Rosco P. Drivetrain is the name given to my 2005 Chevy PPV Tahoe project completed (as though any project is ever really completed) over a year ago (“Part 8: The Finale,” Apr. 2016). The name is eclectic, yet does match the story of the truck and pays homage to one of my favorite automotive TV shows from the past. After all, who doesn’t love The Dukes of Hazzard and that lovable, conniving police officer played by James Best?
The truck, formerly a 2WD Henderson, Nevada, police patrol vehicle, was bought with the intention of building a big comfy capable family wheeler that could go anywhere a built JK could go for a fraction of the purchase price of a dead-stock JK Wrangler. Our plan and the build were successful, although I did run into a few more problems than I’d anticipated and spent more time getting the truck into a drivable state than I would have liked. The “final” product drives great and wheels amazingly well for a big, heavy truck.
The idea was simple, even if the execution of the idea was not. I wanted a JKU fighter with an LS V-8 and 1-ton axles. With a little searching I found a set of axles from a 2012 Ram Mega Cab for just over $1,000, including tires and wheels. I kept the AAM 9 1/4 front axle for Rosco and sold the 11 1/2-inch AAM for $700. My plan was to recreate a Ram/Dodge 3/4- or 1-ton four-link with track bar suspension under the front of a 2WD Tahoe.
Since the last installment I’ve made a few small improvements and additions to the truck and driven the heck out of it both on- and off-road. You’ve seen images of it in articles about adventures to Colorado and Utah, tire tests, and more. With little maintenance and further modification, the truck has taken me on two road trips to California, two wheeling and camping trips to Colorado, and even towed my 1949 Willys CJ-3A to Moab for the 2016 Easter Jeep Safari. The truck is confident on fairly nasty off-road trails and easily does 80 mph down the highway when I ask it to. In short, it drives better than I could have hoped at legal highway speeds with stability and confidence.
Sure, there are still tweaks and improvements I’d like to make to the truck. It definitely needs a spare tire carrier and a real rear bumper. More power is always a good thing. I’d still like to revive the strobe light system and police siren—er, loudspeaker for use on the trail. Some of these things may get addressed in the future . . . or not. But with the Tahoe my primary daily driver, it makes for a great exploration rig since it’s capable and easy to camp in, and I don’t plan on stopping either of those activities with Rosco any time soon.
So to revisit, what did I do on this project? What worked and what didn’t? What would I do again and what do I recommend to anyone who wants their own solid axle’d Tahoe? Keep reading to find out.
For the rear axle I sourced a late-model Chevy full-float 14-bolt from a junkyard and swapped most of the factory brackets over from the Tahoe’s original 10-bolt rear axle. The suspension utilizes adjustable control arms from Rusty’s Off-Road, 3 1/2-inch coils from Skyjacker with custom spring plates, and Sway-A-Way remote-reservoir shocks.
Initially I wanted to use Ram/Dodge coil springs, but later decided to dabble with a set of 2 1/2-inch-diameter, 12-inch-travel Sway-A-Way remote reservoir coilovers. This was a great decision. I love the shocks, and the dual-rate coils up front are perfect for Rosco, although if I gave it to anyone else I love as a daily driver I think I’d add a front sway bar. It leans over pretty far in the corners. I either did the math on the front four-link, which uses Rusty’s Off-Road custom control arms, properly or got lucky, because it works. Either way I’ll take it.
I rebuilt a junkyard NP241C with a slip-yoke eliminator from Tom Wood’s Custom Drive Shafts. The T-case was bolted to the factory 4L60E transmission, which received a rebuild with a 4x4 main shaft and adapter tailhousing. I had a Ram front driveshaft shortened by Tom Wood’s, which also supplied a custom rear driveshaft for Rosco.
The new (to Rosco) axles received 4.56 gears (I should have done 4.88s), an AAM electronic locker up front, and a Grizzly Locker out back. I also added a Yukon locking hub conversion in the front AAM. That was a great upgrade. I love having the locking hubs and knowing the front axle isn’t turning when running down the highway.
The first long trip I took with the running driving 4x4 Rosco was up to Payett Draw, near Payson, Arizona. The purpose of the trip was twofold: I was shaking Rosco down and also checking out the trail for a possible locale for Cheap Truck Challenge 2015. Rosco did well, but I didn’t push it too much since I was alone (although folks knew where I was and where I’d be). The only real issue I had was that the computer clearly was not happy when the truck was in 4-Lo. It wouldn’t shift normally, staying in First and Second only and only shifting between those two near red line, and the engine seemed to be pulling power.
The problem with the computer and low range was one that I should have been able to figure out and avoid. I could have, and should have, added a speed sensor and tone ring to the adapter between the GM 4L60E and the NP241. Instead I have a speed sensor on the output of the transfer case. With the former setup the truck’s computer would never know that the truck was in 4-Lo. As I built it, the truck’s computer freaks out because it doesn’t understand why the rear speed sensor is spinning faster than the transmission’s speed sensor. Lucky for me a workaround prevented me from having to pull the transfer case and add another speed sensor. I sent the CPU to Tilden Motorsports, which was able to reprogram the computer to think like a 4x4 Tahoe CPU.
After Tilden fixed the CPU, Rosco hasn’t batted an eye when in low range, but I do wish it had a little bit more gearing. A T-case doubler would be nice, but I am not sure the NP241 would hold up to the weight and torque multiplication it would see with the doubler. Maybe someday. I’ve also contemplated making room for bigger tires, but right now the truck flexes well and the 37s clear.
I took the truck on two road trips to California for work and then a camping trip to Colorado. In Colorado I found out how capable the truck was and how easy it was to camp out of. During this time I built a front bumper for Rosco and “finished” the project series within the magazine officially Don’t be so sure. —Ed..
I then flat-towed my 1949 flattie up to Moab for EJS 2016, where both rigs spent time on the trail but Rosco’s trail time was cut short because the power steering pump (which might have been original) failed on Fins N Things—but not before I got some pics of the big Tahoe on the trail.
On the second trip to Colorado Rosco saw a bunch of trails around Ouray, including Black Bear Pass, Imogene Pass, and Poughkeepsie Gulch. Some people were amazed that I took a Tahoe on full width 1-ton axles down Black Bear where most only dare to wiggle little Jeeps down. Since the truck is relatively low and stable it wasn’t too horrible, but The Steps just before the Ingram Mill were pretty spooky. I didn’t hop out very often to take lots of photos of the Tahoe on the trail. It required my full attention.