89 C1500...spongy brake pedal

[vzfox]

Probably a common question with many vehicles, but when I stop the brake pedal will slowly travel almost to the floor before stopping the truck. It still feels fairly stiff'ish, not like it just falls to the floor with minimal effort or anything. If im at a stop sign and pump the brake pedal a couple times it becomes really stiff again and doesnt travel near as far, but start driving a bit and stop again and it slowly goes 3/4 way to floor.

Possible master cylinder bypassing or brake booster?? opinions plz

[vzfox]

wanted to give a little more info....

There is no loss of brake fluid and no leaks of any kind. Brake pedal will not go all the way to the floor if holding it at a stop/idle.

It just travels further than it should.

[Schurkey]

Originally Posted by vzfox

There is no loss of brake fluid and no leaks of any kind. Brake pedal will not go all the way to the floor if holding it at a stop/idle.

It just travels further than it should.

First Guess: Rear brakes out-of-adjustment.

Second Guess: Need to bleed the system. One bleeder screw at each wheel cylinder, and one or two at the RWAL (ABS) unit.

Third Guess: Typical defective RWAL unit. It's a poor design and has a tendency for the solenoid valves to stick.

[vzfox]

Originally Posted by Schurkey

First Guess: Rear brakes out-of-adjustment.

Second Guess: Need to bleed the system. One bleeder screw at each wheel cylinder, and one or two at the RWAL (ABS) unit.

Third Guess: Typical defective RWAL unit. It's a poor design and has a tendency for the solenoid valves to stick.

On the third guess....the truck was taken to a mechanic shop and found the ABS was not working properly, so they unplugged the harness from the ABS unit. No lights are on, on the dash that indicate anything wrong.

The truck has been in my family since new, I havent been kept up to date as far as the maintenance that was done but I did ask about the ABS thing and my response above is all I was told.

[vzfox]

With the ABS unit unplugged like it is and ABS not functioning, the brakes are acting as older conventional ones that just simply lock up when "stomped" on.

My question is....is there any way to allow the braking system to build and hold normal pressure without ABS unit hooked up?

Brakes have been bled and adjusted, but issue persists.

[Schurkey]

Originally Posted by vzfox

With the ABS unit unplugged like it is and ABS not functioning, the brakes are acting as older conventional ones that just simply lock up when "stomped" on.

Maybe not. That's one of the failure modes of the RWAL. If the dump valve doesn't seal, the pedal is low.

http://www.aa1car.com/library/abs_kelseyhayes_rwal.htm

[vzfox]

Since we're getting all kinda of technical, let me throw this at ya....

The control valve is located directly beneath the master cylinder, correct? And the combination valve is located directly beside the control valve, correct? (Im looking at the picture via the link you sent me)

When I look at my truck and the way the brake lines are hooked, it appears the rear brake line is the only brake line going to the control valve. Both lines for front and rear come from the combination valve.

If according to your article you posted, there is a malfunction of sorts not only with the comp control unit itself but the control valve by letting brake fluid bypass certain areas of the combination valve, thus for allowing the brake pedal to act spongy and travel further than it should....does all this make sense and correct so far??

If so, let me run this by you.....it appears that the brake line coming from the rear brakes is long enough to stretch just a few inches and screw into the combination valve, thus bypassing the control valve all together. If this were done, could I get my brake pedal back with it holding pressure as it should? I am aware that I would have zero ABS, but at the moment I dont have ABS anyways.

Let me know if this made sense and if it would work.

[vzfox]

even if no one knows what im refering to or if that would work, does anyone have input or ideas on how to bypass the RWAL so I can have "normal" brakes and brake pedal travel?

[ASJT3]

Originally Posted by vzfox

If so, let me run this by you.....it appears that the brake line coming from the rear brakes is long enough to stretch just a few inches and screw into the combination valve, thus bypassing the control valve all together. If this were done, could I get my brake pedal back with it holding pressure as it should? I am aware that I would have zero ABS, but at the moment I dont have ABS anyways.

Let me know if this made sense and if it would work.

I've contemplated doing this with my C1500 as well. As far as I know this works, it's how the lines were hooked up on pre-ABS vehicles anyway. Just make sure the pipe fittings are the same and you can plug & play baby (remembering to bleed the brakes again).