Combination valve stuck? "Brake" light on...

[AM Woody]

So, a while back I was out of town and the wife calls me and says the Brake warning light came on in the GW. I coached her on the phone, and topping off the master cylinder made the light go off, and the pedal go back to normal. This process was repeated for a couple days until I got back and discovered the front to rear brake line had a small hole. I replaced it, bled the rears but the pedal stayed soft and the light stayed on. Meanwhile, I discovered the shoes were down to zero and a pad had gone metal to metal, so I parked it.

Scheduled some other work and finally got rebuilt calipers, new wheel cylinders, linings, and one new rotor on. Gravity bled the brakes twice, got fluid out, got air out. Pedal is hard. Crank up the engine, Brake light is still on. Pull out of garage, pedal effort is high, truck barely stops. Back it back in.

Now, we get to the Mystery Combination Valve. I've done a lot of searching on this site, and looked at a couple different manuals. What I'm piecing together here is my '90 GW has the "W" valve, and the brass plunger on the front has to be pulled "out."

The brass plunger was sticking out @ 3/8ths inch. It did not want to move by hand or by pliers in or out. Should the plunger move easily?

Next, I gently tapped on it and it moved "in" about half way, and stayed there. It doesn't want to move out at all now. No change in the brakes, light still on. Also, the plunger seems to stick out at a slight angle, as if someone bent it in the past.

It seems like maybe everything is bled properly, hence I have a high pedal, but maybe the valve is stuck, restricting fluid flow? Anybody have any thoughts or suggestions?

Thanks,
Andy

[Chevelleguy]

Sounds like you need a new valve. I would get a used one from a wrecking yard.

[krob725]

mine won't move at all. i am having trouble bleeding the rear brakes. everything is new,MC, calipers,wheel cyl,shoes,pads.
is there a way to rebuild the valve?

[AM Woody]

Okay, anybody else?

I guess the main question is: how easily should the plunger move?

I just want to be on the right track here, before I pull the valve. I've never worked on a valve like this before.

Thanks,
Andy

[paddyp]

btt

[andy d]

had a similar problem after replacing a coupla brake lines. one turned out to be sucking in air. a 1/2 turn of a union solved my problem.

[Ernzo]

I had to replace my combo valve. I elected to purchase a new one, as it plays a critical role in stopping my 5800 lb. Louise. I tried bleeding, tapping, draining etc.

AS you know there are 2(maybe more??) kinds, I have the pull out kind, you can locate one in a parts store and go in and take a look, try the plunger etc.

My understanding is that the valve equalizes the pressure between front and back so that the front doesn't just lock up. What was happening to me was when I had a hard stop, the front right tire would lock. One Wheel Brake.

Replacement took a couple of hours, brake fluid everywhere, followed by a complete bleed. I wish I had added speed bleeders at the same time. Don't forget to buy a large vessel of Brake Fluid, and don't bleed 'em with the motor running.....(did it once...)

Of course, be careful with the fittings, they are a little hard to get lined up and if stripped would add a few additional bananas to the mix!!

[Ralph]

The brake light is activated by a switch that is attached to the parking brake pedal. It is literally no more than an indicator that the parking brake pedal is depressed. The brake light is not an indicator of any activity anywhere else in the brake system.

Leave the proportioning valve alone unless you are certain you have no rear brakes; the most common cause of p-valve failure is a leaky wheel cylinder (rear drum brakes) that is left unrepaired for some time.

A new p-valve is available from a Jeep dealer. Wholesale or commercial cost is about $65; I don't know what retail price is. But they're also easy to get from a junkyard, and providin the system has remained closed and not rusted it should be okay.

When replacing the p-valve, be careful to use two wrenches, preferably line wrenches, when removing the brake lines. If you find one of the brake lines is stuck, get the other line off first, then unscrew the p-valve from the stuck line.

[ October 16, 2003, 01:56 PM: Message edited by: Ralph ]

[Chevelleguy]

Ralph, you are mistaken. There is a switch in the p-valve that will turn on the brake light is the valve is moved from center.

[letank]

i have heard that brake shops can recenter the valve.....

Michel

[Ralph]

Hmmm, that's what I get for offering good advice: someone to contradict me and give, ahem, CORRECT advice! Thanks chevelleguy.

[Chevelleguy]

Just do'n my job, Sir. ;)

[ October 17, 2003, 07:59 PM: Message edited by: chevelleguy ]