TomP

Okay, so last night, I'm driving around a turn at about 30 mph, and this guy was stopped in the middle of the road- I slammed on my brakes. He moved, I kept going... as I came to a stop sign, I lost my power brakes. The RPM's bounced around 300-400; and the car acted like it was going to stall. When traffic cleared, I went- the car stumbled, then took off like normal. As soon as I came to a stop again, I lost my power brakes, the engine nearly stalled, ran rough, low rpms, etc. When the light went green, I accelerated, and the car acted normal.

I came to my parking spot, stopped, & let the car idle. Same thing; very low rpm's, rough idle, and it finally stalled. I couldn't get it started again unless I played with the gas pedal. When it started, I could rev the engine and it'd be smooth; when I let off the gas, the car would want to stall again. I thought it had something to do with heat, so I went inside, figuring the car would cool off.

I came back out- same deal; car wouldn't start unless I played with the gas, and it had a rough/low idle. As I drove, it'd be fine, but when I came to a stop, I started to two-foot it (to keep my power brakes). When I'd leave the stop sign, the car would drive normally- smooth, not missing, powerful, etc. After driving with two feet for another two stop signs, the problem's gone.

All I can figure is that something happened with the brake booster when I slammed on the brakes. I remember someone on here talking about a replaceable brake booster check valve... could this have caused it?

Also, lately, unless my hearing's gotten better (doubtful- too much loud music), it seems that I'm hearing a "whoosh" every time the car's at low RPM's and I hit the brakes. I don't think it was there before, because it's starting to get annoying. The whoosh won't be there if I'm driving, but if I'm in stop in go traffic, or in a parking lot, I hear it. Is this "whoosh" noise a sign of anything going bad? I just don't remember the sound before... and with what happened last night, it makes me wonder if the two are connected.

Thanks!


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-Tom P (Hot rodded 1986 Firebird 2.8l)

nicmike85

The whoosh sound is a vaccume leak from your booster. I believe you have to replace the power booster. When you hit the brakes it creates a vaccume leak, kills the motor and you don't have power assist without vaccume.

SC88

Before changing the booster make sure that the vaccum hose to the booster is not dry rotted or cracked or burnt.

ViciousZ

iTrader: (1)

I'll bet there's something more wrong than the booster or checkvalve. You said once you parked it, it idled bad, stalled, and was hard to start. That doesn't sound like the booster, especially the hard to start part of it. Maybe a vacuum leak in the hose could cause it, but if your car is fuel injected, it wouldn't run bad enough to stall it. Maybe when you start to come to a stop, your engine is already idleing so low that there's not enough vacuum for the booster to pull. My suggestion is that if it happens again, unplug the booster line from the manifold and put a plug over it. If your car is still idling bad with the booster unplugged, then your problem lies elsewhere. Of course the 'whoosh' sound does sound like the booster.

TomP

A few times, I've left the booster hose off (usually when playing with the distributor), and when I went to start the car, it would run poorly, barely idle, stall, etc- so the fuel injection I have isn't able to compensate. If the "whoosh" noise is typical of a bad booster, looks like I'm up $hit's creek, then. But that's a damn good idea, Vicious, I'll plug the vacuum hose next time and see what happens. The car's been fine since that incident; I tried to re-create it last night at my house by slamming on the brakes, but the car ran fine.

Would brake fluid leaking into the booster ruin it?

I ask because I think on that "slammed the brakes" incident, I ripped the rear seal on the master cylinder. I was looking at the booster last night, before I left work, and noticed something disturbing. Right where the master cylinder meets the booster was a run-mark- and it was brake fluid. The m/c reservoir nearest the firewall (for front brakes) was at it's minimum mark, yet, the frontmost m/c reservoir was full.

I drove home slowly; and popped the hood when I got there. There was a second run mark of brake fluid, with a drip hanging off the edge of the bottom of the booster. I filled the m/c reservoir, and wiped off the run marks. I didn't spill any brake fluid anywhere, and the cap came off "clean".

I hopped in the car, hit the brake pedal a few times, and looked at the m/c-to-booster area. There was a new run-mark, with a drip.

So if brake fluid could kill a booster...

Thanks guys! I appreciate it; college is starting up again in a few weeks, and I better get this car in tip-top shape for it.



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-Tom P (Hot rodded 1986 Firebird 2.8l)

ViciousZ

iTrader: (1)

Yeah, brake fluid will definitely ruin the booster, so get that m/c off of there fast. The m/c is pretty cheap to replace: $15-20 for a reman, $40 for a brand new one. But the vacuum booster is gonna cost you a lot more than that if you ruin it. Maybe if you change the m/c now it won't be too late for the booster.

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91 Z28
Come see The Vicious...

TomP

Yipe... dammit, and I have no time. I'm working this weekend, and need to work straight until Wednesday night (important yearly stuff going on). Damn. I suppose I could do this in one night... man, I hate brake fluid. Thanks again for the info!!

Oh- and I'm going to avoid buying a rebuilt m/c at all costs this time (except buying new, of course). I swapped from rear drums to rear discs, and got myself the correct J65 master cylinder. I had no brakes at all- and got the brake warning light- after repeated bleeding of the m/c. Turned out it was a bad unit... probably leaking internally. With advice from this board, I turned it in for another rebuilt one, and got my brakes back the next day. I have a sneaky feeling that these rebuilt m/c's are sitting in a warehouse somewhere, in the heat, and the seals are drying up. So if I rebuild it myself, I know it's done right... (see my new message about pre-bleeding the m/c)

Thanks again dude!


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-Tom P (Hot rodded 1986 Firebird 2.8l)

PunXsRock

I just replaced my booster this afternoon. I know the story. It's your booster dude. I know, it's hard as hell to press down on the brakes. That swooshing sound is air escaping from the booster. Trust me, it's a bitch to get the top right and left bolt off. I'd advise bleeding your brakes afterwards too. I noticed a great improvement in braking.



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Manny

84 Trans Am