Hey guys,

Just before I head to a dealer to have it looked at, I wanted to run this by you. I have a 99 GMC Sierra 5.3L "3-door" w/ 56,000 miles. It seems all the sudden my ABS seems to trigger WAY too easily. It had always been ABS happy, like going over a steel bridge joint while slowing down, but this is very different. This is straight line, normal stopping on dry pavement from normal speeds at a normal rate. It seems like the ABS is kicking in.
Except its not the "ABS Feeling" I'm used to. Its not a ultra-quick pulsation, but more like an aggressive clunky grab in succession.
I'm wondering if it could be something else other than ABS? The brakes were redone about 10k miles ago, all the way around new rotors and pads. Aside from a heat shield that I had to bend out a bit, I didn't notice any problems.
Its very freakish feeling and I think rather loud, as I think a few cars looked at me when it happened a ton of times today (did alot of driving today).

Any thoughts so I can have an idea what the dealer or other GMC/chevy dealer will spit out at me? The car is kept in pretty good shape, oil changes, air filters, tire pressure, etc etc. never any major problems except a sticky throttle blade (jerky throttle action), but that was replaced under warranty. Aside from the "one running light" malfunction that it seems every truck of that year had (fixed) and the "piston slap" like noise on startup, its been fine.
Any thoughts? And are ABS sensors expensive?

thanks,
BTW, this is a 2wd/4wd/auto 4 wheel with a 4L60E and trailer package, if that makes a difference at all.
matt

Possible loose caliper mounting bolt????

Someone local suggested a (high or low?) I forget spot in the rotor since I don't drive it much anymore. Is this realistic?

Thanks guys

matt

I'm no ABS expert, but it does sound like a sensor, sensors or the wiring to them. You might not be getting any output from one of them, the computer sees it as tire locking and engages the ABS. You would need to determine which wheel is causing the problem. You could also remove the ABS fuse and drive it a short distance to be sure is not a mechanical problem.

My 99 5.3 Silverado was like that even when it was new. I put Rancho RS-9000 shocks on at about 4K miles, and the problem went away.

Matt,
My 99 Tahoe has done the same thing since it was new. It acts like there is a thickness variation on the rotors. The strange thing is it comes and goes. It will be fine for weeks at a time and then it will do it a few times. It is always at slow speeds too, like stopping for a light in normal traffic. I did the brakes at about 60 k miles. The rotors measured fine with absolutely no runout so I left them alone. I think if it was a rotor it would always do it.
If you figure it out let me know, I have gotten used to it to the point that it doesn't bother me any more. The truck stops great and I have never had any issues with the ABS. The only time it has come on is during a couple of hard stops in the rain, and in the snow.

I'll keep you guys posted. I'm going to get it checked out when I have some spare time. Have to find a close-by dealer in boston to look at it.
I'm only worried since its not the normal ABS feelings. I've felt the ABS once or twice for real stopping in hard rain, and then the fact it engages very easily (but briefly) if I'm slowing down normally over say some steel bridge joint.
Its just this is a much "slower" grabbier feeling. I'm going to be busy the next two weeks, but am going to make an appointment. If they say anything noteworthy, I'll let you know. Its just not a normal ABS feeling, and its dry pavement from like 35mph to 5-10mph slowdowns in normal stop & go traffic.

matt

My 99 GMC Sierra 3 door Z-71 has done this since new also.. many trips to dealer and NUTTIN WRONG.. Ya get used to it I guess :clonk:

Shoulda bought a Chevy and an 02 instead of a 99. ;)

What did you find out about it? I just got a recall on my 01 for the front ABS sensors triggering the brakes when it shouldn't.

My 2003 Sierra has always been ABS happy too. Maybe I will see a recall also.

It just started happening about two weeks ago. I got a recall notice in the mail yesterday for 10 to 3 mph stops (exactly what i was noticing). Musta caused a few rear enders..

