excessive brake pedal travel

[TonyMadrid]

Hi everyone,

I'm new here and maybe I could impose on some of the gurus here to help me with a brake problem I have been having.

I have a 1999 Blazer with an Auto Tranny and 4-wheel disc brakes. This past Friday I started to have the problem. When I apply the brakes at cruising speed the pedal is hard and the brakes are effective as I can feel the vehicle slowing down. However, just before the vehicle comes to a stop the pedal travels, almost to the floor, and I hear a noise coming from just under the hood on the drivers side near the firewall.

I checked the master cylinder and the level is full. There are also no leaks at any place along the various brake lines. My front inner pads were worn, but not to the point of nearing the audible wear indicator. I installed new pads anyway but it had no effect on the problem. I also followed a diagnostic check on the vacuum booster as outlined in a Haynes manual and the booster seems to be working fine and there is excellent vacuum at the manifold hose.

I looked through a Haynes Manual and it appears that I have a Kelsey-Hayes ecbm310 system. The Haynes maual really isn't that informative and just makes mention of checking the codes. For those who don't have a code scanner the manual suggests using the ABS light to check for flash codes. It mentions to locate the the data link under the dash and to place a jumper between the A and the H terminals and then to turn the ignition to the ON position and observe the sequences of flashes of the ABS warning light.

Problem - I located the data link under the dash but the terminals are not marked alphabetically, they are numbered. Nonetheless, I tried various combinations of jumping the terminals but none of them caused the ABS light to produce flashing codes.

Has anyone had a similar brake problem with a Blazer and what were you able to determine the problem or cause was?

Also, any help regarding the data link jumper method to produce the ABS flashing codes would be appreciated.

Tony

[GMMerlin]

What might be happening is that a wheel speed sensor loses its signal at low speeds...so the ABS module thinks the brakes are locking up and activating the ABS system.
Sometimes the loss of signal is so slight that it will not set a code in the ABS module...to determine which sensor is the culprit, driving the vehicle with a scan tool to monitor the wheel speed sensors while you slow down to see which one drops out is about the only way.
You can check wss resistance and a/c voltage output, but this is rather time consuming

[TonyMadrid]

Thanks for quick response.
If it is a wheel speed sensor what should I expect to pay a dealer to diagnose the condition and replace the sensor, including labor & parts.

Tony

[airforceone]

My rear wheel speed sensor for my 1992 (rear) was about $90, and took about 2 hours to replace. I did it myself, wasn't too hard.