crimlwC6

I have a 99 FRC racecar. I run a square setup and the car weighs 2850ish with no fuel or driver. I've ran without ABS for about 2 years. The solution is simple, it is just a wheel sensor. Fellow racers, would you repair the abs or rip it out or leave it there but disabled. If option 2, who has done this and what is involved?
I've raced without abs and I can obviously do it but does the 99 have the ICE problem and if so will disabling the yaw sensor cure that. I never run with traction control or any other nannies.
Thanks in advance,

96CollectorSport

ICE mode is a function of the ABS programming, the only way to avoid ice mode is to not stab the brake pedal. Every time I've talked to a driver after they experienced the hard pedal they told me that they stabbed the brakes or hit the brakes "pretty hard".
When you hit the brakes you have to somewhat smoothly engage the brakes and increase the pedal pressure, stabbing the brakes is a one way ticket to ice mode and the infamous brick pedal.
The reason that the pedal gets hard as a brick is because the ABS module is closing all the circuits at once because it senses a 4 wheel lock-up it coming (in reality it's more likely that both rears are about to lock up at the same time). So what it's trying to do is get all of the tires to get back to the same or similar speed. If it sees that both front wheels are going 120 mph and suddenly both rear wheels are only going 100 it needs to even things out.
The only way to get the ABS out of ice mode is to lift off the brake and re-apply without stabbing.
It's all easy to describe but obviously if it happens there is a lot more stuff going on and all you want is a good pedal and the brakes to slow you down.
With the 97-00 cars you are pretty much stuck with what you've got either you learn to drive with it or you disable it. Those are your options - unless you want to go stand-alone with Bosch or something and that get's pricey pretty quick.
Not sure if that's what our looking for but hopefully it helps.

redtopz

But I will add there are more variables than just stabbing the brakes as I've activated ice mode in the middle of a brake zone numerous times with constant pedal pressure. In my case I think it was a combination of bumpy tracks, stiff rear springs/shocks, not much rear down force, and too much rear brake bias. You can do some things to alleviate the problem (besides gradually squeezing on the brake pedal which is always a good idea) such as softening rear shock compression and/or rebound, less aggressive pads in back, and a proportioning valve to the rear calipers. My ice mode issues became really bad this year after some setup changes I made, but then I adjusted brake bias and shock settings and my next test day I never had ice mode so fingers crossed.

LateBreak

I'd leave it in there, you're not talking about a huge amount of weight even if you're not using it. I do have some level of hope that there may be a simple solution in the future for repairing it, ABS is a nice feature to have on a racecar.

redtopz

I wish someone would figure out a way to disable ice mode in the C5 abs module. I've heard the C6 systems have done this.

96CollectorSport

I guess I should have elaborated a little more and Bill is right on there is more than just stabbing the brakes and not stabbing the brakes.

It all has to do with the amount of friction at the tires so anything you can do to keep weight on the rear end under braking should help keep the car from going into ICE mode.

Bill did the indecent you talk about happen with your T1 car or your ST2 car?

Typically cars without aero are much more likely to go into ICE mode because they typically transfer around 650 - 700 lbs to the front axle during braking, by running a rear wing you can cut that in half. That's why cars with wings feel so much better under braking. Although I do know of 2 cars with aero that both had ICE mode issues at the track - come to think about it they were both early C5's.

Also if you stiffen up the front shocks (or run a higher front spring rate) you should be able to help the weight stay back under braking.

Rake has a part in this too, by running too much rake you help transfer weight forward as well.

The last thing would be the tires and this is often overlooked when it comes to braking (and ABS), compound isn't the only thing here either - although very important - it is wise to run the same compound on all four corners for more reasons that just overall balance.
But what you don't typically think about is what you are doing to the diameter of the tires when changing tire sizes in relationship to the ABS. Going square changes what the rear wheel speed sensors are seeing - it actually should see the rear wheels speed up in relation to the fronts. The difference between the front and the rear tires on a stock C5 are 1.1" (25.6" F 26.7" R) for a base model and .7" (25.4" F 26.1" R) for a C5Z. So if you change to a square set-up the rear wheel speed sensors are always seeing the rear tires traveling faster than they actually are (which should actually help in the case of ice mode but I really can't say that for sure - it's got to mess with the ABS a little bit when making such a change in tire diameter.)

