The Stovebolt Site Forums The Shop Area Engine Shop Brake problem

Okay, I know this ain't drivetrain, but it seems better to post here than any of the other forums.

My 61 flatbed seems to have a leak somewhere in the brake system. When I got it, the system was dry, so I put some fluid in it, and it was okay, but needed bleeding. Then, right around christmas, I bled the system, (mostly) and had it working pretty well. Well, I just went home, and it was dry again. The system acted like it was dry clear to the wheels, and I know it took several pumps before the hydrovac started moving. (could hear it suck air) Any idea where I'm leaking? The truck was not run, and was not used in any way - it just sat. I also saw no evidence of a leak, that is, no pudddles or wet spots on the ground. My dad's 63 also seems to have the same problem, but I blamed it on the microlock being left on. Any ideas?
Thanks ~ John

Well , I know nothin' about the big rigs ,, but I'm going to throw a wild guess in anyway ..
Is it possible for the fluid to leak into the hydrovac , leaving no evidence of leakage on the ground ??

Wheel cylinders make my list of "usual suspects."

I have owned my 62 C60 since like 89 and it has always done the same thing. Yet never have I seen a puddle or even a wet wheel. It especially happens when sitting. I know to check the level on a regular basis and keep it topped up or I will have to bleed it. Everything is working perfect. It never happens during use. I always check the level before a return trip and it never needs any, just after sitting.

It's still nice to know why. I know the tow truck i just bought doesn't seems to do it, and it's other wise the same, athought the po replaced the hyrovac unit recently. I've got a bad feeling that's what it is. Still strange that there's nothing on the ground - that's alot of brake fluid. Well, the truck's for sale, so I've just got to get it to work well enough to get up here, then sell it.
~John

There is a thread somewhere on this subject. I think one of the comments was that if the fluid is being ingested through the vacuum system, that is not a good thing!

That's for sure....

Once it's into the vaccum system could it end up getting burnt with the fuel, and that's why there's never any puddle on the ground?

You are almost definitely losing it through the Hydrovac and into the intake manifold if you can not find any leak source elsewhere.

If you lose it when the engine is not running, then it's still weeping out somewhere, but if it is losing fluid when the engine running and you can't find wet wheels or puddles, the Hydrovac has failed and is back siphoning the fluid into the intake and then it's burned off. Running a little rough at all? Sounds like you got a pretty good leak to pull down the entire system in a short period of time. How long did the truck run before you lost everything?

If you use DOT 5 fluid, well...nevermind.

Pull that Hydrovac unit and have it rebuilt and I think your problems will disappear. No I don't know where to have that done but there are tons of brake rebuilders out there and I"m sure many can do this for you.

Let us know the final outcome.

From what you describe, it is leaking into the hydrovac. If you were to dissasemble the hydrovac you would find all the fluid. If you were to continue adding brake fluid long enough then it would accumulate enough so when you apply the brakes the engine would suck some of the brake fluid into the engine and it would really smoke out the tail pipe. Your best thing to do is get another rebuilt hydrovac.

That last thing rings a bell for me. If I brake really hard I get a plume of smoke. But I never knew where it came from. I kinda suspected a wet wheel cylinder making the smoke when hard brakes are applied, but it could be from the exhaust pipe. I really have to brake hard though, normally never see it.

It seems to leak with the engine off, and there's no evidence it's sucking into the manifold. I would think that if it was pooling in the hydrovac, I would get a nice cloud of smoke on start up. The truck lost the entire resirore, plus whatever was in the lines, and that's a bit of fluid to just disapear. Still, it makes sense. How much would I expect to pay for a rebuilt unit? Better yet, is it something I can do myself? I really don't want to pu too much into this truck, since I plan to sell her, but I don't want to just ignore it either. Also, I think the 63 has the same problem, so it'd be nice to know how to fix it.
~John

I dont know if our trucks have the same problem. But mine has been doing it as long as I owned it. I have probably put it about 5 cans of brake fluid just topping up since '89. But, since it doesn't happen during driving, it doesn't seem dangerous to me. Just check the level before every time you start it up.

Sell it the way it is. You won't get your money back.