Odd brake problem

I converted to disk brakes on the front axle and I have a soft pedal. I know. The first thing I thought was air in the lines. So I Bleed the brakes. Still not Good. I Bleed them some more. Still no air in the system.
Seems a little strange. With the old drum brakes. I could just touch the brakes and the Jeep would stand on its nose.
So my next course of action, rear brakes out of adjustment. Found them to be paper thin. So now I have new brakes in the rear. Drums have been turned. Disks are new, still soft pedal.
So. If you were to push down on the pedal a little ways. You could tell the brakes are grabbing. Push some, more almost to the floor. The wheels lock up. My thought. Still air in the lines.
Then I take the Jeep to a brake shop. They bleed the brakes. They tell me there is no air in the system and that maybe the brakes haven't seated.
Any ideas? chainsawguy

 

even if the linings weren't seated in yet, the pedal still shouldn't go to the floor
does the pedal "pump" up ?

 

No.

 

No mention of Bleeding the Master Cyliner....yeah.... I know.....some people have NEVER done this.....but it could be causing your issue....

Whenever system wide brake work is done, there is the possibility of air being entrained in the MC.

 

I'm going to try putting in a new master cylinder.

I did plumb in the Combination Valve. Do you think that's the problem? Not sure how it works.

 

You said you did or did not put a residual pressure valve in the front line (2 lb)?

http://www.earlycj5.com/forums/showthread.php?t=75698&highlight=bleed

Read that. Even after new master cylinder, residual valve, and basically new everything, and power bleeding through...still air.

 

My master cylinder and brake booster is from '86 S-10. Disc brake parts and Combination Valve is from '85 CJ. Both vehicles had Disc and drum brakes.

 

I had a similar problem. I used about a gallon of brake fluid trying to bleed the air out but didn't work. I took the system apart one brake fitting at a time looking for a problem. I changed the master and rebuilt the calipers. This was all on my dana 30 with disks. It was driving me crazy so I had a buddy come over and he (eventually) spied the problem at which time he started to laugh.

The problem ended up being the pass side brake caliper was a drivers side model so the bleeder wasn't at the high point, thereby trapping air in the system. To bleed it I have to remove the caliper and rotate it so the bleeder is high, then bleed, then bolt it back on. If you do this don't forget to put a block of wood in the caliper so the piston doesn't pop out . . . .

 

Agreed. Even with a vacuum bleeder, if you don't bench bleed the master, there can be air in the system.

 

I was having some problems with the old master cylinder. So I thought I'd put a new one on. Now I just need to fix the clutch before I can test it out.

 

Fixed the clutch and installed a heat shield between exhaust pipe and slave cylinder. Then I installed a new master cylinder and bleed the system. Still a soft pedal. I even ran a whole, large bottle of brake fluid through the lines. I don't get it. I can't figure what's wrong. chainsawguy

 

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Which line goes where coming out of the master. Might want to verify that before you sink any more money/hair tearing out. Wouldn't be the first time that's happened.

 

Large reservoir to disk brakes, small reservoir to drum brakes. From that picture the rear reservoir should be your front disk brakes.

 

That's how I have it plumbed.

 

You got it backwards-------

Smaller piston in the M/C will give more pressure, but less volume for the same stroke, and pedal force, as a larger piston will.

 

Simple physics

I suspect that the fact you have to push harder on the larger piston makes it feel like the pedal is no longer "soft".

Consider a lever and fulcrum setup, with a heavy weight to be moved.

If you have a lot of lever on your side of the fulcrum, and a short lever on the weight side, the lever will move easily----feel "soft"

Now, move the fulcrum so you are on the short side, and the weight is on the long side, and it will no longer be easy to move, thus no more "soft" feeling.

 

Re: Simple physics

But the master cylinder came off a 86' S-10 pick up. That vehicle had disc and drum combination.:?