I just purchased a car that was sold because the owner couldn't figure out the brake problem he was having. He had down-to-the-floor brakes that would barely stop him.

He replaced the pads, shoes, calipers, hoses, disks, and the master cylinder. Simply bleeding the system at the corners didn't seem to help, so... I think I need to consider bleeding the MC.

With that, what is the best way to do this with it still in the car? Do I simply jack the rear of the car up to level the MC, disco the brake lines (one at a time) at the MC, bring a tube from that particular line port to the top of the MC (in the fluid) and slowly pump the brakes with a break between pumps?

Or would I simply be able to position the car so that the MC is level, and continue to bleed the brakes at the corners until the air is forced all the way through?

Sorry for the long post, but I would appreciate any responses. Thanks ahead of time. - John '89 L98

 

It's essentially the same as bench bleeding a MC.

You run tubing from the master cyl outputs, directly into the reservoir. Have someone pump the brakes a few times while you hold the tubes, you'll see the bubbles if you have them.

They make plastic adapters to screw in the MC to bench bleed, but I dunno if you can get them without buying a new MC.

 

You can crack the fittings at the MC if you don't have the bleeding tubes. Very messy though

 

So, let me get this straight... I have to remove the brake lines (one at a time) from the MC, insert those little plastic fittings, and bleed each port back into the top of the MC until all the air is out. Is that right? Is it important that I keep the MC level? Should I start with any particular side or port? After that, I assume I'd have to bleed the four corners again, correct? Thanks. - John

 

Close, You do both ports at the same time. Then you completely bleed the whole system and voila!


EDIT: When you bleed the four corners it should go without saying to start at the farthest point from the MC

[This message has been edited by 87RS402 (edited February 04, 2001).]

 

Correct, it's a pain, but that's how you do it.

 

All right... I couldn't locate a MC bleeder kit of some sort, so I did it by simply cracking the lines several times, (all 4 at the same time) and bleeding them that way. Before I started though, I raised all four corners and was able to turn the wheels by hand with the brakes applied.

By bleeding the MC, I was able to get quite a bit of air out. After I bled the MC, I bled the 4 corners again, and was able to get even more air out (must have traveled all the way down from the MC, as it took awhile). Now three of the wheels will stop with the brakes applied, but the rear right can still be turned. Also, the pedal travels quite a bit (probably 3/4 travel) before getting firm and stopping the car.

I tried adjusting that drum, but it didn't help. The assy. simply doesn't want to move until the brake pedal is all the way to the floor. And even then it barely moves. I also noticed that while I was bleeding that one line at the MC, as well as at the right left wheel, I didn't get all that great of a flow. There's no air being released, but the flow is just really low.

Would that mean I have some sort of blockage in the line, or could it be a problem with the MC again? Could the type of pedal travel I'm experiencing be affected by that one rear wheel? I'm going to try to locate a plug for that port on the MC (1/8" right?) to see if I still get the same problem. Any other suggestions in the mean time? Thanks again. - John '89 L98

[This message has been edited by John'89L98 (edited February 05, 2001).]

 

A little update... I took the damn car into a couple of brake shops, and I got two different answers to my problem. One place said it was the rear self-adjusters. And the other said it was a leak in the right rear brake hose. I saw the leak myself (although I don't recall it being there last night, and they are fairly new).

The self-adjusters just needed to be cleaned up a bit. They seem to work fine now, and the right rear wheel now stops when the car is in the air, and the brakes are applied.

As for the brake hoses, I replaced both the rears, bled the MC again, and proceeded to bleed all four corners. No help. I just don't understand. Why do I have so much brake travel? When I bled the MC again, there wasn't any air expelled, and the rears were the only lines with any air in them.

What's my next step? Anybody? Thanks. - John '89 L98

 

John, unless I mis-read what you typed, you didn't bleed the master cylinder. You said you cracked all "4 lines at the same time"- do you mean all 4 bleeder screws?

To bleed the m/c, first you need to take care of the two ports coming out of the m/c. After that, you move on to all four wheels.

You need to try to find fittings that screw down into the m/c ports and seal them up. Then, you'd have someone press the brake pedal SLOWLY down to the floor. When it's at the floor, you (messily) crack the fittings open. The dude in the car should feel his foot sink down to the floor. Now, tighten the fittings. Then, tell the guy to let the pedal up slowly.

When fluid "explodes" from the ports when you crack the fittings, that means there was air in there. When you crack the fittings and fluid drips out, there's no more air.

Hitting the pedal slow is important. The master cylinders have a "quick take-up valve" in the m/c base. You can see this by looking at the base of the m/c body (not reservoir, body). Near the brake booster, the m/c body gets thick. The quick-take-up valve is there. It stores fluid that gets into the brake lines more "quick" than pulling it from the reservoir. Anyway, if there's air in this quick take up valve, the only way to get it out is to hit the pedal slowly.

You can also look for a one-man brake-bleeding kit. These come with a small plastic bottle, a few lengths of tubing, and some conical fittings. You push the conical fittings into the m/c ports. Then you do the brake-pedal-pushing and look at the clear tubes (from the kit) for air bubbles.

It also helps like you said before to have the m/c body level, which means raising the back of the car pretty damn high.

Remember, brake fluid eats paint, and the front-most reservoir is for your rear brakes. I forgot that a few times in all the running around the car I did.

You could also go to a brake shop and just tell 'em to pressure-bleed your system!

You could also make a home-made brake bleeder. I did this; it helped me pinpoint my master cylinder. I couldn't bleed the m/c directly, but I used the tool on the lines right below the m/c- the prop valve. By using it, I was able to ensure that no air was inside the brake lines below the m/c. If you want, I could type it up quickly- the webpage that explained it the best is missing (dammit).


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