Failing brake booster?

A few months ago right after installing a new vacuum pump I noticed that at idle I sometimes had a stiff brake pedal or would only get soft pedal for one push and then it would be like I had no vacuum left. But the truck stopped fine at highway speeds and around town so I just ran with it. Today I bought a vacuum gauge to see if my pump was bad but it seems OK. 22 inches vacuum when plugged direct into pump and 21 inches vacuum when plugged into the tree. I am new to diagnosing/replacing the brake booster. With a vac pump putting out enough vacuum for spec is it likely I have a failing brake booster? I had also read something about the booster "check valve" getting stuck/failing. Can the check valve be replaced separately/repaired/cleaned? Sorry for the noob questions but I learn as things break.

So yours is doing the same thing mine does. I'm almost certain my booster is leaking.

Make SURE it's the booster before buying a new one. Several people have gotten them bad right out of the box.

Hook a new vacuum line directly from the pump to the booster. Use NEW hose. This will eliminate all other vacuum hookups as possible leaks. If your symptoms are the same it's likely the booster.

Test the check valve by blowing through it. You should be able to blow through it one direction but not the other.

How long does your pump take to build 22" of vacuum? A slow pump could be part of the problem too.

I have several brake boosters here,
its yours for the cost of shipping.

Thanks for the replies. At the tree and directly on the pump it builds 20 inches of vac in just a few seconds and it takes about another 15 seconds to build that last little bit.

Thanks IDIoit, I PM ya when I determine it's the booster.

Following this because my brakes seem to do the same as yours. Work fine while in gear but if Im rolling in neutral the pedal gets stiff and I need twice as much road to stop.

Had stiff brakes in the crew cab last year. Pump was getting weak, but the vacuum line going into the cab was my biggest issue. It was broken and I didn't know it until after I swapped the pump out. Fixed the vacuum line and all was right with the world.

Not 100%, but every time I've had a booster leak, I could hear it leaking. Any hiss from the booster?

Heath

I had the exact same issues that you are having and replacing the brake booster fixed the problem. My advice is to replace it as soon as you possible can, I almost got into a couple of fender benders in traffic because i kept putting it off.

I can't remember.
Are all of the new boosters the "zero loss" units?

Sent from my SAMSUNG-SM-G935A using Tapatalk

Is the vacumme pump for a 94 idi different from older 7.3 idi? Or is it just the pulley that's different?

I think it's just the pulley--v-belt vs serpentine.

when my brake booster had gone out I could hear a hissing leak noise from inside my cab, maybe try listening close to the back of the brake booster on the cab if you can and see ignore you can hear anything from there

Serpentine pump and V-Belt pump are different..... not just the pulley.

One, the pump is mounted in 2 different places, the V-Belt is under the alternator, the Serpentine Pump is next to the A/C Compressor.

The mounting holes in the pump are different. If you look at at the 3/92+ Serpentine Belt Pump:



The mounting holes are through holes. but if you look at the 3/92- V-Belt Pump:



The bolt holes are threaded. That means the bolt holes in the V-Belt bracket are through holes and the bracket mounts is in front of the pump and the bolts tighten into the pump. On the Serpentine Pump, the mounting holes are through holes and the bracket is behind the pump, and the bolts tighten into the bracket.

Two, I have yet to see a new pump come with a pulley. You will need to reuse your pulley, or try and source a new one. Make sure you use the proper pulley puller to remove and reinstall the pulley. DO NOT use a 3 jaw puller on the Serpentine Pulley as you will destroy the pulley. Most places list a V-Belt pulley, but I have only seen the serpentine Pulley on e-bay and they are not always there......

Your description sounds just like my truck when my booster was bad. Final check would be to isolate the booster and try to draw a vaccum on it. it should hold until the pedal is pushed if good.

Replaced the booster today with a used unit sent to me by IDIoit. Better brakes while idling and much better "panic stop" braking. Still a bit slow to replenish brake boost at idle but hey it's used and maybe my vac pump is just a tad on the slow side. Thanks again IDIoit.

Now to begin acquiring parts for hydro-boost!!