MASTER CYLINDER PROBLEMIhave

[69YENKO162]

I have a 69 camaro and I cant get the original master to bleed the right way, it wont give me a good pedal. I put on a pep boys master on and it works great. I have tried 2 other U.S.302 masters that have all been redone and they dont work. Any help would be great. http://www.yenko.net/ubbthreads/images/graemlins/dunno.gif

[Belair62]

Are you using silicone brake fluid ?

[69YENKO162]

No. I was told not to by the person who rebuilt it.

[Born30YrsLate]

I'm currently having the same problem with a rebuilt master cylinder I bought for my '69 Camaro....???

[Mr70]

Just out of Curiousity,To the Both of you I ask,Who rebuilt your Master Cylinders?

[njsteve]

Are you bench bleeding them first? You should mount the MC in a well protected vise, install the appropriate sized block off plugs in the brake line outlets to prevent the flow of brake fluid out. Then route two clear hoses from the bleeders back into the resouvoir itself. Loosen the bleeder screws. Fill the res with brake fluid and using a rod or screw driver, push the rear plunger in slowly and watch the air bubbles. Then slowly release to pull in clean fluid. This could take a few dozen times to get all the bubbles out of the internal passages. Push slowly so as not to foam the fluid. Once you get this done, put the lid on and mount the unit in the car. Then remove the outlet plugs, hook up your brake lines to the MC and bleed the entire brake system starting with the wheel that is farthest from the MC first. This should work if your MC is in proper working order to begin with. I would venture a guess that the Pep boys MC did not have the external bleeders that the original GM MC has, and that is one of the reasons why is is much easier to bleed. http://www.yenko.net/ubbthreads/images/graemlins/scholar.gif Good luck

[ssl78]

Do you have the correct length rod in the vacumn booster. There is a long rod and short rod depending on the depth of the piston in the rear of the master. Maybe the after market one has a different depth then the original ones and thats why it works ok.

[Belair62]

Good point John and an obvious one to check first...

[JoeG]

Yep---The outfit I had do the rebuild on mine,back when, sent me a shorter rod --had to use the longer rod.

[Unreal]

Bellair,
What's the issue with silicone fluid?

[Belair62]

I had a tough time bleeding the silicone without using a pressure bleeder.

[Steve Shauger]

I have been using silicone fluid for years and never had a problem bleeding brakes.

[69Chevelle L78Deluxe300]

I spent about 50 hours trying to bleed the rebuilt master in my 69 chevelle with silicone and everyone told me the problem was silicone fluid. What I finally figured out was the original proportioning valve located below the master cylinder was sucking in air when I released the pedal but not leaking fluid out when I depressed the pedal http://www.yenko.net/ubbthreads/images/graemlins/shocked.gif. I put a new one on and had no problem bleeding. http://www.yenko.net/ubbthreads/images/graemlins/smile.gif