Another ABS question

[Alaskaburb]

Good morning and thanks for reading. I have done quite a bit of searching before asking here.

1993 K2500 Suburban, 5.7 with hydroboost, 4x4

Backing down the boat ramp a few months ago and my ABS light came on. I no longer have the 10mph whirring sound that I assume came from the ABS unit. This happened right after I installed a Posi-lock 4x4 kit. Currently both the ABS and brake idiot lights are on. I am out in the boonies with this suburban and there are no shops with the older OBD1 tool to test and bleed my system. It is probably not cost effective or even possible to test, replace or rebuild the ABS unit and get it bleed properly here.

Recently I have a complete rear brake service with drums, pads and hardware kit. Everything seemed great and rig appeared to be stopping well and smoothly. When I was putting my boat in the water a few weeks ago I could not stop my boat without using the E brake. The fronts did lock but as a result I lost steering. I came pretty close to being in one of the videos where the boat pulls the tow vehicle into the water. I could not get my drums to work well enough without the E brake. Once I stood on the E brake I could control my backing speed and the fronts did not lock.

Questions:

1. Do I just unplug all connectors going into the ABS unit to disable it and turn off the lights? I do not have the fuse to pull like on the 95 and newer units.

2. Will bypassing the ABS unit entirely and installing a Wilwood proportioner simplify things for me?

3. Do my rear drums auto adjust? I am pretty sure they do but I just want some clarification.

 

[Schurkey]

1993 K2500 Suburban, 5.7 with hydroboost, 4x4

I no longer have the 10mph whirring sound that I assume came from the ABS unit.

First Guess: The "10mph whirring sound" was telling you that there was something wrong with the speed sensors.

This happened right after I installed a Posi-lock 4x4 kit.

That's the cable-controlled front axle disconnect retrofit?

Currently both the ABS and brake idiot lights are on.

ABS light means the ABS unit is unhappy, and almost certainly has codes stored. Retrieve the codes, follow the service manual procedures for each code.

BRAKE light in the instrument cluster is triggered three ways:
1. Park brake engaged; or park brake switch problems.
2. Hydraulic system pressure imbalance--lack of pressure to front, or rear of brake hydraulic system, or
3. ABS problem

It's possible to have more than one reason the BRAKE light is on. Hydraulic failure + ABS problem, or ABS problem + park brake, etc.

I am out in the boonies with this suburban and there are no shops with the older OBD1 tool to test and bleed my system. It is probably not cost effective or even possible to test, replace or rebuild the ABS unit and get it bleed properly here.

Bleed brakes as best you can. If you still have problems, you're gonna have to find someone with a scan tool, or buy a scan tool, to at least verify the speed sensors and codes and such; if not actually auto-bleeding the ABS.

I'm not saying you shouldn't find a way to auto-bleed the ABS, just acknowledging that you're saying it's not possible to find someone with the proper tools. Maybe you should buy your own.

Recently I have a complete rear brake service with drums, pads and hardware kit. Everything seemed great and rig appeared to be stopping well and smoothly. When I was putting my boat in the water a few weeks ago I could not stop my boat without using the E brake. The fronts did lock but as a result I lost steering. I came pretty close to being in one of the videos where the boat pulls the tow vehicle into the water. I could not get my drums to work well enough without the E brake. Once I stood on the E brake I could control my backing speed and the fronts did not lock.

That's scary. You NEED to find out if the speed sensors are working; and ideally verify the entire brake system including the ABS.

You also need to find out if the rear brakes are working like they should. It's possible that on dry pavement without a load, the truck is stopping because of the front brakes, and the rears don't work at all. I have seen this more than once.

Find a SAFE stretch of road. Get up to highway speed, and brake FIRMLY to a stop. Use an infrared themometer to check the temperature of all four wheels. Both front wheels should be about the same temperature, and fairly hot. Both rear wheels should be the same temperature, and fairly hot. If any wheel is cool...that brake is weak or non-functional.

1. Do I just unplug all connectors going into the ABS unit to disable it and turn off the lights? I do not have the fuse to pull like on the 95 and newer units.

Work harder at getting it to perform properly, before you think about disabling it.

2. Will bypassing the ABS unit entirely and installing a Wilwood proportioner simplify things for me?

Sure. Screwing-up a system is almost always simpler than fixing it properly.

You bypass the ABS "entirely" and you'll lose the metering valve, the safety switch, and the proportioning valve. Then you're going to replace only the proportioning valve.

Guys do this, but it's not a great idea.

3. Do my rear drums auto adjust? I am pretty sure they do but I just want some clarification.

I expect you have the 11.x inch, Duo-Servo rear drums. They self-adjust every time you back up and release the brakes after applying the brakes firmly.

Since the rear brakes have just been serviced, I expect that the adjuster mechanism is in fine condition, or the folks doing the rear brake job didn't do an acceptable job.

