alfonso gomez

Very hard brakes


Almost 2 years ago I had to replace my 87 Coupe's brake booster. The car would not stop and there was a loud hissing sound when the brake pedal was depressed. The mechanic at the shop tested the car and determined I needed a new booster. So, in it went. The car was fine until I got a code 34 last week. Together with the crappy performance, surging, rough idle, etc., I noticed that it was an effort to stop the car.
The pedal was very hard but if I pressed very hard, the car would stop. Let me explain its behavior: the pedal was hard initially. When I kept pressing the pedal it "loosened up" and moved downward a little and it felt like before the problem.
I changed the MAF relays, cleared the code 34 and the car started working OK, except the idle is a bit high and surges from time to time. Like its 600-700 RPM's, climbs to 1,200 RPM's, then goes back to 600.
I doubt the code 34 problem has anything to do with the brakes, but who knows?
I made this test: started the engine, let it idle in PARK. Then I pressed the brake pedal and it was very hard, but has no hissing. When the pedal moves downward, it does not have the hissing sound. I shut the engine and disconnected the vacuum hose from the booster and blew in it. The air passed freely, so there are no obstructions. (I could feel the air go into the plenum).
Then, I blew into the booster thru the check valve but the air did not pass, which I expect is correct. I then tried to suck air thru the check valve (like the vacuum tube would do with the engine running), and air did pass. So, I must conclude that the booster is working properly, or am I wrong?
Anything I should check before going to the shop and throw more money at it?
This is my daily driver and my right foot hurts from the force needed to stop this car.
PLEASE HELP!!!!!!!!
Thank you.

MikeC4

You need to reverse your vacuum check valve! the Plennum supplies suction to this valve, therefor air should pass when sucking from plennum side, not the other way around.....

Mighty-Mouse

If the engine is giving these issues I would suspect that it's the engine not producing vacuum that's the problem. I'm not an engine expert, but erratic engine speed is sometimes a sign of a vacuum leak somewhere.

I'm assuming the engine issues and the hard pedal popped up at the same time.

You did everything correctly in checking your booster and check valve.

And must conclude that your booster is fine as you have.


This maybe a PIA, but if you have access to another car, any car, try hooking up the a vacuum hose to that car's intake connection and see what the brake pedal does. You'll need a longer piece of hose, any hose that seals will do for this test, nothing special needed.

alfonso gomez

I just rechecked and found this: I connected a hose to the booster check valve and sucked first and blew second. No air passed either way. So maybe the check valve is stuck or damaged. Can it be replaced easily or do I have to take it to a shop?

Mighty-Mouse

First remove the check valve, just pull it out it out it won't break.

Then try what you did, also see if you can smell gas from the check valve.

Once you remove the check valve you'll see that it's difficult to install it backwards.

MikeC4

PLENNUM -----<-----<----CV----<----<----Booster
(one way airflow)


Try removing the check valve altogether and see if the brakes improve. I am convinced that your valve is hosed(pun intended) up. You should be able to get a new one at any auto parts store, Pep Boys, Autozone, O'Reilleys, etc.

VetNutJim

DISREGARD THE FOLLOWING, I CAN"T READ.

It's that little black cylinder at the rear of your manifold back right behind the distributor. Got three little hoses connected to it.
Don't put it in backwards.

They cost about 3 bux.
Replace it, that should get your brakes back working, your cruise control cruising and your ECS controller working again.

Good luck with it.

BTW, check your vacumn ball and the lines to/from it to make sure they are in good condition.
Long as you're 'in there'' poking around.