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gotta be the brake booster.

xXamwxxXx

xXamwxxXx

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So my brake pedal has been getting worse lately. I go to press on it and I get the air escaping sound and its hard to get to the actual brake. i try to keep a good distance away from whoever is in front of me since the reaction time is slow. What I did was take some pliers and close off the line going from the intake to the booster and pulled the line off the booster with the truck running. plugged the end of the line with finger and let loose pliers and felt suction, rpms go way up if i let my finger off a little. Put pliers back on hose and turn off truck. Pull 1 way valve out of booster and hear air escape. The valve is good i assume. i can blow through it only 1 way. Since everything seems to be working right and the fluid is all full I figure it must be the booster right? I just wanna be sure since its going to be about 80 bucks. Once the pedal gets past the hard spot the brakes work good and hold, its just hard to get to that point. Can anybody tell me if i'm on the right track? thanks.:waytogo:
 
Lots of effort == no assist, air hissing, both indicators of bad booster. Rare -- usually the master fails -- but it can happen.

-- A
 
thats what struck me. I dont really hear about boosters failing too often. So I just wanted to make sure I am covering my bases. I was going to bleed the brakes but it dosent seem like thats the problem.
 
had this happen to me couple months back, bad brake booster, swapped it out, now the brakes work killer...Usually a bad master cylinder would leak thrugh the rear seal into the booster, and the brake fluid deteriorates the brake booster diaphram, double check the master while its apart.
 
some parts stores, it's cheaper to just buy the booster and master as one complete unit, not sure why, but i ran into this a few times in the past.
 
xXamwxxXx said:
So my brake pedal has been getting worse lately. I go to press on it and I get the air escaping sound and its hard to get to the actual brake. i try to keep a good distance away from whoever is in front of me since the reaction time is slow. What I did was take some pliers and close off the line going from the intake to the booster and pulled the line off the booster with the truck running. plugged the end of the line with finger and let loose pliers and felt suction, rpms go way up if i let my finger off a little. Put pliers back on hose and turn off truck. Pull 1 way valve out of booster and hear air escape. The valve is good i assume. i can blow through it only 1 way. Since everything seems to be working right and the fluid is all full I figure it must be the booster right? I just wanna be sure since its going to be about 80 bucks. Once the pedal gets past the hard spot the brakes work good and hold, its just hard to get to that point. Can anybody tell me if i'm on the right track? thanks.:waytogo:
Click to expand...

This usually means that the booster is holding vacuum as it should and DOES NOT have a leak so your problem is elsewhere.
 
:doah:So if thats the case then what else could cause my symptoms? Brake pedal hardness and air sound. Also If i shut the truck off, pump the pedal a few times,hold down on it and then start the truck the pedal dosent go down like it should. If the truck is on and I push down on the pedal there is some surging of the engine, not much but you can hear it. Another thing is if the truck is off and i start pushing on the pedal when it goes down i can hear some air escaping somewhere around the booster/master cylinder. I would just start taking things apart but my blazer is my 20 mile a day daily driver so I want to get this fixed in one shot. Thanks again.
 
I replaced a bad master cylinder with the "BRAKE" light came on in my dash, then I couldn't bleed the system properly and the pedal was hard but the brakes didn't work very well. Turned out to be a bad booster (contaminated by the leaking master cylinder).

Double check that the vacuum hose is REALLY vaccum hose and not fuel hose or something else. The wrong hose type will collapse under vacuum pressure and prevent things from working right. This will cause lousy brake performance also.

Those are the only direct experiences I've had that are brake-related...


:usaflag:
 
I've had a few P/B boosters that had leaking diaphrams,and they only "leaked" when you applied the brakes--checking the booster with the usual tests as he tried ,it checked out "good",but when you stepped on the brake pedal it wasn't!...I'd hear hissing under the dash,the brakes were rock hard and I was lucky not to hit the vehicle in front of me every time I needed to stop fast (and everyone seemed to know my brakes were not working right,and would stop suddenly without warning of course!)...one of the two boosters I had to replace because of ruptured diaphrams had leaky master cylinders,I've had a few rot out the "bowl" that houses the diaphram too,under the master cylinder..rust ate right thru it!..:(

One of the trucks that I had with a bad booster was a 75 K5 2wd Blazer..I had a booster off a 70's Chevy car and it fit right on perfect--but it had VERY touchy brakes after I put that on it--the weight of your big toe could put passengers into the windsheild easy..had to re-learn how to drive it all over again.
 
xXamwxxXx said:
:doah:So if thats the case then what else could cause my symptoms? Brake pedal hardness and air sound. Also If i shut the truck off, pump the pedal a few times,hold down on it and then start the truck the pedal dosent go down like it should. If the truck is on and I push down on the pedal there is some surging of the engine, not much but you can hear it. Another thing is if the truck is off and i start pushing on the pedal when it goes down i can hear some air escaping somewhere around the booster/master cylinder. I would just start taking things apart but my blazer is my 20 mile a day daily driver so I want to get this fixed in one shot. Thanks again.
Click to expand...

This does sound exactly like a bad booster. There are always exceptions to "the rule". The biggest thing that says a bad booster is that as you hit the brakes and hear the hiss the engine "surges" which is caused by a vacuum leak (bad booster in this case).
 
ok, what im gonna do is find me a used booster off of craigslist and start from there. I would hate to end up hitting somebody especially now that the rainy season is here. i suppose I could compare the amount of air that escaped the booster when pulling the valve with a functioning booster but at this point I think its pretty obvious what the problem is. thanks again.
 
I would not suggest trying to buy a used one off of craigslist as there are several options and unless you know 100% for sure that the one you get is the correct one you'll end up with troubles worse than you already have.
 
Yeah your probably right on that. i know there's dual diaphragms and singles and whatnot. probably better to go new with brake stuff.
 
so i picked up the new booster. In the process of putting it in. (or should I say taking the old one out.) I have a manual that is supposed to cover my truck and it shows how to remove a brake booster and I think a hydro boost. the thing is is the pic shows a brake booster's mounting nuts in the cab and the hydro boosts nuts in the engine bay. Mine are in the engine bay which according to the book is wrong and also a real pita to get off especially since there's this black rubbery crap sprayed all over the firewall which coats the nuts making it hard to get a wrench around them. I'm on the last one though. Its 3:45 in the morning time to give it a rest until tomorrow. any ideas on the mounting discrepancy? maybe not a big deal?
 
It's been some time since I removed a brake booster from a 73-87 GM truck,but I think some unbolted from inside the cab,the bracket was welded right to the booster,and had 4 studs welded to it that pass thru the cab----some others had a booster that bolted to the bracket,which also could be unbolted from the inside...so it could be removed from under the hood or from the inside...

My hydroboost on my diesels have two bolts behind where the master bolts on ,but I didn't really look good at it beyond that point closer to the firewall,but I beleive they bolt up the same as the vacuum booster,as trucks all have the same cab and accept either type of brake boosters so they dont have to make a whole different firewall..
 
Well the new booster made a big difference. Definitely worth the money. Looks a lot nicer too.:D
 
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