 

[Alaskaburb]

Here is what I have learned.

1. I do not have any stored codes using the paperclip method. I am on the list for the community scan tool.

2. When I disconnect the power to the ABS unit by unplugging the wires the ABS light goes out but the brake light stays on.

3. I was thinking I would toss a few parts at it and swap out the front wheel speed sensors. My sensors are held on by two screws and look nothing like anything that comes up when I search. Mine has two T30 torx screws holding on a rectular block shaped unit. I searched 1500, 2500 and 3500 vehicles with no luck.

 

[Schurkey]

1. I do not have any stored codes using the paperclip method. I am on the list for the community scan tool.

I don't think the usual "paperclip method" will retrieve ABS codes. Check your service manual set, maybe you can jump a different pin in the diagnostic connector to get ABS codes.

2. When I disconnect the power to the ABS unit by unplugging the wires the ABS light goes out but the brake light stays on.

Verify the OTHER two things that trigger the BRAKE light.

3. I was thinking I would toss a few parts at it and swap out the front wheel speed sensors. My sensors are held on by two screws and look nothing like anything that comes up when I search. Mine has two T30 torx screws holding on a rectular block shaped unit. I searched 1500, 2500 and 3500 vehicles with no luck.

SUVs had different ABS units from the more-common pickups. I expect your sensors don't plug into the wheel hubs, they're external and trigger off of an external tone wheel on the CV shaft.

 

[Alaskaburb]

Verify the OTHER two things that trigger the BRAKE light.

How do I check hydraulic system pressure imbalance?

 

[Vikingdude]

How do I check hydraulic system pressure imbalance?

The combination valve has a feature, under pressure if the volume of fluid moving on one side is much greater than the other it will move a plunger and block that side. I'd start by doing a good 4 wheel bleed and seeing if you get any flow at all on the back wheels.
As a resident of the Yukon, I know what it's like to live in the boonies and not have access to the right tools or a mechanic. That said, you're currently a danger to yourself and everyone else in the road because you've ignored the dash lights for so long. Get it fixed asap or take it off the road.

 

[Alaskaburb]

Thanks for the reply Vikingdude. The light is fairly new and I am in a very small town yet aggressively working on the problem. It I really get ripping on the way to the boat ramp I might hit 20mph since its mostly gravel and just over a mile away. Last time I took it to Ketchikan is was specifically to have a shop see if they could fix the ABS. They put on new drums, shoes and a complete hardware kit. They bled the system the old school way but lack the proper OBD 1 tool to address the bleeding the ABS unit. Work in progress

 

[Schurkey]

How do I check hydraulic system pressure imbalance?

Disconnect the wire from the Safety Switch on the combination valve. If the light goes out, it was the Safety Switch that was triggering it.

Ground the wire that was on the Safety Switch. Light should come on. Tests the wiring and the bulb.

 

[Alaskaburb]

Disconnect the wire from the Safety Switch on the combination valve. If the light goes out, it was the Safety Switch that was triggering it.

I unplugged the wire with no change.

New question. Oddly enough in this little town of 200 people an acquaintance has a Snap-On Solus Pro and loaned it to me. It does not have the correct adapter for my OBD1 system but it appears the software is on it. I have the community scanner on the way with the adapter for that unit. Looking at the Snap-On site it appears to the same one I need. Do you think I will be able to use that externally powered adapter on this newer unit? If it does I will be able to use the scanner to cycle the ABS unit. Thanks so much for your time and replies!

 

[Schurkey]

I unplugged the wire with no change.

So look at the other two possibilities for lighting the BRAKE light:
The switch on the emergency brake pedal assembly, and
The ABS.

an acquaintance has a Snap-On Solus Pro and loaned it to me. It does not have the correct adapter for my OBD1 system but it appears the software is on it. I have the community scanner on the way with the adapter for that unit. Looking at the Snap-On site it appears to the same one I need. Do you think I will be able to use that externally powered adapter on this newer unit? If it does I will be able to use the scanner to cycle the ABS unit. Thanks so much for your time and replies!

Yup. The Snappy cables 'n' connectors from the MT/MTG2500 can be used with the Solus and Solus Pro. That's what I'm using for GM OBD-1.

I've never tried to bleed the kind of ABS unit your truck has--EBC4. No promises on whether the Solus Pro of any software revision will do an auto-bleed; but you should be able to get all the data on speed sensors and the like.

MAYBE a Solus Pro with the appropriate software revision will work. Mine with 8.2 software will not auto-bleed my '97 K2500; although it will auto-bleed my '03 Trailblazer. A Solus Pro with 14.2 software WILL auto-bleed my '97.

You'll also need two or three of the GM J-39177 "special tools" (or aftermarket/home-made equivalent) for holding the valves open