[poncho62]

A funny thing happened on the way to our trailer today. Coming up to a stoplight, the brakes suddenly felt mushy. Got it off to the side of the road, but noticed that a lot of white smoke was coming out of the tailpipe. First thing I thought of was, headgasket, but what do the brakes have to do with it. Checked the rad....no oil in it. Checked oil...looks clean.

Popped the master cylinder, it's half way down. I have no spare fluid with me. It's only a few miles to the campground, so I decide to limp it there. Every time I pump the brakes, smoke pours out of the tailpipe. By the time I get there, the back half of the master is empty.

OK, I figure that the rear seal has let go in the master and is sucking it into the power booster, then into the engine.. But, when I take the master cylinder off, I see no fluid at the back of it where it joins the booster. The fluid couldn't have gone any where else.

Question is, will the booster suck that fluid in enough to dry it up?

Is my booster OK?

[66GMC]

Hi,

This might be a silly question, but are you sure that the smoke is coming OUT of the tailpipes?

Being that it's the rear reservoir that's being depleted, I have a hunch that the rear rubber hose, or perhaps even a metal tube has developed a pinhole leak and may be spraying fluid onto the hot exhaust near the differential?

Don

[larryblack]

I would think you would have a trail of fluid or the shiny remnants of one. Remember you should have a vacuum which if the seal is leaking, should come out between the booster and master cylinder. Unless your diaphram is shot coupled with the seal in the master cylinder being bad.

Too many IFS here. I suggest you pull the vacuum hose off the booster, plug it and then stomp the pedal to see what happens. Get 2 helpers, I to stomp the pedal and 1 to watch the tail pipe while you watch the booster and cylinder. I just put my thumb on the vacuum fitting.

EDIT Just saw the check the metal/rubber hose. Good call on that one. Makes sense too.

[poncho62]

Not a drop of fluid on the ground.......it's definately coming through the engine and out the tailpipe................tons of smoke. When I stay off the brake, it clears up.

I am concerned that the diaphram in the booster is shot. Can this cause enough suction to draw the fluid out of the master? Have never seen this before.

[larryblack]

remember the master cylinder has an o ring seal to keep the fluid in. It would also have to be worn to the point of leaking for the blown booster diaphram to suck fluid.

Every time I have seen that seal was leak, a trail of fluid was running down the booster.

Try the test I proposed and let us know.

[poncho62]

I took the master off tonight. No sign of fluid in or on the booster. That is puzzling me. Have a new master coming in morning. I am going to put a new master on anyways, only $37.................

I think I will try it with the vacuum off the booster first.

[larryblack]

Sounds like a plan.

[trees]

Ponch, what have you found in your trouble shooting? My guess is a bad booster as well as a weeping master cylinder. When applying the brakes, fluid is being sucked thru the vacuum line into the intake. I suspect it will not smoke with the vacuum line disconnected and you will have brake fluid residue in the MC/booster connecting area (no vacuum to suck it up).

Trees

[poncho62]

Turns out it was a broken front brake line that goes across the crossmember. I could have sworn the smoke was coming out of the tailpipe, and lots of it. I replaced the master cylinder anyways, as I had already bought it and gave the old one in exchange Hooked the vacuum back onto the booster and everything is fine. I must be getting senile. I could have sworn that the smoke was coming out of the tailpipe.

[Henry Highrise]

Glad you got it fixed.

[Centerline]

Originally Posted by poncho62

Turns out it was a broken front brake line that goes across the crossmember. I could have sworn the smoke was coming out of the tailpipe, and lots of it. I replaced the master cylinder anyways, as I had already bought it and gave the old one in exchange Hooked the vacuum back onto the booster and everything is fine. I must be getting senile. I could have sworn that the smoke was coming out of the tailpipe.

Funny how something like that will fool ya. Especially you old senile guys. Yea, I know..... look who's talking.

Glad you got the problem solved.

[larryblack]

Well at least the smoke was ON the exhaust pipe.

Glad to hear things are fixed and stopping.

[66GMC]

Originally Posted by poncho62

Turns out it was a broken front brake line that goes across the crossmember. I could have sworn the smoke was coming out of the tailpipe, and lots of it. I replaced the master cylinder anyways, as I had already bought it and gave the old one in exchange Hooked the vacuum back onto the booster and everything is fine. I must be getting senile. I could have sworn that the smoke was coming out of the tailpipe.

Hmmm ... sorry, I guess I gave you bit of a bum steer telling you to look at the rear brake hose. Thinking about it, and after reading that it was a front line leaking, I slapped myself and remembered that the rear reservoir is for the FRONT brakes

Senility must be contagious?

Anyway, glad to hear its all good now. Brakes are important.