Monster Five-Speed
Cheap overdrive for big Jeeps.
Christian HazelPhotographerPete TrasborgWriter
We all want a transmission that we don't have to worry about. It should be stout enough to beat on, but civil enough so that we don't hate driving it. Also, if the rig in question ever sees street use, we tend to gravitate toward an overdrive unit.
The transmission on the left is an SM465 from a Chevy, which weighs in at 175 pounds and its case length is 12 inches. On the right is the monster, a Spicer 3053A transmission out of a 2 1/2-ton military truck. With a 230-pound dry shipping weight and a case that's 13 1/2-inches long by 17-inches tall by 10-inches wide, it's no small transmission. From the bellhousing mounting surface to the face of the yoke, it's about 17 inches. This trans won't fit in a short-wheelbase Jeep. Also, note the 1.5-inch 10-spline input. That will require a medium-duty clutch, which includes a 13-inch clutch disc. The part that looks like a big green bowl on the Spicer transmission is the stock SAE bellhousing, which won't be needed. Unbolt it, throw it out, or wear it as a hat - whatever.
The NV4500 was the first thing we looked at for our 1968 M-715. However, we quickly became aware it was way out of our budget. So, kind of by happenstance, we learned that the transmission out of an M35 (Deuce and a Half) would work behind any GM V-8. We were definitely using a GM V-8, and we liked the fact that the trans was used in a heavier military truck. We were fairly confident that we wouldn't destroy it in our M-715.
The transmission is a Spicer 3053A, and it was used in Deuces with the multifuel engine. It's a fairly big transmission, but it's still only 1 inch longer than an NV4500. However, no tailshaft adapters are currently available to marry it to a transfer case. So we were stuck either making an adapter, having one made, or using it in a divorced configuration.
Since the M-715 had a stock divorced transfer case to begin with, we decided it wasn't a big deal to stay divorced. We were also able to locate a divorced NP205 from an early '70s Dodge truck with little difficulty.
We got our 3053A off of eBay for $450 plus shipping - it was rebuilt by the military and then never used. We saw pictures of the internals and everything looked good. That and the fact that the seller guaranteed it'd work pushed the purchase. These transmissions are also available rebuilt for $895 from Boyce Equipment and $1,450 from Memphis Equipment.
Once you get the transmission, you'll need to go and scavenge junkyards that have medium-duty trucks - we're talking school buses and box-truck type of vehicles. Find mid-1970s to early-1980s Chevy or GM trucks with a big-block and a less-desirable five-speed manual transmission. You want to get the bellhousing, flywheel, clutch fork, adapter plate, starter, and basically anything else between the transmission and the engine.
That's all you need to bolt the transmission to any 90-degree Chevy engine. You don't have to cut or fabricate any drivetrain parts; everything will bolt up. Of course, there will be the normal fabrication work involved in any transmission swap, but to bolt the trans to the engine is easy as pie. The box truck's clutch fits the Spicer trans like it belongs there, the throwout bearing is the right size for the input-bearing retainer, the flywheel puts the clutch in the right place, and basically everything works out just the way you've always wished things would.
Take a look at the bellhousing and you can see how the stock 3053A input-bearing retainer is the right outer diameter to locate the transmission in the bellhousing. Some parts are needed off of a mid-1970s Chevy, a GMC C-60, or a C-70 with a tall-deck big-block and a five-speed manual transmission. Look inside the bellhousing for a hole where a bolt should be in the six o'clock position - that's the sign you have what you want. There are other bellhousings bolted up under these trucks, but the only one known to have the correct five-bolt bolt pattern is this one. Once you get the bellhousing off, check the casting number on the transmission side of it. On the lower right as you are facing the engine, it should read "32921997 GM2."
Here on our old four-bolt main 350 is the adapter plate, which allows the massive bellhousing to be bolted up to any Chevy engine with the 90-degree bellhousing. The flywheel we are using is huge and won't physically fit inside a smaller bellhousing. The adapter plate is 1/4-inch steel and is definitely needed. Often it's the hardest part to locate. The other parts that you absolutely need off the C-60 or C-70 are the bellhousing, shift fork, adapter plate, and flywheel.
This is a good comparison of a normal GM flywheel and the huge monster that we used. While you may think it will make getting a clutch kit difficult, this is simply not so. Walk into a NAPA parts store and get clutch kit PN MO1919-1, which includes the throwout bearing you will need, clutch, pressure plate, alignment tool, and huge pilot bearing. Also make sure to get a starter, NAPA PN NAE 76103 or Wilson PN 91-01-3806, and a solenoid. With those three things you can install the trans and fire up the engine using the medium-duty parts. We didn't pull the starter from the junkyard, as there wasn't one to be had.
One of the other caveats of this swap is that we know of no adapter for this transmission. The output is a 1.5-inch 10-spline. Since we put the transmission in the M-715, it wasn't a big deal because the 715 uses a divorced-style transfer case to begin with. Also, we wanted to use the stock Deuce jack shaft so that if we ever needed to, we could get an off-the-shelf replacement, so to speak. We went to see Jesse at High Angle Driveline for an adapter for the swapped-in, divorce-mounted NP205.
The bellhousing is cast flat, drilled, and tapped for rear motor mounts. Between the weight of the tall-deck big-block and the weight of the transmission, we decided that utilizing these extra mounts would be a good idea. We used the rubber for a 1971 Chevy C20 and custom-fabricated the mounts out of 1/4-inch plate. Also note the wonderful gasket we used between the transmission and the bellhousing. The bolts holding the bell to the trans are "wet" bolts, and when we removed the stock bellhousing from the transmission, we destroyed the gasket. So we went with some RTV to seal the front of the transmission.
