checking for leaks.

I drove over to my neighbor's 300 acre farm and drove around the trails, doing some hard braking and such. I came back to the barn and no leaks.

I kept the speed way down and didn't go on any hills knowing the brakes could be goofed up.

So did something fix itself in the master cylinder or should I plan on doing a rebuild?

 

[halogrinder]

its air over hydraulic?
regardless, you probably had so much pressure in there, it was slightly pressing the wheel cylinders......

return springs are pushing it back.


and that air hose you used WILL swell trust me.

 

[joshs1ofakindxj]

The M35A2 is air assisted hydraulic brakes.

Not sure how the spring comments are relevant.

That is not an air hose. It is brake hose sold by the foot by Pegasus Racing.

 

[halogrinder]

The M35A2 is air assisted hydraulic brakes.

Not sure how the spring comments are relevant.

That is not an air hose. It is brake hose sold by the foot by Pegasus Racing.

oh ok, gotcha. looks just like air hose lol......

regardless it still has drums. wheel cylinders still expand if you put some pressure behind it.

 

[joshs1ofakindxj]

I guess I understand what you're saying if fluid was coming out of the top of the reservoir due to the brakes resisting, but it was not. It was coming out of the boot that covers the master cylinder's piston rod. This means a seal was being bypassed. I'm just not sure how to address this since the issue only occurred when I had a lot of pressure in the system I guess.

 

[Rustygears]

Maybe the pressure was high enough to open the check valve to the reservoir that fills the cylinder on the draw (return) stroke. The system isn't designed for a high pressure pushing fluid from the reservoir to cylinder, it's designed for a vacuum pulling fluid from the reservoir, so the check valve may have opened per design (but wrong time) due to the unusual situation and that caused fluid to flow out if the cylinder piston wasn't in the normal position when the check valve was designed to open. I wouldn't sweat it. If you blew a piston seal, the pedal would sag when pushed or fluid would still be leaking when depressing the pedal. Keep an eye out for either and you'll likely be ok and ease off of the pressure on the power bleeder!

 

[Keith_J]

DOT 3 absorbs water vapor, DOT 5 doesn't. Meaning DOT 3 needs changing every 2 years, DOT 5 only needs the wheel cylinders drained every 4 years or so.

Now, for your master cylinder leak issue, this is a sign of impending failure of shaft seal or at the least, dirt on the seal-shaft. Changing the fluid probably loosened dirt inside the master cylinder since glycol is a better solvent.

I've never seen any corrosion in DOT 5 systems but have countless instances of 10+ year old systems having completely corroded wheel cylinders. Since bleeders are mounted high on the wheel cylinders, there could be trapped dirt in the bottoms.

On the deuce, wheel cylinders can be removed without fighting the spring, just use the top snail adjusters to extend both shoes out as much as possible. Then the banjo bolt and two fixing bolts retain the wheel cylinder. But you still need to pull the wheels and hubs.

You should never take short cuts on single circuit brake system.

 

[Flyingvan911]

Very nice. I agree, DOT 5 is more expensive but well worth it.

 

[shenkmen]

I would replace or rebuild the master cylinder. They don't fix themselves.

 

[nk14zp]

You should never pump the brakes when bleeding with a pressure bleeder.

 

[halogrinder]

I guess I understand what you're saying if fluid was coming out of the top of the reservoir due to the brakes resisting, but it was not. It was coming out of the boot that covers the master cylinder's piston rod. This means a seal was being bypassed. I'm just not sure how to address this since the issue only occurred when I had a lot of pressure in the system I guess.

BAD BAD BAD BAD

needs a master cylinder.

 

[joshs1ofakindxj]

You should never pump the brakes when bleeding with a pressure bleeder.

I wasn't.

I pumped the brakes after relieving the pressure in the sprayer bottle.

 

[joshs1ofakindxj]

I've never seen any corrosion in DOT 5 systems but have countless instances of 10+ year old systems having completely corroded wheel cylinders. Since bleeders are mounted high on the wheel cylinders, there could be trapped dirt in the bottoms.

This deuce has had a several private owners and as I dig into it more I find more shortcuts were taken, like a bolt in place of a shear pin, so I can't say what fluid was in the truck's brake system, but I know I saw a lot of different colors and consistencies of fluid and some debris.

I've read a lot about DOT 3 vs DOT 5. I just went through all that with my 79 Corvette and ended up sticking with DOT 5 in it.

I wanted DOT 3 in the deuce because I can and will change the fluid when needed and I want to be able to find brake fluid in any gas station.

 

[doghead]

You should rebuild all brake compnents, when changing fluids.

http://www.steelsoldiers.com/1021146-post77.html

 

[joshs1ofakindxj]

I picked up a master cylinder I'm going to rebuild and install.

I also picked up a newer short air pack.

Currently, I have the older long air pack that has the rebuild kits readily available.

Can the short one directly replace the old one? Simple modifications needed?

I plan to pull and inspect my current air pack and rebuild as needed, but should I sell the short air pack and find the correct spare?

Thanks!

 

[Speedwoble]

I had always "heard" when dealing with motorcycles that there was a compatability issue between Dot3 and Dot5 and they should never be mixed. One would cause the other to gel.
Personally, I wouldn't risk it.

 

[joshs1ofakindxj]

I had always "heard" when dealing with motorcycles that there was a compatability issue between Dot3 and Dot5 and they should never be mixed. One would cause the other to gel.
Personally, I wouldn't risk it.

True. My system already showed evidence of mixing based on the ugly fluid in different colors and viscosity that came out of it. I'm running DOT 3 from here out.

 

[doghead]

Either air pack is interchangeable on the truck, with no modifications needed.

Either as a spare, will be useful later on down the road.

You will need to swap the old fittings, anytime you have a new air pack(they do not come with them)..

 

[plym49]

DOT 3 and DOT 5 do not mix. They agglutinate. If there was DOT 5 in your system and you replaced it with DOT 3, it is possible for the brake system to get clogged with clumps from where the two mix.

It is possible that you got away with it by pressure bleeding. It sounds like you used high pressure and hig flow in terms of bleeding each end. You might have pushed any clumps out by pumping a bolus of DOT 5. They never had a chance to intermingle and really gum things up.

It is probably not a bad idea to pull the masted and check inside. Hone it smooth and install new seals. Then bleed it again.

I once had a customer who topped of the front master on his chopper with DOT 3. It was a DOT 5 system; he didn't know. The system clumped up real good, real quick and he almost killed himself. At that point it was replace every component in the front brakes that sees fluid: the master, the lines and the calipers. They were all custom, too, so it was $$$$. But there was no way I would accept the liability (or potentially risk his neck) if some tiny little clump escaped flushing and caused problems later.

Now there is a lot more forgiveness in a six-wheel braking system than in a two-wheel. It sounds like you are OK. But I would for sure rebuild the master, bleed it all again and watch for anything weird coming out. And then, be mindful of the braking performance. If one wheel starts to act up when braking, chances are there might be a clump in the line going to that wheel.

Of course, all of this is moot if your Deuce had DOT 3 to begin with.

 

[plym49]

I had always "heard" when dealing with motorcycles that there was a compatability issue between Dot3 and Dot5 and they should never be mixed. One would cause the other to gel.
Personally, I wouldn't risk it.

You are 100% correct.