Abs Pulsing At Slow Speed

[GAT]

My 2001 2500HD is acting like it is sliding on ice. My abs pulses at slow gradual stops. I was told to clean the ABS sensors but I am not sure how to get to them I assume the front wheels but where do I find the sensors and how do I get to them???

Any help would be appeciated.

Gat

[ukrkoz]

this should help. you have bleeding/diagnostic/sensor locations:
http://www.autozone.com/shopping/rep...00c152801b4a86

[j cAT]

Originally Posted by GAT

My 2001 2500HD is acting like it is sliding on ice. My abs pulses at slow gradual stops. I was told to clean the ABS sensors but I am not sure how to get to them I assume the front wheels but where do I find the sensors and how do I get to them???

Any help would be appeciated.

Gat

first see if you are under the recall....NHTSA has determined that your vehicle has a defect....call dealer with vin #....they will let you know...



second before you bring to dealer make sure that the front rotors will come off....many have had to pay 1200.oo for this FREE recall....just another way to scam you....so you have been warned...


the sensors are under the rotors and rust from the cheap metal they used forces the sensors out of position also you may have a bad wheel bearing ...this is a common problem...

[GAT]

Nothing there to help but thanks, I know it's not a bleeding issue.

[GAT]

Originally Posted by j cAT

first see if you are under the recall....NHTSA has determined that your vehicle has a defect....call dealer with vin #....they will let you know...



second before you bring to dealer make sure that the front rotors will come off....many have had to pay 1200.oo for this FREE recall....just another way to scam you....so you have been warned...


the sensors are under the rotors and rust from the cheap metal they used forces the sensors out of position also you may have a bad wheel bearing ...this is a common problem...

Sorry I didn't see all of this. You are right it is the corrosion or at least that is what I was told, I am going to look into that tomorrow night. As for recall I did see a recall posted back in August of 05 for this very same thing, but Chevy did not want to accept it.

[ukrkoz]

Originally Posted by GAT

Nothing there to help but thanks, I know it's not a bleeding issue.

if you patiently scroll down through the pages, it does tell you how to diagnose possible problems AND sensor location, just like you asked. even has a nice picture.

[kahjdh]

One of your front wheel speed sensors is off, you need to find somebody with a graphing scanner to figure out which one. Dont go by the ABS codes alone b/c they are not always right. What you are looking for is when you come to a stop there will be 3 sensors(RF, LF, and rear) that will decelerate and probably around 5mph one of the will jump to 0mph when the other 2 are still at 5, thats the bad sensor.

[j cAT]

Originally Posted by kahjdh

One of your front wheel speed sensors is off, you need to find somebody with a graphing scanner to figure out which one. Dont go by the ABS codes alone b/c they are not always right. What you are looking for is when you come to a stop there will be 3 sensors(RF, LF, and rear) that will decelerate and probably around 5mph one of the will jump to 0mph when the other 2 are still at 5, thats the bad sensor.

the speed sensors do not read MPH what they do is produce an A/C signal that is generated by the passing of a tooth gear across the sensor face... when the sensor is pushed out of position [further away from gear] the amplitude drops off... at low speeds this signal is so small the computer can't input it to calculate speed...

[j cAT]

Originally Posted by GAT

Sorry I didn't see all of this. You are right it is the corrosion or at least that is what I was told, I am going to look into that tomorrow night. As for recall I did see a recall posted back in August of 05 for this very same thing, but Chevy did not want to accept it.

the only reason for denial may be high mileage...that I can think off....It is GM's policy that if you have over 100,000mi on vehicle it is at the end of its life cycle.....

[GAT]

Originally Posted by j cAT

the speed sensors do not read MPH what they do is produce an A/C signal that is generated by the passing of a tooth gear across the sensor face... when the sensor is pushed out of position [further away from gear] the amplitude drops off... at low speeds this signal is so small the computer can't input it to calculate speed...

This is where we are heading tonight. We are going to remove the wheels tonight, brake calipers and rotors. Then remove the device that senses the wheel speed by removing a set screw that holds it in place and cleaning the contacts that sense all this. My son has a friend that works as a mechanic at a Chevy dealership and said this problem is very common and if you can get the set screw out I should be able to clean the corrosion away and solve the problem. I guess rust and other crap gets in there and pushes it away far enough it does not sense properly just like you mentioned above.

I apologize for my lack of patience and not looking far enough into the link sent by UKRKOZ and also that all of you for help. I am going to try and find some phots of this stuff to help as well.

GAT

[spytearbite]

Do you have warped disc? An out of true or say there is a high-spot on the disc run-out? Then, there is your pulse at slow speed, not an abs problem, but more disc out of true is push the piston back into the caliper on the high spot; is push your pedal back and forth on the slow; you feeling each 360 degree turn on the disc.

[GAT]

Originally Posted by spytearbite

Do you have warped disc? An out of true or say there is a high-spot on the disc run-out? Then, there is your pulse at slow speed, not an abs problem, but more disc out of true is push the piston back into the caliper on the high spot; is push your pedal back and forth on the slow; you feeling each 360 degree turn on the disc.

Don't think so, Both front rotors are new as are both calipers and hubs, all replaced in the spring.

[spytearbite]

Did the new discs come with tone rings? Or say, did they reinstall the matching OEM with some sort of 'ping' signal to the abs wheel pickup? I would assume no ring tone, you would set an abs code?

Any way there is someone with another truck similar or we talking this just started with the new parts?

[GAT]

Originally Posted by spytearbite

Did the new discs come with tone rings? Or say, did they reinstall the matching OEM with some sort of 'ping' signal to the abs wheel pickup? I would assume no ring tone, you would set an abs code?

Any way there is someone with another truck similar or we talking this just started with the new parts?

Worked just fine from spring until late last week just noticed it. I will tear into it tonight and let you all know if it worked. Won't take long once it's back togeather it happens about every thrird stop or so.

[spytearbite]

Right. Won't take long you spin the disc and hold a pencil to the disc then spin it. You see a high spot? You have junk that lasted a few months? And the truck is how old with OEM> Before the disc swap?