Hello, I had a leaking master-cylinder on my 72 Skylark (the rear tank of the M-C was empty and oil leaked on the booster), and no more brake on the rear ... So, a friend of mine gave me his Master-Cylinder from his 72 Skylark as he just had it replaced by a non powered M-C. I bleeded it and i still have no power on the rear, oil is coming out from the brake cylinders but without pressure and the pedal don't move (it stay hard and don't get down - when i bleed the front, there is no problem, it works fine). It seems strange that the M-C is also out of order as it worked nicely on my friend's Skylark. I was wondering if the part on the frame (see pic below (not a pic of my car...)) where all the lines separate to go to the front and rear can have a problem. Is this part only to separate the front line to the 2 front brakes ? But what about the rear?? Why is the rear line bolted in and going out?? Is it to have a place to fit the brake failure switch??? I also noticed that when i push the piston of the M-C i have a lot of pressure going out of the front exit (front brakes) and not much at all coming out of the rear one (as on my own leaking M-C). Note that my car is a 4 drums and my friend's one has front discs!!! I have also seen some brake lines doing some "looping"(like on the pic below), why is it done? Only because they are too long? Thanks a lot if you can help me.... David
David, The master cylinder for all drum is different than the one for front disc brakes. Before installing the MC, you must bench bleed it. This eliminates air inside the MC bore. With most new master cylinders, you get plastic lines and fittings so you can bench bleed the MC. You attach the lines to both ports, and put the ends of the lines into each reservoir. Then manually operate the MC. That is the easiest way to do this. It can be done by holding your finger over each fluid outlet, and operating the MC, but it gets messy, and brake fluid is corrosive.
Yeah, the block on all drum cars doesn't have anything in it. The one pictured is the upgrade to a dual chamber master cyl.
You were probably thinking of the proportioning valve. This is a pic of the brass aftermarket replacement for the original cast vavle.
I agree with Larry. A replacement master cyl needs to be bench bled. When you get a new one, it comes with a little kit of hoses to do the job.
As for the loops you see in some master cylinder lines. I think they are to help with some margin for error between the frame and body geometry. Anybody else want to weigh in on that one?
Many thanks Thanks, i will try to bleed before fitting, i hope it will help... I don't want to buy a new M-C now because i will get one with the Baer 4 discs brakes that i will receive on January.... Is this part (see pic) on my chassis a proportioning valve or not???? it seems it is not the same as the brass aftermarket you show... Thanks again for your help David
Yes, that is a proprotioning valve that you have pitchured there, however that pitchure you showed looks to me like the earlier(70 and earlier)proportioning valve. You said in your first post that your car is a 72 skylark with power disk brakes. Is that correct?? Is that pitchure you posted from your car or another car?? The brass aftermarket proportionong valve that you asked about is for the 71-72 A-body cars with power disk brakes.
72 Hi! Yes, my car is a 72 but with 4 drums... The last picture is from my car and i post it again....it must be different from drums to disc brakes!!! ou: I d like to know if this part is usefull, as i plan to fit 4 BAER discs brakes kit and i don't know if i can remove it or not!? (I will have a BAER proportionning valve with the kit). I think i will dismantle it to see how it works!!! p p
David, Your car has 4 wheel drum brakes. All that is a distribution block that houses the brake warning switch. Only Disc brake equipped cars use a combination valve (which houses a proportioning valve, metering valve and brake light warning switch). You can remove it if necessary when you install the Baer system. BTW, a drum brake master cylinder has check valves in the outlets to maintain residual pressure in the brake lines for drums. These check valves are not used on the front portion of disc brake master cylinders because they would result in the disc brakes dragging.
OK, now it makes sense, you have a 72 Skylark with power drum brakes all around. That pitchure you posted of that proportioning valve looks like the proportioning valve that I pulled off my 70 GS with power disk brakes. I haven't looked at it in awhile so I will have to get it out and make sure of that. The 71-72 power disk brake and 71-72 power drum brake proportioning valves are different. Yes, you can remove that valve from your frame. Usefull? Well you want be able to use it with your BAER setup, so thats really up to you as to whether to keep it or not .
Thanks Larry and Gary for chiming in. There are differences between the early and late cars and I was concerned I would start giving inaccuarate info pertaining to later cars.
Thanks Thanks Larry, Gary , Tom. As soon as possible i will resolve the problem and keep you advised with the solution.... Thanks again.... David
