This ABS Sucks

I don't mind ABS most of the time. I like retaining steering control at max braking, especially in slippery conditions. It makes front/rear brake bias a lot less critical But the ABS module in my 99 Suburban K1500 is complete garbage. I could do threshold braking more efficiently in my sleep than this awful module does. When a speed sensor comes close to detecting lockup, that module kicks on for AGES and basically prevents braking altogether for way too long. This isn't a defect, I remember my 1998 K2500 pickup (which had hydroboost) behaving exactly the same way. It just seems to be a crappiness of all GMT400 ABS setups.

Is ABS controlled by the PCM? Or is it self contained within the ABS module? Is it possible to retrofit a more recent ABS module from a newer vehicle that doesn't suck? Perhaps something that actually pulses the brakes individually rather than lock out the brake pedal for seconds at a time?

Mine does it too, by the time the system does something, the wheel is back on the ground, but it's pulling breaking anyway even though I need it. Usually it's a bump in the road near a stop light that sets it off.

My 94 s
Sub would pulsate the pedal all the way to the floor straight through a stop sign. In the Summer on dry streets.

Pulled it and ran a 1975 Camaro prop valve. Toss you out on the hood after.

'99 ABS should be a 3-channel system. The front brakes are controlled individually, the rear brakes are separate from the front, but the two rear brakes are controlled as a pair. I would be figuring-out what's wrong with the brake system potentially including the ABS rather than merely scrapping the ABS and hoping for the best.

Why is your ABS screwing with brakes that haven't locked-up? Does the scan tool show appropriate speed at the three speed sensors? Is it consistent--you don't have one or more sensors going to "0" when the actual speed is above 3 mph? All three sensors read the same speed all the time? When ABS gets too "sensitive" and activates too often especially at low speed--it's generally a fault with one or more speed sensors or sensor wire harnesses.

Are the rear brakes adjusted? All four shoes contacting the anchor pin when not applied? Park brake holds when the pedal is kicked? Rear brakes can be bled--the rear brake hose isn't plugged, and the cylinders receive pressure and fluid volume? Shoes not contaminated with brake fluid or axle lube? Drums and linings in good condition?

How old are the front calipers? Pistons stuck or getting stiff to move? JB/JD6? Is the Quick-Takeup valve in the master cylinder weak--not moving the pistons in the calipers like it should? Pads have reasonable service life left in them? Calipers float freely on the guidepins?

What happens when you cram your foot onto the brake pedal, then chatter the valves in the ABS unit with a scan tool? Do you feel the ABS activity in the brake pedal? Have you ever properly-bled the ABS unit using a scan tool?

There's a BMW setup the C5 Corvette guys use when they go standalone and ditch the BCM and everything else. It's able to operate as a standalone system and you can put in a rheostat as a sort of global gain knob. I'm sure there are others out there if a guy were to do a search, but you'd need to have 4 channels to hook into so plan to run some brake lines. I agree the 3 channel setup is straight up garbage, when I first bought my 1500 in sig I think I made it a mile or 2, got out and unplugged the damn thing. Dually has a wheel speed sensor out so that one was taken care of from the get go.

Schurkey said:

[a whole lot of stuff that doesn't relate with what I posted at all]

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I didn't say there was anything wrong with the brakes. The brakes work fine. At no point did I imply there was anything wrong with the brakes. They grab, they bring the vehicle to a complete stop quickly, zero issues. Where did you get the idea that there was anything wrong with my brakes?

My complaint is with the quality of the ABS system. It's garbage. I'm well aware that it's a 3-channel system, and I fully understand how that works. My point is, instead of pulsing the locked-up channel to prevent lockup, this system literally locks out the brake pedal for an eternity to allow the wheels to regain momentum. It might only be a fraction of a second, but it's a looong fraction of a second, and in a panic braking situation on slippery surfaces, it makes all the difference between "whew" and *smash*. There's no malfunction here, that's how this ABS system is intended to work, and it's garbage. Every GMT400 vehicle I've ever driven behaved this way. There's testimonials in this very thread that confirm it.

