Can you bleed RWABS with the truck in the air?

Fireball5657 · Dec 4, 2022

I was brainstorming how to bleed my new RWABS module on my '94 K1500 w/ JB5's. Of course I could use a scanner, but those are expensive and I don't know anyone nearby who has one; and I could use a gravel road to get my brakes to lock up, but I'd really like to not tear up my brand new tires; so what if I put my truck on a two post lift, got it up to speed (say 25 mph or so), then slammed on the brakes? The fronts won't be moving in 2WD, and if the new ABS module is working correctly, then the rear wheels will try to lock up, kicking in the ABS module and therefore bleeding the system. I do plan to have jack stands on the front and back crossmembers to make sure the momentum of the truck stopping doesn't break the lift or throw the truck forward. Has anyone tried this before or is this a really dumb idea? Thanks for any input!

Supercharged111 · Dec 4, 2022

Doesn't the RWABS module have a bleeder screw on it?

Fireball5657 · Dec 4, 2022

Supercharged111 said:
Doesn't the RWABS module have a bleeder screw on it?

You must be registered for see images attach

I went out to my truck and looked at everything. On the diagram above, part #3 has a rubber cap at the front of it. Under it is something that looks like a bleeder valve; but I'm not sure if you can bleed the ABS that way. Everywhere I see on this forum, people say that you have to use a scanner to bleed the ABS system, I can't find a thread where someone was able to bleed RWABS by just that bleeder valve. Does anyone know if that could work?

Drunkcanuk · Dec 4, 2022

In the manual for my 91, it says (something like) take that rubber cap off and press it in with a screwdriver or something. Air and fluid will come out, so have a rag handy. It firmed up my pedal that's for sure.
I'd highly recommend NOT doing the lift thing, but if you do...... PLEASE record it and post!!! Lol

Supercharged111 · Dec 4, 2022

Now that I'm rethinking, it may have been the early units that had the bleeder and later ones didn't. That rubber cap is for something else, a valve that trips when you run out of fluid?

Fireball5657 · Dec 4, 2022

Drunkcanuk said:
In the manual for my 91, it says (something like) take that rubber cap off and press it in with a screwdriver or something. Air and fluid will come out, so have a rag handy. It firmed up my pedal that's for sure.
I'd highly recommend NOT doing the lift thing, but if you do...... PLEASE record it and post!!! Lol

Tomorrow I'll mess with it and see if that really is a bleeder or if it's like what Supercharged111 said. Point taken on the lift bleeding, I doubt it'll hurt anything, but if something goes wrong then I'll screw up not just my truck, but also my lift that's bolted into the concrete. Maybe not my best idea.

studigggs · Dec 4, 2022

That little nub behind the rubber cover is the end of metering valve. There is another one underneath the RWAL solenoids facing the ground. You can use special tool J39177 to keep it depressed while you press the pedal, or have a buddy hold a screwdriver on it. This process does purge air from the system and there is no scanner function that I am aware of to auto bleed/actuate RWAL brakes.

Schurkey · Dec 5, 2022

Supercharged111 said:
Now that I'm rethinking, it may have been the early units that had the bleeder and later ones didn't. That rubber cap is for something else, a valve that trips when you run out of fluid?

87-up iron-body RWAL have a bleeder screw.

From '91 or '92--somewhere in there--they switched to an aluminum-bodied RWAL that has no bleeder valve. The '94 service manual I downloaded from the link on this site says to bleed the RWAL with a (Tech 1) scan tool, page 5E3-40. (I've never tried that, and I've never held a Tech 1, 1A, or Tech 2 scan tool in my hand.)

In short, bleed all four brakes. Turn ignition switch "on", then chatter the ABS valves three times with the scan tool. Re-bleed the rear brakes. Hope for the best. Re-chatter and re-bleed as needed. (May take more than one round of chatter-and-bleed.)

When I was in the service bay, we'd run engines and slam on brakes every day for various testing purposes. Never thought a thing of it. But that was ages ago, before the Chinese got into the cheap auto-lift business. This was with professional-level air-over-hydraulic in-ground lifts.

Rustbucket79 · Jan 18, 2023

Im in the process of trying to bleed the rear brakes now after an accidental emtying of the master cylider..
Did a first try as Im used to on other cars (bench bleed MC, bleed rear>front), got superspongy feel and after that read about the RWAL issue.
I have the second version of it, like post #3

I want to avoid removing the RWAL if possible.
Techtool or hard braking is mentioned here to remove air in the unit.

But looking at the thing its only four cables. Two solenoids and a switch?
Seems to be easy enough to move the solenoids with only 12V input, anyone tried it?

WV_Dave · Jan 18, 2023

I've also wondered if you can swap out a late model RWAL unit (w/o bleeder) for an early unit that does have the bleeder. Looks like the same colored wires and plug.

Can you bleed RWABS with the truck in the air?

Fireball5657

I'm Awesome

Supercharged111

Truly Awesome

Fireball5657

I'm Awesome

Drunkcanuk

I'm Awesome

Supercharged111

Truly Awesome

Fireball5657

I'm Awesome

studigggs

I'm Awesome

Schurkey

Supporting Member

Rustbucket79

Newbie

Attachments

WV_Dave

OBS Enthusiast

Similar threads

Latest posts

Staff online

Members online

Forum statistics

Share this page