Truck is a '75 W200. I had decent front brakes before I started this project, the truck stopped fine.

I replaced the rear brake lines, cylinders, and shoes. I bled the whole system and had very little brake pressure. It was just enough to keep the truck from rolling forward in gear. I bled the system again and now I got nothing at all. I can't get any more fluid out of the cylinders. When I step on the brake pedal it goes all the way to the floor with very little resistance, but it doesn't push any fluid out. What's going on?

Also, when I step on the break sometimes I hear a vacuum leak (a sucking noise). When I put the pedal to the floor the truck idles rougher. Could this be a sign of a bad booster/master cylinder? Please help, I'm sick of messing with this thing!

 

The booster and master are separate things that work together. If the booster was good before I doubt there is anything wrong now. Likewise with the master cylinder. Sounds like the system has air in it. When you bleed the wheel cylinders and nothing comes out does the fluid go down in the master reservoir? Did you possibly let the reservoir run dry while bleeding? Are you bleeding all 4 wheels in the correct order when you bleed? Could you have a leak at any of the fittings on the new lines? If you have access to a hand held vacuum source you can vacuum bleed the system.

 

At first the fluid was going down in the reservior, then it just stopped. If I stomp on the pedal I can see a little fluid squirt up into the reservior.

The rear half of the reservior MAY have run dry while bleeding, I'm not sure if my helper caught it in time. Come to think of it, I lost all pressure at the pedal when this happened. If it did run dry, obviously a lot of air got in the system. How do I get it out?

I start bleeding at the rear passenger wheel, then rear driver, front passenger, front driver. There is no leak in any of the fittings as far as I can see, and the only source of vacuum I have is a shop vac.

 

Don't use the shop vac. LOL
If the reservoir is allowed to run dry bleeding the brakes will take an unbelievable amount of peddle bleeding. Peddle bleeding intermittently moves small amounts of fluid with each pump. Vacuum bleeding and pressure bleeding create a constant flow of fluid that evacuates air much better. If you get feed up enough $30.00 will seem cheap. I would not be surprised if you use a full pint or more of fluid to get this right.

http://www.summitracing.com/parts/EQU-3660

 

Thanks SEAL, I ended up renting a vacuum pump from advance auto last night. Today I'll give it a try, wish me luck!

 

Ok, the vac pump didn't work worth a crap, it ended up breaking on me. I figured out my master cylinder was shot, so I bought a reman. Bench bled the new MC, hooked it up and bled the rest of the system.

Now when the truck is off there is good pressure at the pedal, but it does fade a little if I stand on it. With the truck running the pedal goes almost all the way to the floor with little brake engagement. It takes about 75ft to stop from 15mph. If I pump the brakes (as in, put it to the floor, and let it come ALL the way back up) on the second pump the brakes work great, I can stop on a dime (but the pedal does travel a long way in order to do this). Soooo...what now? Still air in the system?

 

ya. it sound like you still have air in the brake line. a bit more bleeding and you should get all the air out.

 

STILL can't get air out of the lines! What am I doing wrong? Here's my process...

Start with right rear, have a helper put pressure on brake pedal, open bleeder screw 1/4 turn, have helper put steady pressue on pedal untill it's almost to the floor, then close the bleeder screw before the pedal reaches the end of its travel. Do the same thing with the rear left, then front right, then front left. I can get a full quart of fluid with no air, but the brakes still don't engage!

Should I pressue pedal down faster? Or slower? I have a couple of loops in the rear lines to shorten them up, could this be an issue?

 

The loops should not matter. Slow steady pressure (maybe 5 seconds per push) is best when bleeding. One thing is not clear in your explanation of the bleeding process. At each wheel you must repeat the process several times until all air is out at that cylinder before moving on to the next wheel.

Are you sure the rear shoes are adjusted properly? If they are not you can use up all the brake peddle travel moving the shoes toward the drums and not have any brakes when they get there.

 

Yeah I usually pump the brakes about 10 times on each side but I never get any air coming out, its solid fluid. I get about 4-5 seconds of fluid with each pump, and yes I do have a hose going from each bleeder screw to a glass jar filled with fluid. I'm positive I'm doing it right, but it doesn't seem to be working!

I'm pretty sure the rear shoes are adjusted properly. They rub just a tiny bit when I turn the wheel by hand. Also, the front dist brakes worked great before I tried to bleed the system, now they don't work at all. I don't think having the rear shoes out of adjustment would make the fronts not work at all, correct? (I say this because the rears didn't even have brake lines going to them before, and the fonts still worked good.)

Should I try bench bleeding the MC again? Or could the proportioning valve have some air trapped in it?