The 1947 - Present Chevrolet & GMC Truck Message Board Network - View Single Post - Autotrac with manual transmission

**JJorgensen52** · 09-20-2020, 02:09 PM

HiHave run into a problem with my latest project - 1999 K2500 suburban 7.4L NV4500 swap, retaining the original NP246 transfer case. Got everything put together and working (GM was kind to me so it went pretty easily!), but I can't get the transfer case controller to work properly.

I have both 2hi, 4hi, and Autotrac *appears* to work, but I can't get neutral or 4lo. I just rebuilt the transfer case and it operates smoothly and easily by hand with the encoder removed. The encoder motor is in working order. When I plug up my scan tool and try to command a range change, it keeps telling me "transmission not in neutral and vehicle speed present".

My VSS is indicating 0RPM on both front and rear driveshafts and I have tried both with and without parking brake, always with clutch depressed.

The GMT400 never came with Autotrac behind a manual, but the S-10 blazer did using the same encoder. The control modules are different calibrations (have tried swapping them and that didn't help).

I am thinking, at this point, that the problem lies in my transmission calibration file, but I'm not terribly familiar with tuning beyond the use of a Tech2.

Any ideas on this one? Different thoughts or ideas appreciated!

09-20-2020, 02:09 PM	#1
JJorgensen52 Simple? What's simple? Join Date: Apr 2007 Location: Southeast CT Posts: 1,472	Autotrac with manual transmission - anyone ever made this work? HiHave run into a problem with my latest project - 1999 K2500 suburban 7.4L NV4500 swap, retaining the original NP246 transfer case. Got everything put together and working (GM was kind to me so it went pretty easily!), but I can't get the transfer case controller to work properly. I have both 2hi, 4hi, and Autotrac appears to work, but I can't get neutral or 4lo. I just rebuilt the transfer case and it operates smoothly and easily by hand with the encoder removed. The encoder motor is in working order. When I plug up my scan tool and try to command a range change, it keeps telling me "transmission not in neutral and vehicle speed present". My VSS is indicating 0RPM on both front and rear driveshafts and I have tried both with and without parking brake, always with clutch depressed. The GMT400 never came with Autotrac behind a manual, but the S-10 blazer did using the same encoder. The control modules are different calibrations (have tried swapping them and that didn't help). I am thinking, at this point, that the problem lies in my transmission calibration file, but I'm not terribly familiar with tuning beyond the use of a Tech2. Any ideas on this one? Different thoughts or ideas appreciated! Attached Images __________________ CURRENT '50 GMC 100 shortbed Gen IV 4.8 LS - 4L65E (Secret truck, Shhh!!!) Build '63 Buick Wildcat Coupe 401ci Nailhead (Very much in pieces) Photos '66 Impala SS convertible 327-QJet-glide (4 speed swap one of these days...) Photos '69 CST/10 4x4 SWB Stepper 350 2bbl - NV4500/NP241C (Broken Truck!) '72 Sierra Grande 2WD LWB fleetside 350-TH350 Refresh '99 K2500 Silverado RCLB 5.7 Vortec - NV4500/NP241C (Daily) '99 K2500 Suburban 7.4 Vortec - NV4500/NP246 (still working out the bugs) SOLD '71 Custom/10 2WD LWB fleetside - '72 GMC K/3500 Dually (Sold to redryder) Last edited by JJorgensen52; 09-20-2020 at 02:16 PM.