rear wheel antilock (RWAL) system - ditch it?

[Daveo91Burb]

My brake light stays on continuously. I've diagnosed it just enough to know for sure it's the antilock system. i.e. light goes out if I disconnect the brake controller by the M/C. Also, light becomes brighter when I engage the parking brake.

Good diagnostic and general info here. https://www.aa1car.com/library/abs_kelseyhayes_rwal.htm

My question: spend the effort for further diagnostics, i.e. pull the codes and then replace whatever the offending part is? Or just ditch the whole thing? I've been driving around with the controller not connected just to keep the light off. But if it was connected it'd be in bypass anyway - if it's throwing a code at all it goes into bypass by default. I know that to correctly eliminate the system I need to remove the ABS control valve and route the hydraulic lines directly to the prop valve so either way I have some brake work to do, I think.

(Probably) unrelated brake question: there are two activator switches mounted to my brake pedal. Of course one is brake lights, but is the other one for cruise control? The second one is failing - it makes a audible, annoying click every time I push the pedal. I don't have functional cruise control now so can I just remove that switch? there's no brake pedal switch for the antilock system is there?

 

[Goldie Driver]

A long time ago, it seems like my buddies 90 ish Chevy pickup ( body style after the squares) had a similar issue and it was a brake light switch. Don't remember if that was RWAL only or 4 wheel anti lock.

He had put black tape on the dash to block the light.

Anyway, it seems like a brake light switch solved the issue.

I don't remember 2 switches, though.

As far as the RWAL, I am personally not a fan.

Great theory, but in a panic stop you could lock the fronts and lose steering while the rears will not lock. Bad plan.

At least that is the way they worked on a 87ish Dodge truck with that set up.

But, if it is a switch, then potentially a cheap fix to get it back to factory.

LMC is just showing a brake light switch, so dunno what that second is.

https://www.lmctruck.com/1973-91-chevy-gmc/switches-relays/csb-1973-91-stop-lamp-switches

Good luck !

Britt

 

[1987 GMC Jimmy]

One’s for the brake lights and TCC lockup disengage. The one for the cruise should have a vacuum line going to it from the servo. It interrupts vacuum to release the servo. If the RWAL system interfaces with a switch, it’ll be the actual stoplamp switch.

I don’t think GM ever really got RWALB electronics down pat. Although, it seems like GMT8/900s have those issues more frequently from what I’ve seen and heard. You just jump pins A and H on the ALDL, and it’ll flash the code, right? It only stores the most recent one if there’s more than one, I believe. Even still, the modules are such a common problem, I’d try to pull the module apart and inspect the board for broken joints or anything burnt, especially if you can’t get a straight answer out of the diagnostic process. That or find a local GMT400 part out and see if you can grab a spare module to try. I suppose it could also be a VSS/DRAC issue, but you’d be having other issues if that was the case. If your brake lamp switch checks out, my money’s on the RWAL ECU.

If it doesn’t unfold into the hassle of the year, I’d keep it. If you’re running around in circles trying to find wiring issues, parts, or run tests, I’d let it go. Cars were made for over 100 years without ABS.

 

[gmbellew]

you can buy RWAL parts here - https://www.carid.com/1990-chevy-su...lter=1&sub-model[ourSubModelName][]=Silverado

i replaced my RWAL control module and got it here.

 

[Daveo91Burb]

Thanks all for the info! Good stuff.

One’s for the brake lights and TCC lockup disengage. The one for the cruise should have a vacuum line going to it from the servo. It interrupts vacuum to release the servo. If the RWAL system interfaces with a switch, it’ll be the actual stoplamp switch.

I don’t think GM ever really got RWALB electronics down pat. Although, it seems like GMT8/900s have those issues more frequently from what I’ve seen and heard. You just jump pins A and H on the ALDL, and it’ll flash the code, right? It only stores the most recent one if there’s more than one, I believe. Even still, the modules are such a common problem, I’d try to pull the module apart and inspect the board for broken joints or anything burnt, especially if you can’t get a straight answer out of the diagnostic process. That or find a local GMT400 part out and see if you can grab a spare module to try. I suppose it could also be a VSS/DRAC issue, but you’d be having other issues if that was the case. If your brake lamp switch checks out, my money’s on the RWAL ECU.

If it doesn’t unfold into the hassle of the year, I’d keep it. If you’re running around in circles trying to find wiring issues, parts, or run tests, I’d let it go. Cars were made for over 100 years without ABS.

Sweet, I'll check for the vacuum line to the cruise switch and make sure I get my switches straight. Can I just remove the CC switch if I'm not going to use cruise? (I may eventually try to get it going again though)

Yeah, I think you're spot on regarding the diagnostics, including the part about it only remembering the most recent code. I'll do the jumper thing over the weekend and see what it reads out. Weird thing is I've had problems with the module in the past, but instead of a solid light it just kept blinking out a code over and over again. But to get it to stop I just had to unplug the module, run it, and then replug it again and everything was cool. Only happened two or three times over a period of years. But this solid light comes back on every time.

you can buy RWAL parts here - https://www.carid.com/1990-chevy-su...lter=1&sub-model[ourSubModelName][]=Silverado

i replaced my RWAL control module and got it here.

Sweet, thanks for the link. Bummer is a few years ago I had a '90 burb that I was parting out and it must have had RWAL brakes, but I didn't think to snag the module or any other parts from that system.

 

[1987 GMC Jimmy]

Was the vacuum line there on the one in question? If so, and you don’t have plans for it, the switch can go if you so desire.