Mysterious brake fluid loss

[3rdmdqm]

I am baffled. I recently replaced all of the rear brake shoes, wheel cylinders, inner and outer seals, inner and outer bearings etc. All brake lines were bled and brakes are rock hard. I also added a remote reservoir under the hood so I could monitor the brake fluid level. Here is the delemma:

Brakes work fine, no issues. If I let the truck sit for a week or so, the fluid level drops in the reservoir. The first time this happened was right after the repairs, after driving the truck and parking it the reservoir was full. When I returned to the truck a week later the fluid level had emptied the reservoir and was at the top of the rubber hose connecting to the reservoir. I then filled the reservoir back up, drove it around, no problems, parked it with fluid level at full, then returned a week later and the fluid level was down half the reservoir again.

I am baffled. There is no evidence of fluid leaking anywhere. Everything is bone dry, all the wheels, master cylinder, brake lines everything. Where is this fluid going?????

The first time I thought maybe it was some air that was trapped in the Master cylinder somewhere that worked its way out. But twice in a row? Anyone know where this fluid could be going?

 

[glcaines]

If you haven't done so already, I would park it on a clean concrete driveway or some other clean area that can be monitored for drips. It is possible that you have a leak somewhere that is dripping but not leaving any wet areas behind to see. Otherwise, keep filling the reservoir and eventually you might see a wet area develop.

I'm still using the small reservoir on my MC on my Deuce and the fluid level has never changed in the 15 months since I picked it up from Fort Indiantown Gap.

 

[dragonwagon]

Are your innear dual wheels clean ? Lot of fluid can leak and mixed in with dirt in the wheels does not get to the ground , nothing obvious i suspect a rear wheel cylender leaking . Nothing on the inside tire either ? I have an innear wheel seal getting bad and leaks a touch , never see any thing on the ground . It cakes up with the dirt in the inside dual .

 

[Kohburn]

do you have fluid coming out of the vent line on the firewall by the air cleaner?

 

[ctmustang]

If he added a remote reservoir chances are he doesn't have a vent line like the normal setup which should not cause a problem. The fluid is going somewhere. I would suspect a leaky connection in the lines to your remote. If not start crawling under your truck and visually inspect all the lines front to back and the inside of the wheels.
CT

 

[Hammer]

Check to make sure it isn't leaking into the air pack.

 

[whyme]

could be filling up in the air pack. mine came off the gl lot with an empty MC and no visible leaks. at some point you'll either get the rock hard petal or have dot5 flowing out the vent tube on the engine

 

[DieselBob]

Maybe slowly filling the airpack ? I would think this would happen when you were using the brakes though.

I really need to type faster.

 

[velociT]

Check to make sure it isn't leaking into the air pack.

This.

 

[hndrsonj]

Did you use a brass swivel fitting for your remote resevoir? If so it's probably leaking.

 

[m16ty]

If you're loosing that much fluid and you can't see it leaking anywhere, it's got to be the airpack.

 

[3rdmdqm]

If it were the air pack, would I see fluid when I drained the air tanks? After every use I bleed the air tanks. Nothing unusual has changed from normal, no fluid comes out of the tanks.

I no longer have a vent line. This was removed when I added the remote reservoir which was from pegassus racing. It has a vented cap. Now I have not capped off the T where the vent lines met however there is nothing coming out of this T fitting either.

If it's the airpack, how would I nail that down?

 

[JDToumanian]

No, the fluid just stays in the airpack. When it gets full of fluid in the air side, the pedal will get rock hard as you will have lost the air assist at that point. There is a little pipe plug in the back cover of the airpack that is for lubrication.... You can check to see if it's full of fluid with that, if you can get it out....

Jon

 

[roger-wilco-66]

I had the same problem on my truck, internal brake fluid loss. It was a semi-stuck valve in the airpack that allowed brake fluid to enter the air pressure cylinder in the back of the airpak. But this was accompanied by dot5 blowing out the vent line of the air pack that normally exits near the air filter in the motor compartment. Each time the brake pedal is released, the air pressure chamber of the air pack is relieved and the air (or dot5, if there) exits through this line. If there is enough dot5 in there I guess it starts to pool rather than blowing altogether out.
I have seen trucks, though, where the vent line was disconnected at the t-coupling mounted on a frame member below the truck , That coupling normally joines the mbc vent with the airpack vent line. I say that because if the airpak blows dot5 it not necessarily exits in motor room. Just follow the airpak vent line and see where it exits.

