Brakes have no stopping power

[paulrowe]

While driving around in my truck today I noticed that the brakes have no stopping power. I check the vacuum on the brake booster. The line seems to be drawing plenty of vacuum and the brake booster seems to be holding vacuum. The brakes were fine up until today and then all of a sudden I have to push them to the floor just to get enough to even come to a small slow down. I just changed the pads and rotors about 2 weeks ago but all seemed fine after that. Is it possible that I need to bleed the brakes after this? Also I have an NP 203 transfer case and I just started driving my truck and full-time 4 wheel drive. Maybe this has something to do with my problems? Any help would be much appreciated.

 

[HotRodPC]

hmmm? Stopping power? Are you saying you don't have any brake pedal? Hard pedal? Or the pedal seems fine but the truck just won't stop?

If I'm understanding the rest of the description with low pedal, it sounds as if your master cylinder might be taking a dump. You can try bleeding the brakes and see if you gain more pedal height. Do you get any pedal fade? As in, do you hold your foot on brake pedal and feel it going away or to the floor?

 

[paulrowe]

I discovered today that I have a vacuum leak at the brake booster. I can hear it whistling in down around the rod by the pedal. I can just barely stopped the truck with this brake booster failing. Is this normal for it to have such an effect on the braking? I thought I'd at least be able to stop pretty easily by pushing very hard with two feet but that's not the case. Well at least I figured out why my idle is erratic yesterday LOL.

 

[HotRodPC]

No it's not normal. It sounds as if you have a failed Vac booster. If you hear the dreaded Wooosh sound when applying the brake pedal and a hard pedal, booster is gone or on it's way.

Wait, I may have mis answered your question, YES it is Normal for the brakes to act this way IF the brake booster is failing.

 

[HotRodPC]

BTW, IF it is indeed the booster is bad and the brakes are in good order otherwise, you have no need to fear losing brakes. Just that you'll need a lead foot and heavy pressure on the pedal to get them to work.

 

[paulrowe]

Thanks for the help HotRodPC. Going to order a new booster on Monday and get this fixed. I have to go down a really steep hill every day and I really feel alot better with power brakes.

 

[highdesertrange]

when you unbolt the master if it's wet between the master and the booster your master is also bad. highdesertranger

 

[paulrowe]

So I replaced the brake booster and still have a hard pedal. The master cylinder was not leaking or wet by the piston. My brake fluid looks really clean overall. I guess I should bleed the brakes? How would air be able to get into the system? Mabye when I compressed the two front calipers to do the brake job air was pushed in the system. I'm pretty well stumped right now and any more advise would sure be appreciated. Should I replace the master cylinder?

 

[HotRodPC]

So I replaced the brake booster and still have a hard pedal. The master cylinder was not leaking or wet by the piston. My brake fluid looks really clean overall. I guess I should bleed the brakes? How would air be able to get into the system? Mabye when I compressed the two front calipers to do the brake job air was pushed in the system. I'm pretty well stumped right now and any more advise would sure be appreciated. Should I replace the master cylinder?

NO, DO NOT replace the master cylinder. Around here we like to diagnose and repair, not change parts til we get it aka Parts Changer !!!

I doubt it's the master anyway. If it were bad, you'd have brake fluid leaking out of it somewhere, OR have pedal fade very bad with an internal leak. So if the pedal isn't going to the floor or fading away, it's not likely the problem.

By your description, I'd swear it was the brake booster. A good brake bleed can be done at no charge, so yes, Give it a try for a good brake bleed and let's see what you have and go from there.

Just in case you don't know, when bleeding brakes, you ALWAYS start from the wheel furthest from the master and work your way to the master. Sooo.... that means start with Right Rear, Left Rear, Right Front, Left Front.
Make sure whoever you have Pumping and Holding know how to communicate and understand exactly what they are doing. They DO NOT let the pedal up until you have the bleeder closed off tight or you'll suck air back into the lines.

 

[paulrowe]

So this morning I bled the brakes and still have a hard pedal. What do you guys think about the problem being in the proportioning valve? Not sure how many options are left. I have a new master cylinder from a 1980 Camaro. Would this work for a replacement if needed?

 

[SkinnyG]

Did you inspect the vacuum hose from the intake to the booster? If it's not ~getting~ vacuum, it's not going to work.

When you bled the brakes, was the fluid coming out at a consistent rate/volume from ~all~ wheel cylinders? (if not, may indicate a fluid pressure differential valve failure - reset (or replace if it cannot be reset) the combination valve)

 

[paulrowe]

So it turns out I had a combination of a leaky brake booster and a leak in the actual manifold line. The leak was actually in the filter in between the two lines going to the booster. I think it's a filter? I hooked the vacuum gauge up to this beforehand and it was pulling vacuum I guess it just wasn't pulling enough. The brakes seem to be working well now thanks for all the help guys. Also while bleeding the brakes I discovered I have a leaky axle seal so now I have another job to to take care of. Really glad to be part of this forum! Everyone here's great! I'm sure I'll have many more questions!

 

[HotRodPC]

That's not a filter. It's actually a check valve. It's purpose is to store vacuum in the booster so in the event you have an engine failure and lose vacuum, you still have power brakes 1 last time to get the vehicle stopped. You can run without it if need be. No problem at all other than if the engine isn't running you won't have power brakes, which most of us are aware of.

 

[Turt13]

Just giving this old thread a thumps up. Answered some questions about my brake system. If I understand what was said , since:
I have a whoosh sound when stepping on the pedal,
Fluid from between master and booster,
Erratic idle,
Safe to say I have a bad master and
At least some sort of vacuum leak in the booster?
I already changed the failed check valve with a good one.

 

[jjester6000]

While driving around in my truck today I noticed that the brakes have no stopping power. I check the vacuum on the brake booster. The line seems to be drawing plenty of vacuum and the brake booster seems to be holding vacuum. The brakes were fine up until today and then all of a sudden I have to push them to the floor just to get enough to even come to a small slow down. I just changed the pads and rotors about 2 weeks ago but all seemed fine after that. Is it possible that I need to bleed the brakes after this? Also I have an NP 203 transfer case and I just started driving my truck and full-time 4 wheel drive. Maybe this has something to do with my problems? Any help would be much appreciated.

Get a louder horn.