Bad brake booster?

[zahc]

The '96 Tahoe I bought recently hasn't had good brakes since I bought it. If you just need to slow down slowly in normal mosy-around driving, you don't really notice a problem except the pedal is mushy. But if you need to stop quickly, you slam on the brakes, and nothing happens, and then you go "OMGWTFBBQITSNOTSTOPPING" but right about that time the pedal sinks and the power brakes kick in and it starts stopping. It acts exactly like my motorcycle used to when the brakes were wet and needed to spin a few rotations to get dried out, and then start working. Only it does it every time. They actually grab very well...you can slide all 4 wheels...but only after coasting too far first. My wife gets in the truck and most of her normal stops turn into extra-hard stops because "it didn't feel like it was going to stop".

I figured when I bought it that they just needed bled, since the pedal felt a bit extra-mushy (this vintage chevy truck always has mushy pedals IME). I bled them. Then I thought it was glazed rotors or someone put ceramic pads that needed to warm up or something, but I just put Napa Safety Stop pads on it and had the rotors turned and it still is doing it. As long as I keep a good following distance and nobody jumps out in front of me I'll be fine, but I would really like to get it fixed.

I'm thinking maybe it's a bad brake booster, since when you hit the pedal it feels hard at first but then it sinks and starts stopping, like it's taking a second for the power brakes to kick in. Kind of like if you push the brakes and then start the motor, how the pedal sinks when the vacuum kicks in.

[Brad Johnson]

Vacuum booster or Hydra-Boost?

Brad

[zahc]

It's a 2wd gas so it has a normal vacuum booster. I've never heard of one going bad but I don't know what else it could be. I'm not sure how big of a job it is to change either.

[Jim147]

Pump brakes up with key off and hold down. Start engine. Pedal should immediately drop.

Does it idle strange when you step on the brake pedal?

jim

[zahc]

Pump brakes up with key off and hold down. Start engine. Pedal should immediately drop.

It does. The problem is, it acts the same way when I make a hard stop. When I first hit the brakes, the pedal feels hard and nothing happens, but within a half second, the pedal sinks and the brakes start to work. I can lock up all 4 wheels, but I CANNOT lock up all 4 wheels as soon as I hit the pedal. There is a lag.

Does it idle strange when you step on the brake pedal?

To be honest it doesn't idle the greatest anyway. I never noticed if it does it when I step on the brake pedal or not. I put new plugs, wires, distributor cap and rotor on it trying to fix the sketchy idle, but it didn't help much.

I found these people while googling. They say they work with my year of truck; maybe they have a kit for my truck.  If I have to buy a new brake booster and go to the trouble of taking it off I might look into it. I don't want to spend a lot of money but driving in Dallas traffic requires good stoppers.

http://www.hydratechbraking.com/Hydratech/brakeunits.html#TXTOBJ7D926717302BC91

[41magsnub]

I had those exact same symptoms in my 95 GMC S1500 and it was a cracked master cylinder.

[zahc]

Didn't you have a leak somewhere, if it was cracked? I don't really see a leak on mine, except the master cylinder reservoir has constantly popped loose in those fiddly rubber washer things and leaked everywhere, so I'm not sure if I could even tell.

[41magsnub]

Nope, it was a hairline crack.  All it did was open up slightly and lose some pressure when I stood on the brakes.  I never did see any kind of a leak.  Same symptoms as you, I would step on the brakes and it would slow down, but when I panic braked it did not seem like it was doing anything more though it would pick up and brake hard after a second.  I drove it for years that way thinking it was normal until I drove my Dad's truck which was the exact same thing but a 98.  First time I touched the brakes as I would in mine it scared the crap out of me..  way stronger.  After the master cylinder mine braked the same way.

[zahc]

Excellent news then, master cylinders aren't even that expensive. Although I'm not sure how hard they are to install (I'm garageless so I still do everything in my apartment parking lot).

[Phyphor]

Getting the MS off shouldn't be too hard, just make sure you have the proper wrenches for the line fittings!  You do NOT want to strip those nuts out.......


