Brake Booster "check valve"?
06-02-2016, 11:50 AM
#1
Nordschleife Master
Thread Starter
Brake Booster "check valve"?
Hey guys,
Been awhile since I've needed help.
Have an issue with the 951... step on the brakes, and the pedal is slow to return. The pads wind up dragging for a second or so before they fully release.
Now, leading up to this, I:
- Installed fresh brake lines @ all 4 corners
- Fluid flush
- Adjusted the rod @ the pedal to lower the pedal height a little
I started to notice the sticking brakes AFTER I adjusted the rod at the pedal. Originally I adjusted the rod because I had it set to bite RIGHT at the top, and noticed that, in traffic, the pedal wasn't going down far enough to trip the brake lights on light application of the brakes.
The day after adjusting the rod, I noticed they were sticking. I went back, raised the pedal a bit (and figured out how to adjust the switch) and it worked for a few days before the sticky pedal came back.
Some searching here and @ Google, and figured maybe I had a caliper that needed to be rebuilt... so I completed that last night. No improvement. More Googling, and some random posts (here and elsewhere) have suggested bad brake booster (with follow-up posts stating a new brake booster didn't fix it) and a bad master cylinder (also with follow-up posts stating the master didn't fix it). My booster is original but the master was replaced a few years ago, so at this point I don't want to just start throwing parts at the car (since I already did with the caliper refresh...)
I'm going to raise the pedal a little more (likely just put it back to where it was) but I'm wondering if perhaps something else coincidentally failed? Some threads suggested the "check valve" was bad.
Anybody else run into this?
Been awhile since I've needed help.
Have an issue with the 951... step on the brakes, and the pedal is slow to return. The pads wind up dragging for a second or so before they fully release.
Now, leading up to this, I:
- Installed fresh brake lines @ all 4 corners
- Fluid flush
- Adjusted the rod @ the pedal to lower the pedal height a little
I started to notice the sticking brakes AFTER I adjusted the rod at the pedal. Originally I adjusted the rod because I had it set to bite RIGHT at the top, and noticed that, in traffic, the pedal wasn't going down far enough to trip the brake lights on light application of the brakes.
The day after adjusting the rod, I noticed they were sticking. I went back, raised the pedal a bit (and figured out how to adjust the switch) and it worked for a few days before the sticky pedal came back.
Some searching here and @ Google, and figured maybe I had a caliper that needed to be rebuilt... so I completed that last night. No improvement. More Googling, and some random posts (here and elsewhere) have suggested bad brake booster (with follow-up posts stating a new brake booster didn't fix it) and a bad master cylinder (also with follow-up posts stating the master didn't fix it). My booster is original but the master was replaced a few years ago, so at this point I don't want to just start throwing parts at the car (since I already did with the caliper refresh...)
I'm going to raise the pedal a little more (likely just put it back to where it was) but I'm wondering if perhaps something else coincidentally failed? Some threads suggested the "check valve" was bad.
Anybody else run into this?
06-02-2016, 07:28 PM
#2
It sounds like air in the lines. Bleed them starting from pass rear, drivers rear, pass front and clutch slave cylinder. Not sure why pedal adjustment was necessary but as long as it is in spec. I do not recall ever having to adjust brake pedal height except maybe with a new master cylinder.
06-02-2016, 11:19 PM
#3
Nordschleife Master
Thread Starter
Pretty sure it's the booster 
Capped the vac supply line and rode around the block. Brakes snap back instantly.
I guess a failing booster could explain the wooden feeling brakes at the last track event I did.
Capped the vac supply line and rode around the block. Brakes snap back instantly.
I guess a failing booster could explain the wooden feeling brakes at the last track event I did.