Master Cylinder issues

[thedudeabides86]

Hey everybody! I hope the weekend went well for you all. I had an issue over the weekend with my '72 C20 3/4 ton. I checked the brake fluid in it and noticed the front chamber of the master cylinder was empty but the back one was full. I filled the front one adequately and tried taking a drive. I could barely keep the engine running and it kept stalling and dying on me. I got back to the house and pulled the ol turkey baster out and sucked out the brake fluid I had just added and the motor started right up and stayed started. In fact, I drove it 60 or so miles round trip for the first time in 10 years. So, What might be the problem? Was I sucking brake fluid into the motor? Cutting off air to the motor? Do I only have the rear brakes working since the front chamber is empty? Most everything I do to repair this truck is a "learn as you go" kinda deal for me. I appreciate all the help I've gotten over the years from you all out there. Thanks in advance!

[jocko]

Well, that sounds odd... There really is no reason that brake fluid presence (or absence) in either reservoir should affect how your engine runs.

One note for you though - if your front reservoir is empty, pretty sure that means no rear brakes on a C20. Trace the lines back and I think you'll see that the front res ultimately goes to the rear brakes. So, worst case, you're driving around on front brakes only (which is better than rear only, but still not ideal..)

[B. W.]

X2 with Jocko, one of your rear wheel cylinders is probably leaking. Look for fluid leaking down the backing plates or on the wheels.

As far as the engine stalling, a bad booster can cause that or it could be an unrelated issue. my guess would be a stuck choke. (it "unstuck" after you stopped & sucked out the brake fluid)

[El Dorado Jim]

sub'd please let us know what you find

[thedudeabides86]

Jocko and B.W.

Thanks for the input. I did notice a while back that my right rear (passenger side) wheel looked damp on the inside whilst I was laying underneath the truck. I felt it and it was wet. I mean it didn't leave fluid on my fingers. It was reminiscent of oil soaked cardboard as it looks wet, but doesn't pool on the surface. My father in law and some family friends thought maybe I had a booster with bad seals which was causing fluid to dump into the carb via the vacuum line. I've never dug into a brake system. I just put this motor in a year ago after it had sat for 10 years and doing that, I was learning as I go from this forum and coworkers. So, that being said, I'll keep researching and trying to find what might be a solution. Thanks again.

[jocko]

A vacuum leak in the brake booster line can affect perf/cause rough idle, but it wouldn't go away all of a sudden when sucking brake fluid out - so there may be some sort of coincidence in this case. Not really a way for brake fluid to get into the booster and then the engine - unless maybe a bad main piston leak that sheds out the back of the mc into the opening of the booster, but I've never heard of that happening - not sure it could.

[thedudeabides86]

Thanks for all the input. I'm not sure where to go from here. Should I just replace the master cylinder and booster both? Bleed the brakes? I've got leaves and grass I'll be taking over to the leaf pile in the coming weeks and once that's done, I'll store it for the winter in my garage and work on the necessary fixes for being ready for the spring. Now if I just had a heated garage.....