So in reality two cars with the same brakes and tires can behave very differently under braking based on all of the above.

Bill is lucky that he has a bias **** and shock settings to play with for those that don't you may have to change rear pad compounds from track to track. If your rears are locking up at a certain turn at a certain track then you may have to run a less grippy pad in the rear at said track.

I sent out a lot of e-mails and made a few calls about this topic a few months ago and this is what I came up with.

For the early C5 guys (97-00) I'm sorry to say your stuck with what you have, either you run what you've got, disable it and go no ABS or go aftermarket. Those are the only options that I've found.

For the late C5 guys (01-04) there may be one option out there but it requires you to run a square set-up preferably 315/315 there is a GM Racing calibrated ABS module out there designed to run 315 square (I don't see why you couldn't run 315/335 Hoosiers since they are both 25.6" in diameter) - I can't say for sure if it eliminates ICE mode but it would at least tighten up programming so the ABS knows what size tires you are running. It does eliminate traction control / active handling and changes the dynamic proportioning setting to add more rear brake. I haven't found any of these modules so I don't know pricing or availability but I do know the exist or at lease existed at one time.

The C6 guys have even more options because they can use the stock program or the C6Z program - I can't seem to find different listings for the base C6 and the C6Z module but apparently there is a difference.
There also is a version of the GM Racing T1 module for the C6 again requiring a square tire set-up and disabling active handling. However it will only be good for 05-08 C6's since they change to Bosch ABS from 09-13.

This is all of the info that I have found on the ABS I will post back in this thread if I find out price and availability.

crimlwC6

Thanks for all the info and advice. I've got a wing on the car and I always run less aggressive pads so I'll fix the sensor and give it a try. Not having the abs has actually been great for forcing me to be smooth With my footwork.

RX-Ben

Those GM race modules for a C5 must be more rare than a white buffalo. This is the first I have heard of them.

crimlwC6

I do get rear lock up occasionally, especially when the rear pads are new. Ah the sweet irony, I want abs partially so I'm less likely to have to rear someone's rear bumper but if I get ice mode I might be replacing much more. On another note, I had the factory metal line from the master cylinder to the abs module split two weeks ago. Thank god it was found during a pad swap and bleed at the shop instead of on the track. I couldn't believe that line would fail. I had to have a custom one built that day since no one had a line in stock.

96CollectorSport

Hey look what I found!!!



Well it looks like all my e-mailing had potentially paid off it turns out that I can get my hands on these modules.

They are $750 each (better than I expected I figured around $1000)
The C5 module is designed for 25.6" tires front and rear (actual listing shows 17x11" C4 Grand Sport wheels with 315/35R17 tires - but as far as ABS is concerned the diameter is all that really matters.)

The C6 module is also designed for 25.6" tires front and rear (actual listing shows 18x11" front and 18x13" rear with 315/30R18 front and 335/30R18 rear - but again Hoosier 315 and 335's run the same 25.6" diameter)

Here is the most interesting part thought traction/active handling and dynamic proportioning are turned OFF!

So now you can put your own proportioning valve in line to set things where you want to. Now it doesn't say anything about ICE mode so I can't say it will eliminate that from happening but if you use the correct tire diameter it at least gets your ABS and your tires on the same page.

So who wants to try one and let me know how it works?

MySR71

I have been told that the C6 module eliminates the need for tire pressure monitoring sensors too. If this is a feature of interest, you should double check that this is indeed the case.

RX-Ben

Why in the world is DRP disabled??

redtopz

My ice mode issues have all been in my 99 FRC car in ST2. I sold my T1 C5Z car last year. Now I'm using my 99 for both ST2 and T1. I did have some abs issues with the C5Z, but never ice mode. It was ebcm issues which would cause abs to just stop working and then the drp would stop working and the rear brakes had too much bias. In the end this turned out to be a ground problem.

Here's the story behind my ST2 car and I'm learning as I go. It came with Stoptech ST60 front calipers, stock front calipers moved to the bck, a larger master cylinder, and a wilwood proportioning valve. The 99 abs system does not have dynamic rear proprotioning from what I understand. For a couple years my brakes worked fine and I would hit ice mode once or twice a year and just live with it. At Miller nationals I realized my rear brake bias was too high when I cut a wheel speed sensor in the first lap of the championship race and my rear tires locked at the end of the front straight spinning my car off track. I didn't realize what caused the problem until I put the car back on my lift at the shop.

