PDA

View Full Version : Brakes dragging/applying themselves??



Josue
04-17-2016, 05:57 PM
Just got done with the disc brake swap on my '68. Parts are a C5 master cylinder/booster, Wilwood adjustable prop. valve, C5 fronts, and LS1 rears.

I've put about 30 miles on the setup so far, and no issues, other than the stiff pedal. The car had manual drum brakes all the way around originally, and it doesn't make very much vacuum (maybe around 11hg), so I was prepared for no improvement over pedal pressure. I would have hated myself if I didn't at least try to go with a power setup though, and between re-tuning the car for the new torque converter I installed, and vacuum pumps/canisters if that still didn't work, I was and still am confident that I can get more hg out of the car and get a better feel to the pedal.

Drove the car home from work earlier though, and again, no issues. Then, I changed real quick, and got back in the car to head to my parent's house. It was then that I noticed the brake pedal was stiffer than usual, by a TON! Almost like something was inside the booster, blocking the rod from traveling with the push of the pedal. I also noticed the brakes were dragging....it seemed to worsen the 4 miles to their house, and at it's worse, the car would come to a pretty quick stop on its own when I let off the gas. Parked it at their house, did some stuff, came back to move it into the barn 30 mins later, and it was fine again? Like nothing happened?

Any ideas? The brakes bled out seemingly ok on the 4 corners. I don't believe there's any binding/drag on the booster rod when I hooked it up to the pedal, it can still be wiggled a bit. The only worry I had through all this, was I didn't bench bleed the master cylinder prior to install. Opinions were hit and miss on the topic, and I thought I might be fine since it was a used unit, and not brand new, so it already had fluid ran through it. Worse case, I disconnect the lines, and bleed it right on the car....if that's even what this issue could be.

Josue
04-18-2016, 05:49 PM
Forgot to mention that there is a significant vacuum leak around the brake rod, you can hear it over the engine/exhaust it's so loud! '

Talked to a GM tech friend of mine, and he thinks the booster is bad. It would make sense, I got it used from a salvage dealer, so chances are it might have gotten messed up in the accident, from the driver having his foot on the brakes at the time of collision. Or, he asked if I spun the rod around, and unfortunately, I have. He said the rod is connected to a diaphragm in there, and it's not really supposed to be spun....so maybe I broke something loose in there and it got lodged, making my brakes stick.

I would go back to the place I got it from, but with the possibility of me being the cause of malfunction, I'll just buy a new one. They're only $110 on rock auto, and I won't even have to re-bleed my system again. Hopefully I'll see an improvement on pedal pressure as well, since all the vacuum has been leaking out!

68GTOstrowski
04-23-2016, 03:27 AM
I went through this same thing you have explained on a Jeep.For me it was a heat issue. Ended up wrapping parts of the front and rear lines that were picking up too much heat near the headers/exhaust. Turns out the new lines I installed were better at picking up heat. First I would bleed your brakes again and check for any air especially at a high point like the master to rule that out.

Josue
04-23-2016, 05:32 AM
Thanks for the tip, I will look into that!

New booster should be here today, gonna try and get it on tomorrow or Monday, see how it acts then.

AUTODYNAMICS
05-25-2025, 03:24 AM
Did you ever find the answer to your problem ?