I need to understand ABS so I can aruge....

[Renthorin]

Took my 98 Blazer to the shop for new lower ball joints and an idler arm.

I got it back and now the ABS is coming on when I stop. Nothing to do with how fast or hard I am stopping....but at about 3 mph as I am braking it comes on.

Took it back and the guy said...."well now that you have new ball joints things are tighter and it is more sensitive".

I think that is BS but don't know how ABS works to agrue the point.

How does ABS work? What might they have damaged in the system?

Thanks for any info

 

[ALXTTA 1]

This is probably oversimplified, but the way I understand it, each wheel has an ABS sensor. The sensor monitors how quickly the wheel is spinning and the computer compares that to the other wheels. If some wheels are slowing down much quicker than the others, the brakes are locking up, so the ABS modulates the caliper just enough to relieve the condition. The basic traction control systems work the same, just in reverse.

Bottom line, and I'm certainly no expert, but I don't see how tighter ball joints would have anything to do with it. Sounds to me like they f'd up a sensor? I'd raise the BS flag fer sure.

 

[Renthorin]

That is pretty much what I was thinking. I need to find out where the sensors are and look at them.

Could a big glob of grease on one mess it up? I will also look for nice shiny parts indicating something rubbed/hit them pretty hard.

Do they 'look' at the wheel or is there a magnet or other object that they are looking for?

Thanks for replying.

 

[gn85]

I had a '92 Jimmy. The wheel sensor on that looked like a 'gear'. It has teeth like a gear and a small magnetic sensor attached. It's located donw by the rotor. If they did ball joints, it's distinctly likely they had to disconnect all of that. Perhaps they forgot to plug the sensor back in, or they indeed messed it up on reassembly.

I know on my '92 there was actually a method for checking the codes with a paper clip, just like our ALDL. I had a somewhat similar problem when my truck was under warranty and was close to going out of warranty. I had a rear sensor go bad which required a lot of work. I took it to the dealer two times and they said "Oh, we needed to reset the computer. It's fine now". Of course, I knew what the code was and what the truth was. A week after the firs time the light came back on. I took it back. The second time, the light came on when I was driving home from the dealer. Needless to say, I turned right around and EXPLAINED to them that I had ASE certifications in brakes and that I KNEW what the code was saying. Next day I had a new sensor and never had a lick of trouble out of it since.

They may very well be taking you for a ride or did something stupid. Sorry, I don't know if the '98 has the similar paper clip method.

 

[thomas_quinn]

Ball joints wouldnt effect the abs system usually when the abs activates at low speeds it is a wheel speed sensor. They might of damaged it when the worked on it.

 

[Marc87GN]

Originally posted by thomas_quinn
Ball joints wouldnt effect the abs system usually when the abs activates at low speeds it is a wheel speed sensor. They might of damaged it when the worked on it.

I would agree 100%. How ABS works is, with 4 channel anyway, each wheel has an exciter ring or reluctor wheel and a sensor. Each sensor is basically a magnet and when the tooth passes by or breaks the magnetic field, it induces a voltage and that travels up the wire to the control unit. when the control unit doesn't receive any voltage, it knows that a wheel(s) have locked and the ABS system turns on. In short, they are FOS.

 

[John Larkin]

isn't it amazing that no one does a test drive after a repair anymore? Just a buncha parts changers, not mechanics.

 

[myclone]

Originally posted by thomas_quinn
Ball joints wouldnt effect the abs system usually when the abs activates at low speeds it is a wheel speed sensor. They might of damaged it when the worked on it.

Agreed.. The ABS could care less if the ball joints are new, worn out, or not even installed. The "mechanic" is either an idiot for telling you that or was busy and hoping you were an idiot so he could get back to work.

A damaged sensor or reluctor ring could cause an ABS problem as well as a misaligned wheel sensor. Any/all that could have easily happened if the mechanic was sloppy with the disassembly or reassembly of the suspension when he replaced the ball joints.

If it was me Id take it back, make em fix it, and never step foot in there again considering the crap theyve been feeding you.

 

[85HOT-T]

That shop is BS'N you for sure. Raise some hell that usually works good. You need to make sure it is when there is a lot of customers around, and put down there work many times. That is about the last thing a manager wants to hear in his shop.

 

[Renthorin]

thanks all..... this gives me the info I was looing for