Rear brakes lock up need help


Old 10-13-02, 06:16 PM
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Question Rear brakes lock up need help

Hi I'm new to the board and of coarse I need some help,
I have a 1985 3/4 ton Chevy 4x4. The other day I took the truck for a drive and the brakes worked great. Today I get in to move it a couple feet and when I pressed on the break the rear brakes locked up. I'm not sure if they both did but I saw a skid mark for the left rear. It seems like the rears are very touchy when you put on the breaks, Peddel pressure seems ok. My brakes are power if it matters. If you guy's have some idea's for me I would appreciate it. Thanks in advance
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Old 10-13-02, 09:14 PM
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It sounds like your proportioning valve needs replaced, or adjusted if it's an adjustable type (probably not though). Your proportioning valve controls the amount of pressure between the front and rear brakes, by the way your rear brakes should lock up before your fronts. That way your steering should remain unaffected, for safety issues.

I'd say it's a replace and bleed deal and you should be back in business. It should be a block with some brake lines coming in and out, usually near the rear axle.

Shoot me an e-mail if you have any more questions, maybe I can point you in the right direction.
Old 10-14-02, 03:44 AM
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May be fluid related, could also be mechanical. Might have a broken piece of hardware inside, a stuck brake shoe, etc, etc.

Take the wheels off and have a look. Replace any questionable parts (friction, hardware, wheel cylinders, etc).

It could also be the proportion valve as well.
Old 10-14-02, 07:43 AM
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Thanks guy's I'm hoping to take at least the drivers rear off today because I know that ones locking up for sure. I did bleed the rears last night and it didnt help. It's just wierd that it goes from working very normal one day to locking the next. Thanks
Old 10-14-02, 08:38 AM
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I would check them both, the one that is grabbing may be the only one working back there. Look very close for leaking cylinders. If it were me I would put new brakes on the back. If you can do it yourself the cost is very low. I think the brake light would come on if it is the valve. Maybe not.
Old 10-14-02, 10:42 AM
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Well, I just went for a ride, by the end of my ally they started working properly. As you guy's suspected there's more than likely some things that need replacement in the rear brakes. I wont be able to get to it till next weekend. Thanks for the input, I suppose I'll just replace everything while I'm in there.
Old 10-15-02, 07:49 AM
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This post grabbed my attention. I have a '98 GMC 4x4 fullsize that has done this since new--but only when very cold out and only when you are just starting out then it quits. I also, noticed that our fleet of work trucks 2000 and newer 2x4 f150's also do this on occasion. I wouldn't worry about it unless it became very frequent or dangerous.
Old 10-15-02, 10:17 AM
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Dang Redneck,
I think you may have hit it on the head. It has been colder here latey in Wisconsin and sice it happened to me that one day the brakes have been working like a champ since then. I'm still going to check them out as soon as I get the chance (hopefully this coming weekend). If I find anything or not I'll make sure a report my findings either way. Thanks
Old 10-17-02, 01:29 PM
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Yep, we get it sometimes, I am in Michigan and it usually happens in the winter mornings--then works ok after first few blocks--like I said I bought my truck new--and never took it back under warranty.

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