Author Topic: Grabby brakes when first starting truck  (Read 891 times)

Offline robosmurf

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Grabby brakes when first starting truck
« on: November 17, 2018, 04:24:07 PM »
I've got a 84 Chevy C20 camper special with 87 454 tbi. It's got the larger size brakes.  13" I think in the front and the one ton heavy duty rear end.

 Ever since I've had it the brakes have been grabby when the truck is cold. I press the pedals slowly then they will suddenly grab and lock up.

I've done a little work to the brakes since then. I removed the load sensing valve that seemed completely frozen up then gravity bled the system twice but still the same problem.

I've run through the service manual steps to trouble shoot the booster and everything seems to function properly.

Any tips on what else to check out?

Should I swap the old metal body master cylinder for a newer one?

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84 c20 Camper Special
454ci with TBI

Offline VileZambonie

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Re: Grabby brakes when first starting truck
« Reply #1 on: November 17, 2018, 05:49:25 PM »
Vacuum or hydro?
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Offline 75gmck25

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Re: Grabby brakes when first starting truck
« Reply #2 on: November 18, 2018, 07:06:59 AM »
I have the same 13" drums on my '75 K20 Camper Special, and the rears are grabby whenever the weather is cold and humid.  However, it burns off after about two stops, and I then quit looking like an idiot who locks up the brakes at every stop sign.  The other issue with these pads is that if I leave the parking brake set for a long period of time, sometimes it does not want to break loose when I first drive forward, so I have to rock back and forth a couple of times to get it to roll freely. 

I replaced a leaking master cylinder and the front pads last year and it had no effect on the lockup problems.

I assume there is moisture that gets in the lining, and the material gets very grabby when damp.  I had the rears done by a shop several years ago, and I don't know what brake shoes they used.  Its such a PIA to get them apart with a 14 bolt FF that I don't really want to pull the drums. 

My brakes work fine otherwise, so I've just decided that its infrequent enough that I can live with it.   However, I'd be interested if you find a better solution.

Bruce

Offline robosmurf

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Re: Grabby brakes when first starting truck
« Reply #3 on: November 18, 2018, 10:09:59 AM »
Vacuum or hydro?
Vacuum

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84 c20 Camper Special
454ci with TBI

Offline zieg85

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Re: Grabby brakes when first starting truck
« Reply #4 on: November 18, 2018, 12:44:32 PM »
same thing on my C30 with hydro.  Never had a pedal that is so high.  I barely drive mine so I am thinking rusty rotors and drums.  It is a touchy brake pedal though
1985 C30 Custom Deluxe Ext. cab 5.7L TH400 3.21 
1985 C20 Scottsdale 7.4L 4 speed 3.21
1986 C10 under construction
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Offline robosmurf

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Re: Grabby brakes when first starting truck
« Reply #5 on: November 18, 2018, 06:19:09 PM »
So this weekend I put new front brakes on. They were both down to the squeelers.

I also replaced the brake booster vacuum check valve. I don't know if it was bad. There was still vacuum after sitting for a week.

Anyway I went to go bed in my brakes and there was no grab when I went to drive it. Maybe there was too much travel in the front brakes since they were almost gone?

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84 c20 Camper Special
454ci with TBI