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Old 08-09-2019, 02:31 PM
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Intermitent Brake pedal feel

Not a hot rod, but while looking for a solution this problem is getting worse. 2000 chevy 3500 Express (van) just over the 100,000 mile mark.
For the first 97,000 miles had no brake problems. Had a definite feel of how the pedal normally is. One day instead of the pedal going about 1/3 way down to stop, I hardly touch it and the fronts lock up in the stones. The pedal is high, has almost no travel. It went away and the pedal and brakes seem normal again. Over and over at no apparent time, speed, or temperature, just a little touch of the pedal results in very hard braking. Sometimes (at a stop) pressing it harder, the pedal will suddenly drop to where it normally should be and the brakes work great. When pressing hard on the pedal and it drops, you can hear a weird noise that I can't quite describe. Somewhere online I had found the same symptoms and it said it was the hydro boost (I can't find the website again). I replaced the hydro boost. It still did the same thing. I replaced the hydro boost again, along with the master cylinder and the problem still persists.


It's not so bad having a high pedal that is very sensitive, but when you never know when it's going to suddenly drop a couple inches and act "normal" is the scary part.

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Old 08-10-2019, 10:35 AM
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That thing is new enough I'd think a code reader could be used to get a clue as to where to look.

That is probably to only real advantage of the computer controlled and monitored system found in today heaps.

Shot gunning, usually followed shortly after surfing the web. Can get expensive really fast. Where as grabbing data from the on board computer. Might cost 50-100 bucks, do not know price ranges.

But for sure not talking about the you fix it in the parking lot part store readers.

Could be worth while, maybe look around for a shop that offers such a service. Sure it will be an open door for them to make the repair.

But I would think an honest shop would or could offer a customer. A data dump for one price, and knock it off if they get the job. That way they recover the hardware and application (software) cost. A dealer might even offer such service?

That would work to your advantage.
1 knowing what is mot likely the problem
2 with the knowledge gained, decide if it is something you want to tackle.

Nothing wrong with information seen on the web. But one needs to be able to sort thru the large amounts of chaff.
Pep

Last edited by rip-tide; 08-10-2019 at 10:44 AM.
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Old 08-10-2019, 05:13 PM
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I forgot to say that I hooked up my cheap scanner and it showed nothing. Then I had a local parts store parking lot deal (like you like so much) scan it with a better scanner that he says does pick up anti lock brake codes and it didn't find anything. I talked to my mechanic friend with a really good and expensive scanner and he didn't mention it could be scanned, but then he is 600 miles away. I know his scanner cost in the thousands and just to keep it up to date costs a good bit every month. Even though he can't scan it, I'll ask him if his scanner would possibly find something like that.

Oh, by the way, the brake warning light in the dash does not go on. Come to think of it, I'll have to turn the key and make sure the bulb works!

The anti lock brakes seem to work fine, I've tested them going down my steep driveway when it's wet.

I'll also start looking for a garage with a good scanner. It costs what it costs. Also I may ask at a chevy dealer to see if I can get any info out of them, free or at cost. There really isn't anything that I know of besides the booster, the master cylinder, and the anti-lock unit that could do it.
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Old 08-10-2019, 06:23 PM
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If the ABS light does not go on, there are no codes to read. Most of the problems with the brake system will not set a code. Check for bad M/C, bad booster, bad flex lines, or bad caliper.
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Old 08-11-2019, 07:51 AM
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Quote:
Originally Posted by joe_padavano View Post
If the ABS light does not go on, there are no codes to read. Most of the problems with the brake system will not set a code. Check for bad M/C, bad booster, bad flex lines, or bad caliper.

Thanks. Already replaced the master cylinder and the booster. I'll check the calipers for sticking. What could the flex line do to give it that symptom?
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Old 08-11-2019, 08:09 AM
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The flex lines get weak and expand or retract.
I just replaced a stuck Caliper with symptoms like yours on a 94. Not a hydro boost though.
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Old 08-11-2019, 10:15 AM
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I just came in from checking the calipers. They seemed as if they were not sticking but I removed them anyway and cleaned off the surfaces that must slide in and out. I put a thin smear of caliper grease on the same surfaces and the guide pins. Tested in the driveway and still the same. Hoses looked good. I've heard of hoses collapsing and acting like a check valve, but I never get what feels like a dragging brake, and the pads are wearing evenly. I swear it feels like the hydro boost unit but I replaced it twice.

Just now before posting this I was searching for internal diagrams of the hydro boost and stumbled upon this as a response in a truck forum:

"Looked in the 87 service manual. No symptom of excessive pedal travel in the hydro boost section. Only ones they listed were as follows:
1. Slow pedal return
2. Grabby brakes
3. Accumulator leak-down"


I do believe sometimes the pedal is slower to return. And it sure as hell has "grabby brakes".
I got my replacement unit from a O'Rieleys, I'm thinking of instead of getting the brand they have on the shelf, to order one from a different company. Or I suppose I could get one from GM?
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