Supercharged111 said:

There's a BMW setup the C5 Corvette guys use when they go standalone and ditch the BCM and everything else. It's able to operate as a standalone system and you can put in a rheostat as a sort of global gain knob. I'm sure there are others out there if a guy were to do a search, but you'd need to have 4 channels to hook into so plan to run some brake lines.

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I have one of those BMW MK60 setups that I was planning to install in my 96 Buick Roadmaster wagon build. They're really nice and provide excellent ABS control for a surprisingly reasonable cost. But like you said, they're 4-channel only and would require installing individual wheel speed sensors at the rear. That's why I was hoping that an existing, more modern GM 3-channel module might be available to retrofit.

Nahh, the 3 channel era was a bit of a transition. I got to thinking after posting though, might be worth a shot to split the VSS 2 ways and treat the single rear channel as 2? Chances are you're locking a front wheel and not a rear, so it might actually work out decently.

GoreMaker said:

I didn't say there was anything wrong with the brakes. The brakes work fine. At no point did I imply there was anything wrong with the brakes. They grab, they bring the vehicle to a complete stop quickly, zero issues. Where did you get the idea that there was anything wrong with my brakes?

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I'm not there to drive it, or to view data on the scan tool.

I am entirely used to people blaming the ABS when in fact they have brake system problems apart from the ABS, or--sometimes--in addition to ABS problems. I'm trying to be thorough.

YOU said that the ABS "module kicks on for AGES and basically prevents braking altogether for way too long. This isn't a defect." Yes, of course that's a defect. And making a wild guess with too-little evidence, I bet you've got weak signal from the front wheel speed sensors; the ABS thinks the front wheels are locked, so it "prevents braking" in front, leaving your truck relying solely on the rear brakes. But it could be something else--a plugged rear brake hose on my '68 'Camino resulted in truly pathetic stopping power. Say you've got a plugged rear hose, and then the ABS shuts down both front brakes due to sensor problems. Now you've got no brakes just as you've described.

THEN you say "Perhaps something that actually pulses the brakes individually rather than lock out the brake pedal for seconds at a time?" Well, sure. THAT'S EXACTLY HOW YOUR EXISTING ABS MODULE IS SUPPOSED TO WORK, if something wasn't WRONG WITH IT, and almost certainly fixable. You should have three separate channels of independent anti-lock action.

GoreMaker said:

My complaint is with the quality of the ABS system. It's garbage. I'm well aware that it's a 3-channel system, and I fully understand how that works.

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You don't give that impression. You seem to think that all three channels get blocked whenever one channel senses lockup.

GoreMaker said:

My point is, instead of pulsing the locked-up channel to prevent lockup, this system literally locks out the brake pedal for an eternity to allow the wheels to regain momentum. It might only be a fraction of a second, but it's a looong fraction of a second, and in a panic braking situation on slippery surfaces, it makes all the difference between "whew" and *smash*. There's no malfunction here, that's how this ABS system is intended to work, and it's garbage. Every GMT400 vehicle I've ever driven behaved this way. There's testimonials in this very thread that confirm it.

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Your first post claims you've got a vehicle that "prevents braking altogether for way too long" and your next post says "At no point did I imply there was anything wrong with the brakes. They grab, they bring the vehicle to a complete stop quickly, zero issues." What am I supposed to think?

Maybe you need to provide better descriptions of what is going on in the FIRST post of a thread you start.

Once again...when was the last time you bled the ABS with a scan tool? Do the speeds registered by the speed sensors agree with one another?

Or maybe you had a predisposed opinion and that colored how you read my post. Everyone else who replied knew exactly what I was describing and concurred

For what it's worth, that "newbie" tag by my name applies to my time on this forum, not my expertise. I've been building brake systems from scratch for over a decade: manual, vacuum assisted, hydroboost, with and without ABS... I'm plenty qualified to declare that the ABS module on GMT400 vehicles is garbage. I was asking for advice on a suitable replacement.