1968 M-715 Military Jeep - Over The Road M-715, Part IPosted in Project Vehicles on October 1, 2008 Comment (0)
You first met our '68 M-715 in the Nov. '06 story "28 days to Failure." This author nearly killed himself turning a derelict and incomplete military Jeep into a runner in a mere 28 days. In the end, the truck ran, but the engine was a total goner, so the planned excursion to Ouray, Colorado, didn't happen. After that heartbreaking incident, the M-715 earned itself the moniker the evil truck.
Next, you saw us replace the tired, smoking '73 Camaro 350 that doomed the trip with a hot little 290hp 350 crate engine from GM Performance Parts in the July '07 issue, "the evil truck revisited, Part I." the following month, we added a detroit Locker and a nice new Beachwood Canvas Works replacement top. And that's how we've been enjoying the evil truck for the last year or so.
However, now that we've got a nice top to keep the rain off our heads and a strong, reliable engine, we've been feeling the itch for longer, extended road trips. It's nothing the stock t-98 can't handle, but the factory NP200 isn't exactly known for its ability to operate at sustained freeway speeds without burning up. And with the stock 5.87 gears, it's not like we'll be roasting our t-case for any semblance of rapidity. the lack of an overdrive and the military-spec gearing garner a whopping 3,300 rpm at 60 mph.
Out With The Old, In With The Bold After taking stock of our inventory on hand and doing some head-scratching, we determined we could add overdrive, clean up our storage shed, and even get a few inches of rear driveshaft length in one fell swoop.
We had equipped an SM465 transmission with a Novak PN 463r dana 300 adapter years ago. It's since been on the shelf. the Novak adapter is only 3.2 inches long and utilizes a new main shaft that had Something old, something new ... well, you get the idea. here's our new drivetrain. From front to back it's the ranger torque Splitter with 27 percent overdrive, an old SM465 we readied to be installed in a previous project and have since been holding on to for years, and an Atlas II highlander. You may think it's a long combo, but thanks to our M-715's divorced t-case we'll actually be gaining length in the rear driveshaft. For FSJ-truck, Wagoneer, and Cherokee guys, a setup likethis may be the hot ticket. to be installed in the tranny.
For overdrive, we've always wanted to try an Advance Adapters ranger torque Splitter. Although it's available in 1.7:1 underdrive, we've always eyeballed the 0.73:1-overdrive model. In addition to being compact, rugged, and simple, the ranger can be built with any combination of GM, Ford, or toyota Land Cruiser bellhousing bolt patterns, so it can double as an adapter. We asked Advance to build ours with a 4.686-inch bellhousing index hole on the engine side to match our existing Chevy bellhousing and a 5.125-inch transmission bearing index to match our SM465. But you can also use a ranger to mate a Ford engine to a Chevy tranny and so on. the ranger can swallow 420 lb-ft easily and will turn our 5.87 axle gears into 4.29s for much better freeway rpms.
To back up our new drivetrain we insisted on an Atlas II from Advance Adapters. With its 3.0:1 low range, the Atlas II highlander model we spec'd out gives us a great final crawl ratio without totally killing our fun in the dunes or mud. We had the t-case built with 32-spline front and rear output shafts because our M-715 is a heavy truck that may someday see a lot more power than we have now. The Atlas II offers incredible strength in an unusually lightweight and compact package.
This month we'll show you some of our prep work to get the drivetrain ready to come together. Next month we'll cover the actual installation into our fullsize Jeep.