Brake booster not working?

[mjp1080]

I'm running a 2000 S10 booster in my buggy and its not assisting with braking at all, there's manual brake pressure, but no vac assist. I've got 12 inlbs vac at the booster at idle and 27 inlbs at 2500 rpms. I have gone through the entire system and have no vac leaks, plus I am running a vac reservoir can. This makes no sense, the booster worked fine a couple months ago when I drove the s10 and it has not been tampered with or modified. I didnt even take the master cyl off of it to install it. I was hoping somebody had run into this before and might have an idea of wtf is going on.

 

[leadfoot067]

do you still have the check valve installed? was this master/booster hooked up with the rockwells before the re-build?

 

[mjp1080]

I do have the check valve installed in the booster and there is one on the vac can as well. This is not the booster from the old truck, they have never been connected to the rockwells before.

 

[PHILLBILLY1]

You can figure out if the thing is bad by doing this:

With the engine stopped, depress the brake pedal normally, several times. The brake pedal must be depressed before the engine is started in order to remove vacuum from the booster.

With the brake pedal depressed, start the engine. When the engine is started, vacuum is created and operates the booster. This causes the brake pedal to go down.

If the brake pedal goes down slightly, the booster is operating normally. If the pedal does not move, the booster is not recieving manifold vacuum or is malfunctioning.

Not trying to state the obvious, but did you check the pushrod for proper adjustment? Maybe it isnt throwing far enough with the new setup.

 

[TrikeKid]

What's your regular manifold vacuum at idle? 12 in/lb is low, should be more like 17-20 unless you're at way high altitude.

 

[t1h5ta3]

its in/hg ie: inches of murcury....
12 in/hg is crap! i can usualy get that out of a 9sec small block... ether that things way outa tune, has vac leaks etc...

most boosters require 15" min. you say your getting 27" ( coff coff bs ) @ 2500 rpm, do the brakes work good then?
if not im definetly guessing the diaphrams blown.

 

[jimijam19K]

Hydroboost!!! :stirpot:

:corn:

 

[mjp1080]

I have done the pump pedal and start up test about a dozen times and I get nothing frome the pedal. I just retested the vac and I am still only getting 12 inHg at idle and 22 inHg (not 27, my mistake) at 2500 rpms. I just dont see what the hell would have caused the booster to go bad in a few weeks of not being used. I think I'll just get a different booster can first and then look into a separate vac pump.

 

[ceb0217]

check the one way valve. in backwards or mabe some thing in it??