1997 K2500 ABS activates on first stop after start-up

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slovcan

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Hi folks,

Well, I am almost there in getting her back to almost like new daily driver condition.

Recently I noticed that instead of just getting the ABS test cycle practically before I get out of the driveway (or maybe in addition to that) I am getting a definite ABS activation when almost stopped at a stop sign. This will be 400 meters (~1/4 mile) from the house. There is nothing to feel in the brake pedal as such, just that fast ratcheting sound most times. Occasionally it won't make that sound, but will get a single thud type of thing that I do feel in the brake pedal. This is almost at a stop on dry roads and normal - even gentle - braking.

The first time I really noticed this was a couple of days ago. I got to a stop sign and the truck went dead - engine stopped dead - suddenly. It was a momentary total electrical failure. First time that or anything like it ever happened. I had it happen on a bike once. I took off the battery terminals and cleaned them, put them back on and it never happened again. Anyway, when it happened on the truck even the clock lost its time and went to 1:00. As quick as I looked at the dash I had the normal key on-engine off indicator lights so I slipped her into neutral and started her right back up. At the next stop sign - again about 400 meters - I got the ABS activation. I discovered the battery ground terminal was just a bit loose. I have a top post battery (pretty new) and have a lead top post adapter that the original side terminal screws into. I cleaned it and reconnected it - tight.

A few days before that I had started noticing a single kickback in the brake pedal if I pressed it too quickly - not hard, just quick - and in the first little bit of pedal travel. I checked the power steering fluid (hydroboost) and the dipstick was dry. Now, there are no leaks and the master cylinder reservoir is at the normal level. I think it must be from a year or more ago - almost two even - when I had the steering box changed. It must not have been fully bled and the level dropped after a while. There has never been any noise or any other indication of low fluid level. I topped it up with fresh GM power steering fluid and the symptoms have not changed.

Last thing, about 1000 kms ago I had new tires put on - 265/75x16 Cooper Discoverer AT/S instead of the stock 245/75x16.

So guys, any ideas? Preferably inexpensive ideas...

Thanks,
Glenn
 

Nad_Yvalhosert

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Ahhh, the notorious "Unwanted ABS activation at slow speeds". All too common... GM trucks have long suffered from this affliction.
Aside from a loose wheel bearing, after time and rust, the ABS Sensor pulls away from the reluctor wheel inside the wheel bearing, increasing the air gap. The system then pulses the ABS under 3 MPH because it thinks the brakes are in "lock up"

"Fix 1" pull the ABS fuse and ignore it.
"Fix 2" pull both front calipers and rotors. Carefully remove both sensors, put an old tire valve stem cap into the hole to keep shavings/debris from entering the reluctor wheel cavity. Grind the bearing surface clean of rust, treat the metal with an anti-rust paint. Then reassemble and hope for the best.
"Fix 3" replace both wheel bearing assemblies.

Both my old '99 Jimmy, and my '98 Suburban 2500 have had this problem.
 
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slovcan

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Ahhh, the notorious "Unwanted ABS activation at slow speeds". All too common... GM trucks have long suffered from this affliction.
Aside from a loose wheel bearing, after time and rust, the ABS Sensor pulls away from the reluctor wheel inside the wheel bearing, increasing the air gap. The system then pulses the ABS under 3 MPH because it thinks the brakes are in "lock up"

"Fix 1" pull the ABS fuse and ignore it.
"Fix 2" pull both front calipers and rotors. Carefully remove and sensors, put an old tire valve stem cap into the hole to keep shavings/debris from entering the reluctor wheel cavity. Grind the bearing surface clean of rust, treat the metal with an anti-rust paint. Then reassemble and hope for the best.
"Fix 3" replace both wheel bearing assemblies.

Both my old '99 Jimmy, and my '98 Suburban 2500 have had this problem.

Awesome, thanks man. The wheels have been off and on a lot in the past couple of months. May have affected the ABS sensor. I will give fix #2 a try first.

Cheers,
Glenn
 

Ehall8702

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Ahhh, the notorious "Unwanted ABS activation at slow speeds". All too common... GM trucks have long suffered from this affliction.
Aside from a loose wheel bearing, after time and rust, the ABS Sensor pulls away from the reluctor wheel inside the wheel bearing, increasing the air gap. The system then pulses the ABS under 3 MPH because it thinks the brakes are in "lock up"

"Fix 1" pull the ABS fuse and ignore it.
"Fix 2" pull both front calipers and rotors. Carefully remove both sensors, put an old tire valve stem cap into the hole to keep shavings/debris from entering the reluctor wheel cavity. Grind the bearing surface clean of rust, treat the metal with an anti-rust paint. Then reassemble and hope for the best.
"Fix 3" replace both wheel bearing assemblies.

