ABS Logic

[RADustin]

Not really tune related, but curious what information you guys have about the ABS computer on these trucks. Most of you guys are real smart and have loads of info, so I'm hopeful someone may have a tip.

I'm looking to understand more of the logic of the ABS tone rings and how it monitors them vs VSS or if at all. Basically, does the tone ring tooth count matter, as long as all 4 wheels are the same??

I'm using LML guts in a project with a Ford front axle. Front axle is 60 tooth tone rings with seal unit bearings. LML rear axle is 48 tooth, full float hub. So the easiest way to make everything the same is make a new ring for the rear for it to be 60 tooth and match the front. ABS/stabilitrak from the LML will be active.

any thoughts? TIA

[GMC-2002-Dmax]

If you look at data on a tech2, at least on the older models the rear speed sensor will show the same pulses as the fronts if the factory tire size is left alone in the ecm code.

If you alter tires size significantly, then difference in size can be adjusted closer by re-calibrating the ABS module to a larger tire size to make the front and rear sensor pulses read the same.

That being said I would assume if the fronts and rears match there should be no issues, and I do think the VSS is set up for how ever many teeth.

On a Tech2 when you set a older LBZ with 34" speedo roll out an the fronts are still around 30.7" the difference is seen easily on the scanner inputs for rear and front L/R.

[RADustin]

so you're saying on the older trucks you can change the tire sizes front and rear to get the pulses/rev to closer match up?

This is not the case on the newer trucks. I do plan on running the same size tires front and rear. And I do plan on running the same amount of tone teeth front and rear. The question is basically will the abs function normally with 60 teeth instead of 48? It's much easier to make everything 60 rather than the typical 48.

[GMC-2002-Dmax]

On older models, pre TMPS Insanity over FORDs blowing car tires out under-inflated on SUV's there was a method using a TECH2 to recalibrate the tire size in the ABS Module to whatever was available.

After the hysteria over the FORD Explorer tire issues they started e to remove certain changes on those modules.

I would guess that if the teeth match and the ABS sees the same pulses per wheel the system will be happy, but calibrating to a non-stock tire may or may not cause issues, I have set the internal ECM as high as 116" roll-out in LML's and not had any issues.

[RADustin]

I was thinking about this as well.

Adding pulses though makes the tires seems smaller. I know if you go too big the abs freaks out. No info if you go "too small".

Sucks there isn't much more info out there on the abs and how it works.

[turbo_bu]

From what I know, the main issue with tire sizes has to do with the older trucks and the 3 channel ABS. For those systems, the ECM was outputting the "high resolution" (e.g. Vehicle Speed Output Circuit 128K) speed signal to the ABS for the rear wheels. If you recalibrated for the tire size with the ECM, but didn't recalibrate the 128k output, the ABS didn't know it and would get mad due to speed mis-match. My guess on the newer systems (assuming it's a true 4 channel ABS system) is that as long as you have matching number of pulses on all 4 corners, it should be good.