early ABS triggering

[grave77]

I have posted long time ago when I upgraded my calipers to 4 piston calipers and I had early ABS intitiation, the replies was all about bleeding and pressure bleeding.

I have pressure bled the system when I upgraded my transmission to manual since it uses the same fluid container, but the problem still persists. I whould like to know what would trigger the ABS system as my brakes hold much better before the ABS is triggered, once its on the car seems to slip on the road more forward than it should be.

I once hit the brakes at high speed few times and made the disk hot, when I observed the disk I saw the traces of the contact area which was in the middle of the disk but the both sides were still white " without the darker blueish colore" so it seems that the pads are not in full contact .. I made the bedding procedure to make sure they are in place but still no use !!

any advice ?? ... thanks in advance

[Interceptor]

In what state are your tires and brake pads? Has the rotor developed a lip?

[grave77]

well with the same tires the brakes were better at lower speed with old calipers. the lip on the edge is acceptable and within the range, the rotors are less than 2 years old.

[stu1]

As I understnad it, if the system is working then the only thing that can cause the ABS to trigger is a wheel either not rotating or very much on the verge of not rotating. If your ABS is firing earlier after you've upgraded the brakes it pretty much makes sense.

Even with standard brakes (OK, slightly upgraded to Brembo discs) mine will fire across bumps under moderate braking; imho the wheel 'stop time' is too short before the ABS starts pulsing.

[Interceptor]

well with the same tires the brakes were better at lower speed with old calipers. the lip on the edge is acceptable and within the range, the rotors are less than 2 years old.

Maybe the brakes are more efficient so you get a feeling of earlier ABS triggering due to more braking power?

[632 Regal]

Barry, just to eliminate a question are all of your tires the same size?

another idea is this, you changed out the trans right? OK, I may be way off but isnt there a sensor in the trans that checks the rotation at the output and tells the ABS what rpms the rear is at comparing it to the front wheels?

and yet another: did you just replace the front calipers and leave the rears stock? This would require more fluid going somewhere that the abs doesnt know what to do with?

I really dont know how to say what im thinking here.

[grave77]

ok .. I will tidy up ur thoughts ... I have 265 rear and 235 on front. the ABS checks the wheels rotation from the speedometer sensor and compares it with the proximity sensors on the wheels that looks like the crankshaft sensor that gathers the synch signal to the DME, I do have the OEM rear brakes still. I thought that the rear wheels might be stopping earlier than the front, as this gides to that the fluid pressure on the front is less than the rear. but I dont know how to find out what is causing the ABS to trigger, maybe I need one of those holywood cameras mounted on the side of my car capturing the wheels :P

does the brembos require more pressure to byte?

[grave77]

well thats what is happening to me, with moderate press on the brakes the ABS starts. but this is making the braking less effective than the single piston caliper.
one technicas told me that he can adjust the front sensors to start the triggering later. but that sounds like ******** to me.
is there a fuse for the ABS system that I can remove to disable it for test sake?

[632 Regal]

does the brembos require more pressure to byte?

shouldn't as long as the pads have broken in..which it doesnt sound like you could have because you need to do some serious braking to accomplish this. You might want to go and email Bruno on this as he is the man that plays with this stuff and might be more familiar with this kind of swap. I still think its something stupid that we arent figuring on.

[grave77]

before I forward this prob. to Bruno, I would think of changing the pads, I used the old pads installed on the calipers from the scrap yard, I also didn't like the blue area left by the pads when I intentionaly heated the disks. so changing them wont harm and I'm also starting to hear some sounds on the front brakes, some rough sounds ... so seems that the pads r ****ed up, then I'll see ...