Both my old '99 Jimmy, and my '98 Suburban 2500 have had this problem.


We pull em, buff em clean paint and then thin layer of grease and put grease around the sensor where it meets bearing surface to prevent water intrusion and same issue happening again. We use sum real thick grease, which I think was made for the big horse shoe thing on a semi that hooks to a trailer. It's THICK and doesnt seem to go away bc of brake heat. Have seen it still there almost a year later when doing brakes on a vehicle I cleaned the abs sensor up on atleast a year ago. Great advice, sensors are about $60 and parts store bearings are $180 , so a good budget option, unfortunately most of the sensors we try and pull out don't come out bc rust has locked em in and end up needing a new sensor. Have to take a small piece of rag and stuff down over tone ring and use die grinder to clean the bore the sensor sits in. Here in the UP we have to combat rust on EVERYTHING!
 

slovcan

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We pull em, buff em clean paint and then thin layer of grease and put grease around the sensor where it meets bearing surface to prevent water intrusion and same issue happening again. We use sum real thick grease, which I think was made for the big horse shoe thing on a semi that hooks to a trailer. It's THICK and doesnt seem to go away bc of brake heat. Have seen it still there almost a year later when doing brakes on a vehicle I cleaned the abs sensor up on atleast a year ago. Great advice, sensors are about $60 and parts store bearings are $180 , so a good budget option, unfortunately most of the sensors we try and pull out don't come out bc rust has locked em in and end up needing a new sensor. Have to take a small piece of rag and stuff down over tone ring and use die grinder to clean the bore the sensor sits in. Here in the UP we have to combat rust on EVERYTHING!

Thanks for the advice, Ehall. I suppose I should get a sensor just in case before we start the job. Worst case I'll have a spare for the future. Are the sensors all equal with regard to functioning? I bought an aftermarket one last year for my Rover 75 and it was worse than the original one I took out. I put the original back in and will have to buy the expensive factory one.

For what it's worth, my truck has no rust, even still has the original exhaust and muffler after 278,000 kms. Maybe I can dodge the rust bullet on the sensors.

Thank you,
Glenn
 

Ehall8702

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Thanks for the advice, Ehall. I suppose I should get a sensor just in case before we start the job. Worst case I'll have a spare for the future. Are the sensors all equal with regard to functioning? I bought an aftermarket one last year for my Rover 75 and it was worse than the original one I took out. I put the original back in and will have to buy the expensive factory one.

For what it's worth, my truck has no rust, even still has the original exhaust and muffler after 278,000 kms. Maybe I can dodge the rust bullet on the sensors.

Thank you,
Glenn
We only buy the acdelco sensors, I can't tell the difference between cheap ones and acdelco ones but am very sure the build quality is better on acdelco. I personally , if it was mine, just buy a new wheelbearing from Detroit axle ( same or less than sensor ) and just put a new bearing in. Takes me about 30 minutes to put a bearing in but I do more than a dozen a week so I've got it down to an art, not quite as easy for alot of ppl. I run and recommend detroit to all my personal customers. Better than anything u can get off the shelf locally and WAAAY less. Moog is garbage, mechanics choice is ok but still twice the cost of detroit, skf is good but is roughly $250 for one. Every bearing u can get locally is owned by federal mogul and just plain over priced junk imho.
 

slovcan

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Thanks for your recommendations Ehall. I'm afraid up here in the Great White North we don't have the same parts availability as you folks. Most bearing hub assemblies are made in China even if sold by a Canadian company and shipped from Canada. Even then they are $100 and up each. Proper name brand ones are $250+. I'm going to have to go the clean up and cross my fingers route. If I have to replace them I can get a pair of AC Delco sensors for $120.

Cheers,
Glenn
 

Ehall8702

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Thanks for your recommendations Ehall. I'm afraid up here in the Great White North we don't have the same parts availability as you folks. Most bearing hub assemblies are made in China even if sold by a Canadian company and shipped from Canada. Even then they are $100 and up each. Proper name brand ones are $250+. I'm going to have to go the clean up and cross my fingers route. If I have to replace them I can get a pair of AC Delco sensors for $120.

Cheers,
Glenn
I'm in the great white north myself lol, just the one attached to the lower 48...Idk how much harder shipping is to Canada but unless ur rural asf prolly not to bad. Jut saying, hope it works out for ya with just the sensor tho!

https://www.ebay.com/itm/150694487684
 
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