fatbillybob

Does anyone know if there is a way to disable the ABS safely for the ABS/AH/TC electronically for a test of brake bias when swapping to aftermarket calipers? I just want to see what my brakes feel like at threshold with new calipers if I loose my ABS. I don't want any surprises in a race if say I loose a wheel speed sensor and that screws the ABS and I'm diving into the braking zone at triple digit speeds.

mgarfias

Pull the ABS fuse?

davidfarmer

disconnect any of the wheel-speed-sensors and it will shut down the entire system

StArrow68

One of the exercises at the old Bragg-Smith was to pull the ABS fuse and
brake on water with no ABS, should do the trick. When they got done they
put the fuse back and everything went back to normal.

vettehardt

My dad works for Bosch (used to be Bendix and Allied Signal) and we had a picnic at the proving grounds once. Dad took another members 91 to the test pad and demonstrated ABS vs. no ABS. As others have suggested, he pulled the ABS fuse to disable it.

At the proving grounds, there is a 500ft long strip of ceramic tile that they wet down to simulate ice. Dad took the 91 vette with th ABS off at 60mph and hit the brakes as soon as he was on the pad. He went the entire length with the wheels locked up. He then did the same thing with the ABS on and came to a stop about 1/3 of the length down.

geerookie

Fuse or sensor will do the trick!
On the '97 - 2000 cars the ABS fuses are under the hood and are numbers 58 (20A), 52 (40A) and 5 (10A)
On the '01 and newer cars there are only two fuses (also under the hood) 52 (40A) and 5 (10A).

I would imagine pulling any one of the fuses would disable the system but #5 is the ignition trigger that tells the system the car is on.
The other fuses are the primary power for the ABS pump and control circuits.

trackboss

How is front to rear bias controlled with the the abs disabled? I was always under the impression that on cars with abs it was electronically controlled.

Han Solo

CAUTION! After being use to driving with ABS be prepared to flat spot some tires with it disabled.

Ask me how I know.

Solofast

While it's obvious to pull the fuse(s), I tried that with a 94 and had no joy...

At Ionia one year we had a bad patch of pavement at the braking/turn in point and the car was going into ABS/Ice mode and it was killing us.

I pulled all of the fuses, breakers or anything else that seemed like it could have anything to do with the system that were marked ABS and the darn thing still worked. With earlier cars you could pull one fuse and disable the system, but I don't know what or how to make it stop on later cars.

Just saying that it wasn't as easy as I thought it was going to be.

geerookie

Can't speak to a C4 but on a C5 it just the fuse.

geerookie

As far as C5's are concerned only on '01 and newer.
Try this post
http://forums.corvetteforum.com/1575519509-post6.html

Bill Dearborn

01 and newer C5's and C6's have Dynamic Rear Proportioning. I don't know how much it might affect brake bias but I do know when I lost the ABS I discovered it had been masking a slight rpm mis match when I was downshifting. I went into T1 at the Glen carrying a pretty good head of steam and when I downshifted the rear wheels locked up under braking. I mentioned this to another instructor when his EBCM failed a few weeks ago and despite years of driving a Historic Race Vette he had the same lock up happen.

Bill

fatbillybob

Is this possible because perhaps the AH was still active and what you were really feeling is AH activating the brakes? Just askin are'nt they related in an incestuous way?

fatbillybob

By the way this whole ice mode ABS thing is an issue. One of your T1 guys ran in the support race at the LBGP this year. He blasted off the end of the track and some number like 140 with no brakes hit the tire barrier and destoryed the car. never did understand what actually happened but somehow we can go into a "icemode" of sorts and it is not up to use when that happens and I have no idea how to deal with it.

SIK02SS

pull the 2 ABS fuses under the hood; sorry i didn't call yesterday, I don't have much of a voice right now--fighting a cold

geerookie

If ABS fails in anyway AH is disabled automatically.

Solofast

The ice mode is pretty easy to understand. The computer senses wheel speed, and from that it calculates a deceleration rate based on the change in speed. If the change in wheel speed is too great the computer figures that the car is on ice since if the wheel decelerates at maybe 5 or 10 g's that can't happen because the car can't decelerate that fast.

When that happens the computer assumes that the car is on ice and limits deceleration to a lower rate (I think it's 0.1 G). The problem is if you hit the brakes hard when a wheel is light, the wheel stops quickly and the computer goes into ice mode. Same thing if you hit the brakes hard and one wheel is on gravel or sand, that wheel stops very quickly and the computer goes into ice mode.

With the C4 if you got ice mode you would have quickly lift off the brakes and then brake hard again, not exactly a natural reaction, but you do what you have to do. With learning, you got to know what was happening and the lift and reapplication could be pretty quick. It definately gets your attention, but if the car isn't stopping, cycle the pedal. With the C4 it only took one wheel to put the entire system into ice mode. I don't know if the C5 system is more sophisticated, since I've not encountered it. Hard braking onset and pads with a lot of bite will make is worse, since it can cause the wheels to stop faster.

Hope that gives you an idea as to how it works in general, maybe some others can chime in on how the logic works if just one wheel is declared to be on ice.

In the case where the T1 car went off, it could also have been that the car was light on all wheels and that could possibly set off the system on all wheels.

Olitho

Is there a way to turn off/disable the Ice Mode from the computer since we never race these cars on ice?

I would love to get that change into the CRB or justify the mod in T1 based in safety.


Oli

fatbillybob

Solofast thanks for the description. Oli...I bet that algorithim is buried deep into the ABS programing. But if someone could get it out I bet you have the technical resources to figure it out. I am starting to think one important issue may be to use pads with less inital bite and respond more progressively to the pedal. I don't know what that pad might be. I'm thinking we did not have this problem with the stockers but if everyone goes to new 4 pot calipers that "clamp" when we say clamp we may start seeing more of this "icemode" problem next year when everyone is on new brakes. I hope you guys have some extra bumpers stored because as you know I'm always in the back.

trackboss

Does anyone know how to completely remove the abs system without the computer having any issues or throwing codes? I can easily re-plumb my system, but am not sure about the electronics.
I have not looked over the diagrams, but I am assuming the abs ebtcm is it's own computer.