no rear brakes

93 Wrangler brakes felt spongy. Opened master cylinder and front resivoir was empty, topped it off with fluid. Brakes were fine. A week later they felt spongy again. Opened master cylinder and both resivoirs were full. I believed I trapped air in the line. Tried to bleed rear brakes but no air or fluid will come out of either side. Now my brake light has come on too.I'm thinking that it is the proportioning valve located below the master cylinder. Is there a way to re-open the valve to the rear brake line? Any help is greatly appreciated.

Thanks.

Hi Brice70

First see if the front reservoir that was empty supplies the front or the rear.

Did you see any wet spots where brake fluid could have been leaking from??

The proportioning valve won't block fluid to the rear brakes. There is a metering valve in the line to the front disc brakes that will prevent flow below about 125 psi on a standard disc/drum system so unless you have had a petroleum based oil in your system, I wouldn't think of those as a source of you troubles yet.

Take out the bleeder screws and check them for blockage. Clean them out with a small drill to make sure the main hole and the side hole at the base of the threads are clear.

Reinstall them and try bleeding again...

This is the procedure that I use. You need a helper unless you have one of those one man bleeding systems and I'm not so sure about some of them.

When your ready to bleed get a helper to pump the brake pedal.

Bleed the master cylinder first. Just loosen the line fittings while the helper pushs and holds down on the pedel untill you have retightened the fittings.


then in this order RR LR RF LF(double check the manual on this order, some vehicles are different)

When bleeding, have your helper pump the brake pedal 3 times and hold firm force on the pedal like a slightly harder than normal brake application. Tell her (my wife usually helps me) not to let up untill you tell her to pump again. That will be after you tighten the bleed screw.

so......... The order goes like this.

1 bleeder says "pump"
2 pumper pumps 3 times and says the word "HOLDING"
3 bleeder opens the bleed screw and lets out BF and air. The pedal will go down and you close the bleed screw.
4 repeat #1 again

DO NOT LET THE MASTER CYLINDER RESERVOIR RUN DRY.

TOP IT UP EVERY 5 BLEEDS OR SO.

Repeat this cycle as many times as you need to clear the air from that wheel. you may have to go through the the four wheels again after to make sure that all the air is out.

On the last few bleeds, I like to close the bleed screw before the pedal reaches the end of it's travel.

I also use a partly filled clear container of brake fluid and a clear hose that fits tightly over the end of the bleeder screw. That way I can see the air bubbles if there are any.

GOOD LUCK (any other questions- pm me)

JD

The proportioning valve is actually a combination valve.It can and will cut off fluid to either the front or rear brakes if you have a leak.The fact that your brake light came on indicates that this is what happened.The switch for the light is on the valve.Basically if you lose pressure in the rear brakes the valve is pushed over by the pressure in the front.That closes off the circuit to the rear and the light comes on.The easiest way to reset the valve is to pump up the brakes and open up one of the bleeders in the front and hopefully there is enough pressure to center the valve.Then you obviously have to bleed the system.

Hi xj31

I have appreciated you experienced insights and advice on jeeps and their repair as you have posted. :) This is the only time that I have disagreed on any part of one of your posts. :frown:

Actually, the proportioning valve is one of the valves in the combination valve. The proportioning valve is there to reduce the pressure to the rear brakes under hard brake applications. The proportioning valve reduces the effect of servo action and self-energization in the drum brake and reduces the chance of rear wheel lockup as weight transfers to the front. It will not cut off the supply of fluid to the rear brakes under any circumstances.

The other end of the combination valve houses the metering valve. This is used when disc brakes are installed in the front and drum brakes in the rear.

The metering valve delays the application of the disc brakes until pressure in the front brake line is about 125 psi. This is approximatly the pressure needed to extend the rear shoe return springs so the shoes begin to touch the drums. It is a timing valve so the front brakes do not apply before the rears. It will only block fluid flow to the front brakes under 125 psi and there is a deactivation plunger provided and used mainly when using a pressure tank to bleed the brakes.

The differential pressure switch is located between the front and rear brake line inlets to the combination valve. If pressure is lost in one circuit, the piston moves toward the circuit with a leak and grounds the indicator light and it illuminates in the dash. It will not block flow to any wheel location.

Reset of the valve is as you described. Many times it will reset during the course of bleeding the brakes but sometimes it is a _itch aint it. :banghead:



:2cents: Jeeper61

Thanks jeeper61.You are absolutely right.I should have said the proportioning valve is a part of the combination valve.I guess I blew it by oversimplifying my response.You gave an excellent explanation of how things work.