brake problem

i have a 97 gmc suburbun with 150,000 miles on it.when i apply the brakes, the work alright untill i get almost to a stop than the pedal drops another inch. some times on the dry pavement it acts like the abs is engaged. i took a trip to florida, from michigan, and had it looked at. he said it wasn't the pads or rotors, maybe a master cylinder going bad. he didn't recommend any further work at that point. took the trip,everything went fine. the problem is still there and i'm beginning to wonder.any info would be appreciated. thanks in advance.

 

guess I was wrong... see following post

 

You need a wheel speed sensor, but I could not tell you which one without hooking a scan tool up. What happens, the EBCM monitors wheel speed. When it detects too much variance between the 3 sensors, the ABS is enabled. So, you have a sensor dropping to zero before the other 2, causing the ABS to activate. What needs to be done here, is a tech needs to connect a scan tool, and monitor the wheel speed data while braking to a stop. This will save you the money of just throwing parts not knowing which sensor is at fault. I can gurantee though, that it is either the right or left front sensor. We hardley ever see the rear speed sensor take a dump.

 

Charliet, I sent you a private message!!

 

While, as a general rule, I agree with Mr. Dummas that you should not just go "throwing parts" at a situation, at the same time I'm not sure that taking it to a shop will actually SAVE you any money. By the time you pay for the diagnostics, scan, parts, and labor for a qualified "tech" to work on your car you could have just bought BOTH sensors and replaced them yourself. The REAL risk of working on your own car instead of taking it to a shop is that if you don't know what you are doing you can cause more problems than you fix or worse yet, you could get hurt. Make sure you know the procedure and feel confident that you can do it before you attempt to fix your own vehicle.

I did have one question before I concede that I agree with Mr. Dummas' diagnosis. How long have you had this truck?

 

This is a very known problem on these style trucks. We do at least 2 a week here at the dealer. Most shops will not charge to go for a ride with the customer and monitor a scan tool to determine which wheel speed sensor is bad, since it only takes a minute to do. I had offered to do this at no charge for charliet, we live only miles apart. Also, this site is to aid the do-it-yourselfer, which I intend to do for everyone I can. I'm not out to make money, just to help you all out with my sources. When I feel there is something that HAS to be done at the dealer, I will advise and recommend this to the person with the problem.