A couple of weeks ago I changed for the first time, the frontpads and rotors on my 84 NA.

After I changed them the pedal felt sligltly softer but not too much and this was offset by an increase in stopping power.

Yesterday however, when i put my foot on the brake pedal it emitted a hissing noise. Its stops when i push all the way down. Also if i push the break twice in quick succesion on the second time, it feels like the booster is not working.

I am assuming that i have some air in the system and it just needs a good bleed. However when i searched on here it mentioned that the booster might be bad. It wasnt bad before i changed the brakes but can air in the system make it go bad?

Thanks in advance

 

Having the same exact problem.
Interested in an answer to this. I've bled my brakes a couple time already, to no avail.

+1

 

Me 3 ..... I just did all 4 pads, rotors, and caliper rebuilds. My pedal is soft, but it stops on a dime. I've bled almost a gallon of fluid through it ($$$$) and nothing changes.

I think its the pads I'm using. They require more brake pressure to stop. (PBR metal masters).

Thats all I can figure anyway.

 

Im having this issue to with an '87 NA. There isnt a proportioning valve or something i missed is there?

 

Just to add as well.

I noticed today that when at a stop and i push the brake so it is hissing, my idle drops from 900 to 800 and it runs a little rough

 

Sounds like you may have bad brake booster or a vacuum leak around the booster an hoses.

 

my guess would be a vacuum leak around the brake booster...i removed the brake booster from my car (going with manual brakes with the v8 swap...for now) so you should be able to stop fine without the booster boosting...but i don't know if a booster can actually go bad other than losing vacuum...that takes it back around to the beginning of this post where i say that it might be a vacuum leak.

i'll shut up now...
Ethan

 

Thanks for the replies.

Job for the weekend!

 

It's the booster. The dead giveaways are the hissing, and the double confirmation is that you don't have boosted brakes on a second quick application. The brake booster acts as a vacuum reservoir. If its leaking, you run out of boost in a hurry.

 

Aw crap... I hate removing the brake booster... I should have replaced it when it was out before.

 

Just an update on this, bled the crap out of the brake, suprise suprise no change.

So as stated, have some sort of vacuum leak. I checked the hose that goes to the booster, and it seems fine. To be honest I have little knowledge about this and dont really knwo what I am looking for.

The hiss from the pedal makes me think the leak is there? Is this even possible?

Id rather not replace the whole booster (expense). Would replacing the hoses have a chance of fixing the problem?

 

I think it's your booster. But to be sure, you can test.

You need a vacuum gauge. Find a good spot to hook it up to. Start the car. Note the reading you get. Stop the engine. Disconnect the hose from the brake booster. Plug it. Start the car. Is your reading higher? If so, you have a bad booster.

Next booster test, with everything hooked up and the vac gauge on, hit the brakes. The gauge should dip. Let off the brakes. It should quickly return to the base reading. If it does not, you have a bad brake booster. Pump the brakes. You'll likely see the reading keep on going down and only very slowly returning.

One more thing to test while you're in there....the one-way valve (looks like a small "pancake" fuel filter on a small vac line coming from the brake booster). It has an arrow on it. It should only flow in that direction. You can test with with a mityvac or similar. It should flow freely when you are drawing from the side with the arrow, and should not allow anything through when you hook up to the other side. But I doubt this is your problem, as the hissing is the dead giveaway of a torn diaphragm in a brake booster.

 

Thanks very much for this, exactly what i was looking for.

Just one small other question, where would be a good place to hook the guage up too?

 

I would probably hook it up to the brake booster directly to the line that the one-way valve is on (without the 1-way valve between your gauge and the booster).

 

Awesome,

Thanks again.