61 Buick C5 Vette disc front end Original 13" drum rears 7" Dual booster with Corvette Master. a bit over a week ago I lost all vacuum and got a super hard pedal The booster has been playing up for a while, works, doesn't work I just never changed it. Now I had to. Got a new one. Installed it. Rears lock almost immediately and pedal is so touchy it's crazy. Appears in the 5 years of daily driving this the booster never really worked. Or not well anyway, as now this thing is so touchy. Locking the rears ain't fun. So it had no prop valve in it. I installed one over the weekend. Bled it, drove it, still locking rears and pedal goes literally to floor before it grabs. the push rod in the booster where it connects to the master is so hard to adjust. If I use the measuring tool, to adjust it, car drives fine for 20 mins then locks the rears and I can't drive it. So today I adjusted the rear shoes all the way in, so they are so loose that the park brake cannot even be adjusted (runs out of adjustment) for the park brake to hold. Again cold driving, pedal to the floor then rears lock up. 20 mins into driving, awesome. Solid comfortable just right pedal, not too touchy, and starts to brake with about a 1/2 press on the pedal, front won't lock but they grab before rears and pulls the car up nicely. This is driving me nuts. I'm at a loss why cold braking has no pedal and locks rears (even with them adjusted so far inwards the park brake doesn't work) but once everything warms up (20 mins of driving) it's perfect. Anyone ever had this problem.
You have an issue with the push rod between the booster and the master cylinder. I have changed quite a few boosters thru the years and this has happened on all of them. The aftermarket can't seem to build a correct length rod. You will need to cut and grind to find the proper length for your set up. What is happening is that the mis-adjusted rod is partially applying your brakes.
Wow, not sure I have the skills to do that. I know the rod adjustment is a problem, I've had it all the way in (no pedal) and all the way out (locks rears) and many positions in between. I've even used a measuring tool, hopeless. The bit that confuses me is that when car is cold pedal goes to floor and no brakes will lock, but it will slow the car, albeit nerve racking. 20 mins later once everything gets to temp, pedal now is awesome and rears lock just before fronts. It's this difference between cold and hot temps that's confusing me right now. I can't see how the booster would cause this issue
