Hey gang, I have been having some trouble with new master cylinders leaking from the boot area in my 52 chevy truck. I will trying a new one this weekend. My stupid mistake may have been in not "bench bleeding" the master cylinder in advance of installation. Any advice on how best to do this? And as an aside, I don't really understand why bench bleeding accomplishes anything other than the bleeding we do of the whole system after installation. Any help on this one? Eric
Follow the thread below to post #10 by Nate. He tells it like it is on how to bleed the master when it is in the truck. I just totally did my brake system over and followed his master cylinder bleeding procedure. worked great. BTW, I also have a brandy new master in my truck and there is a "drip" of brake fluid around the boot as well. I just thought it was normal. Maybe I'm wrong. https://talk.classicparts.com/showthread.php?t=6687&highlight=proper+bleeding Andy
Yeek ! I'd say that ' new ' master cylinder is defective and possibly dangerous so keep a weather eye on the fluid level and see , if it drops and the drip continues , return it before it kills you . I guess it is possible the rubber is just a bit dry from sitting and it'll be fine once you've bled it and begin driving it but please *do* keep a weather eye on it for a few weeks . The purpose of " Bench Bleeding " is to facilitate the bleeding of the split systems found in 1967 and newer vehicles . It's usually unnecessary in our oldies . I'll go have a look at post # 10 in that other thread , see if I said anything useful .
Boy Is My Face Red ! Andy ; I just went back and re read that old post # 10 , it was chock full of spelling errors and missing a few sentances too ! I didn't even explain how to do The Stick Trick so I added that too . Lemme know if you like the changes , I didn't remove anything .
Hey Nate, can you use one of those power/pressure bleeders? The one I'm speaking of has a holding tank and is pressurized by air. When you put the lid on the MC and turn on the pressure, then all you do is go to each wheel cylinder and open the bleed valve until the fluid runs clear of bubbles. Larry R.
I never bench bled a MC when it was mounted on the frame. Put a level on the MC and you'll see it's level on the frame. I believe the notion that you must bench bleed come from the fact that modern MCs are mounted on the firewall and tend not to be level. For that reason air can get trapped and you need to bench bleed it.
Pressure Bleeding Yes Larry ; Indeed you can and probably should . If you follow the other posts Andy linked this thread to , I describe how to do it in detail and provide a link to a good , inexpen$ive pressure bleeder . I don't put any fluid on my pressure bleeder so it stores neatly in it's cardboard box . Be aware that brake fluid instantly ruins any paint it touches so storing a wet pressure bleeder is tricky.... It only take 3 PSI MAXIMUM to pressure bleed so don't go crazy , that's the # 1 mistake mechanics make in using these handy devices . If you have an oldie with black brake fluid , changing it out by pressure bleeding , won't cause any leaks like pedal bleeding occasionally does . Brake fluid should be changed every two years at the outside , doing so will mean you never have to change out the cylinders again once you've restored the system . -Nate
