I have a 1948 GM Velox - I am running a L300 front end with discs and borg warner diff (chrysler) with drum brakes. I am reaching out because I simply can't seem to get the brakes to bleed and firm up. They are soft but do pull you up - eventually. The car has laid dormant for about 8yrs and has now been rebuilt - everything is new or refinished. I am running the same but now refreshed booster to the original modified master cylinder and same specs for the pedal and push rod to the booster. I've bled the brakes twice. There are no leaks in the system. All lines are double flared. I have yet to pull the drum covers off the rear to check the functionality of the slave cylinders and free them up if they need. I had the master cylinder off today to check the booster pin/rod - it is like it has been before and it worked perfectly fine. I adjusted the rod from the pedal to the booster to see what extra length I could get - not much - maybe 1/2 an inch. I'm doing another bleed this week, just because I think I need to. It can't be much - not sure what I am missing. The booster and mc are under floor mounted and fed by a remote twin reservoir in the engine bay. This is all the same set up as last time - only difference is soft brakes. Ive read blogs, asked mates for advice, dismantled it and reassembled it a couple of times - googled stuff on the interweb. It is bugging me no end. Anyone? Cheers.
I don't know if I would spend more time and energy bleeding the system again. You already did that twice. Seems like every single time this happens and we can't get them to bleed, it turns out to be an issue with the master cylinder. And then it's like, "Oh... guess I didn't have to bleed the brakes 16 times." Good luck!
Brakes not being properly adjusted is a common issue. The big issue I have seen over the past 60 years is guys who just flat ass don't know how to bleed brakes right. Unless you have a good helper you have to use a pressure bleeder. A vacuum bleeder works somewhat but usually not perfect. With the master cylinder full of fluid, you have your helper pump the pedal S-L-O-W-L-Y, pumping the pedal to fast is one frigging mistake too many people make including a few helpers that got their ass chewed out when they did it when helping me. Then when you tell them to HOLD IT they have to hold the pressure down until you tell them to pump it again. No letting up until you have the bleeder closed and tell them to pump again. Too many want to take their foot off the pedal the second it hits the floor. Start at the furthest from the mastercylinder line wise and bleed it first. Then the next furtherst and so forth. You can make a simple and inexpensive pressure bleeder with a small pump weedsprayer. The hard part is finding the correct cap to fit the master cylinder to modify to use as the cap for the bleeder setup. The pressure gauge is nice but not a necessity. you want 15 lbs of pressure in the tank when you start bleeding. Build a Brake Bleeder (ibmwr.org) The catch jug setup is nice to keep fluid off the floor and fresh paint any time. The cost of that is the length of plastic hose.
Does the pedal firm up a little after a number of pumps in very quick sucession? Also, I'm curious as to what you mean with the 1/2" extra length you found. Is there still free play between the master and pushrod with the pedal pulled up (this only needs to me minimal, more of a feel thing really than measure with a rule). Chris
You might look into “speed bleeders”, I’ve not used them, but have heard good things about them for “solo brake bleeding” jobs.
At my first mechanic job, I got my ass chewed for pumping up a brake pedal. I was told that it can make MORE air bubbles in the lines, etc. It made sense and I have not done it since. I had a guy helping me on my Ford, he owns a shop... I changed a brake line and he was helping me bleed the fronts. He goes to town pumping the piss out of the pedal. I asked him to stop, please humor me. Which he did. With a good master (not a "Corvette style"..) and good drum adjustment, I can usually have a good pedal by the 2nd time around the car. Having a person who LISTENS working the pedal is essential.
Hey Chris - it was about the pushrod from the pedal to the booster - I had some adjustment there to tighten up the 'push'. All good now, $1250 later, I've got all new brakes front an back and can actually stop - still bedding them in, but it is a firm pedal all the way.
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