All new brake system disc/drum, w/ a jegs universal under dash pedal/booster/master assembly. Bled, no leaks. Pedal never really fully returned but there was resistance there so i had assumed i had brakes. Been chasing vacuum leaks this week, and isolated the booster to make sure it wasnt there...i dont believe it was...engine still ran shitty with or without. found vacuum leak at carb base. put everything back together incl. vacuum line to booster and started motor...idling much better, but when i went to hit brake pedal it was GONE. to the floor, nothing there, and would not return at all. thoughts?
No such thing as a "universal" master cylinder. If you thought it would fit any size wheel cylinder/caliper combo, that's your first mistake. But you still ought to have at least a little pedal resistance. I'd look at the adjustment of the push rods on each side of the booster, then for fluid leaks throughout the system. If the problem isn't in the booster, the fluid must be gone (or full of tons of air bubbles). Now if the system works together as a whole, and gives you reliable stopping, is yet to be seen after you get some pressure back in the lines.
Universal their words not mine....thanks for the input...know i'm not the only guy using this pedal setup.
Are your drum brakes adjusted correctly? Is there free play between the master and the booster? If no to either of these that is your problem.
What is the bore size of the master? Caliper and wheel cylinder sizes? You can’t just throw brake parts at something and expect them all to work…so far you have said everything is good but they don’t work…
How about the free play? Easy to test, just add some washers between the master and the booster and see if that helps. No need to even break the lines, just pull the master away from the booster to do this.
There is a lot of free play in the pedalbefore it "engages"/feels like it's pushing against anything..
Are you only relying on masters internal spring to bring your brake pedal back up to where it should be? Your pedal should have it's own return spring so piston inside master can go back all the way so brake fluid from reservoir can get into bore after every stop.
A return spring on the pedal helps a lot but many hanging pedals don't have one from the factory. On a hanging pedal you can get by with a reasonably light return spring, just enough to pull the pushrod back off the piston and hold the pedal up against the brake light switch Get down so you can work the pedal by hand and see how far the push rod moves before you feel the resistance from the piston. You want about 1-1/16 to 1/8 free play before the pushrod contacts the piston. Most of the "universal" kits have adjustable pushrods. On bleeding the brakes, there are as many wrong ways and lame ass wrong ways to bleed brakes but only a couple of correct ways. With a helper pumping the brakes make sure that you keep the master cylinder full. Make sure that the helper pumps the brake SLOWLY and then holds the pedal down until you tell them to release it from the floor. Work from the wheel with the longest line to the wheel with the shortest line. My 42 year old daughter has helped me bleed brakes since she was 4 and she is the best at working the master cylinder that I have had help me. It takes someone who is paying attention to what you need done. There are instructions on making a pressure bleeder out of a small weed sprayer on the net and you can do it for under 20 bucks with the hard to find part being the correct cap to fit your master cylinder so you can modify it. Vacuum bleeding works ok and lately I have found that the red vacuum pump you find at HF works better than most of the plastic ones do. Gravity bleeding is some lame nonsense that guys who want to sound like they do brakes toss out but in truth can't work effectively.
There was been discussion here on the HAMB about this exact set up doing to same thing as Op's is. Return spring solved the issue. Not all pedal assemblies are built the same and some get to heavy against master.
Thank you all for chiming in. I've adjusted rear drums, lengthened pushrod out.of.booster, and just bled brakes for third time with son at the pedal. Still as soon as you start the car, pedal sinks almost all the way in and feels.like.mush
The question still is do you have 1/16" of free play between the master and the booster push rod? This is a MUST.
You have to watch the push rod and figure out if it is "about" 1/16 movement. Or be able to feel the movement to contact with your fingers.
"IF" I read that correctly you have a brake booster - and the pedal is "moving toward the floor" when a vacuum is applied to the brake booster. There are two (2) adjustments when using a vacuum brake booster. 1. The push rod from the brake pedal to the firewall side of the vacuum brake booster. There is excellent advice on this adjustment in the posts above. 2. The stick-out (push rod) that goes into the brake master cylinder. The flange to piston depth varies for different brands and part number. These templates were made from the instructions in the respective vehicle shop manuals. Russ
The last time it was bled, did you get any air out of it? Also the column of fluid should be strong and steady on the last round. Go out in the dark with a flashlight and look at all connections. Leaks show up better this way at least for me. You could have a bypassing master, not all that uncommon these days. Post a picture of your set up.
You say that as soon as engine starts pedal sinks? Well that must be a problem with Vacuum booster... yes??
Exactly what parts make up this system? If they’re OEM, post the application they came from, with part numbers if possible. If aftermarket, specify make and model.
11" gm brakes up front included in mustang II IFS from jwrodgarage. nicad lines. 2psi residual upfront. 53 pontiac rear drums w/ 15/16 wheel cylinders all rebuilt. 10psi residual and wilwood proportioning valve in line. jegs booster/master, under dash pedal assembly 8" dual diaphragm booster, corvette style 1" bore master https://www.jegs.com/i/JEGS/555/631...SGDheDBKJq_l7LU7mvD0fa0jv9xE0AeQaAo7_EALw_wcB
Time for process of elimination. Install master direct to firewall and make up some temporary lines to existing lines and see what happen's.
This is a critical measurement, so please do not ignore it. Can be done with a straight edge and a rule, so I doubt your claim is correct! Does require some thinking and simple math to work out the clearance between the two components. A vernier caliper makes it easier. Or there are cheap adjustable measuring tools specifically for the purpose which look very like the setup templates pictured earlier. If you have insufficient clearance you can get symptoms as you are experiencing. Its not simply a case of bolting a booster and master together. The rod that goes out of the booster into the master is adjustable. Will look for some links for the setup tool. Edit. Google brake booster depth gauge. There's an explanation on classic performance products website and they mention a tool #cp2003, but I can't find it in their items for sale, but Google will sort you out anyway. Chris
I looked into Op's unit from Jegs and opened PDF file for installation and it does not cover this. Nor does it state if unit is pre-assembled as picture "suggest's". Any rate, I agree there hasn't been much response to this from Ron Stumpf to really know if it's been addressed correctly.
I've adjusted the pushrod coming out of the booster...might actually be too long now, ordered depth guage to check....Ordered new master as club member suggested maybe ruptured seals in original given it never built up pressure or stiffened pedal
Okay well I adjusted the push rod coming out of the booster using the pushrod depth gauge and installed a new master cylinder after bench bleeding and then bled all four corners twice starting with the right rear and still when you start the motor you lose the pedal so I disconnected the booster plugged off the line started the motor and I still have some manual brakes so I got to believe the only thing left is a bad booster?
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