Im still trying to get this beast straightened up. CAR 72 Lark Custom (350-4) Stock 4wheel drums. PROBLEMS: 1st the brakes lose fluid. Ive traced a souce to a minor rear wheel cylinder leak though this sucker isnt leaking as much as it used to appear to. 2nd - the front wheel has a bit of fluid on the tire and possibly trace ammounts of brake fluid leakign from there? 3rd main leak seems to come out of the master cylinder the top of the gasket is wet with fluid and i can see it leak down the back of the MC. MY GUESTIMATES: I figure the 1st problem was minor but due to the other guys taking up the slack there is less pressure in the lines now at the rear wheels so thats why the leak seems to have gone away I think the front wheel cylinder is just by happen chance. This is where I need help. Is there normally pressure inside the MC? Though I do not know much about brakes I figured it there shouldnt be any pressure here. If this is the case is there a problem then with the MC or with the Booster? Technique I did make sure the surfaces havent been used and checked the car by running it and pumping the brakes... then I checked for leaks and found some on the right front tire, and at the master cylinder. Thanks in advance... I am limited by time on this endevour.
Well, firstly you might get a larger number of replies if you posted this in "the whoa and the sway" which is the brake/suspension forum But about your problem, no, there really shouldn't be pressure in the M/C. I mean, you can just pop the bailer and take the cover off with no problem, and how would you get brake fluid in there if it were pressurised? The system itself sees 300 psi. There is a small junction block on the frame just under the M/C. Contrary to what a lot of people think, on our 4 wheel drum cars, this is not a proportioning valve. It is a simple switch. if you look closely, you'll see a wire going into it. Pressure in the system on each side of the switch keeps it from making contact and illuminating the brake warning light. Each side of that sees 150 psi- when the pedal is depressed. If the psi drops, pressure shoves the switch over. The brake fluid on the tire is telling. You have a problem there to be sure. Combined with the rear of the M/C being wet, it is my first impulse to say you have not just a leaky wheel cylinder (they don't fix themselves), but you may have a M/C that is going bad, too. The fluid loss at the rear may have appeared to have cleared up, but beleive me, it's still there. What's probably happened is that simply, since you're low on fluid, and the rear lines are longest, you've sucked in a column of air long enough so that you have insufficient pedal travel to actually push fluid out as often as before. Replacing a M/C isn't all that hard, and if you need to do this, I recommend a new brake booster as well. I did this same job 3 years ago under almost the same circumstances you describe. The only problem I had was that the replacement M/C's power piston rod (the thing that goes to the brake pedal) wasn't the same length as the old one and I had to adjust where the rod attached to the pedal. It didn't take away pedal travel, but it did require some thinking. I bought my M/C and booster as an assembled unit from OPGI. I have to say however, it looks great, but there is now a small internal vacuum leak in the diaphragm in the booster. I am not pleased about the lack of quality in this part. the original lasted 30 years on a daily driven car and the replacement lasted one tenth the time!
yep change those parts out. dont want to fool around with your brakes. my sis had the MC leak along the booster aswell. the return from the wheel cylinders is what causes the leak at the back of the MC. I had my rear brakes go out (brake line broke) while trying to get the 3700 lb beast to stop with the front drums only I blew out both front wheel cylinder seals. amonth later I later blew out the seals on both rear cylinders a day apart. if you replace one side be sure to replace the other. this also goes for hoses and ball joints of vehicles. had a friend with a broken brake hose to the front wheel and inspected the other side just to see the condition it was and it looked like the napa replacement part not the OEM :af: coulden't have been much diffrence in date of replacement (maybe 9 months) Nate
