Scary ABS problem after fitting front brake kit
18 June 2006, 12:12 PM
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Scary ABS problem after fitting front brake kit
Can anyone help? ....
Car is '95 WRX, with the usual single-pot rears with redstuff pads in them. The front recently received a 4-pot compbrake kit, with fast road pads that differ from those on the back (they're Hawk HPS).
In fitting the kit I removed the shield from the inside of the disk and, I think, disturbed the ABS sensors a little (twas a bit tricky to remove). Whilst bedding in, I had the ABS light come on a few times (and sure enough, the ABS wasn't operational). After that, no problems, the ABS light stayed off and I could get the ABS to come on only under extreme braking, and it seemed to be modulating much better than before I fitted the new front brakes. So far so good.
Now, a few hundred miles later, I'm getting really inconsistent ABS behaviour. First prod will sometimes cause the ABS to cut in stupidly early, then immediately re-applying the pedal will give smooth normal braking. I'm not jabbing the pedal, by the way, this is smooth progressive braking.
Then, out of curiosity, I tried continuing the pedal pressure after the ABS had cut in early, from about 100mph (with plenty of space on all sides of the car, I should add) - this is where it got scary, with the back end swaying violently until I released the pedal. This wasn't just the usual brake-dive sway you get from stronger-fronts-than-rears, it felt more like the ABS was preventing the fronts from doing any work, whilst the rears were braking ok.
The recently-fitted new front calipers, pads and disks appear ok on inspection.
Does this sound like damaged ABS sensors, or some other ABS problem? The '95 WRS ABS is 2-channel (front/rear) isn't it? (the pump unit under the bonnet has 3 cylinders and 4 pipes coming out of it).
Finally, I tried to pull the fuse to test whether this really is ABS-specific, and found the diagram to be all in Japanese! Could someone post up a pic in English of the fuse diagram for a '95 WRX?
cheers
Andy
Car is '95 WRX, with the usual single-pot rears with redstuff pads in them. The front recently received a 4-pot compbrake kit, with fast road pads that differ from those on the back (they're Hawk HPS).
In fitting the kit I removed the shield from the inside of the disk and, I think, disturbed the ABS sensors a little (twas a bit tricky to remove). Whilst bedding in, I had the ABS light come on a few times (and sure enough, the ABS wasn't operational). After that, no problems, the ABS light stayed off and I could get the ABS to come on only under extreme braking, and it seemed to be modulating much better than before I fitted the new front brakes. So far so good.
Now, a few hundred miles later, I'm getting really inconsistent ABS behaviour. First prod will sometimes cause the ABS to cut in stupidly early, then immediately re-applying the pedal will give smooth normal braking. I'm not jabbing the pedal, by the way, this is smooth progressive braking.
Then, out of curiosity, I tried continuing the pedal pressure after the ABS had cut in early, from about 100mph (with plenty of space on all sides of the car, I should add) - this is where it got scary, with the back end swaying violently until I released the pedal. This wasn't just the usual brake-dive sway you get from stronger-fronts-than-rears, it felt more like the ABS was preventing the fronts from doing any work, whilst the rears were braking ok.
The recently-fitted new front calipers, pads and disks appear ok on inspection.
Does this sound like damaged ABS sensors, or some other ABS problem? The '95 WRS ABS is 2-channel (front/rear) isn't it? (the pump unit under the bonnet has 3 cylinders and 4 pipes coming out of it).
Finally, I tried to pull the fuse to test whether this really is ABS-specific, and found the diagram to be all in Japanese! Could someone post up a pic in English of the fuse diagram for a '95 WRX?
cheers
Andy
Last edited by Andy916; 18 June 2006 at 12:17 PM.
19 June 2006, 03:53 PM
#3
Andy,
when one of my ABS sensors failed on my old car, I found exactly the same: the back end of the car was very light and unstable during braking.
I can't remember 100%, but I believe the ABS system limits the pressure to the rears to prevent them locking up so early, but with the ABS disabled, this limitation is removed. Cars fitted without ABS as standard will have a manual pressure limiter in place.
Under heavy braking, the fronts do about 80 - 90% of the work, and the rear are just to stabilise the rear. With one of the rears locked, then you lose this stability.
When I got the sensor replaced (got one from a breakers yard), braking thankfully returned to normal.
John
when one of my ABS sensors failed on my old car, I found exactly the same: the back end of the car was very light and unstable during braking.
I can't remember 100%, but I believe the ABS system limits the pressure to the rears to prevent them locking up so early, but with the ABS disabled, this limitation is removed. Cars fitted without ABS as standard will have a manual pressure limiter in place.
Under heavy braking, the fronts do about 80 - 90% of the work, and the rear are just to stabilise the rear. With one of the rears locked, then you lose this stability.
When I got the sensor replaced (got one from a breakers yard), braking thankfully returned to normal.
John
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