First post here...looking for some help. Truck in question is a 96 w/ 4.3l

1) When idling it runs perfectly, once you hit the brakes there is a hissing sound and it starts idling rough.
I've searched and I believe it's the brake booster

This second problem I need some help on. The abs light is on, I took it for a drive just down the street and the pedal was very hard to push in. Almost didn't think I would stop at first. The pedal finally went down further and it stopped kinda suddenly but the back brakes locked up....I think the back driver tire.
I turned around and took it home right away before I got out into traffic lol

Any ideas?

 

check the large vacuum line coming off the brake booster.

 

brake booster is bad. the hissing sound you are hearing is the vacuum from the engine. the diaphragm in the brake booster is either ripped or torn. happens from time to time. thats why the engine starts running crappy when you hit the brakes, it then has uncontrolled air going into the motor and not going past any sensors.
as far as the abs, im not too sure. your brakes did what they did because you are still getting some vacuum, but not enough. thats why when you had your foot hard on the brakes, it stopped all of a sudden. the rear driver side locked up because its not the drive tire, and when the brakes grabbed you had all the weight transfer to the front of the car.
replace booster and go from there. it is more than likely not the reason that your ABS light is on, but it needs to be fixed before you do anything else. at least after its fixed, you can drive it, you just have to be careful when stopping.

 

Big vacuum line is good

 

i would imagine the vacuum line is fine.
its inside the brake booster where your problem lies.

 

yeah I've been searching and that's what I've come up with....will get it changed soon and report back.
Just wasn't sure if that would cause the brakes to lock up. I jacked up the back and put it in neutral and it spun free so nothing bad there

Need to find a good tutorial on it, doesn't look too bad

 

well you already experienced what a bad booster is. hissing from under the dash, hard pedal, barely stops, and when it does, it about throws you through the windshield because you have to have your foot buried in the brakes just to get it to slow down. thats why the rear locked up, too much pressure on the pedal and when the front grabbed, that caused all the weight to transfer off the rear. minimal weight + high brake line pressure= rear tire locking up.

they arent hard to change, just make sure that your master cylinder isnt leaking fluid into the booster. if it is, you need to fix that too, otherwise it will waste your new booster.

 

It's not leaking any fluid as far as I can tell....I'd obviously know when I go to change the booster right? There's be brake fluid in it, if you can see in it?

 

yeah, when you take the brake master cylinder off there is a seal on the back of it where the rod for the pedal goes. if the seal is blown out, you see fluid in there. plus it might be a little low in the reservoir.

 

Honestly how hard is the booster to change? I've been searching and they al say the nuts holding it OJ are the hardest part.

Would like to save some money and do it myself.
All the nuts are accessible thru under the Hood or do you have to go on inside the vehicle to do anything to them?