I've been nursing my 91 SE (one owner car BTW) so I can get my last daughter through High School with it. However, over the years the boost to the brakes has deteriorated to the point that it takes too much effort for my kid to quickly apply brakes hard. I've replaced all brake components at the wheels over the past couple of years, but nothing under the hood. I've done the FSM tests for the brake booster and it seems to pass. I've never changed the booster hose; it isn't cracked, but it is 25 years old. There could be some slight leakage in the one way valve; like it doesn't seal correctly, but it didn't seem to affect the FSM booster tests. It looks like I can get a replacement booster for about $100 but the molded booster hoses seem to be discontinued everywhere—not sure if standard vacuum hose will work. Ideas?

 

you can throw on vac hose on the booster and you should be good to go.

how's pedal feel? is it just hard to press and when you press down it doesn't seem to really slow the car down?

have you looked into the pads and lines?

 

A good flush and bleed will take any air out of the lines that might exist. I thought my 94 GXE had deteriorating braking performance until I had a shop do a brake job and flush/bleed. The car stops like new.
Did you look at the rubber flexible hoses leading to the front brake calipers? In a car that old, sometimes the inside of the rubber hoses can start breaking down and clog the passageway causing poor brake line pressures.

 

The brakes are not "spongy". It just feels that I have an old '70s car without power brakes. I can tell there is some boost but not much. For example, if I remember the FSM test, if I press the brake pedal with light leg force and then turn on the car, the pedal depresses further with the same amount of leg force. The car stops well—you just have to press hard. All brake hardware at the wheels have been changed: calipers, pads, hoses, discs. The brake fluid was flushed and bled. I even took the car to a brake shop to flush, bleed it again, and inspect my brake work; there was no change. The brake shop just said it was an old car and I should expect to press harder. I think I'll replace the boost vacuum hoses and the one way valve. If that doesn't do anything, I might replace the entire brake boost.

 

I guess eventually you'll solve the problem by replacing everything! Both my GXE's had good linear-feeling brakes with good/not-too-much power assist. But when I messed around with the brakes a couple times, I remember the pedal pressures had changed, for whatever reason. I'd take it to a shop and they'd get it straightened out for me. I'm still on the original booster and master cyl on my 94 with all good pads/shoes. Did you say you replaced your master cyl? You should be ok using stock hoses for the booster hose. I don't think that vacuum will collapse that big of a hose. I also need a new booster hose because the motor end is kind of chewed up from taking it off and on so many times. But it still works so I'll just put it off until it starts leaking.

 

Still on original master cylinder, but I'll probably focus first on boost components since the issue is not stopping the car but the amount of effort. I've pulled that intake manifold off at least 8 times fussing with those dreaded injectors over the years and so the intake end of the booster hose in my car is also cracked, but no obvious leakage.