Why is brake fluid puking out the resevoir cap??

[chevytruckguy70]

As BLT gmc mentioned above, be sure to check the power brake booster (if you have power brakes). Master cylinders sometimes leak out of the rear seal. If you have manual brakes the fluid will show on the inside of your truck around the drivers feet. If you have power brakes the vacuum booster gets the fluid and the engine sucks the fluid up and burns it out the exhaust which would explain the no leak issue. I've had several older cars to this, both manual and power brakes.

Good luck. Hope this helps.

[68basket]

Well i may have overthought the whole problem. I decided to try the simple things, i filled the fluid, bleed the calipers and wheel cylinders, sanded the top of the master to smooth, and bent the wire hold downs to squeeze the cap tighter. Checking now in the garage while pumping the brakes fluid no longer comes out around the cap seal. I will test drive tomorrow to confirm. On a side note, i contacted the seller on ebay and he was very hellpfull and willing to exchange the master at no charge if i sent him in the old one. he seems like a stand up guy.

[litew8]

Bet you bled that master cylinder too. If not, good luck.

[toolboxchev]

Hmm interesting, I have the same problem today. The entire system was all replaced with Cardone components 7 years ago. Lifetime warranty stuff.

Since then I have replaced the booster 3 times and today the Master is puking out the top.

So with more components on the way I was interested to see this thread from 2 years ago.

I will figure this one out either way. If anyone has any updates feel free to share what solved your problem.

Thanks!

[davepl]

Just FYI, bench bleeding is only needed when the master is mounted at an angle such that you could get trapped air. I don't know if ours qualifies as enough angle. I've seen it done by raising the back of the vehicle instead of bleeding the master, and they apparently have great success with that.

[snipescastle2]

Ive seen rebuilt master cylinders do this, when it comes to brakes, your life is worth far more than the difference you would save buying a cheaper unit.
My late step-father taught me how to do brakes and he said there are several things you don't do with regards to doing brakes...one is never buy rebuild kits for master cylinders, never use your emergency brake (parking brake) in the winter unless it's a bonafide "Emergency" (I learned the hard way on that one during one winter...must have dragged my rear wheels for 7 miles before I felt something "Bang" then the car felt as if I had broken several belts in my tires.
I thought I must have thrown wheel weights or bent a rim, found major flat spots on the tires from where they were dragging, turns out my parking brake cables had iced over in their housings. And always bench bleed your master cylinders..
Ben

[mooseboy84]

I dont know why people are saying not to bench bleed the master cylinder?

There are somethings you can get away with not doing, but if you install a new MASTER CYLINDER (or rebuilt), you should bench bleed it.

I am shocked anyone could say they didnt bleed the master and just installed it. Most of the time if you try to do this, even with bleeding the wheels, the second you step on the brake it will go to the floor.

ALWAYS BENCH BLEED THE MASTER CYLINDER. Maybe some people have those expensive electric vacuum machines that can really force fluid through the MS, but otherwise, just bench bleed it.

I know manufacturers seem to be cheeping out nowadays and NOT installing the little tubes and ports, but you can buy MS bleeding kits and use them. The last 3 MS I have bought for various cars did not come with the bleeding kit, but it still needs to be bleed!

[RedRoad]

Im still suffering the same issue as well, bench bled, gravity bled, power and vacuum bled and it still pukes all over the alternator.

Brakes work great but leaks unless its half full, dont like it at all. Even DirtyLarry had the issue but has not responded to say if he fixed it or just sold the truck

http://www.67-72chevytrucks.com/vboa...d.php?t=335002

[BILT4ME]

Something that no one has really mentioned here:
Is that the CORRECT master cylinder for the truck? Many of these trucks have been bought/sold many times. Each owner does something to it. If someone has replaced the MC with one for disc brakes and the truck only has drum brakes, it will NOT operate correctly, and the MC will push MORE fluid for a disc brake setup than a drum brake.

It is the opposite for a drum brake MC being installed on a disc brake setup. The brakes will be insufficient because there is not enough volume for the disc brakes.

Just a thought. BTDT, done the research to confirm.

[toolboxchev]

Well for ****s and giggles I took off the top clip spring and bent it up a tad so it will be tighter. This morning I took off and the brakes were considerably stiffer. Now I know I need to bleed out every cent of the crappy old fluid.