For the transmission's rear we used a normal Chevy transmission mount and modified the stock crossmember so it would bolt on. Also, we fabricated a bracket that bolts to existing holes on the back of the transmission, which were used for the Deuce trans mount. This way, we've got a standard mount. Also, while the angle of the picture may be misleading, we can drain the transmission as it sits. This mount, coupled with the front trans mounts (or rear engine mounts), allows us to pull the engine at will and not have to worry one bit about wrestling the 230-pound transmission around under the truck.
Here's a look from the top. On the M-715's original T-98A transmission, the stock dual transfer-case shift levers bolt onto the transmission. We fabricated a bracket that allowed us to bolt the three stock levers onto the transmission in the stock location. The bracket bolts through three bolts in the top cover. This allowed us to leave the floor in one piece. Even the shift rod sticking out the back of the transmission's top cover (A) cleared the floor. That shaft actuates the transfer case in the stock 2 1/2-ton military truck application. It moves when the transmission goes into reverse or low gear, so make sure there is plenty of clearance left for it. In our case, it cleared everything with no problems.
Those of you who have driven Jeeps with T-18s, T-98s, or T-150s will recognize the center and left of this shift pattern. On the right is where it gets weird. After Third, you go over and down for Fourth, then back up for OD (Fifth). It's a bit strange and takes some getting used to, but it's really not a problem. The only issue arises after you drive a more modern vehicle or trans where First is up and to the left - we've almost run over the car behind us a few times, forgetting what we were driving. Most of the time, though, First isn't even needed on the road, so we start off in Second gear and there is less confusion all around.
While we were able to save the floor, the stock transmission tunnel cover had to undergo some surgery. The half-moon hole is where the stock T-98 shifter came through, and the gaping hole to the right of that is to clear the top of the transmission. The 3053A is taller than the SM465, T-98, and most of the others, so odds are quite good that clearance will be needed for the top cover.
Because the shift tower sits farther forward, the actual stick has to be bent to clear the dashboard. Most FSJ dashboards are the same at the bottom, so this is a pretty universal step. If you are putting this trans in a CJ-8 or something similar, we'd be interested to hear what you did for clearance. In our case, we heated up the stick and bent it to clear the dash, but we also cut about 4 inches out of it so that the shift knob wasn't next to our head when we were shifting. Also visible here is the transmission cover in its finished but uninstalled stage with the boxed-in area to clear the top of the transmission.
One minor snag that we ran into in the course of this swap was our planned engine. We were going to use a four-bolt main 350 from a 1991 Chevy truck, but we didn't think about the flywheel. The flywheel that the clutch bolts to is from a mid-1970s truck and was hung off the back of a two-piece main engine. In 1986, Chevy V-8 and 90-degree V-6 engines went to a one-piece rear main seal. This design required the redesign of the end of the crankshaft. So the flywheel we needed to use would not bolt up to the engine we were going to use. The engine on the left is a four-bolt main 350 with a 3.58-inch-diameter flywheel bolt pattern, but we couldn't use it as we had already blown it up. The engine on the right is out of the 1991 with a 3.00-inch-diameter bolt pattern, and the difference between the two is readily apparent.
This is before we put the adapter on the jack shaft and the bellhousing on the front of the transmission, but it's a good photo to illustrate how it all goes together. In a divorce-mounted application, each component has its own mounts and supports its own weight. Also, with the stock Deuce jack shaft, we ended up with equal-length driveshafts front and rear. The 3053A was only in the Deuce and a Half's with the multifuel engine. There were three variations of this transmission available: the 3052 with a 7.16:1 First and a 1.00:1 Fifth, the 3053 with a 6.00:1 First and a 1.00:1 Fifth, and the 3053A, which is the overdrive unit. Look for the data plate on the transmission (seen here on the top right side of the trans) for the right model, or spin the input shaft and count the rotations of the output shaft.
The stock crossmember for the truck is located right behind the transmission. The curved line at the top of it is where we had to cut additional material out to clear the monster output yoke of the trans. We cut along the curve and then welded in some plate so that the stock C-channel was retained for strength. We also had to hammer the floor of the truck up a bit to clear the Chevy clutch fork and then use a modified CJ clutch linkage complete with Z-bar to finish setting up the clutch.
This is a comparison of pilot bearings. One of the other issues with the swap is that the nose of the input shaft is 0.75 inches in outer diameter, and the inner diameter of the pilot bearing is 1 inch. Shown here from right to left is a normal small flywheel pilot bushing, a pilot bearing for a small flywheel, the pilot bearing for the large flywheel with the 1-inch inner diameter and 2.5-inch outer diameter, and a brass adapter bushing with 0.75-inch inner diameter and 2.5-inch outer diameter. We ended up using the stock sealed ball bearing with 2.5-inch outer diameter and 1-inch inner diameter, then we machined a 0.125-inch wall spacer, as we're partial to pilot bearings over pilot bushings.
This transmission was originally used in trucks rated for a gross vehicle weight of 23,800 pounds. It was even used for the 1-ton land-speed-record trucks. We doubt you'll be able to break it. We said it won't fit in an SWB Jeep, and that's mainly because of the lack of an adapter to marry a transfer case to it (rumor is Rube-Adapter may be working on one). If you were to solve that issue, it'd fit in just like an NV4500 (look at the case lengths below). Here's a quick comparison between the Spicer 3053A and the famous NV4500: