Question about 1997 GMC Safari
I have a 1997 GMC Safari 2wheel drive (181,000 miles) with the 4WAL antilock brakes. I keep the vehicle well serviced. When coming to a "normal" stop, the brakes work perfectly, coming to a smooth, safe stop. However, today I had to execute a "hard" stop at a traffic light, (traveling about 35 mph) which engaged the ABS. (It had rained earlier in the day - road was wet, but no standing water). Prior to this stop, the van would have stopped well before reaching the intersection without problem. This time It jerked, made lots of "bumping noises" and felt like trying to stop a locomotive! The van finally stopped in the middle of the intersection. None of the ABS warning lights have flashed. No prior ABS problems during hard stops. I then tested the van on a secluded road. If I quickly "pump" the brakes for a quick stop short of engaging the ABS, the van stops as it should. Hit the ABS, and it keeps going and going while the ABS bumps and thumps and does not stop as it should. There is a lot of "feedback" to the brake pedal. One instance, after stopping with ABS, the brakes would not release unless I pressed the brake pedal rather firmly all the way down, then it released. Although I have not measured them, the brake pads, rotors and drums appear to be within spec, although there is some normal wear. Brake fluid level was in the normal range. I would appreciate any guidance you could provide towards correcting this hazard!
Yes, I never did like ABS brakes because of this. What you have experienced is the ABS system working as it is designed to do. I know, it doesn't seem like you should still be moving after slamming on the brakes, but here is how it works;
When you apply a fast and hard pedal and the ground beneath you is wet the wheels stop at different times. There are sprockets mounted to the rear of the rotors, with magnetic sensors that monitor the wheel info. for all four wheels mounted next to the brake calipers. On a hard stop when the sensor detects one wheel stopping and another still going, these sensors send "pulses" to each wheel until the vehicle has stopped without the brakes having to lock up. The pulsiing is what you experienced and is a normal part of the ABS function.
Please rate this and let me know if it helped.
Posted on Feb 11, 2009
Rust and corrosion builds up under the ABS wheel speed sensors. Fixed them a few times on 96 and up safari's. Some GM vehicles had a recall on this but for some reason not all affected have. I didnt read you entire post cause I am in a hurry. But if you have antillock activating at slow speeds it sounds like this issue, if you remove the sensors, clean the surface where they mount very well and add a little bearing grease then re install you should be find if you have the same issue I have ran into. I did run into one with a broken wheel sensor, that or it broke when taking it out cause it was stuck in there. Just cannot believe they get by without recalling all of these.
Posted on Oct 07, 2012
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Posted on Jan 02, 2017
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