The Missing Brake Fluid Mystery Depends

[RAC68]

A couple of weeks back I started a thread about a lower level in both the clutch and brake portion of the sections of the reservoir. As a result of forum suggestions and physical investigation, only slight sweating was found in the clutch slave and, although it didn’t seem equal to the reservoir loss, the missing fluid could easily have leaked onto the road during a drive. A quick rebuild of the slave cylinder and the problem was eliminated….so I thought.

This past Saturday, preparing for a club show drive, a pre-check of the reservoir showed the brake section was close to half below proper level. This was doubly concerning as a quick check found no lost fluid or any indication at each wheel or line.

Today, I decided to do a thorough investigation and started with de-installing and dismantling the brake booster. I chose the booster since it is the only place that the missing fluid could collect (in the air piston chamber) and stay incognito. Contrary to anticipation, no fluid had collected inside the booster.

One last point, the only place I haven’t considered is the brake master cylinder. The reason for my confidence in the M/C is that no seepage was indicated and no loss of pressure was noticed when applying the brakes.

Since I have already ordered the rebuilding kits for the booster, rear wheel cylinders and calipers, I will continue on that plan. However, I would appreciate any ideas as to where this fluid could be escaping as the brakes were functioning perfectly prior the dismantling.

Thanks all,
Ray (64BJ8P1)

 

[TimK]

"Depends" in title should be edited to "deepens".

But what about the engine vacuum which powers the booster drawing brake fluid into the engine if you have a bad booster seal/diaphragm or whatever (I don't have this system, so I'm just guessing based on prior forum discussions. I'm sure the experts will sign in.

 

[Jeepster]

I would say its a problem with your brake servo (booster). I had huge loss of fluid some time back and it was leaking inside the servo. Servo was reconditioned and problem solved.

 

[John Turney]

I agree with TIm on both counts: fluid being drawn into the engine from the booster and you don't want brake fluid in your Depends.

 

[RAC68]

Hi Guys,

Thanks for your inputs as was also on that path of thinking and the reason for my dismantling the booster. The booster had no brake fluid in the air piston chamber and the vacuum tube to the intake manifold was dry. I think it would be impossible for all the fluid to be sucked into the engine without some indication or residue in the booster or vacuum tube.

The booster is dry and clean so I guess that rules out the booster as both source and destination for the leak. This is the reason for my frustration and the new thread. Everything pointed to the fluid being held in the booster, but it wasn’t. What’s next.

Ray (64BJ8P1)

 

[Patrick67BJ8]

Hi Guys,

Thanks for your inputs as was also on that path of thinking and the reason for my dismantling the booster. The booster had no brake fluid in the air piston chamber and the vacuum tube to the intake manifold was dry. I think it would be impossible for all the fluid to be sucked into the engine without some indication or residue in the booster or vacuum tube.

The booster is dry and clean so I guess that rules out the booster as both source and destination for the leak. This is the reason for my frustration and the new thread. Everything pointed to the fluid being held in the booster, but it wasn’t. What’s next.

Ray (64BJ8P1)

I had a leak several years ago and it was the resevoir to master line causing the problem. The line had been rubbing inside the meatl clamp that holds it tight against the wheelwell. It was very hard to spot since my engine compartment was filthy! While doing my frameup I've been replacing most of the orginal brake, fuel and wire harness clamps with "adel" clamps used on aircraft.

 

[DerekJ]

Have you checked the carpet in the drivers footwell to see if you can find traces of the fluid. That's where mine ended up when I had a cylinder leak.

 

[RAC68]

Hi All,

Patrick, I have been checking the lines and, as yet, have not found any indication of the lost fluid. I intend to continue the search when I start to rebuild the wheel components and booster. Although everything I’ve touched seems in very good condition after 20+ years (I believe due to my use of silicon brake fluid), its time for a redo.

Derek, I checked the carpet in my search and found it dry. However, since I only checked the carpet’s surface, today I intend to pull it back and see if there is any fluid on the padding. I doubt I will find any fluid as the rubber caps on the clutch and brake masters was dry.

Last night I went through the system in my mind and put the search results down to review:
1. Strong solid brake peddle with no sinking.
2. No fluid on the surface of the driver side foot well below the M/C.
3. No fluid in the brake drums.
4. No fluid on any side of the front disks.
5. No fluid in the booster air chamber or vacuum line.
6. No fluid on any component connector.
7. After rebuilding the clutch slave, its reservoir section stayed at proper level.

And the search goes on. The thing that intrigues me is there was no sinking of the peddle when the brakes were applied. This seems to indicate to me that either the lost fluid was very small, easily compensated by the reservoir and at the less critical rear brakes or, as Patrick indicated, between the reservoir and master cylinder. My next target area is from the reservoir to the master cylinders.

Thanks for all the ideas and suggestions.
All the best,
Ray (64BJ8P1)

 

[Johnny]

I'm going to assume the brake and clutch pipes aren't reversed on the reservoir revealing only a problem with the brakes leaking somewhere correct?

If that's the case you might want to jack up the car and re-do a thorough check from front to rear of all the brake lines especially the lines at the rear of the car over the axles.

 

[nevets]

I googled "vanishing brake fluid"...quite a few entries on the subject some of which mention the booster, including this one
https://www.odyclub.com/forums/52-2005-2010-odyssey/88029-vanishing-brake-fluid.html

FWIW

 

[RAC68]

Johnny/Nevets, thanks for your assistance. I have dismantled the booster and found the air piston chamber and vacuum tube dry. Since I would expect at least some fluid residue in the chamber and on the walls of the vacuum tube, I don’t think the booster is my problem. However, I will be rebuilding the booster since I already have it dismantled.

As far as checking the other components, lines, and connectors, I will be rebuilding the calipers and rear wheel cylinders (along with the booster) and am checking every line and connector.

In a conversation with a good friend, multi LBC owner, and master mechanic, I was informed of something new to me. As previously mentioned, I have always had a solid and even brake peddle when applied. Well, he indicated that it was not uncommon for the master to leak when at rest and seal when applied. When applying the brake, pressure would expand the seal and eliminate any leakage. If the leak was small, you may never notice it by the paddle’s feel.

In modern disk/drum equipped cars, a pressure valve is incorporated in one of the external components (possibly the proportional valve) that keep a small amount of pressure on the system at all times to assure the seal is kept expanded. This valve is not in our LBCs and, therefore, we could experience this condition. Tomorrow, I am going to double check the rug and pad below the master cylinder to make sure my initial examination and conclusion was correct.

Thanks again,
Ray (64BJ8P1)

 

[Keoke]

check the carpet just below the cylinder on the firewall for leakage.