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Old October 10th, 2006, 07:51 PM   #1
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Default 90 chevy 1/2 ton brake issues

ok guys I got a 90 chevy half ton 4x4 5.7 with about 130K on the ticker. ever since the day my dad bought it (in 92) he has had somewhat spongey brakes. they have gotten progressivly worse over the years.

well I have owned it for over a year now and I am sick of it. Last year I replaced the front calipers and I just replaced the rear lines, shoes and wheel cylinders. I got a good bleed out of all of the brakes and the brakes are still soft I can literally stand on the brakes and the truck will come to a slow gentle stop. the brakes will not lock up!

what else could it be? were these trucks known for something that I cant find? I doubt it is the booster or the master cylinder (althought I could be wrong) could it be the proportioning valve?

Please....any help here would be greatly appreciated!
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Old October 10th, 2006, 11:15 PM   #2
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I had the same issue went thru everything even put 3 big bottles of brake fluid thru the system. I was told that the valve sticks in the prop valve. Then one day I had to make a panic stop and jammed the brakes with both feet. They have been great ever since.
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Old October 10th, 2006, 11:47 PM   #3
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Prop valves are a PITA to bleed if they ever get air in them. Also you may have bad seals in your master, OR your brake pedal may need to be adjusted. How much free play does it have before you feel pressure?
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Old October 10th, 2006, 11:59 PM   #4
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There is a TSB to replace the brake booster. Part number for this booster is 18012114.
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Old October 11th, 2006, 06:40 AM   #5
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I had the same issue went thru everything even put 3 big bottles of brake fluid thru the system. I was told that the valve sticks in the prop valve. Then one day I had to make a panic stop and jammed the brakes with both feet. They have been great ever since.
I have jammed on the brakes many a time and the truck still comes to a nice smooth stop, and it does not help. Last week when I was driving it to the poker run, there was 1 stop that I seemed to have really good brakes, so that leads me to believe there is something sticking.


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Prop valves are a PITA to bleed if they ever get air in them. Also you may have bad seals in your master, OR your brake pedal may need to be adjusted. How much free play does it have before you feel pressure?
I feel pressure pretty much right away, but it does not start to get firm until about 1/2 way to the floor. Then pressure is consistent all the way to the floor. It never gets completely hard, if I keep pushing it will go all the way to the floor.

as for adjusting the pedal, it has never been messed with. my dad has always replaced the pads/shoes. the only time it has been in the shop for brake related issues is when the brake lines rusted out and they needed to be replaced.

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There is a TSB to replace the brake booster. Part number for this booster is 18012114.
thanks muddypaws, do you know if this will fix the soft pedal issue?



thanks for your input guys, I will continue to work on it
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Old October 11th, 2006, 06:43 AM   #6
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The '98 cevy I just bought has he same issue. After some 'net reading I found out that if there has been any brake work done in the past (mine had a brake booster replaced) that the ABS sometimes needs to be reset. What was suggested was performing a hard stop on a slick type surface. I did the hard stop thing 4 times on some wet grass, the pedal is firmer, but it's still not where I'd like it to be.
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Old October 11th, 2006, 07:14 AM   #7
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my p/u does not have ABS, thanks for the input though
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Old October 11th, 2006, 01:51 PM   #8
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may be air in the master cylinder. bleeding the brakes sometimes does not get all of the air out of the master cylinder. try to bench bleed the master cylinder.
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Old October 11th, 2006, 07:49 PM   #9
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Later chevy trucks have a rep of spongy brakes but they usually will still stop the truck fine. I didnt think this would apply to earlier c/k trucks. Ive heard the only way fix brakes on the newer silverado/sierra was to replace the rubber hoses with aftermarket braided... but like I said the brakes still worked fine, just didnt "feel" right.


If you can get the pedal to the floor and theres still no brakes I doubt it is the booster.


Personally I have never seen a master cylinder cause your symptoms but I couldnt rule it out.


Still sounds like air in the system somewhere to me, I know you said youve bled them... but if I did a brake job and felt what your describing I would have kept bleeding them till I found that last bastard air bubble.

That or something with the prop. valve but Ive never seen that one either.
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Old October 11th, 2006, 08:00 PM   #10
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well I think I know whats wrong. you have old style super metalic pads. you need to get rid of them and by the cheapies. I worked at the chevy dealer doing these brake systems and they had terrible trouble with the factory style pads when they got rusty. they would get so hard they didn't grip the rotor and you couldn't get the truck to stop no matter what you did. by the way all the trucks from back then had "rwal: (rear wheel anti Lock) and they have like 4 major codes to look for , but they ussally get set from spinning the tires in the snow and hitting your brakes. unhook the battery and clear the codes and see if it resets.

by the way do some revese backing and stab the brakes real hard while doing so. it makes the auto adjusters work and takes out any slack in the rear.
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Old October 11th, 2006, 08:09 PM   #11
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k, I do have the cheapy pads and shoes cuz the good ones eat the shit out of the rotors/drums

I replaced the MC tonight, bench bled it, and rebled the whole system until there was not a snowballs chance in hell that there was a bubble still in the system.

brakes are still a bit spongy, however now if I lightly touch the brakes (almost to prime them) let off for a second then apply them they work great! I can actually lock the brakes up now!

thanks everyone for your input, it is greatly appreciated!


p.s. on a side note. if you get brake fluid on a cigerette and then smoke it is that a bad thing? I am feeling rather light headed!
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Old October 12th, 2006, 11:01 AM   #12
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when my master went in my 78 i would have great breaks for some stops and almost nothing on others(and the pedal would go to the floor on the bad ones). it never leaked exterally so the fluid level was fine. I couldnt get it to pump up when it lost pressure either. if i remember right you take the cover off the master and if it squirts fluid wile you aply the brakes you have a bad seal. it is normal to have a squirt of fluid wile you release the brakes though. you'll need a friend to help you with that test. also my 93 had a really soft pedal but it would lock the front breaks up not the rear because of the abs.

didnt read the last post before writing this but ill leave it for the hell of it
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