Hey all. I just put in a rebuilt booster and have problems. The master cylinder went bad on my previous one and since i bought the booster and master cylinder as one unit, they wanted the entire unit for a warranty replacement. When the car is off, the brake pedal is hard (maybe move 1/2" or so when brakes are applied). When i start the car and press the brakes, the pedal travels quite a ways (maybe 2") and are EXTREMELY touchy. The pedal is pretty darn soft and there is no gradual braking, it's all or nothing. I about got whiplash backing my car out of the garage and gently hit the brakes. I had always thought that if a booster has a bad seal/vacuum leak, that there will be no power assist and you will have the same pedal feel as if the car was turned off. If i had air in the system (master cylinder or lines), wouldn't the pedal be soft all the time? Let me know your thoughts. On the old system, the pedal feel was pretty close when the car was not running. When i started the car, the pedal would go slightly softer but nothing like this new booster. I'm sure the problem is easy but i'm not thinking too clear at the moment. This is on my 70 mach btw.
Brake Booster problem
- Thread starter jbuening
- Start date
I did not get from the post whether you can brake at all, or you have to step too hard to brake. If you cannot brake at all, it may be internally bleeding master cylinder assuming you have unbleeded system, and don't see any leaks. It happens occasionally first, and eventually you won't be able to brake. Pumping the pedal helps. If the braking is hard it may be booster. But this thing seldom breaks.
pabear89
Active Member
check the booster to master rod adjustment.
there's too much travel in it now and the booster
goes past center and gives you that quick over pressured braking.
My first spot to look.
PB
there's too much travel in it now and the booster
goes past center and gives you that quick over pressured braking.
My first spot to look.
PB
From what i've been told on another forum, i think Pabear hit the nail on the head. I believe my master cylinder pushrod is too short. I do have brakes, but when the the engine is on the brakes are extremely touchy and just barely touching the brake pedal (after it travels for a few inches) the brakes are on full effect. Without the engine on, the brake pedal is firm as if there is no air in the system. If the booster had a vacuum leak, the pedal would be firm all the time regardless of whether the engine is on or off. Work has been crazy lately, but i plan on hopefully tearing into it soon to adjust the pushrod length. I'm seriously hoping this is the issue, as I had a royal pain in the arse removing the old booster/MC and installing this replacement one.
BarnStang
Founding Member
Is the brake pedal the original pedal that came in the car? And, did the care originally have power brakes? We ran into this on a 70 Boss clone car we did. Touch the brakes and they were ON all the way. could barley touch the pedal. We added power brakes to this car. Had to change the brake pedal out. The power brake pedal mounts in the hanger differently. Once we did that, the brakes were perfect. You said the brakes were ok before the new booster. i wonder if the old booster had a leak, and the new one is now working at full capacity? Other than that, the rod being too short is the first thing to check. It should be just short of touching the master cylinder when it's bolted up.
Yeah i converted the car from manual drums to power brakes and i definitely switched to the power pedal that mounts at the top of the pedal hanger assembly.
I pulled the M/C yesterday and following the Ford Shop Manual it appears that my pushrod length is spot on to what the factory recommends. This leaves the possibility of air in the lines (for which i've bled them three times now, enough to flush the system twice) or a bad booster/MC combo. I will have my wife assist me in bleeding the brakes the old fashion way, as i've been using a one-man bleeder system. Thanks for all of the responses.
The way it is now, i can press the brake pedal with my pinky finger and it will slam on the brakes. It is that touchy. It's almost as if the booster is adding way too much assist.
I pulled the M/C yesterday and following the Ford Shop Manual it appears that my pushrod length is spot on to what the factory recommends. This leaves the possibility of air in the lines (for which i've bled them three times now, enough to flush the system twice) or a bad booster/MC combo. I will have my wife assist me in bleeding the brakes the old fashion way, as i've been using a one-man bleeder system. Thanks for all of the responses.
The way it is now, i can press the brake pedal with my pinky finger and it will slam on the brakes. It is that touchy. It's almost as if the booster is adding way too much assist.
2nd Mustang
Founding Member
I've been fighting a similar problem since February of this year in my 67 coupe. My booster was changed about four years ago when it developed an internal leak that wouldn't allow my engine to idle.
In February, my car started locking up the brakes, so have been systematically changing parts. Everything in the braking system was changed, except for the booster. Now I'm beginning to think the booster is the problem, as I've adjusted the pushrod from one extreme to the other. It locks up less when I take out all the adjustment on the rod.
I did notice that when it locks up, the brake pedal stays down. Pulling up the pedal with my toes doesn't release the brakes, but when I tap hard on the pedal it will release the brakes. This makes for some interesting driving techniques. Isn't there a release spring inside of the booster?
Sorry to hijack your thread.
In February, my car started locking up the brakes, so have been systematically changing parts. Everything in the braking system was changed, except for the booster. Now I'm beginning to think the booster is the problem, as I've adjusted the pushrod from one extreme to the other. It locks up less when I take out all the adjustment on the rod.
I did notice that when it locks up, the brake pedal stays down. Pulling up the pedal with my toes doesn't release the brakes, but when I tap hard on the pedal it will release the brakes. This makes for some interesting driving techniques. Isn't there a release spring inside of the booster?
Sorry to hijack your thread.
Make sure that you have all the air out of the system first. If you have front disc brakes, you will probably need to remove the caliper and position the bleeder at the 12 o'clock position, open the bleeder and let it gravity bleed until you get nothing but fluid out. With the caliper mounted the bleeder screw is at a lower postion an will not allow all the air to be removed from the caliper.
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