*ahem* not that I'd know or anything... *whistles*

[Tallpine]

Might check the vacuum booster line first 

[Hawkmoon]

I assume it has ABS? If so, my bet is that the problem is the ABS manifold. Don't remember where I saw it, but awhile back I read a report by someone who cured all his brake problems by simply eliminating the ABS system with a home-made by-pass manifold. IIRC, it was in a Tahoe.

[zahc]

Well I certainly ain't scared to eliminate the ABS. Up north everyone pulls the ABS fuse in these trucks so that they will stop when it gets slippery out. I like the idea behind ABS, just don't buy into most implementations. Thing is, if I eliminate the ABS module, I assume that's going to make my ABS light come on; does anyone know if that will make my car fail TX inspection?

So right now it could be either a MS or the ABS system mucking things up. The truck is actually stopping better with the new pads, but the system lag problem remains.

[Zardozimo Oprah Bannedalas]

does anyone know if that will make my car fail TX inspection?

Very much doubt it. All they tested on mine was the horn and the various lights (headlights, brake lights, blinkers).

[sanglant]

water in the brake lines acts like that to, so you might want to try flushing it first.



fine with light pressure, and the water boils at high pressure.

edit: if it's been more than a month since you bleed the lines. it might just be water getting in some where. think condensation or a small hole. i would try bleeding again unless it's just been a couple weeks. could be the crimp connectors at the shocks. ah and does it have metal brake lines(at the wheels) if so i would go back to rubber.

[zahc]

I've bled them like crazy. All the fluid is brand new.

It still has the original equipment rubber hoses going from the frame to the axles, and I've heard that those can cause strange brake problems, so I was thinking about trying new hoses. Maybe I will put new ones on when I put the new master cylinder on, just so I can combine brake-bleedings.

[sanglant]

it sounds like my last set of brake pads was acting. here are some links if they keep doing it.(after you've tried everything else[more aggressive pads make driving the car "different"])

OMG, the best (sport) brake wright up on the net has been taken down. (posting the link hopping someone has it saved)

this is close, but nowhere near as easy to read/understand.(this is on how to choose pad material, it's what was wrong with my car the site has links for the rest of brake information)

these are the brake pads, i went with the last time on my obs, they work well. cold there just like the stock pads, but when the old pads would start fading. the new set are starting to grip even better. next set i would like to try some ebc reds.

[Boomhauer]

Thing is, if I eliminate the ABS module, I assume that's going to make my ABS light come on; does anyone know if that will make my car fail TX inspection?

My '99 Silverado's ABS is completely disconnected and the car's computer doesn't even notice that it's gone.


Chevy ABS units are always wonky, or go wonky in short order...because it's rediculously expensive to fix the ABS module when it goes nuts, it's far easier/cheaper to disable it.

[sanglant]

you might want to check your insurance to see if there's a discount for having abs, i bet they wouldn't want to pay out if you have a wreck and are getting the discount and have the abs system disabled.

[Hawkmoon]

After searching Google with no success, I accidentally found the write-up I had in mind -- right here on APS

http://www.armedpolitesociety.com/index.php?topic=23878.0

[zahc]

I replaced the master cylinder and it's no different. Now I think that it's a restriction in the lines, because that's consistent with the pedal being hard to press when you press it fast but the brakes working fine when you apply them gradually. I unplugged the ABS module and like Avenger29, the truck doesn't seem to care...the ABS idiot light on the dash just doesn't flash when I first turn the key on. I'm going to remove the ABS module, and if that doesn't fix it, I'll put new hoses on.

[Declaration Day]

The restriction may be in the ABS module.  Remove it and do the modification I did.  If you have any questions you can call me @248-212-8549.

[Brad Johnson]

You can also have the ABS module flushed.  Has to be done at the dealer because the module must be cycled during the flush.

Brad

[zahc]

The ABS module has been yanked. It looks much better under my hood without that 15lbs of junk on the fender. I'm currently building a pressure-bleeder out of old paintball parts, because I'm afraid to ask my wife to help me bleed my brakes again, and this time there's going to be a lot of air to get out.

[cassandra and sara's daddy]

I'm afraid to ask my wife to help me bleed my brakes again,


i understand only too well