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10-06-2014, 09:41 AM | #1 | |
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'89 C2500 rear brakes lock up
Hey fellas,
I just picked up a C2500 with the 350 and 250,000 miles on it. Looks like the brakes were redone in the past few years. The problem is, whenever you stomp on the brakes, the rears lock up immediately. It will spin out easily in the rain and squeal like hell on dry pavement, so slow controlled stops are necessary. I'm not sure what could be causing this. Before I go tearing apart the system, does this sound familiair to anybody? Whoever replaced lines to the MC didn't coil them underneath the MC, is that an issue? Thanks and sorry for the noob question. -Alex
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10-06-2014, 03:58 PM | #2 | |
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Re: '89 C2500 rear brakes lock up
First thing I would check would be if the axle seals are leaking onto the brake shoes. No the coiling will not affect the braking.
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10-06-2014, 03:59 PM | #3 | ||
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Re: '89 C2500 rear brakes lock up
Quote:
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10-06-2014, 08:42 PM | #4 | ||
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Re: '89 C2500 rear brakes lock up
Quote:
While you're in there, assure that the primary shoe is forward, and the secondary shoe is to the rear. Verify that the star-wheel adjuster isn't damaged or seized--and that the shoes are therefore properly adjusted. If the bearings are defective, the axle shafts will be defective, too. The bearings ride directly on the axle shafts. Thanks, GM. Wonderful engineering.
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10-06-2014, 09:49 PM | #5 | ||
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Re: '89 C2500 rear brakes lock up
Quote:
One can get offset replacement bearings that ride on the remaining undamaged part of the axle shaft. |
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10-07-2014, 12:01 AM | #6 | ||
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Re: '89 C2500 rear brakes lock up
Quote:
Semi-floating just means the axle shaft is load-bearing at the outer end, as opposed to a full-floating axle where the hub carries the weight and the axle shaft does nothing but provide torque to the hub. Yes, I have a set of those on my El Camino. The downside is that the grooved, worn part of the axle shaft becomes a stress-riser. If it's bad enough, the axle could eventually crack there. Fine for Granny, not so great for a performance application.
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10-07-2014, 07:49 AM | #7 | ||
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Re: '89 C2500 rear brakes lock up
Quote:
for the most part this type set up works for several hundred K miles ,but this is with the axle not being stressed out... like easy driving. hard driving bad road will kill this type design .. GM did a poor job with this ... |
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10-13-2014, 03:42 PM | #8 | |
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Re: '89 C2500 rear brakes lock up
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10-13-2014, 04:43 PM | #9 | |
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Re: '89 C2500 rear brakes lock up
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10-13-2014, 05:48 PM | #10 | ||
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Re: '89 C2500 rear brakes lock up
Quote:
Does the "RED" brake light come on when cranking the motor?
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10-13-2014, 11:01 PM | #11 | |
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Re: '89 C2500 rear brakes lock up
A proportioning valve does not activate until the pressure is quite high. Therefore, no proportioning valve action at typical mild- to medium-braking.
There's nothing in the master cylinder that can provide excess pressure to the rear brakes. Might be that the front brakes are somehow weak, leading to over-use of the rears.
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10-14-2014, 08:24 AM | #12 | ||
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Re: '89 C2500 rear brakes lock up
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with bleeding the front brakes , this should show , open the bleed screw place hose on the fitting and have a helper hit the brakes see how the brake fluid flows... with bleeder screw open use C clamp push back caliper see what the brake fluid looks like dirty/air/discolored >>>>. always use a clear tubing so you can see what the brake fluid looks like coming out the bleeder screw... |
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10-14-2014, 09:52 AM | #13 | ||
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Re: '89 C2500 rear brakes lock up
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10-14-2014, 10:02 PM | #14 | |||
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Re: '89 C2500 rear brakes lock up
Quote:
Quote:
Which leads into your last quote
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10-15-2014, 01:21 AM | #15 | |||
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Re: '89 C2500 rear brakes lock up
Quote:
If "P/Valve" is short for "proportioning valve", keep in mind that the proportioning valve has NOTHING to do with front brake operation, which is controlled in part by the metering (holdoff) valve. The safety switch is between the two (front and rear) hydraulic circuits. Quote:
If there's a failure in the secondary circuit, the primary circuit can still generate pressure when the secondary piston bottoms-out. Whichever circuit fails, creates additional pedal travel to get the other circuit to generate pressure. Having one hydraulic circuit fail cannot induce extra pressure into the other, but the brake pedal will probably be pressed harder to get two brakes to do the work of four; especially if it's the front brakes that fail.
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