Dash Brake light comes on after a couple minutes of driving

[Slooptin]

Recently did a hydroboost conversion on my 90 v1500 suburban. Everything works as it should except the brake warning light on the dash comes on after like 3-4 minutes of driving. brakes feel firm and were bled after the install. The possible culprits I can think of:
1. I'm having is the pump whines every once in a while, but I can't see how that's tied to the brake warning light
2. Maybe I need to bleed the system again but I was pretty thorough the first time and it doesn't feel like there's air in the system
3. During install, I had the switch on the proportioning valve unplugged as well as the "ABS controller" mounted next to the master cylinder and those got a little bit of brake fluid on them. Maybe I need to replace the switch, which I plan on doing when I bleed the system

Can anyone provide any insight here?

 

[Oldbear42]

I thought mine was something complicated, but it was not. The parking brake pedal spring is old and the cable was not tight so it would settle on the switch that turns the dash light on. Fixed it by readjusting the park brake cable (was not in one frame bracket near the RH fuel tank).

 

[TotalyHucked]

Is your ebrake hooked up? When I had cut my cables to pull the axle out for a rebuild, I never hooked it all back up, just zip tied them to the frame rails. Because of that, the ebrake pedal would droop just ever so slightly sometimes and cause that light to come on

 

[saltdog]

Definitely check that parking brake- sometimes its that easy.

 

[SquareRoot]

LS Swap

 

[rwjtexas]

Agree with others .. the two areas that cause the parking dash light to come on .. (older ones for sure) is the Proportioning Valve connection and the Emergency Parking Brake Switch ... as others said make sure the Parking brake is fully returning to the off position .. I had to crawl under and lube up the swing connection to where the spring would return it to the proper position ... in addition, I had to replace the switch due mine being damaged when I had a new parking brake cable installed.

 

[mlsceo]

My dash warning light was doing the same thing. Changed the master cylinder, (it was weeping fluid) and the light issue disappeared.

 

[Slooptin]

So E brake is hooked up and return spring is still good. When I release the e brake after starting the truck, the light disappears. It really takes anywhere from 3-5 minutes of driving around for the light to come back on and I've made sure it isnt the e brake.

Master cylinder is brand new and so far no leaks present. I'll check the prop valve as it could have moved during install and after looking into it, i might need to reset it and bleed the system again

 

[Slooptin]

Update: I verified that the valve was centered and re-bled the whole system with the valve centering tool in place of the switch. The issue is still present and I'm wondering if it has to do with the hydroboost install? it's still a disc/drum setup so nothing has changed and I double checked that the small reservoir is set up for the rear and the large reservoir is connected to the fronts. Other than replacing the whole valve/distribution block, I'm stuck on this one

 

[Slooptin]

Ok, so I did some more digging and found this thread below:

Replaced hydroboost, now brake warning light comes on?

www.dieselplace.com

Same symptoms I'm encountering and it looks like I may have disconnected the RWALS/ABS module the wrong way or done something to set a code in the RWALS system. I'm not familiar with these or how they work but I'm going to try and clear the code, and if that doesn't work, I'll figure out how to remove the system entirely. It seems like these are popular trouble makers for early gmt400 guys and it looks like they have tons of info on how the system works (or is supposed to since I've never actually felt it work) and how to remove them

 

[Blue Ox]

Mine has a defective switch on the combination valve that has similar symptoms. I'd just try disconnecting the wire on the valve and see what it does.

 

[Slooptin]

Mine has a defective switch on the combination valve that has similar symptoms. I'd just try disconnecting the wire on the valve and see what it does.

Thats what I think I'm going to try.

I also found the below for anyone who's having this issue or wants to learn more about these early abs systems

Kelsey-Hayes RWAL Antilock Brakes

It looks like I need to reset my DRAC to reflect tire size & gearing changes because apparently the DRAC feeds vehicle speed info to the abs module

 

[Slooptin]

Ok, well I figured I'd provide a final update and wrap this up. I found the light was consistently coming on when the speedo hit 37 mph. I tried resetting the RWAL controller and still nothing. Lo and behold, i was pulling out of my driveway yesterday and noticed my brake lights were on despite me not being on the pedal. Pulled the under-dash cover plate off and noticed that the brake light switch wasn't fully "closed" when the brake pedal was at the neutral resting position. pushed the switch in to where it closed when the brake pedal was at rest and voila! no dash light and my rear brake lights only come on when the pedal is applied. Occam's Razor at work

P.S.: Doing some more digging, it looks like the original hydro-boost equipped trucks used a different pedal assembly than the vacuum boost trucks. The pin that the rod attaches to is slightly larger and at a slightly different location on the arm which would account for the "gap" between the pedal stop and the brake switch location. Either way, the switch is adjustable so not a big deal anyway. If I wanted to do this the "right way" I would have sourced a hydro boost pedal and swapped that in and I just might down the road, but the whole system works either way and the pedal feel and braking power are night and day compared to the old vacuum system

 

[Snoots]

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