HTH
Mark

 

[rlwm211]

There is a seal in the air pack that separates the hydraulic side from the air side, at the compensator. If this is leaking it can flow into the air pack air valve and then either dump out of the air vent line or else into cannister for the air piston. You need to be absolutely sure it is not leaking out of a hose, or any other spot in the hydraulic system. I know from experience a leaky wheel cylinder can lose more than a pint of fluid before it shows on the outside on a wheel. I would also make sure your master cylinder is not leaking on the secondary seal which is the one closest to the plunger that operates the master. This seal does not operate under pressure but is designed to hold the fluid in the master until it is needed on the other side ot the piston (the high pressure side) or else vented back to the resevoir.

If you do not find a source of the leak in the hydraulic system you need to either rebuild or replace the air pack.

Hope this helps

RL

 

[3rdmdqm]

Thanks to everyones comments and suggestions, I may have isolated the problem.
Today I did a thorough inspection following all of the brake lines from the reservoir to the master cylinder to each wheel. I have found absolutely no leaks or evidence of any leaks anywhere. There is also nothing leaking from the master cylinder, airpack exterior, vent, or anywhere else.

I then pulled off the protective cover plate under the airpack to check the airpack. The smaller side of the airpack with a rounded front points toward the front of the truck. There is a small hex head plug on the front of that (picture #2). I removed this plug and brake fluid comes out. Is this the lubrication hole you were referring to?

What is the fitting for in picture #3 (Looks like a bleeder valve or grease port)? Or did you mean the plug located below this fitting in picture #3? I did not take that plug out.

So if brake fluid is coming out of this hole, what is my next step? Airpack rebuild?


Thanks in advance.

 

[cattlerepairman]

Thanks to everyones comments and suggestions, I may have isolated the problem.
Today I did a thorough inspection following all of the brake lines from the reservoir to the master cylinder to each wheel. I have found absolutely no leaks or evidence of any leaks anywhere. There is also nothing leaking from the master cylinder, airpack exterior, vent, or anywhere else.

I then pulled off the protective cover plate under the airpack to check the airpack. The smaller side of the airpack with a rounded front points toward the front of the truck. There is a small hex head plug on the front of that (picture #2). I removed this plug and brake fluid comes out. Is this the lubrication hole you were referring to?

What is the fitting for in picture #3 (Looks like a bleeder valve or grease port)? Or did you mean the plug located below this fitting in picture #3? I did not take that plug out.

So if brake fluid is coming out of this hole, what is my next step? Airpack rebuild?


Thanks in advance.

The airpack is the fat round thingy. The slim round thingy is the master cylinder and we all hope that it is indeed full of brake fluid. The fitting on top is the bleeder nipple - when you bleed your brakes, you always bleed the master cylinder first, and now you know where to do that! It would have needed bleeding right away, after you replaced the rear wheel cylinders.

Move to the rear of the air pack - there is a thick J-shaped pipe coming out of it pretty much in the centre; below that is the small plug that was referred to in earlier posts. You can also remove the J-pipe fitting to get access into the air pack.

 

[3rdmdqm]

Thanks, I'm confusing myself now. Picture 1 below is what I refer to as the master cylinder. Yes, the fitting I was referring to earlier was bled. I'm getting my terminology confused, sorry. You are referring the J-pipe in picture 2 below correct? The one that enters the center rear of the airpack (far right of attached photo) correct? I have not checked that yet. Thanks. It's all starting to make sense now.

 

[hndrsonj]

Thanks, I'm confusing myself now.

I don't think you are the only one confused. You make sure there is fluid in the master cylinder then bleed the air pack. You are right the master cylinder has the resevoir and rubber boot, the airpack is the other whole assembly.

 

[cattlerepairman]

Yes, that is what I meant by J-pipe. In your first picture, you can see the master cylinder sitting in front and above the thick air pack. I,too, should have been more descriptive and called the slim cylinder "the hydraulic part of the air pack".
My air pack never had brake fluid leak into the air side, but I gather from others that brake fluid would come out from the back of the air pack, once you remove the little plug. You may not ba able to budge the plug; spray it with AeroKroil or similar and let it sit before you yank on it.