Power Brake Experts Needed!!!!

[DT1]

Just to clarify, The brakes work well when slowing but when I come to a stop I need to apply more pressure than necessary to completely stop. I took it out a few minutes ago and pinched off the booster vacuum line. Big difference! So, I know the booster is working. Just not as well as it should. In my experience, when a booster is bad, it's very hard to brake and while the brakes are applied the engine will lope because of a massive vacuum leak. This is not the case. I can still lock them up and the idle does not change at all.

[DT1]

OK, Today I replaced the booster I got a couple of weeks ago with another re-manufactured unit. I'm happy to state that the brakes are as good as new.

[DANTIP]

Originally Posted by DT1

OK, Today I replaced the booster I got a couple of weeks ago with another re-manufactured unit. I'm happy to state that the brakes are as good as new.

That's Good News!! Thanks for following up with the fix!

[snacks]

with the motor running take some needle nose pliers and pinch the vaccume line off,your idle may drop alot,meaning internal vaccume leak replace booster

[sean1969c10]

My 88 GMC has the same problem and I have been very suspicious of the NAPA power brake booster that I installed. I have 18" of vacuum to the booster too. It's easy to over look a new part that is defective.

[DT1]

Originally Posted by snacks

with the motor running take some needle nose pliers and pinch the vaccume line off,your idle may drop alot,meaning internal vaccume leak replace booster

It makes a lot of sense and that's what I did. The vacuum remained the same and that's why I was having trouble blaming the booster.

[DT1]

Originally Posted by sean1969c10

My 88 GMC has the same problem and I have been very suspicious of the NAPA power brake booster that I installed. I have 18" of vacuum to the booster too. It's easy to over look a new part that is defective.

This is not the first defective booster I have bought. A while back I installed a Reman in my Mustang but I could tell it was defective from the get go. When I applied the brakes, the car would barely stop and the engine loped from the massive vacuum leak. This time it was quite different. The truck would still stop but with more effort than normal and there was no vacuum leak. I pinched off the vacuum line and it was extremely difficult to stop. Until now I have never experienced a partial failure.

[sean1969c10]

This seems to be what I have going on too. I have had my share of defective replacement parts, it's so frustrating to spend your hard earned money and time to have to do a job twice.

[DANTIP]

I finally replaced the booster and Problem Solved!!!

Thanks for the responses!!

[jocko]

I had a hard pedal, as in SOLID pedal, almost wouldn't budge. (this does not sound like your problem, but I'm throwin it out there for consideration) my problem was the master cylinder - the piston was sticking in some scoring in the bore. I chucked it and replaced (with a 2 reservoir version for added safety -(this is in my 66, originally single re mc)) and problem was gone.

Having said all that, the fact that you're able to still troubleshoot, and drive, tells me this probably isn't the issue. I agree, it does sound like the booster.

When you DO push (hard) on the pedal, does the truck stop normally? Any surging? i.e. possible clogged line, or something. If yes (to normal stop) and no (to surge) then I'm thinkin it's gotta be the booster.

[Rooster's 67]

You were experiencing a faulty valve internal to the booster. The valve that allows atmospheric pressure to the back side of the diaphragm of the booster was probably only partially opening, or was plugged partially not allowing the pressure differential to grow fast enough to give a proper amount of "Assist".

[DANTIP]

Originally Posted by Rooster's 67

You were experiencing a faulty valve internal to the booster. The valve that allows atmospheric pressure to the back side of the diaphragm of the booster was probably only partially opening, or was plugged partially not allowing the pressure differential to grow fast enough to give a proper amount of "Assist".

That sounds like the problem. The side with the check valve was fine (held vacuum).

Thanks!