This year, I reduced the downforce of my car (for scca rules) and experimented with stiffer springs. Ice mode became much worse and basically occurred instead of abs working. At this time, I dialed back the rear prop valve and softened the rear shocks. We will see if this cures the problem, but so far so good.

You were smart to run with no abs for a while and get yourself and your brake bias dialed in. I don't think you will have any issues going to abs now. Looking back, I would have been much better off running a weekend or at least a test day or two with no abs to dial in the rear brake bias. My rears were locking way too easy. I tend to learn things the hard way...

redtopz

It sucks when abs fails in an 01+ C5 because the rear proportioning sends too much bias to the rear. It would be better to have your own proportioning valve, dial in the bias, and then run abs. If it fails, your bias would still be fine and you could keep racing.

96CollectorSport

It would make sense to omit the tire pressure sensors on the C6 but I can't say that for sure.
I wish I could tell you that I have first had experience with these modules but the truth is, I don't. At the start of this thread I knew that they existed now I know how to get a hold of them. The final step is to bolt them on and see how they work on the track - if it doesn't work we can always put the old module back on.

It seems like for these modules to be effective you will need to have a pretty good idea of how well your car is balanced both suspension wise and obviously brake bias wise.

Ben, I think that they turned off DBP so that you can build in the bias that you see fit. With DBP the bias is constantly changing so you are always shooting at a moving target. My thought is that there still is bias built into the system but it is just set at a fixed point as opposed to being variable with the DBP.

Now I don't know for sure how much rear brake bias is dialed into the stock ABS systems, I've heard as much as 70/30 - but with DBP it is constantly changing anyway. I also remember reading that the GM racing calibration sets brake bias at 55/45 so you'll have to figure out how to bias it for your individual set-up. For some reason I remember hearing that there was a 15% change in brake bias from stock to GM Racing so that seems to be in line.

However I do know how much brake bias is built into the factory brake systems (just the hydraulics) - I just have to run it through a brake bias calculator.

The C5 for example:
Just the hydraulics have a 63.5% front brake bias -
So if you are running a square tire set-up you will be at 63.5% front bias at the tires.

If you are running the stock C5 tire sizes then the bias would be 64.4% at the tire. (Since the rears tires are larger it will lower the rear brake bias)
If you are running the stock Z06 tire sizes the the bias will be 64% at the tire.

So now you just have to figure how much braking the rear can handle and adjust from there.

JerryTX

Where did you find this info? Where is the part number for said module for the C6? I am a base C6 racer with no TPMS sensors, no active handling/yaw/steering angle sensor, only thing I want is ABS. DRP doesn't work anymore on my car and it would probably help rotate the car better while trail braking but I live without it.

As to would I recommend fixing ABS, if you were my competitor I'd say NO!

96CollectorSport

I got this directly from GM Racing, the part numbers are

01-04 C5 - 12216561 (Same as for a regular late C5 brake module)
05-08 C6 - 89060341 (Same as for a regular early C6 brake module)

However these modules have been re-programmed with the above calibration for racing only.

Out of curiosity how did you get the DRP to stop working?

If anyone wants more info PM me or call me at Corvette Sports
(920)467-2833
I'm typically there from 8 am - 6 pm Central time.

I think these will be most helpful for guys with aero on there cars, where you can actually use more rear brake bias without issues.

Thanks,
Joel

JerryTX

Thanks Joel I'll look into the module. DRP can't work if there is no Yaw/Acceleration/Steering Angle input to the BCM/EBCM.. I have all that disconnected.

John B

The Great White Buffalo. Nice find Joel. I have been carrying around half my inop system for years. I'm hesitant to bring back to life as it tried to kill me several times in 2003 1 lap. Flat spotting a tire once in a while is better than a crashed car. ABS is all fun & games until something goes wrong while counting on it.

crimlwC6

I forgot to mention my doesn't have AH (wasn't optioned on the car). I'm not sure if that changes anything. I'm guessing it doesn't since it sounds like ICE mode lives in the abs module.