Its not the ABS happiness that I noticed after 56k miles. Its an ABS malfunction I noticed after 56k miles. Then the recall comes just days after I notice it..

Odd..

matt

I have the same truck and mine did this as well.I had to replace the rear hubs because the rust out really bad.I changed brakes all the way around and problems went away.The rears were rusted really bad and heard this is a problem with gm. I also got a recall last week IN THE MAIL ON THIS.bill

These trucks are known for premature abs operation. Usually the abs kicks on when you're slowing down and close to a full stop. If this is what is happening, the front abs sensors have a rust buildup under them. This causes the sensor to lift up, away from the tone wheel inside the wheel bearing. More air gap between the sensor and tone wheel and the weaker the signal. sooooo, if this is happening to you, pull the wheel, caliper and rotor off, the sensor is bolted into the spindle behind the hub with a 4 or 5 mm hex. Pull the sensor out carefully. Clean the rust with a file and also file the metal ring around the bolt hole in the sensor a bit. Apply anti seize to the surface and re install. Hope this helps your situation.

Here's a copy of the bulletin that describes this problem:

Document ID# 1205328
1999 Chevrolet Chevy K Pickup - 4WD


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Antilock Brake (ABS) Activation At Low Speeds (Clean Wheel Speed Sensor Mounting Surface) #02-05-25-006A - (Nov 26, 2002)
Antilock Brake (ABS) Activation At Low Speeds (Clean Wheel Speed Sensor Mounting Surface)
1999-2000 Cadillac Escalade

1995-1999 Chevrolet Silverado (Old Style)

1995-2000 Chevrolet Suburban, Tahoe (Old Style)

1995-2003 Chevrolet Astro Van, Blazer, S10

1995-1999 GMC Sierra (Old Style)

1995-2000 GMC Yukon, Yukon XL (Old Style)

1995-2001 GMC Envoy, Jimmy

1995-2003 GMC Safari Van, Sonoma

1995-2001 Oldsmobile Bravada

This bulletin is being revised to change model information. Please discard Corporate Bulletin Number 02-05-25-006 (Section 05 -- Brakes).

Condition
Some customers may comment on ABS activation at low speeds, usually below 8 km/h (5 mph). Upon investigation, the technician will find no DTCs set.

Cause
The cause of this condition may be an increased air gap between the wheel speed sensor and the hub reluctor ring due to rust and debris built up on the sensor mounting surface.

Correction
Measure AC voltage and clean wheel speed sensor mounting surfaces.

Raise the vehicle on a hoist.
Disconnect both the front wheel speed sensor harness connectors.
Place a DVM across the terminals of each sensor connector.
Rotate the wheel with hand speed and measure the ACmV's. The reading should be at least 350 ACmV's.
If the reading is between 200 and 350 ACmV's, remove the wheel, caliper and rotor in order to gain access to the speed sensor.
Remove the wheel speed sensor and plug the hole to prevent debris from falling into the hub during service.
Clean the speed sensor mounting surface on the hub to remove rust and corrosion.

Important
Make sure that the sensor sits flat on the hub. If the sensor flange is distorted, replace the sensor.


Apply a thin layer of bearing grease to the hub surface prior to sensor installation.
Install either the original sensor or a new one in the hub and secure the sensor. Ensure that the sensor is seated flush against the hub.
Install the rotor, the caliper and the wheel.
Place the DVM across the sensor terminals and recheck the voltage while rotating the wheel by hand. The voltage should now read at least 350 ACmV's.
Warranty Information
For vehicles repaired under warranty, use:

Labor Operation
Description
Labor Time

H2412
Sensor, Wheel Speed (Front Both) - Replace
Use published labor operation time




GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information.
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© Copyright General Motors Corporation. All Rights Reserved.


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Document ID# 1205328
1999 Chevrolet Chevy K Pickup - 4WD

rear shocks
been through this with my gmc and my dodge
they just let the wheel skip a little and the abs goes nuts