Big N Littles V/S ABS

Hold on, before you keelhaul me for posting anything about ABS on a "Classic" forum please bear with me for a moment.

Pops and I are using a 2004 Trailblazer with the Hotrod 6 for power as a donor (no we're not putting a V8 in it).

Since the TB has ABS alreay, and we are using as much of the drivetrain as we can (including the huge-mongous brakes) I would like to keep the capability, instead of loosing it.

So far all of the performance street vehicles that my father and I have put together have a staggered tire size some call "Big N Littles" (some get pissy and say the "bigs" aren't big enough and the "littles" aren't little enough, but I figure that starts to matter after they start buying us tires ).

We do put them together to go around corners, agressively, and the ABS isn't mandatory, but with two significantly different tire heights I can see it coding out and not working.

So my question is, has anyone heard of being able to reprogram the ABS for that?

If no, maybe some of you have another forum in mind that I could search, or ask that (yes, I did search for that here before starting the new thread ).  

hmm...    your brake bias is going to be off also..    but with 4 wheel discs and ABS brakes there no easy way around it..

the issue is... how much will the stock ABS computer adapt to the different spinning wheels...

does the Trail blazer also have traction control.     i am not an antilock brake expert.. i usually handle fuel injection and other electronic issues..  

take a look at the RPO sticker if you still have the body of the trailblazer
4 Whl Disc Brk (JF8)
Traction Ctl (NW7)
see which system your donor was equipped with.


take a look at the factory service manual.. see if you can get a training manual for that system also.. sometimes available..

the abs system uses reluctors/tone wheels .. a pick up coil mounted a specified distance from the tone wheel...  as the wheel rotates the tone wheel spins past the pick up coil.. _-_-_-_-_-_-_-_-   this creates at very low speeds a similar sinewave ac signal..  but most of the time. the faster the wheels go.. the higher the voltage from the pickup coil...   the abs computer compares the individual signal voltages to control the brakes when the brake pedal is depressed..   if one of the wheels has lower voltage than the others...  it will isolate and release some pressure from that line... various abs systems can isolate and relieve pressure.. others have a multimotor assembly with individual cylinders like a master cylinder that can also modulate the pressure to the individual wheels..    there was an issue back in the 90s.. when usually the right front wheel speed sensor got damaged...  it would send voltage spikes above all the other wheel speed sensor voltages... the computer thought the other 3 wheels were slipping because their voltage was lower than the defective wheel speed sensors wheel.. so it would isolate and release the other 3 wheels.... and you would glide through what ever was in front of you.. stop sign... red signal...    truck.. car..  what ever it was you only had one wheel braking..

on some rear wheel drive cars and trucks.. they used speed sensor mounted on the back of the rear end yoke.. and they had different tooth counts to compensate for different gear ratios..


this would be the saving point for you... as you could either find the proper amount of toothed tone ring to equalize the speeds between the fronts and the rear..  i see that the trailblazer can be equipped with either 3:73 or 4:10 gears..  i don't know if that is going to be close enough to compensate for your big and littles.. if you have the 410 gear set and you install a 3:73 tone ring.. and i don't know how the rear tone rings are.. if they are at the back of the rotors pressed on the axles.. or on the pinion shaft.. i looked at several sources and could not easily in 5 minutes find out..

the other option is the electronics patch.. that would need to look at the signal waveforms and create a module to vary the speed sensors output voltage in a different ratio to the voltage signal to the abs controller..

don't forget that you also need a brake pedal position sensor.. the brake light switches hooked up properly..  as some of the wires control the abs controller..


please attempt to save and transfer the RPO label and the what ever its attached to ... and mount it on your hot rod truck... or take a decent digital photograph of it to keep for your records..

how are you going to handle the Passkey antitheft system  that comes with that model.. will only allow you to crank the engine and let it run for 2 seconds before shutting off the fuel injectors..  

All you should have to do is recalibrate it for your rear tire size. If that doesn't do it, I wouldn't get too involved in trying to make it work. I would get a hold of wilwood or baer and explain the situation. I'll bett someone can help you. You just want a bigger brake bias on the rears...

Bob  

WayneP7122, thank you.

It has a 3.73 gear set, as I recall the tone ring is the same on the rear (8 1/2" or 8.6" 10 bolt as I think but I'd have to look again to be sure).


Pepsi1, thank you.

I have thought of contacting Wilwood but Baer hadn't come to mind.  

When I installed 2000 fulsize on my 50 I installed 20" front and 22" rear and had no problems with the abs it works fine,but don't know how much big&little you are useing. On the 55 custom i built i stayed with original sizes because the drive by wire throttle on the LS2 left me no cruise without the ABS.Hope that helps.