One of the best parts about swapping in a Ford 302 is that there are
several excellent manual transmissions available that bolt right up to
it using factory bellhousings and clutch parts, so you don't need any special
adapters. Some choices include:
| Transmission | First | Second | Third | Fourth | Notes |
| T18-A | 6.32:1 | 3.09:1 | 1.69:1 | 1:1 | |
| T19 | 6.32:1 | 3.09:1 | 1.69:1 | 1:1 | Synchro'd 1st gear |
| NP435 | 6.68:1 | 3.34:1 | 1.79:1 | 1:1 | |
| WC-T5 | 4.02:1 | 2.37:1 | 1.50:1 | 1:1 | 0.76:1 OD, Synchro'd 1st gear |
The WC-T5 is a fairly light-duty tranny, and is what the 5-speed 5.0L Mustang came with from the factory. I've included it because it's possible to swap a Jeep T5 output shaft into it, replace the tailhousing with the Jeep T5-D20 adapter, and end up with a 5-speed powertrain solution that uses 100% factory parts. This would be an option for CJs or other vehicles with the front driveshaft on the passengers' side.
There are other transmission options, including the German (ZF-5?) that I know nothing about, and several automatics, including the C4 and C6. NOTE: the 302's computer and wiring harness are different, depending on whether it was originally bolted to a manual or auto tranny. If you want to run an automatic, save yourself some headaches and make sure you get an engine that was originally bolted to one!
Personally, I prefer a manual tranny. I chose the NP435 because it has a slightly lower first gear, and I was told by some Jeepers that owned them that they shifted smoother than the T18 and T19. I did have access to a wide-ratio T19, but decided against it anyway. Experience has since made me glad of that. While a synchronized first gear sounds like a good thing, it only matters when you want to downshift into first while moving. Let me tell you, that first gear is so damn low that you'd pretty much never need to do that! My only reservation about using a 4-speed was the lack of an overdrive gear. But after some emails with Jeff Reynolds (aka Jefe), my mind was put as ease. As it happens, 35-36" tires with 4.10 axle gears are a good combo for a 4-speed. The engine runs at about 3k rpm at 70-80mph. Not bad.
The T18/T19/NP435 are all very tough transmissions, and they're relatively plentiful and cheap in the local wrecking yards. Ford used them in their 3/4 and 1-ton trucks, so they're plenty strong enough for a Jeep! They're also quite short, which helps reduce the overall length of the powertrain - a good thing in a 94" wheelbase YJ. Every inch of rear driveshaft counts, especially in a lifted Jeep. The NP435 is just under 11" long, about an inch shorter than the T18 and T19. It's quite tall though; I ended up needing a 1" transfer case drop, and even then almost the entire top cover is inside the cab. In the picture below, you can see my NP435 painted in Hammerite red, with the custom-made adapter that bolts to its rear sitting beside it.
Before this picture was taken, I rebuilt the transmission using a bearing, seal, and gasket kit purchased from the local Lordco. It was amazingly cheap, too, and came with good, US-made Federal-Mogul bearings and seals. The rebuild was very straightforward, especially considering I'd never rebuilt a tranny before. Some photocopied instructions from the Ford shop manual collection at a local library came in very handy. You know you're dealing with a very simply-made, no-nonsense gearbox when the factory rebuild instructions call for the use of blocks of wood during reassembly! In addition to the wood, all I needed were some snap-ring pliers, a good-sized hammer, and a few SAE wrenches (no metric bolts here!). A bearing splitter and puller set did come in handy a couple of times, though.
The transmission's output shaft was shortened and resplined by Moser Engineering, in order to mate with the 27-spline input gear of the NP203 transfer case. This is the 2wd version of the Ford NP435 - it's different from the 4wd version in that the four-bolt pattern on the rear (facing us in the above picture) is square. On the 4wd tranny, the lower two holes are spaced further apart, and the output shaft is longer and thicker after it exits the tranny. The shafts are interchangeable, and I actually used a 4wd shaft, although either type can be modified to work with the NP203. The instructions I sent to Moser on how to modify the shaft are here (MS Word 97 document). Note that my numbers assume a 2.25" thick adapter! Note also that the instructions assume the use of a 2wd NP435 shaft. For a 4wd shaft, ignore the references to the dimple and the second snap ring groove.
