Brake booster trouble, or is it? - 3000GT/Stealth International Message Center

Ming696 · 03-15-2005, 06:44 PM

I recently rebuilt my clutch master cylinder, and in the process I decided to rebuild my brake master cylinder as well. I pulled both the master and booster to get to the clutch master. Today I got the brake master rebuilt, and the whole system rebleed with fresh fluid, and I have a very hard pedal. I go for a test drive and the brakes stop real good, but almost to good. I get about 2 miles away and they feel like they are draging. Going down a hill I put it in neutral and cost only to find they are dragging and very hard. I pull over to let them cool a minute while I look under the hood for anything suspicious. I get back in to leave and the car won't move. I killed it 3 times trying to leave and I even reved it up to about 5K let out real quick. The car moved about 5 inches and died. I fired it back up and decided to unplug the vac booster. As soon as it lost vacuum the car started to roll backwards. I forgot to pull the e-brake and I had to jump in real quick before it rolled out into traffic! After getting it home without a vacuum booster I got out the factory service manual and did all the checks to determine if the booster is bad or not. Well all three checks turned out OK...WTF? My pedal is still hard as a rock, but when I try and move the car with the booster hooked up it won't roll?

So is this a booster problem? Do I not have the pedal adjusted properly? Is my freshly rebuilt master cylinder to blame?

Ming696 · 03-16-2005, 05:17 PM

Well I guess I'll answer my own thread in case anyone was wondering. The pushrod that comes out of the booster and pushes on the master cylinder piston was out of adjustment. I got it adjusted, but it wasn't enough. They still drag just a bit. After a short stint to 70mph the brakes got hot enough to slow me down pretty quick. The pedal felt tons better to start with, but when the pads got hot the pedal got real hard. I may still have a booster problem, but first I'm going to adjust the pushrod somemore and see if that fixes it.

StealthCRF · 03-17-2005, 01:00 PM

just saw this, definetly sounds like thats your problem.. when the rod goes in it basically is trying to get help from the vacuum assist. adjust the rod some more, jack the car up off all 4 and turn the wheels by hand to make sure you're not dragging/heating your brakes up, it would be sad to burn them all up just because they "feel" like they are fine.

Stealthee · 03-17-2005, 02:21 PM

Is the check valve in the vac line possibly messed up? I dunno man. Good luck getting it fixed.

StealthCRF · 03-17-2005, 04:41 PM

bad check valve would cause lack of power assist when getting on the brakes after/during boost.

your plunger (in pic) is probably right at the verge of sealing the cylinder and the vacuum is causing it to drag, w/out vacuum it backs off

Ming696 · 03-17-2005, 08:42 PM

Well I adjusted the pushrod somemore today and it made all the difference in the world. I still think there may be just the slightest bit of drag, and I will adjust it again tomorrow. My pedal feels really good, but I think its to high. I need to play with it and get it where I want I guess.

The check valve checked out ok.

03-15-2005, 06:44 PM	#1 (permalink)
Ming696 Forum Member Join Date: Dec 2001 Location: Olathe, Kansas Drives: '93 Stealth RT/TT Trader Rating: (3)	Brake booster trouble, or is it? I recently rebuilt my clutch master cylinder, and in the process I decided to rebuild my brake master cylinder as well. I pulled both the master and booster to get to the clutch master. Today I got the brake master rebuilt, and the whole system rebleed with fresh fluid, and I have a very hard pedal. I go for a test drive and the brakes stop real good, but almost to good. I get about 2 miles away and they feel like they are draging. Going down a hill I put it in neutral and cost only to find they are dragging and very hard. I pull over to let them cool a minute while I look under the hood for anything suspicious. I get back in to leave and the car won't move. I killed it 3 times trying to leave and I even reved it up to about 5K let out real quick. The car moved about 5 inches and died. I fired it back up and decided to unplug the vac booster. As soon as it lost vacuum the car started to roll backwards. I forgot to pull the e-brake and I had to jump in real quick before it rolled out into traffic! After getting it home without a vacuum booster I got out the factory service manual and did all the checks to determine if the booster is bad or not. Well all three checks turned out OK...WTF? My pedal is still hard as a rock, but when I try and move the car with the booster hooked up it won't roll? So is this a booster problem? Do I not have the pedal adjusted properly? Is my freshly rebuilt master cylinder to blame? __________________ Current Mods List!

03-16-2005, 05:17 PM	#2 (permalink)
Ming696 Forum Member Join Date: Dec 2001 Location: Olathe, Kansas Drives: '93 Stealth RT/TT Trader Rating: (3)	Re: Brake booster trouble, or is it? Well I guess I'll answer my own thread in case anyone was wondering. The pushrod that comes out of the booster and pushes on the master cylinder piston was out of adjustment. I got it adjusted, but it wasn't enough. They still drag just a bit. After a short stint to 70mph the brakes got hot enough to slow me down pretty quick. The pedal felt tons better to start with, but when the pads got hot the pedal got real hard. I may still have a booster problem, but first I'm going to adjust the pushrod somemore and see if that fixes it.

03-17-2005, 01:00 PM	#3 (permalink)
StealthCRF Gixxer Fixer Join Date: Feb 2002 Location: Dallas/Fort Worth Drives: on empty Trader Rating: (3)	Re: Brake booster trouble, or is it? just saw this, definetly sounds like thats your problem.. when the rod goes in it basically is trying to get help from the vacuum assist. adjust the rod some more, jack the car up off all 4 and turn the wheels by hand to make sure you're not dragging/heating your brakes up, it would be sad to burn them all up just because they "feel" like they are fine. __________________ 92 Stealth RT/TT Best time: 13.2 @105

03-17-2005, 02:21 PM	#4 (permalink)
Stealthee Damage Control Join Date: Jul 2003 Location: 1 hr south of Pitt Drives: 1994 Stealth Trader Rating: (76)	Re: Brake booster trouble, or is it? Is the check valve in the vac line possibly messed up? I dunno man. Good luck getting it fixed. __________________ Kbizzle [11:25 P.M.]: my ass is really sore Kbizzle [11:25 P.M.]: this is most displeasing

03-17-2005, 08:42 PM	#6 (permalink)
Ming696 Forum Member Join Date: Dec 2001 Location: Olathe, Kansas Drives: '93 Stealth RT/TT Trader Rating: (3)	Re: Brake booster trouble, or is it? Well I adjusted the pushrod somemore today and it made all the difference in the world. I still think there may be just the slightest bit of drag, and I will adjust it again tomorrow. My pedal feels really good, but I think its to high. I need to play with it and get it where I want I guess. The check valve checked out ok.

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