ABS/brakes spongy after hard accelleration
06-13-2018, 05:36 PM
#1
ABS/brakes spongy after hard accelleration Ok i've noticed when i hammer the gas at lower speeds to say maybe 70 the brakes feel normal. When i go to pass but stay in it longer than necessary(55mph-90 say) and i go to touch the brakes they feel almost as if the ABS is activating. I have new used(can't buy brand new) ABS/Speed sensors in the back(4 channel system) but i'm seriously wondering if the fronts are bad... Anyone else have something like this? this is my 3rd F-Body and none of the others did this. No ABS lights on the dash and they DO work as i know when i had to get replacement sensors for the rear.
06-15-2018, 07:53 PM
#5
TECH Regular
Interested in what you find out because my car has always done that pretty much since I've had it (2001). It only does it if I'm moving pretty good and then have to hammer on the brakes. First time it happened to me it scared the SH*T out of me. I quickly downshifted and pulled the ebrake. I've changed the rotors, different pads, better fluid. Nothing has ever changed. I just know better now.
06-15-2018, 09:00 PM
#6
Mine is also on new pads, rotors, fluid and i'm not sure what it is. It's honestly acting like the ABS is activating which can only be a few things causing it. I'm pointing towards the front ABS sensors being dirty or something but as far as i know they can't be taken out and are part of the hub.
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06-16-2018, 07:33 AM
#8
if it had breaks in wires it would be throwing a code. I measured the gap last year when i did my 8.8 Ford swap because my TCS wouldn't work and i found out the sensors were bad. This issue was here before when i had my 10 bolt as well so it's not 8.8 related i'm pretty confident. The guy that fabricated my 8.8 and also the axle combo has never once had an issue with this type of thing. I'm not getting any codes or ABS/brake lights. I know on the GMT800/900 trucks the front sensors can get dirty and need to be cleaned because it causes a similar issue under heavy braking occasionally or when you are doing a low speed braking and hit a bump of any sort... This is a similar type of feel just it does it at higher speeds
06-18-2018, 06:39 PM
#13
I don't know if this is useful at all, but if it is actually activating the ABS solenoid, I have experienced the low speed version of that misfire on several GM vehicles. The parking lot at my work has a speed bump on a short downhill section that almost always trips the rear ABS as the axle goes over it. My 1992 Bonneville SSEi did it badly (rear drums, TC). My 2002 S10 does it (rear drums). And to a lesser degree, my 1998 Trans Am would sometimes do it (4 channel TC, disks). The faster you go, and the colder the weather, the more likely it was to happen. Perhaps there was a legitimate wheel-speed mismatch as the tires came off the speed bump, but I always felt like it was just a programming flaw in GM's ABS. I think I may have even been in some other cars that have done it, but I don't recall.
Another reason I bring this up, is because hitting the gas followed by the brakes would initiate a substantial rear-to-front weight transfer, which is not unlike my speed bump example. Maybe take the car out to a big empty parking lot or road and do some hard, full ABS lockup stops to see if you can get a feel for what is happening. If nothing else, it's good experience for a real emergency when you won't be thrown off by the pulsating brake pedal because you're already used to it. Cleaning the sensors also sounds like a good idea, as the ferrous bits stick tenaciously to the wheel speed sensor magnet.
Another reason I bring this up, is because hitting the gas followed by the brakes would initiate a substantial rear-to-front weight transfer, which is not unlike my speed bump example. Maybe take the car out to a big empty parking lot or road and do some hard, full ABS lockup stops to see if you can get a feel for what is happening. If nothing else, it's good experience for a real emergency when you won't be thrown off by the pulsating brake pedal because you're already used to it. Cleaning the sensors also sounds like a good idea, as the ferrous bits stick tenaciously to the wheel speed sensor magnet.
06-18-2018, 06:39 PM
#14
your abs is activating due to the rear wheel speed sensors reading differently than one another. i been through this personally and ultimately had to delete the abs because of it. do yourself a favor, go to gm and "rent" a tech 2. by rent i mean pay for a half hour of labor or a full hour if they require, and have them watch what the sensors are all reading while you drive. i found out that my passenger side stopped working after 80 mph. the others would continue to climb while the pass side stayed put and sometimes just dropped out. think about it, if you are doing 95, with 3 wheels reading 95, and the other one reading 80, it thinks that 80 mph wheel is locking up since its different than all the others, thus activating your abs. we tried 2 different sets of sensors, both had the same result. as well as taking the harness and connecting to the opposite wheel. we confirmed there isn't much we could do.