Step By Step
Heres what you look fora big old truck in a wrecking yard. Even though this is a two-wheel-drive, many conversions can use these trannies with only a bit of adaptation, and some will bolt right in to a 4x4. Dodges came with a variety of manual trannies, but the most common was the NP435, in both two- and four-wheel-drive versions.
This is an NP435 with a granny low gear in a Dodge. Other versions of the same tranny came in Fords and other vehicles. A cast-iron case and aluminum top cover is a quick tip to spot these babies, which were used from the early 60s to the late 80s. While the output shaft and bolt pattern are similar, the front bolt pattern, input shaft diameter and spline size, and bearing retainer may all differ between years and makes. Advance Adapters offers a great compilation of transmission information in its manuals, a real must-have before you start pulling transmissions out.
Chrysler autos like this TorqueFlite 727 are super-strong and adapt into almost anything. Fitted into big-block Chrysler cars and trucks, they were also used in many Jeep and AMC products. This unit is slung into a Jeep with an Atlas II transfer case and a big-block in front of it. Adapters are made to hook the tranny to zillions of different engine and transfer case combos, as well as the stock applications. Look for a smooth, round bellhousing as your first clue, along with lots of shift linkage on the driver side of the case.
Just say no to car-type three- and four-speed trannies like this Saginaw out of an early Chevelle. While these and similar Muncies and Borg-Warner T-10 trannies are good for cars, the lack of a low first gear is a bummer. If you want to build a sand Jeep with a stick, this might be the hot ticket, and Advance Adapters can fit it to your transfer case.
Big and beefy is what the SM465 four-speed is all about. Used by GM in most light trucks from 1968 on, the 6.58 low gear is just right. Look for a bulge on the driver side of the case (with a cast-iron top) to verify the SM465 from the earlier SM420. This is one of the most durable truck trannies around and makes a great conversion unit for many applications.
Our all-time favorite is the GM SM420 with a 7.05 first gear. Relatively small, light, and short for a real truck tranny, it suffers from lack of parts availability. Look for a bulge on the case on the passenger side, and threaded lower mounting holes on the bellhousing side. Used in most 47-67 GM trucks, these trannies are still available in many yards. Lots of industrial units used them such as aircraft tugs and street sweepers, so finding a low-mileage unit is possible.
The TH400 from GM is the beefiest and biggest tranny you should ever need and is adaptable to nearly any transfer case. The front pattern of the bellhousing shown fits Buick, Pontiac, Oldsmobile, and Cadillac applications. The housing comes to a point in the middle for Chevy uses, and even AMC units are out there with a round pattern. The pan has a unique Texas shape unlike any other, and the guts are switchable between nearly any unit for homemade adaptation heaven.
A popular slushbox nowadays is the GM TH700R4 auto, used in many cars and trucks. The tranny suffered from reliability issues when first introduced, but the low first gear ratio and overdrive made it a popular unit. A big square pan and a four-bolt tailshaft pattern are the first clues, and the lack of a governor on the passenger side separate it from a TH350.
The Borg/Warner T-18 is as famous as they come. Used in nearly every variety of truck made, the zillion different versions of this tranny make swapping a nightmare for some. Input shaft length, stickout, spline diameter, and count are all important. Not only that, but internal differences in tooth count, ratio, and synchronizer cone diameters on the mainshaft can screw you up when swapping out gears. Be careful; the earlier T-98 is nearly identical and even shares many common parts. Bone up on what you need and what you want before searching for this desirable low-geared grunt case.
The most common and popular auto for all but the heavyweight dudes is the GM TH350. A square pan with a corner whacked off is a good ID, and the four-bolt rear housing pattern is another. These units can be built, beefed, adapted, and modified more than most other trannies, and they have found their way against Chrysler and Ford engines with adapters. Be wary of the word METRIC embossed on the pan though. Just say no to these imitation low-lifes that are really TH200s.
Getting greasy and grimy is all in a days fun when youre scrounging for a junkyard transmission, but knowing what youre looking for before you go is definitely important. Wrenching under a teetering hulk to pull that perfect truck tranny is all good, until you get it home and find out it wont fit your rig. Weve nearly done that a time or two, and now we do our research before we trundle off in search of gold.
When youre building up that ultimate trail rig, its more than likely you will need to swap out the weenie stock transmission for some major beef, be it automatic or stick style. But what fits what? And what can be adapted? We could write a book on the subject, but for now well concentrate on a few proven performers of big American ironour favorites. Dont get us wrong; theres lots of smaller stuff from around the world that has its place and makes for fine conversion, but we prefer bulletproof components that give us back trouble as we heave them around from the junkyard to the garage.
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