LMM Atlas Low Range Tuning

[Jaygee]

Hey ....Im new to the forum.

Want to post a question about fitting an Atlas transfer case to the LMM.

Basically how do I go around changing the Low Range ratio and where is it located? ECM or TCM ?

[THEFERMANATOR]

It's in the TCM, but others have said the GEN IV ALLISON TCM doesn't respond to the gear ratio change in reverse. Somebody else put a NP208 behind a 6 speed ALLISON, and he said it goes into limp mode everytime he is in 4 low and goes into reverse.

[Jaygee]

It's in the TCM, but others have said the GEN IV ALLISON TCM doesn't respond to the gear ratio change in reverse. Somebody else put a NP208 behind a 6 speed ALLISON, and he said it goes into limp mode everytime he is in 4 low and goes into reverse.

Thx Thefermanator, I was pretty sure it was in the TCM just not familiar with the process yet.

[THEFERMANATOR]

Just looked and it's H5061 in the TCM for the transfer case low range ratio. I know one person who tried to change it and he said it worked fine in forward, but would limp as soon as he moved in reverse. Another person opted to move the oss sensor up to the output of the trans, and cut the 4 low input to the TCM and ECM so he didn't have to worry about the limping issue.

[LB72004]

Another person opted to move the oss sensor up to the output of the trans, and cut the 4 low input to the TCM and ECM so he didn't have to worry about the limping issue.

wouldn't that trip the anti-lock brake codes and/or the traction control with the wheel speed being different than what the ECM/TCM thinks it should be or cause some other issues related to that?

[Jaygee]

.... yeah I did think VSS at the back of the trans might be the best option Thefermanator.Curious why changing that setting didn't work for reverse gear? Have put it to Steve at Advance and he informs me they have a piggy back system that emulates the switching but does not alter the difference in signal.
I guess bringing all the inputs into line with the conversion may not always be the best solution. I could always connect the Low switch to the dash on its own.?

LB72004 Im pretty sure in 4 LOW it disregards those parameters..... don't hold me to that just a guess given loss of traction is inevitable at some stage off road!??

[LB72004]

from what i remember reading, on those that did the solid front axle swap and converting 2wd to 4wd in the process could not get around 4 low ABS errors. it may have been related to just the ABS "knowing" that the font should not be "slipping" the same as the rear wheels without the brakes applied. what they did to prevent the errors was disable 4 low and only use 4 high.

it was, if i am not mistaken, caused by the VSS speed sensor located at the tail end of the of the transmission and the ECM/TCM/ABS being programmed to see a particular wheel speed in relationship to shaft RPM. with having a transfer case that is not controlled by the ecm then the ABS module will see the shaft RPM and the wheel speed not correspond when 4 low is engaged, thus the ABS errors.

[THEFERMANATOR]

Yep, I need to cut the 4 low signal to my ECM to get rid of the pesky P0500 code in 4 low from the ECM. Since my ECM is no longer connected to the databus, it no loger receives speed sensor input from the ABS, and codes a speed sensor error in 4 low. As for moving the VSS, yes it would cause ABS issues in 4 low. There really isn't anyway around some of the stuff in the newer electronics to allow some customizing. As to why it does it in reverse, the TCM may have a different gear ratio factor for reverse, and we don't have that parameter with EFILIVE. It's sort of like the 600RPM slip limit, EFILIVE has it mapped out for 02+ OS to get around it, but 01's are not mapped out yet we know for a fact they have the same slip limit built into the programming in them. It is just done with a different definition than the 02+ TCM's use.

[Jaygee]

from what i remember reading, on those that did the solid front axle swap and converting 2wd to 4wd in the process could not get around 4 low ABS errors. it may have been related to just the ABS "knowing" that the font should not be "slipping" the same as the rear wheels without the brakes applied. what they did to prevent the errors was disable 4 low and only use 4 high.

it was, if i am not mistaken, caused by the VSS speed sensor located at the tail end of the of the transmission and the ECM/TCM/ABS being programmed to see a particular wheel speed in relationship to shaft RPM. with having a transfer case that is not controlled by the ecm then the ABS module will see the shaft RPM and the wheel speed not correspond when 4 low is engaged, thus the ABS errors.

Just to fill in some more info.... the LBZ or in this case the LMM is a conversion so I am fortunate to have a standalone ABS system already on board. This doesn't mean the dash (also LMM) doesnt remind me to "service air-bag, service trailer brake, service transfer case... etc". Ive effectively dodged the ABS issue if not ignored the link with the ECM.
Regarding using the VSS on the end housing of the transmission... I have used that method before on a similar conversion with good results. I guess having the ABS module connected to the ECM with no or incorrect input speed will throw the codes you refer to.

Having said that is it possible to recalibrate the the TCM somehow...?

[DURAtotheMAX]

Did anyone ever figure anything else out about this?

It would be nice to be able to use this 4wd low range input to make a sort of selectable "tow/haul mode" on 2wd standalone setups...then we wouldnt have to keep the BCM wired up etc.

Ben