1-TON PARTS TRUCK
QWhat would be the best truck to buy and get as many good parts to build a rockcrawler with 40-inch tires? My wish list would be a 14-bolt rear axle, NP205 transfer case so I don’t have to buy an Atlas 2, and a Dana 60 front axle. I’m assuming I’d invest in heavy-duty end forgings and kingpin high-steer knuckles for the Dana 60. I’d like to run 5.71:1 ratio ring-and-pinion gears to avoid having to buy a doubler for the transfer case. I’ll upgrade the driveshafts to at least 1350 U-joints. Since my knees are shot, I’d like to have an automatic transmission with a granny-low First gear. Thanks for all you do. I’ve been an avid reader for many years.
AALFRED RICCI VIA EMAIL
Given your list of desirable parts, it sounds as though you should start with a 1-ton truck. I am assuming the frame and body will get tossed and the parts will make their way onto whatever rockcrawler chassis you have planned. Dollar for dollar, it will be pretty hard to beat an ex-military M1008 11⁄4-ton GM truck or any of its derivatives. These came with a kingpin Dana 60 front axle, GM 14-bolt rear axle, and the bombproof TH400 transmission. The only hang-ups are the NP208 transfer case, which can be swapped out relatively easily, and the pathetic 6.2L diesel. You can usually pick up a non-running M1008 for less than the cost of the parts. The second option would be the ’77-’91 GM K-series 1-ton truck. This truck would have come with the same Dana 60 front and 14-bolt rear solid axles as the M1008, but could have been had with a gas V-8 engine. Some even have a big-block 454. Most of the 1-ton GM square-body trucks came with a TH400 automatic transmission backed up to the NP205, but the NP465 four-speed manual transmission was also available. The TH400 doesn’t really have a granny-low First gear, it’s only 2.48:1, but TCI (tciauto.com) offers 2.75:1 and 2.97:1 aftermarket First gear ratios that can get you a little bit lower.
The Dana 60 front axle has gear ratios available down to 7.17:1; however, the 14-bolt only has gear ratios available down to 5.38:1. With 5.38:1 as your deepest available axle ratio and a stock TH400 First gear, you’ll be looking at a crawl ratio of about 26:1, which really isn’t low enough. Switching to a Dana 60 or Dana 70 rear axle and 7.17:1 ratio axle gears would get you a crawl ratio of about 35:1, which also still isn’t all that low. You may need the transfer case doubler to get the crawl ratio into a suitable range. You’ll want to aim for at least a 50:1-60:1 crawl ratio with an automatic transmission for extra-heavy rock use. A low crawl ratio like this will give you the slow speed control you need in the boulders and help keep the slushbox transmission from overheating.