After I got this shaft (and the modified NP203 output shaft) back from Moser, I had the modified sections case-hardened. I figure this is a very important step, to add a little strength to the shafts but also (and more importantly) to extend the lifetime of the splines, by making them more resistant to the wear that occurs during use. Trouble is, most modern case-hardening techniques require that the whole part be done at once, which can cause unwanted distortions in long parts like these, especially when most of the part is already hardened (again, like these). Fortunately, I heard about another option. There's a product called (believe it or not) Hard 'n Tuff, which can be applied selectively to steel parts and case-hardens them to a depth between 0.003" and 0.006". Not bad, considering the alternatives. We put the shafts into a driveshaft welding jig (a lathe would work even better), and spun them while heating the section to be hardened with a torch, so it was heated evenly. Then the Hard 'n Tuff is applied with a flour sifter, again while the part is being spun. Then it's quenched, and a quick test with a file reveals confirms that it's now got a good, hard outer shell. The dimensions weren't measurable affected, either, and I couldn't see any distortion. We put two applications of the stiff onto the modified section of both shafts, for a little extra insurance.
The adapter started out as a piece of scrap hexagonal mild steel stock that had a hole bored through it. That's the only reason for its outer shape. Its overall thickness is 2.25" - this is about as thin as it can get before the snout on the NP203 input gear touches the tranny's output bearing snap ring. The important features on the transmission side of the adapter are:
The machining was done by a very generous (and capable) CNC machinist Jeeper friend at his workplace. He and I designed the adapter on the fly (cut, test, cut, test, etc) over the course of several Saturdays. Sorry, I don't have any detailed drawings or machine files for it, but with some patience you ought to be able to do the same thing. Here's a close-up of the front face of this adapter, and the gasket I made for it:
The other side of this adapter is discussed in the NP203 section.
Ah yes, the clutch. This was a topic of a lot of debate. Initially, I'd planned to use the Mustang's T5 bellhousing, clutch, flywheel, and starter. Even had the flywheel turned in anticipation, but I didn't have any great ideas for adapting the 'Stang's clutch cable to the YJ's pedal. Then, Glen Hogenson and I actually sat down and took a real close look at that bellhousing. As it happens, the T5 bellhousing is NOT compatible with the NP435 tranny. The NP435, T18, and T19 all have the same input shaft and front bolt pattern, but the T5 uses a slightly different one. The bellhousing looks like it can be redrilled and made to work, but it just ain't so. It's too thick (front to back), and the hole for the tranny's input bearing retainer is slightly too large. Fortunately, a better solution presented itself.
For a few years in the mid- to late-80's, Ford used an external-cylinder hydraulic clutch system on the F-series trucks with the 302 and the 4-speed (ie T18) tranny. So off I went to the wreckers, and found me the right bellhousing. Some further searching turned up a complete hydraulic clutch (master and slave cylinders, and the connecting hose). Unfortunately, the Mustang flywheel, starter, and clutch don't work with this bellhousing, so Ford truck parts were used instead. I actually ended up with a Ford 300 I6 flywheel, and had it rebalanced for the 302. The silver lining to this cloud is that I ended up with a (relatively) humungous 11" clutch, instead of the Mustang's 10.5" disc.
Anyway, the important thing to keep in mind here is that the bellhousing and everything inside it (including the steel dust shield thing that bolts between the BH and engine) are Ford truck parts. None of the Mustang stuff (with the exception of the pilot bearing!) can be used. I used an '86 F250 (the >6800lb model) with the 5.0L and T18 as an application for the counter guys when shopping for these parts at wreckers and parts stores.
Here's some pictures of the bellhousing and clutch parts:
The factory ford clutch hose ended up fitting fairly well, once I found a way to route it without kinking or interfering with anything else.
In case you're wondering, I did try using the YJ master cylinder before installing the Ford unit. It just didn't move quite enough fluid to disengage the clutch. It was close, but not quite enough. Also, splicing the Ford and YJ hoses together is no simple thing; the Ford hose is made of plastic, which doesn't like being clamped or crimped.