No Brake Pressure

[jd8001]

Hello All!
Excited to be here and working on this jeep. I'm new to jeeps and the forums.

Bottom line up front: I have replaced everything in the brake system yet cannot get any pressure on the brake pedal.

I've been following the threads but haven't posted until now. I have a 1983 Jeep CJ7 that is all stock except for a flowmaster muffler. I've been working on the brakes for a while. When I bought it it had a significant leak in the rear line right past the proportioning valve. It also had some extensive rust throughout the entire hydraulic brake system so I wound up replacing all the lines, the proportioning valve, the front calipers, and the wheel cylinders. I have also replaced the Master cylinder. I did this in two steps: Master cylinder and front calipers were step one, step two was wheel cylinders, prop valve, and all new hard lines. Upon completion of step one I still had a mushy brake pedal but I assumed that was due to the leak. Now I have no brake pressure. I have run about 2 quarts through the system checking for leaks then bleeding. I have no leaks along the lines. I can't pump the pedal and get pressure.

Ok so mistakes I know I have made. First I did not bench bleed the MC. At this point I have bled the system so much that I assume any air that was in it is now gone. Also, I have not messed with the proportinging valve stem during the bleeds. I read somewhere that if you bleed front, back, front you can omit the step with the proportioning valve. That is what I have done.

When I bleed the system I get reasonable fluid flow/pressure on the back brakes and very minimal on the fronts.

At this point I'm thinking I damaged the master cylinder or I got a bad one. My amateur mechanic skills tell me that since I can't pump the brakes and get pressure that the problem is not air in the lines but something else.

Any advice from the truly jeep savvy?

 

[Hedgehog]

First, bite the bullet and bench bleed the master.

 

[Old Dog]

Hello All!
Excited to be here and working on this jeep. I'm new to jeeps and the forums.

Bottom line up front: I have replaced everything in the brake system yet cannot get any pressure on the brake pedal.

Ok so mistakes I know I have made. First I did not bench bleed the MC. At this point I have bled the system so much that I assume any air that was in it is now gone. Also, I have not messed with the proportinging valve stem during the bleeds. I read somewhere that if you bleed front, back, front you can omit the step with the proportioning valve. That is what I have done.

When I bleed the system I get reasonable fluid flow/pressure on the back brakes and very minimal on the fronts.

First I would try working the proportioning valve and see if that helps.
If not than I would take the MC back and get a new one.

The way I read this, you have bled the MC now, if not than start there.

 

[mtnwhlr]

It sounds like a master cylinder problem to me. I would pull it and bench bleed it and if that doesn't work replace it.

 

[jd8001]

Thanks guys. I bench bled the master cylinder and now I have great brake pressure. Stops better than it ever has!

 

[mtnwhlr]

Glad to hear you got it working.

 

[Hedgehog]

You bet that now I'm dancing like a happy banna, why? I win oh yeah I win, First responder and my advice actually is correct .... Oh yeah I win!

Sorry, a little foolishness on my part..... Glad the solution was simple. It is amazing what a relatively small bubble can do to your brake system.

 

[007]

I'm getting ready to go through this to some degree... Just replacing the master cylinder. How do you bench bleed these?

 

[Hedgehog]

Some master cylinders come with a bleeding kit with them. Also you can buy them at parts stores. I made my own using some spare brake line and fittings. The idea is to remove all air from the master before installing it. How it's done? Place the master cylinder in a bench vice, make sure it's level all around. There will be a couple fittings that go in the brake line holes. Install these in the hole, then attach clear hoses that go on the fittings with the hose going back into the brake fluid reservoir. Using long smooth strokes pump the "ram", I use a BIG philips screw driver, watching the fluid that comes out of the hoses. air bubbles will come out of the hoses for quite a few strokes, then deminish. I like to tap the master cylinder a few times to help release bubbles clinging to small spaces.

When the bubbles stop, carefully remove the cylinder from the vice and install it in the vehicle. quickly remove the provided fittings and attach the brake lines, but leave them a little loose. Have a helper press on the brake bedal until fluid seeps from the fittings. While continuing to press the pedal, tighten the fittings. In theory this removes the air in the fitting holes before it's pumped into the system. Does it really work? Yes and no. It's not perfect, but it doesn remove most of the air. For a perfect job you'll need to bleed the system as usual.

 

[Petescj]

You bet that now I'm dancing like a happy banna, why? I win oh yeah I win, First responder and my advice actually is correct .... Oh yeah I win!

Sorry, a little foolishness on my part..... Glad the solution was simple. It is amazing what a relatively small bubble can do to your brake system.

You finally got one!!!

Just giving you . Great having you around. Im just waiting for the adventure parts of your Cj stories now that its up and running.