94 Chevy gmt400 rear brake problems

[Dylan Fulkerson]

I have a 1994 Chevy Silverado 1500 4x4 5.7 auto trans with rear drum brakes. I have completely rebuilt my rear brakes and have they are getting fluid but I still am only stopping with my front brakes. I have ten adjusted where they should be also. And my brake light is on also. Any ideas? Thanks!

 

[RawbDidIt]

I have a 1994 Chevy Silverado 1500 4x4 5.7 auto trans with rear drum brakes. I have completely rebuilt my rear brakes and have they are getting fluid but I still am only stopping with my front brakes. I have ten adjusted where they should be also. And my brake light is on also. Any ideas? Thanks!

When you rebuilt, did you install new cylinders, or just new shoes and hardware? Did you bleed the lines? Pull the drum again and make sure there isn't fluid leaking from the cylinders. If properly adjusted, the parking brake should work, does it?

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[Dylan Fulkerson]

Yes I replaced the cylinders also. And yes I did bleed The lines several times. I have checked for leaking fluid a few times and nothing is leaking. No the parking brake does not work.

 

[RawbDidIt]

Yes I replaced the cylinders also. And yes I did bleed The lines several times. I have checked for leaking fluid a few times and nothing is leaking. No the parking brake does not work.

Well then, how did you adjust the brakes? The shoes should be just rubbing in the drum. Adjust the shoes after you've installed the drums. If that's what you did, then remove the drum and make sure you're getting pressure at the cylinder. Have a friend look while you press the brake pedal, or in a pinch, you can set up your phone to record a short video. If pressing the brakes doesn't move the drum cylinders there's either a leak (check the line and bleeder valves), or the master cylinder isn't directing pressure to the rear brakes. It's also possible that the brake booster isn't functioning correctly. Should be a vacuum line going to the brake booster, check to make sure it's in good shape, and check your vacuum as well. Without the vacuum system in good shape, it'll feel like you've got no brakes until the lost 25% or so of brake travel.

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[HotWheelsBurban]

Has the brake hose for the rear ever been replaced? 26 year old truck, it could be coming apart internally. That'll clog up the works. Also look at the the master cylinder

 

[Dylan Fulkerson]

Well then, how did you adjust the brakes? The shoes should be just rubbing in the drum. Adjust the shoes after you've installed the drums. If that's what you did, then remove the drum and make sure you're getting pressure at the cylinder. Have a friend look while you press the brake pedal, or in a pinch, you can set up your phone to record a short video. If pressing the brakes doesn't move the drum cylinders there's either a leak (check the line and bleeder valves), or the master cylinder isn't directing pressure to the rear brakes. It's also possible that the brake booster isn't functioning correctly. Should be a vacuum line going to the brake booster, check to make sure it's in good shape, and check your vacuum as well. Without the vacuum system in good shape, it'll feel like you've got no brakes until the lost 25% or so of brake travel.

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My brake pedal will almost be to the floor before I come to a complete stop.

 

[RawbDidIt]

My brake pedal will almost be to the floor before I come to a complete stop.

So the pressure is not getting there, the line as hotwheelsburban pointed out may not have a leak, but may be messed up internally and absorbing the pressure rather than directing it to the wheel cylinders. The vacuum system may be at fault, the booster, or the master cylinder. Look over the entire brake line while a buddy pumps the brakes. If that checks out, and there's no leak at the cylinder either, check vacuum. Not sure how to test master cylinder or brake booster. Does anybody else have some direction there?

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[Schurkey]

Is this the ****** leading/trailing shoe rear drum brakes?

If the park brake doesn't work, the shoes won't self-adjust. FIX THE PARK BRAKE, adjust the service brakes, and assure that the master cylinder isn't defective.

If the pedal is that low, and there's no air in the system, no external leaks, and the rear brakes don't work--the seal on the master cylinder piston that pressurizes the rear wheel cylinders is leaking. An alternative is that there's an air bubble in the system you haven't removed. Often, a person has to raise the rear of the vehicle so the master cylinder is tipped "down" in front, and then lightly push the brake pedal a few times to get all the air out of the master cylinder.

Two things light up the "Brake" light--the park brake pedal isn't fully retracted; or there's a pressure imbalance between front and rear brakes. Either one--or both--could be the problem in this case.

Has the brake hose for the rear ever been replaced? 26 year old truck, it could be coming apart internally. That'll clog up the works.

If the brake hose were plugged, the rear wheel cylinders wouldn't bleed, and the pedal would be HIGH not LOW.

The vacuum system may be at fault, the booster, ... check vacuum.

If the front brakes work, and the rear brakes dont...how is that a booster problem?

 

[RawbDidIt]

If the front brakes work, and the rear brakes dont...how is that a booster problem?[/QUOTE]

My understanding is that the booster is mainly (not exclusively) to help the rear brakes. Same pressure over smaller cylinder requiring greater movement in the rear as opposed to the front disc brakes which have a larger surface area for the braking system pressure to act on, and less distance to travel before engaging.

On a side note: If I'm wrong, be constructive and explain why, don't just jump on and make everybody trying to help and asking for help feel like an idiot.

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[Erik the Awful]

The brake booster is merely a vacuum diaphragm that aids in pushing on the brake pedal. That's all it does. Any division between the front and rear brakes happens at the proportioning valve, which is after the master cylinder.

Dylan, you have two tasks before you, and you need to do them in this order.
1) Adjust the rear brakes until the parking brake works, because when it works, you know you have the rear brakes adjusted properly.
2) Bleed the brakes again, from scratch, all of them. Start at the right rear, left rear, right front, left front - at least ten pumps each. Don't ever let the master cylinder run out of fluid. Back when I was a tech, we'd poke a small hole in the seal on a small bottle of fluid and just upend it in the reservoir. If the fluid level drops below the seal, air can get in and fluid will flow out into the master cylinder.

If you're doing it yourself, you can make a DIY one-man-bleeder. Note that there is a vent hole in the lid.
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EDIT: Man, that fluid looks nasty! That's what came out of my Stepside. I'll dump that fluid and put some fresh stuff in before I bleed another brake system.