Brake Fluid All Gone/Mystery

Today I attempted to get the E (67 OTS) out of winter storage. It has been stored in an enclosed trailer in a storage lot since November. I anticipated some possible problems as we have had a cold winter (Colorado), with IIRC 4 or 5 days straight of 15 below weather. Surprisingly, it started right up, in no small part to Ray’s EDIS, I am sure. However, the brake pedal went right to the floor, and inspection revealed both front and back reservoirs empty, and no evidence of fluid on the trailer floor, although it is difficult to be sure in the enclosed trailer with no flashlight. I completely overhauled the brake system, including the master cylinder, in 2004 as part of the restoration, and have not had any issues since, except routine pad and front rotor replacement. I added fluid but that did not restore the pedal. That did not surprise me as I am sure I will have to bleed the system via the wheel cylinders, which will be a lot of fun in that tight trailer.

Does anyone have any idea where the fluid may have gone? I know there is a failure mode where fluid ends up in the vacuum reservoir, but I think that only affects the front brakes, and I don’t think that could happen in storage with out the engine running.


This is remote, but crazier things have happened. The bellows or diaphragm in the power brake booster may have ruptured, and I have seen this drain a brake system in no time. As to the fluid, it will evaporate, but it takes a while, as it will actually absorb moisture, so it could have leaked somewhere in the system or the lines.

I’d always heard that when the pedal went to the floor and there was no fluid puddle, that it was your booster. My S2 69 coupe was kind enough to do this in my driveway, right before a planned drive. Bought a brand new unit anf stuffed it in. The other half of the story is that they built the car around the booster. Whatever. Got it in and worked great.

Mine ended up in the booster, seal on the slave was leaking. If memory serves it would empty both reservoirs eventually, the seal in the cylinder between the circuits is tapered, and it will pass fluid in one direction. I found that out while pressure bleeding the system after replacing the seals. Mind you I likely needed all the seals as I wouldn’t expect gravity to be able to push the fluid past the seal.

No puddle? Two places that it goes, but the cause is the same for both. First, the master cylinder may have a bad rear seal. This will allow the fluid to leak out into the pedal box, from whence it soaks into the carpet. Stick your head under the dash and look up. you’ll see the inside of the pedal box, and may find your fluid there. Also take up the driver’s mat and check underneath.

The second place is similar. The rear seal on the slave cylinder may have failed. In this case, fluid would end up in the booster capsule. It would be neater, because the leak is contained. But the repair requires removing the entire servo/slave mechanism, which is a chore.

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Also check brake light switch, mine was leaking thru its spade connectors and took awhile to locate.

Thanks for the responses. Right now I am betting on the servo/slave, but I have to get the car out of the worlds smallest garage to be able to investigate further.


In 46 years of stewardship, I’ve had this happen three times, the latest while the engine was out being rebuild by me. I see it as a rite of ownership…sigh.
Maybe I should buy better rebuild kits?

Mine went into the booster (but not all at once)…

Obviously someone used red Castrol prior to my ownership.

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Hmm. I suffered this many times 27 yrs ago when i first bought the car. After 3 rebuilds over 2 years turns out it was the non return valve in the vac line allowing petrol vapours into the booster and destroying the diaphragm. Quick change solved the problem.
best regards mike Clarke

Finally got it home and got the car out of the tiny garage. There is no evidence of fluid from the pedal box. Ditto for under the car, so it looks like a new or rebuilt servo in my future. I still do not understand how both reservoir emptied. Two failures, front pistoncup, then shaft seal? On my way out of town for 2 or 3 weeks, so the fun is on hold.


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Back in town, pulled the servo, pulled off the end cover, inside dry and clean. Again checked for evidence of leakage everywhere, no joy, no indication of where the fluid from both reservoirs went. I’m developing a conspirator theory, somebody broke into the trailer and drained the reservoirs. Seriously, think I should have refilled the reservoirs, bled the brakes and gone on from there, which is what I think I will now do, although now I will rebuild the servo before reinstalling. If anyone has any other alternatives to offer I would be pleased to hear them.


No leaks… not in the servo… the only other way out I know of is the tailpipe.

Have you checked the fluid level in your reservac tank? Does your vacuum check valve still hold vacuum?

I had considered checking the reservac tank for fluid, but have not as I considered it improbable, especially with regards both fluid reservoirs being empty. However, it seems the time to check the improbable has arrived.


With that, I’m going with space aliens. It is the only possible explanation.

And just be glad you were a victim of the “DOT Fluid Scavenger” aliens and not the anal probe ones instead.

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Maybe first just inspect the hose and check valve. If it’s wet, there is your fluid. Maybe check tank with a dip stick. What a PIA to take out to drain. I would try to vacuum somehow.

Gents, how would you suggest fluid is getting to either the tailpipe or reservac without passing through the servo?

There’s a leak somewhere.

Well, it could leak out the small piston and in theory go directly to the vacuum reservoir. I am not sure the layout of hoses would lend to a sitting car draining over to the vacuum reservoir and not to the booster. But even that would only drain one brake bottle, not both. Rod says that both front and back bottles were dry- I assume we should read that as both front and back brake bottles, not front clutch and rear brake bottle.
So it does seem a mystery as Michael said, that both bottles drained and not through the booster.
On the other hand, Rod, you say it has worked great since the 2004 brake system rebuild. I would think rather than spend too much time trying to confirm what critter crawled in and drank the fluid, since it has been 19 years since your last rebuild, it may just be time to rebuild the entire system.

Leaking little plunger at front of m/c. Sucks it right to the tank.