Brake Booster

[WhiteArrow3800]

I've had an intermittent brake light on the dash for a few weeks on the '93 SSE. About a month ago it came on and flickered (door chime sounded off every time it did ). Noticed a drop in brake fluid level in the MC reservoir so I stopped driving the car until I figured out where it was leaking. Discovered both rear wheel cylinders were leaking and replaced both, bled the system and continued on. Nothing weird happened for a week or so but then the brake light on the dash came back on intermittently. Sometimes it stays on the whole drive, sometimes it's flickering, sometimes it doesn't come on at all. The last couple days however it's been solidly on. I don't have another vehicle to drive right now since as some may know from Facebook the '01 has a blown engine (un-diagnosed but it's not good). So I've been checking the brake fluid level often and it hasn't gone down from the fill mark since topping it off when I did the rear wheel cylinders. There's no fluid loss and the brake pedal travel feels normal. I unplugged the fluid level sensor at the MC which resulted in no change as far as the dash light is concerned. So I had sort of chalked this up to be a brake pressure switch/sensor issue. But yesterday I heard a hissing sound that would go away when I hit the brakes. When I got home I popped the hood and it sounds like it's coming from the brake booster area. I checked the vacuum hose running to it and it appears fine. But I sprayed starting fluid around and the engine idle stumbled when I sprayed near the bottom of the brake booster. So I think that more or less confirms it's leaking, but I'd think the brake pedal would be very stiff if that has a leak, right? Also, would a leaking brake booster set the dash light on?

[96 SSEi]

hi, the b. booster doesnt care what pressurizes it - a small leak wont affect it very much. It sounds stupid, but if the idiot lights are shared, your parking brake may be not fully up- retracted. please check this just for fun...lol. you can also check the float device in the resovoir of MC - if it is a float, it should move freely with tiny pressure.

my 82 malibu, backing plate would shift, causing the piston to exceed its normal travel distance and, under hard braking on bumpy roads, cause the pistons to shoot out of the cylinder - I dont see how this would trigger the light without fluid loss.

[crash93ssei]

Agreed, small booster leak can still result in normal pedal feel and may even seal up when pushing the pedal in. The light is likely caused by just a bad parking brake switch or fluid level switch.