1990 C1500 ABS (RWAL) removal.

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I'm a little late coming to this but I am also having the soft pedal issue despite replacing master cylinder, and servicing front and rear brakes. I was about to upgrade the front rotors and pads and replace all of the flexible lines. After reading this thread I did some further research and found this article on the Kelsey-Hayes RWAL system. They pinpoint the dump valve as a common cause for poor brake performance. GM didn't specify a regular brake fluid replacement interval. The dump valve is very susceptible to moisture and any crud in the system can can cause the valve to stick open allowing fluid to leak into the accumulator and allow the pedal to drop.

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

Quote:
"If a small piece of dirt or rust gets into the unit, it may prevent the dump valve inside the EH valve from closing. The dump valve will then leak fluid into the accumulator when the brakes are applied. The misrouted fluid allows the pedal to drop, and the pedal may go all the way to the floor without applying the brakes. No ABS warning light or fault code will be found either because the limited diagnostics on this system can't tell if the dump valve is fully closed or not."

After reading this thread I'm unsure if anyone had tried just replacing the dump valve?

I appreciate all the work people have done to try and fix the problem. In fact there has been so much effort for so long that the amount of information is vast and a bit confusing. I'm looking to improve the crappy braking on my truck but I don't want to just throw money and parts at it until something works.
 

GMCTRUCKS

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Good info.

Hey guys my truck GMC 1993 F/S Ext/cab 1/2 ton what size brake shoes do I have yes it can be one of two sizes?????
 

OlSmokie

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I just did this to my 90 C1500 and the difference in braking on my truck is remarkable. It finally feels like I have brakes on all four wheels.
I did need an adapter which NAPA had in stock for under 10 bucks.
You must be registered for see images attach
 

OlSmokie

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I'm a little late coming to this but I am also having the soft pedal issue despite replacing master cylinder, and servicing front and rear brakes. I was about to upgrade the front rotors and pads and replace all of the flexible lines. After reading this thread I did some further research and found this article on the Kelsey-Hayes RWAL system. They pinpoint the dump valve as a common cause for poor brake performance. GM didn't specify a regular brake fluid replacement interval. The dump valve is very susceptible to moisture and any crud in the system can can cause the valve to stick open allowing fluid to leak into the accumulator and allow the pedal to drop.

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

Quote:
"If a small piece of dirt or rust gets into the unit, it may prevent the dump valve inside the EH valve from closing. The dump valve will then leak fluid into the accumulator when the brakes are applied. The misrouted fluid allows the pedal to drop, and the pedal may go all the way to the floor without applying the brakes. No ABS warning light or fault code will be found either because the limited diagnostics on this system can't tell if the dump valve is fully closed or not."

After reading this thread I'm unsure if anyone had tried just replacing the dump valve?

I appreciate all the work people have done to try and fix the problem. In fact there has been so much effort for so long that the amount of information is vast and a bit confusing. I'm looking to improve the crappy braking on my truck but I don't want to just throw money and parts at it until something works.
I removed the dump valve from my 90 yesterday and it made a huge difference for me. Maybe my dump valve was defective, but I've had this truck for over 15 years and at least 2 brake jobs and the brakes have never felt this good.
 

blackdeathmessenger

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Out of curiosity, has anyone found a way to keep the 2 second brake light that comes on when you turn the key on? In my state, we're about to go to fun police emissions (california), which means all the lights have to work properly
 

David Hazel

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I just bought a 94 'Burb and after reading this thread and thinking I need to do the ABS delete, I looked under my hood and the ABS module looks nothing like the images. I'm assuming that mine has 4 wheel ABS. The module is much bigger and further forward with more lines attached. Does anyone know if some of these vehicles came with 4 wheel ABS?
 

Supercharged111

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I just bought a 94 'Burb and after reading this thread and thinking I need to do the ABS delete, I looked under my hood and the ABS module looks nothing like the images. I'm assuming that mine has 4 wheel ABS. The module is much bigger and further forward with more lines attached. Does anyone know if some of these vehicles came with 4 wheel ABS?

4 wheel 3 channel ABS but I thought that started in 95. I retrofitted lines from an older truck to my 98 and then performed the delete with the adapter fitting to get rid of ABS.
 

WILWAXU

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Out of curiosity, has anyone found a way to keep the 2 second brake light that comes on when you turn the key on? In my state, we're about to go to fun police emissions (california), which means all the lights have to work properly

Brakes are not part of a normal California emissions test.
 

idlook2

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I just put a new rear wheel abs unit on my 1990 K1500. Bled the brakes at all 4 wheels and the pedal is still soft. The service manual says that I need to use a Tech 1 tool to perform a "function test" on the valves. Are there any alternative bi-directional scan tools that can be used on these trucks to operate the valves?
 
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