Brake Problems

Hey

So I bought a 87 AMC Eagle several months ago and I have been dealing with brake problems ever since and I would like some help. So first of all, the brake pedal would always slowly start to sink when I applied pressure, so I replaced the brake master cylinder and in the process broke a brake line which I spliced and fixed and I am pretty sure it is not leaking from there.

Now my current problem is that braking force leaves a lot to be desired, I can hit the brake pedal but the car just slowly stops, not at all what I would expect from the force to the pedal. It doesn't seem like the pedal travel or braking distance changes after several attempts. Also when I apply the brakes I hear a hissing sound inside the cabin, probably would hear it if I was outside as well but I cant apply the brakes and have a head in the engine bay at the same time.

So what do you guys think could be my problem and solution?

The hissing sound could be the brake booster.

booster leaking maybe? I've never experienced it but an air leak when pressing the pedal would point towards it I would think
bleed the system really good and make sure there aren't any other leaks in it but if you have a solid pedal then that shouldn't be the problem.
MC's are tricky to bleed, but if it had air in it it wouldn't be consistent like it is imo
first step is always bleed the hell out of it though, bleed the lines at the MC as well, maybe gravity bleed them one at a time then do the pedal method one at a time.

Yeah could be some kind of brake booster problem contributing to it. I'd say disconnect it and plug the vacuum line and be ready to work your leg in manual mode, see if the braking is consistent and you get a sensible amount of braking power (for unassisted brakes).

If you are hearing a hiss when you step on the pedal, that would indicate a leaking diaphragm in the brake booster.

Could that be contributing to the weak braking force?

It would mean more effort is needed to actuate the pedal. If you press hard enough - REALLY hard, you should still get full braking force with a damaged booster.

Yeah, your booster is leaking. You probably get at least a subtle change in engine speed when you hit the brakes. I'm going through this with my Cherokee. I have a booster sitting in a box waiting to be installed. It makes a helluva difference in braking power.

Yeah it is surely the brake booster then, the engine speed drops and occasionally stumbles when I press on the brake. What a drag, sunlight is in short supply and its dark after I get out of classes and its going to be winter and cold and I get to do this outside on the street.

How much might a shop charge for a brake booster install? I might consider that depending on price

while it does sound like there are problems with the booster.. you never mentioned if you put new brakes on the car? bad drums/rotors and pads/shoes can do the same thing you are experiencing.

Not to mention if part of the rear brakes failed.

My last saab (not the current one) had inorperable brakes in the rear when I bought it. That was a fun ride home

No I have not yet replaced the drums, calipers, shoes, pads and rotors. I really should.

fritzsch wrote: Yeah it is surely the brake booster then, the engine speed drops and occasionally stumbles when I press on the brake. What a drag, sunlight is in short supply and its dark after I get out of classes and its going to be winter and cold and I get to do this outside on the street. How much might a shop charge for a brake booster install? I might consider that depending on price

Book time shows 1 hour labor to do it.

I once did brakes out on the street.. in the snow. I had been putting it off and putting off due to the cold.. and finally they flat out failed in one corner. (pad fell out) so I was forced to do the dirty job right then and there..

At least I finished up before the blizzard actually hit

I changed the booster+MC on my Samurai once with another guy, took less than an hour.