Our buddy, Mike, is something of a manual-transmission nut. He geeks out on knowing the gear ratios for most manual transmissions, especially those with granny gears, or found in Jeeps and Ford trucks. Mike has a 1975 CJ-5 that is understated and works well. If it's just on a run to the hamburger shop or the parts store—or even driving the Jeep to the Rubicon Trail—it's just about perfect for whatever you toss at it.
One thing Mike (and we) really likes about it is its transmission, which is a New Process 435 manual transmission. This is one of the newest of the granny geared 4-speeds, and a transmission we want to spend more time with. It's also very similar to the Ford T-18 which has a large following in the aftermarket granny geared 4-speed transmission world. As a result the NP435 and Borg Warner T-18 are relatively easy to swap into just about any 4x4 with a few aftermarket parts and a little backyard engineering. Also the junkyard, at least the ones around us, are littered with them.
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We just got done rebuilding an NP435 (with a tech story to come) that we initially planned to put behind a Buick V-6. We've contemplated a few other powerplants, and wanted to share how this transmission could be swapped behind just about any GM engine and more. Here's what we did to make the most common NP435, the Ford NP435, fit behind our engine.
Finding the correct bellhousing
Basically what we are doing here is making the front of our NP435 look as much like the front of an SM420 as possible—with the exception of the input shaft, which will have the 1-1/16-inch 10-spline machining. This means you'll need a GM clutch disk with a Ford center and a 10.5-inch outside diameter. According to Novak Conversions, this clutch has a part number as a clutch for a 1976-1979 Jeep clutch. Also we are running a Novak machined input bearing retainer to match the GM bellhousing. This part is available as part one of several parts that should help anyone adapt the NP435 to a GM bellhousing.
Buick V-6 Bellhousing
Some Jeeps came with Buick V-6s but many of those lived in front of T-14 transmissions that use an input shaft that is much longer than the NP435/or T-18. For that we need to find a bellhousing from a later Buick Car that had a manual transmission like a 1976-1978 Buick Century or Skyhawk, Buick Special, Apollo and so on. This will allow us to bolt the NP435 to the back of this bell once we make some modifications to it. Novak also sells rebuild parts for the NP435 as well as the clutch forks, pilot bearings, hydraulic clutch conversion parts, clutch discs, pressure plates, and so on. The clutch disc we need to use with the Buick flywheel and clutch pressure plate is available from Novak Conversions and Centerforce Clutch.
AMC 2.5 with S-10
Similarly to the Buick V-6 swappers, anyone who wants to retain their AMC 2.5L 4-cylinder can make the SM420 work as well as the NP435 work. To do this you need to find a bellhousing from a Chevy S-10 or Camaro that had the GM 60-degree V-6 and a manual transmission. Find more details on making the SM420/AMC 2.5 combo work from our friends at Four Wheeler. You'd have to use a combination of parts and methods from this article and the article in the previous link to make a NP435 mate to an AMC 2.5L.
GM small-block V-8
The vast majority of info needed to bolt the Ford NP435 to the back of a GM small-block is the same as when using a Buick bellhousing (subhead, above). For one, you'll either need the GM bellhousing with the smaller center bore and the machined down input bearing retainer, or you'll need the GM bellhousing with the larger center bore and the reducer ring (PN: BR4) to center the front of the trans in the bellhousing.
Transmission "Bonus Ears" and DIY conversion tabs
Some NP435s have "bonus ears" cast into the front face of the transmission. These are undrilled mounting ears that will help you mount one of the above bell housings to the transmission's front face. First, with a bare transmission housing, we fitted the custom Novak bearing retainer. Then we slid the bellhousing we have onto the transmission. The upper two holes nearly line up and only require opening the mounting holes a bit. From there, we can drill one bonus ear for the lower driver side of the front face of the transmission (right side in the photos of the front face). Then we drill and tap the other "bonus ear" so we can make and mount a small bracket made out of 1/4-inch plate and a bit of steel tubing.
Aftermarket Bellhousings
There are also plenty of aftermarket bellhousings that can be used to make several transmissions work behind all kinds of engines. We are running a Ford T-18 behind an even-fire Buick V-6 using an adapter bell from Advance Adapters (712583). We also geeked out on the internet one night and discovered that several bellhousings, including many from Quick Time can be used to adapt one of several engines to the front pattern were focusing on here. For example, PN RM-7041 will allow us to match the NP435 to an GM Ecotec 4-cylinder to a Saginaw or Muncie transmission (like the SM 420), assuming we can find a clutch disc that will work or get a custom clutch disc with the correct 1-1/16-inch 1-spline hub and 9 inch OD, we can make this engine work with a NP435. That's a little powerplant that uses modern tech to make close to as much or more power than an odd-fire Buick V-6, especially when combined with the available turbos and superchargers.
Advance Adapters, 800.350.2223, www.advanceadapters.com
Centerforce Clutch, 800.932.5882, www.centerforce.com
Novak Conversions, 877.602.1500, www.novak-adapt.com
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