Howdy, I am having problems with my 96 silverado 5.0L. I had just replaced the rear brakes shoes and wheel cylinders on the both sides. I had noticed the brake fluid was blackish in color, obviously no good. I sucked out the fluid out of the MC with a syringe, wiped it clean and put in new fluid in intentions on the new fluid pushing out the bad as I bleed. I went to bleed the brakes and there is no fluid getting to the left rear wheel and very little to the right rear wheel. No obvious leaks in the lines, master cylinder has slight seepage near the rubber grommets on reservoir. Any ideas, a clog or restriction in the system, bad valve or MC? Also, it appears there is no fluid leaving the reservoir when pedal is pumped. I'm going out now to see if front brakes are working.

 

I would start by disconnecting the main steel brake line going to the flex line that goes to the T splitter on the rear axle.
Check the flow.
If it flows well on the main rear steel line? I would replace the rear flex line and compress L and R wheel cylinders at the same time (2 People) to create a back wash of fluid to clean the T connection.

 

Ok I disconnected the main Line from the flex and nothing but a few drips. Any idea what I should check next?

 

With the rear main supply line disconnected... Get somebody to step on the brake peddle so you can see if you have good strong flow. Good flow will tell you your master is fine and that your restriction is at the rear of the truck.

 

Ditto to what In2Trux said. Pop the line off the master that heads to the back of the truck and press the brakes and see if fluid comes out of the master. You'll probably need to bench bleed the master after you do this though. If you're master is good, you'll see a jet of fluid shoot out of the hole. If your master is bad, no fluid will shoot out, or very little.

Thankfully, at this point, the master is already 75% removed from the truck

P.S: I have the exact same identical truck. A '96 with a 5.0L 4x4, and my rear brake cylinders also have some seepage. When it warms up a bit I'll be redoing my rear brakes as well, probably replace the front calipers too.

 

Thanks for the help but yes when I disconnected the line from the flex line on the rear I did have a friend pump the brake and had nothing but a few drips come out. I guess I'm ganna try disconnecting the line from the master that goes to the back. I am a bit nervous of this of doing this because I've never bled a MC let alone bench bleed one. Sorry if I sound like a novice but I went to school for diesel work with air brakes. Is there and actual bench bleeder I have to use to get this done?

 

I just checked it out and the steel line going from the rear goes directly into the abs it looks like not into the master cylinder. But I disconnected the two lines coming off master cylinder one at a time and both had good flow. I'm going to bench bleed master cylinder also it seems simple. So does this mean there is air in the abs or in the line? A restriction in either possibly? Also I just remembered the abs light is on but it has been on for a while.

 

It could very well be a problem with the ABS module then. The ABS has a small tank inside of the module that stores brake fluid pressure.

The way ABS works is it controls wheel lockup during breaking. For example, if your passenger front tire hits ice while you're breaking, the wheel will lock up momentarily because of the extreme lack of friction between the tire and the road. The ABS module will release brake fluid pressure from that one brake caliper until the wheel begins to spin again.

There are solenoids inside of the ABS module that control how the fluid moves around in the system. These solenoids are "normally open" or when in their natural state, allow brake fluid to pass through the ABS module like normal. If one of these solenoids goes bad, it could be that your rear bake fluid is being diverted into the pressure container. On your truck, your ABS is a three channel system, which is a left front tire, right front tire, and rear end system. Meaning, because you have drum brakes, when the rear tires stop spinning momentarily on ice, all the pressure that goes to both rear wheel cylinders is released into the pressure container, versus one wheel at a time.

So, TLDR: Get your ABS codes read, could possibly be related, or could indicate a bad ABS solenoid block/ABS module. The fluid you got out of the master indicates that you have a good master cylinder.

As long as you understand how a basic bench bleed is supposed to be done, you should be alright. Take tubes from the master cylinder outlet ports, put them into the reservoir, fill with fluid and work the brakes slowly several times until the bubbles are gone. You might need to buy a kit that has leak free fittings that help keep the fluid where it needs to go.

 

Thanks a bunch I'm ganna look into the abs module. i was hoping it wouldn't come down to that it sounds exspensive. I'm ganna try and rule out a restriction in the line going along the frame rail, and then get someone here with a abs reader when he gets off work

 

Yup that's a great plan. Next what you could do is take the line off of the ABS module that goes to the rear of the truck, and take a rubber tip air gun and an air regulator and run some compressed air through that rear line. Crack the bleeders open first, and try to blow the line clear. I personally wouldn't go with more than 10 PSI at first, maybe less. Plus if you do have a restriction, it could likely dislodge and get stuck somewhere. So maybe unscrew the lines from your wheel cylinders and then try the compressed air.

Hopefully it isn't anything ABS related.