Brakes 1980 CJ7 Front Brake Bleeding Issue

[inthegarage]

I have a 1980 CJ7 with standard brakes, disk front/drum rears. I just finished replacing the entire brake system, lines, wheel cylinders, calipers, etc.

I cannot get the front calipers to move or feel any pedal pressure for the front brakes. The pedal goes easily 1/2 through its travel then gets very hard. The rear brakes work very well.

The first time I bleed the system, I had the original combination valve installed (W-Type). By pulling on the pin in the front, I was able to get a little pressure in the fronts, but as soon as I released the pin, no pressure again. The pin is brass and eventually I muitlated it so much, I couldn't grab it anymore. I bought a new PV2 valve (looks identical externally) with the bleeding tool that installs where the brake warning sensor goes, but had the same issue. Back brakes work great, but nothing from the front. Purchased another PV2 valve and have the same result. I see fluid at all four corners and bleeding seems normal. Every time I've introduced air I see bubbles, but can bleed enough to get back to pure fluid. I've followed the sequence from the back passenger, back driver, front passenger, front driver.

Besides pulling the pin in the original combination valve, I haven't been able to get any pressure in the first 1/2 of pedal travel and the calipers are not moving. The new PV2 valves don't seem to have the same pin in the front (there is less to grab on) so I haven't been able to pull that pin for the second two attempts. All of the literature I can find seems to indicate if you use the bleeding tool for the PV2, you don't need to mess with the pin in the front.

I have no idea what to try next, has anyone run into a similar problem or have any suggestions? Anyone switch to a different combination valve with success?

 

[TSB8C]

My first thought is whether the plunger in the proportioning valve is centered. Are you sure the tool is fully inserted such that the tip is in the groove of the plunger to keep it centered during bleeding? There is a smaller groove the tip of the tool could sit in when the plunger is slightly forward already. My other thought is the master cylinder. Disk calipers require a larger volume of fluid. Since you can see bubbles after introducing air, and you can also bleed back to pure fluid (with the bleeder screws open), and all three prop valves have exhibited the same issue, perhaps the master cylinder is failing to apply sufficient pressure/volume to the front. And a quick question: When you replaced the lines, did that include the ones from the master cylinder to the prop valve as well? Any chance that one line from the master cylinder to the input on the prop valve for the front brakes has a kink/clog?

 

[inthegarage]

I replaced the lines from the MC to the combination valve and when I've removed them to install a new combination valve they flow easily.

Is there anyway to tell when the combination valve is in the correct position visually? I moved it around on the second valve, but didn't have confidence I was doing it right, so for the last valve, I just didn't touch it and inserted the tool. I did test that the switch was not activated. I'll try to recenter it the next time I work on the brake system just in case.

Could the MC be bad?

 

[TSB8C]

If the bleeder tool is fully screwing into the valve until it sits flush, I would take that as evidence that the plunger is centered properly. If you remove the prop valve and look into that hole, you can also see the groove in the plunger when it is centered.

Certainly the master cylinder could be bad. Bleeding doesn't require near the pressure as needed when actually applying the brakes. So you would get fluid into and out of the caliper bleeding screws while perhaps not enough pressure when actually applying the brakes. You didn't mention the status of the brakes prior to all the work you've done. Were the brakes working before, thus indicating that the master cylinder was OK before all the other work you've done? Or were the front brakes not working earlier, thus leaving the master cylinder as the only original part still in place?

 

[exheep]

You didn’t install your calipers backwards did you? They are left and right specific. Bleeder screws at the top.

 

[inthegarage]

The master cylinder is new, so unfortunately, I don't have a comparison. Calipers are installed correctly with bleeders up (thanks to the infamous post here )

I'm not confident on the plunger being centered. I tried to shift it by leaving the back bleeders open and fronts closed, but nothing changed. I've order a new MC now. I'll update as soon as it is installed.

 

[Manic Mechanic]

Did you bench bleed the master cylinder?

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