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Mystery of the disappearing brake fluid


tjthorson

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OK - bear in mind, I have been working on cars for over 20 years, but I have a real head scratcher - and Im hoping the Riviera collective might know something that Im missing. I have a 1964 Riviera, 425 dual quad. Factory single chamber master cylinder. Previous owner looks to have replaced front brake hoses, and rear hard lines that are on the axle. I have had all 4 drums off and all 4 wheel cylinders are dry, no moisture on the drums either. The master cylinder keeps emptying - even if not driven. I see no evidence of fluid on the frame anywhere along the brake lines. Hoses are dry. I can fill the master cylinder, check it a week later and its bone dry. Intersting part is - if I fill it, there does not appear to be any air in the system - ever. Brakes all work perfectly when you fill it back up. If I sit and hold the brake pedal - pedal is not spongy and doesn't sink at all.

But - here is the weird part.... The rear axle appears to have developed a leak... almost as if its overfull. Its not coming out the pinion seal. Question is - is there any way that brake fluid could be leaking into the axle assembly itself, causing the axle to overflow onto the ground? The brake lines run over the top of the axle and look new.... This is driving me crazy. But Im confused by the rear axle suddenly leaking appearing to be overfull - but the wheel cylinders being dry, and new lines running over the axle and not appearing to be leaking....

Logically I know its going somewhere - anyone ever seen this before????

I wiped down the front crossmember now that I replaced the front main seal to see if maybe under the grease and grime its leaking in the front hard line.... But then I would think I would have spongy brakes, sinking pedal, and obvious puddles on the ground....

Any weird Riviera thing I might be missing?

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Very possible the fluid is getting past one of the piston seals in the master cylinder and entering the brake booster. Usually you will see an external drip on the front of the booster below the master cylinder but not always. Unbolt the master cylinder from the booster and see if there is fluid there on the rubber seal.

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I agree with Paul K, as this is the most likely scenario, and I've experienced it myself. Another thing you could try is to cap off the line leading to the rear axle, refill the master cylinder, and see if the condition recurs. This may give you some direction as to where the problem lies.

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I had the exact same thing happen on my 65, and I've never figured out where the break fluid was going. So thank you for helping clear up this mystery. I do have a related question. If the brake fluid is leaking into the brake booster, is it also possible that the brake fluid could start leaking inside the firewall and start soaking into the carpet? I ask because the carpeting on the drivers side floor has several unusual stains that I had thought was the result of a bad heater core, or the leaky front window, both issues when I bought it. I just figured I would replace the carpeting (schedule for the spring, YAY). But when I felt the carpeting it didn't so much feel wet as it felt greasy. Could the brake fluid have made it inside?

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That would make a lot of sense. Im going to do the research to go ahead and move to a dual chamber master since I prob have to replace it anyway.... Thanks! Ill let you know what I find when I pull the master... I would imagine the fluid contamination ruins the booster as well, correct?

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That would make a lot of sense. Im going to do the research to go ahead and move to a dual chamber master since I prob have to replace it anyway.... Thanks! Ill let you know what I find when I pull the master... I would imagine the fluid contamination ruins the booster as well, correct?

Usually brake fluid will eat away at the vacuum diaphragm on the booster and cause it to fail eventually at a later date. If you take the car on out of town trips I would suggest

you go ahead and change out the booster while you are in there, if you find that fluid has been getting inside it. The dual chamber master cylinder is an excellent safety upgrade, as you normally won't lose

all of your brakes if either the front or back springs a leak. Another upgrade you should do on a car that is driven sparingly is to change over to DOT 5 silicone fluid. That will eliminate having your master and wheel cylinders start leaking every five years from moisture absorption. Some of my collector cars have had the same brake hydraulics for more than 25 years with no failures because I 've used silicone fluid exclusively on my old cars since 1984. Another added benefit of the silicone fluid is you can't damage any paint on a detailed undercarriage if you spring a leak somewhere.

Edited by Seafoam65 (see edit history)
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Thanks again for all the help. While I wanted to do the dual master - I ended up just replacing the existing master with a $49 "new" single master. It was definitely leaking out the back - but not into the booster at all. It looks like the PO replaced the booster. I can see where it was leaking down onto the power steering box. The inside of the master was silver and dry. There was a cup with rubber seals that kept the fluid out of the booster.

Brakes are all bled and ready to go. Some year Ill do that dual master. This year I did the alternator, power steering pump, PS hoses, timing chain, water pump, front gaskets and seals, fuel pump, radiator recore, hoses, belts and thermostat. Im pretty tapped out on funds....

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Another upgrade you should do on a car that is driven sparingly is to change over to DOT 5 silicone fluid. That will eliminate having your master and wheel cylinders start leaking every five years from moisture absorption. Some of my collector cars have had the same brake hydraulics for more than 25 years with no failures because I 've used silicone fluid exclusively on my old cars since 1984. Another added benefit of the silicone fluid is you can't damage any paint on a detailed undercarriage if you spring a leak somewhere.

Seafoam, theoretically this is true and I don't doubt your good luck with the brake systems in your other cars.

Silicone brake fluid in not hygroscopic and does not absorb air (and water), however, air still enter the brake system. Instead of the air and its water content mixing with the fluid as with glycol based fluids, with silicone fluid the water settles to the lowest point of the system and sits there causing major pitting. From what I have read, this is worse with brake calipers vs wheel cylinders due to the difference of their shape.

I imagine a lot of this depends on where you live and the humidity.

FWIW, I did a full brake rebuild with new wheel cylinders on my Rivy about 7 years ago but have driven very few miles since. I used regular DOT 3 fluid. I had a bad brake pull recently and discovered a frozen wheel cylinder from corrosion. I checked and rebuilt all the other cylinders and they all looked pristine. Their fluid looked fine too. Makes me wonder if the metal of the frozen cylinder was not the same as the others.

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  • 1 month later...
Another upgrade you should do on a car that is driven sparingly is to change over to DOT 5 silicone fluid. That will eliminate having your master and wheel cylinders start leaking every five years from moisture absorption. Some of my collector cars have had the same brake hydraulics for more than 25 years with no failures because I 've used silicone fluid exclusively on my old cars since 1984. Another added benefit of the silicone fluid is you can't damage any paint on a detailed undercarriage if you spring a leak somewhere.

I did the same thing to my cars back in the mid 90's and have not had an issue with a frozen caliper or wheel cylinder since. I have also converted over other people's older cars too when I replaced the brake lines. Great stuff.

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