Brake advice?

The fluid has likely gotten into the booster as well and destroyed it. Better check.

When the seals go bad on the primary piston (the shiny silver inside the snout), fluid will leak out and collect between the master and the vacuum booster. The little drain hole is there to *try* and keep the fluid from building up in the gap and being forced (or sucked) past the booster's seals, slowly filling the internal chambers with fluid and eliminating the "boost" part of "vacuum booster".

Time for a new master, and as suggested, check the booster for fluid inside, or any air leaking in/out around the booster's front pushrod seal.

chambers with

==================== Thank you very much - that makes perfect sense.

I pulled it off and the pushrod came out with it - It appears to have a sma ll spline on the front that was stuck a bit with age. There is no damage to the seal, it is still supple and there is no fluid behind it. It does not appear to be a pressure fit or anything - just a seal held in place by the bolting together of the two pieces.

I experienced no symptoms that I had read elsewhere of a damaged or malfunc tioning booster, so I think I can assume all is ok on that front.

My parts guy here has suggested a Cardone 10-1423 as a replacement. 1976 wa s a transition year - I ran into that issue on another repair I had to do p reviously - mine has no bleeder screws on it, but I am not sure if that Car done unit has the drain hole. It certainly seems like a good idea on the ba sis of this experience. I'll check that Raybestos unit out further.

Entirely possible that the fluid is leaking from the back of the MC into the booster. You won't see it dripping on the ground because it'll be sucked into the intake and burned by the engine.

I'd just pull the MC slightly away from the booster and inspect; if there is any evidence of leakage then rebuild/replace the MC.

nate

reservoir and little from the front. I have not pulled the wheels and calipers yet, but I did notice that after a little spin around the court here that there appears to be some fluid collecting and running out of a machined hole maybe about 1/8" on the bottom of the Master brake cylinder that seems to go right through the cylinder, just in front of the brake booster.

replace the seals, but it is a lot of fluid going missing in a short time, so I suspect more than one issue.

The good news is that your problem is obvious. It's obvious that your master cylinder is leaking and has to be replaced. You could probably buy a rebuild kit and replace the seals for hardly any money. Ditto for the calipers. I enjoy doing this kind of work. Have fun!

ear reservoir and little from the front. I have not pulled the wheels and c alipers yet, but I did notice that after a little spin around the court her e that there appears to be some fluid collecting and running out of a machi ned hole maybe about 1/8" on the bottom of the Master brake cylinder that s eems to go right through the cylinder, just in front of the brake booster.

replace the seals, but it is a lot of fluid going missing in a short time, so I suspect more than one issue.

Yes - I dropped a new master into it today after priming/purging it on the bench. So far so good. Never done it before, but I have brakes, so that loo ks promising.....

When I get a bit of time I'll jack it up and tear the front tires off and e xamine the calipers and probably end up with new seals (if there is no pitt ing)and pads.

bench. So far so good. Never done it before, but I have brakes, so that looks promising.....

examine the calipers and probably end up with new seals (if there is no pitting)and pads.

Good for you. I've had the master cylinder fail on me twice. I'm not sure how that happens. It is not a good thing.

The first time it happened I panicked and just stood on the brake the whole time. Luckily there was a sturdy tree conveniently nearby. These days I know the correct procedure is to pump them brakes!

This was for a Chrysler mini-van. I replaced the master cylinder but the funny thing was that the rebuild was faulty too. The parts guy replaced it with no questions. Hopefully, they got a more reliable supplier.

Oddly enough, one of the most common ways for a master cylinder to fail is after other brake work - at least if you pump-bleed the brakes. What happens is that the seals in the MC wipe over an area that they haven't traveled over in literally years, and a slight buildup of corrosion and/or pitting can rip up the seals in the MC and cause them to fail shortly thereafter. I've had that happen to me on two different vehicles... then I got smart and bought a pressure bleeder and haven't looked back. Pressure bleeders are wonderful things!

nate

Interesting. I have no doubt that you're smarter than I am. Maybe even a lot smarter. :-) When I think about all that time I spent under cars shouting "up!" and "down!" with my Mickey Mouse jar, trying to keep the tubing in the bottom of the jar, it really makes me feel like a big dufus. One time I drilled a hole in a bottle of brake fluid and stuck my tubing in there. That was my pro setup. :-)

OTOH, bleeding brakes is pretty relaxing. I used to like laying with my back on the cool concrete floor. Sometimes, I'd just fall asleep down there. My friend would say "are you taking a nap"" and I'd wake up a little disoriented. If it was me doing the pumping, I would have quietly gotten out of the car, turned off the lights, and left... that would have been funny as hell.

that old saw again. but i'm in a good mood so i'll be polite - that's a completely unqualified statement. /some/ [cast iron] master cylinders will "fail" if pumped, but the fact is, that cylinder has failed already because it's become corroded inside. but with aluminum cylinders, that's almost never seen, and yet seals still fail. why? because the new brake fluid used in bleeding shrinks the seal rubbers.

even if you have a completely non-moving, non-wearing seal, they can still fail a couple of weeks after fresh fluid if the system was not regularly bled to schedule and the seals allowed to swell.

What

if that cylinder has corroded, it should be replaced anyway - it'll fail just as comprehensively after any emergency braking too. if you "discover" this failure when brake bleeding, that's a good thing, not bad.

pressure bleeders won't help you if the seals shrink.

by way of perfect illustration, i had a proportioning valve seal fail recently. the vehicle is new to me, and i replaced front, rear and master cylinder seals. the only thing i didn't touch was the o-ring on the proportioning valve - and technically, you're not supposed to go there because the bolts on the valve are both tamper-resistant and sealed after assembly. right on schedule, two weeks after the above work and fresh dot-4 fluid, the proportioning valve seal started to leak. no mythology or witchcraft about "pumping" would have prevented that.

Yep, pressure bleeders make it SO much easier. Test strips for the fluid are another handy tool.

for a single person operation, pressure bleeders are the only way to go. but shade trees shouldn't be afraid of pumping. if they discover their master cylinder needs replacing, that is the time to find out.