Swapping an NP435 Transmission & Early Bronco Dana 20 into a Jeep With a 4.0L

Why an NP435 and a EB Dana 20?

When fourwheeling over technical terrain, it is common knowledge that slower is better. By having the control to idle up and down obstacles instead of gassing it or riding the brakes, you save parts and minimize body damage. When I was looking into a bulletproof transmission I wanted a really low granny first gear, simple operation, a good reputation and easy availability of spare parts. For a t-case a was looking for a gear-driven, cast metal case that had a good aftermarket following (in case I ever wanted to put in lower gears). My original choice was a Dana 300 out of a late CJ mated to an NV4500 (6.3:1 1st gear with an overdrive) but the only two problems with this set-up are the front output is on the passenger side (I needed a driver side drop) and the expense of getting an NV4500 out of a new Dodge truck. So in the end I chose an EB Dana 20 and a NP435 out of a ¾-1 ton Ford. The EB Dana 20 and NP435 are the perfect combination mainly because there is no need to replace output or input shafts on either of the units because the NP435 has a 28 spline output and the EB Dana 20 has a 28 spline input. How perfect is this!?

The NP435 has a first gear of 6.69:1 and the EB D20 has a low range of 2.46:1. With my 4.10 gears that equates to around a 70:1 crawl ratio without any further mods. In order to mate the two you will end up with an adapter about 8 inches long. The 435/D20 combo is about 1 inch or a little more SHORTER (even with the 7.5 inch adapter) than the AX15/NP231 SYE combo. This was a very important aspect of my swap because of the I have a SOA with 3.5" springs which doesn't yield a good rear driveshaft angle. On top of that I have a Ford 9" in the rear, which makes the angle even worse. After all was said and done I ended up with a rear driveshaft that runs at 24 degrees and is 4-5"s longer than my old one.

Transmission - NP435

When you make your way out to the wreckers you need to keep in mind that there are more than one type of NP435 transmission. Some of them came with a 32 spline output and some came with a 28 spline output. You also need to keep in mind that there is a difference between the 2wd and 4wd version of the transmission. To make things easy for you look for one that came out of a 82ish or earlier Ford truck that was 2wd. When you find the transmission it should have a 6.5" 10 spline input, a 28 spline output. If you do find one with a different spline count or input shaft length pass it by. Also in the early 80s Ford switched to a T-18 transmission. This is a good transmission but not the one you are looking for. The main difference between the 435 and the T-18 is the T-18 has BORG WARNER cast into the side of it, it has a cast cover instead of an aluminum one like the NP435, and has a screw in shifter instead of a spring loaded pop-in one like the NP435. The easiest way to find out which transmission you are looking at is to simply bring a magnet. If the magnet is not attracted to the cover then you have a NP435 since aluminum is not magnetic.

Now that you have your transmission at home it is time to take it all apart and replace all the bearings, seals and gaskets. I went to Bert's to get all the bearings and such. I wouldn't recommend not replacing all the replaceable items since doing the bearings in a year after you put the transmission in will be a long job. I found Bert's very helpful in that they had all the stuff I needed in stock and it only cost me around 80 bucks for a complete rebuild kit. I am not going to take you through the rebuild of the transmission as there are very well written manuals on it at large libraries. The shop manual breaks every step down very well and makes the job quite easy. The rebuild is not very hard to do and the only thing I can recommend is to place everything in a row the same way it came out.

With the transmission all painted and the rear output clear of the speedo gear and snap rings, set it aside to start on the t-case.

Transfer case - Early Bronco Dana 20

Trying to find a EB Dana 20 is not the easiest thing to find mainly because they have been out of production since 1977. When picking out a D20 the best one to find is one out of a 66-73 EB with a 3 spd manual transmission. From 66-73 the Dana 20 had a T style shifter and had a low range of 2.46:1. In the 74-77 models the shifter was a J style and the low range was only 2.34:1. Regardless of the year you find you NEED the adapter for the 3spd transmission. The adapter is 6.5" long and has two large wings on each side of it with holes in them to anchor to the EB skid plate.

After I picked up my D20 I made another trip to Bert's for the rebuild kit. It turns out that the parts, mainly the bearings, are not the most popular bearings. They had the seals in stock but had to order in the bearings. The other thing about the D20 is unless you order a gasket kit from a Bronco place in the 'States, you are going to be making your own gaskets. It was very easy to make my own gaskets because Lordco sells rolls or sheets of gasket paper that I cut up to whatever shape I needed.

After you photocopy a shop manual for the D20 at the library it is time to take it all apart. If you want to make the t-case "twin-stickable" then you need to remove the interlocking pins that are at the bottom of the case. They are located inbetween the shift rails that are in the case housing. The way to get them out is to remove the shift forks in the bottom of the case, unbolt the 3 little bolts on the outside of the case located beside the shift rails (blue arrows). After this slide the two rails out and look down the holes to try and see the pins that are in between the two rail inlets (green bars). Then shake the case on its side till they slide out. To make sure they are all out stick a screw driver in one bolt hole and see if you can see it in the shift rail inlet that is on the opposite side of the bolt hole. Confused yet? So after you reassemble the case with new bearings, seals, and gaskets you should be able to slide the shift rails independently.

I will give you a very good idea to get all the roller bearings back in place on the counter shaft. Without this technique that Chris Waterman told me about I don't know how I would have got them all in. On the counter shaft there is a spacer, then a set of roller bearings, another spacer, another set of roller bearings and finally the last spacer. You will need to go to a hardware store and get a piece of wood dowel that is the same diameter as the counter shaft hole. Then cut the dowel so it is the same length as the gear set and coat the wood with lots of grease. Then just stick all the bearings in the right spot with the spacers and washers on each end. Then slide the gear over the bearings and install the dowel/gear in the case. Now take the counter shaft and start tapping it in the same way it came out and this will cause the dowel to be pushed out the other side at the same time the countershaft is being installed. Great idea hey? For the 10 or so roller bearings that the input shaft run on the best way to install them is to get a socket (either 5/8th or 11/16, can't remember) and place it in the middle of the hole. Then just drop the bearings in one at a time and with some tweezers stand them up. After they are all installed they actually lock themselves in the perfect position. Put a little oil on them and slide the input shaft in and bolt it down.

Now that you are done with the transmission and t-case it is time to make the adapter to mate them together. You can either get one from Advance Adapters or make your own like I did. When you are planning out your adapter you need to take into consideration such things as making sure the output shaft of the NP435 runs perfectly in-line with the Dana 20 input shaft. There are a few ways to do this but using the input shaft as a jig is by far the easiest. Another consideration that needs to be addressed is how to seal the two units from each other. The last thing you need to figure out is how much to clock the t-case. After I took some measurements I decided to clock the t-case so the front output yoke measures 5"s lower than the rear output yoke when the transmission is sitting perfectly flat. This turned out to be the perfect clocking for what I needed.

To make the adapter I used three ½" aluminum plates. In order to make it all work two of the plates need to be bolted to the transmission (put a hole in the middle of the plates to allow the output shaft to pass though).

Keep in mind that the inner plate will be a smaller rectangle than the outer one because of the bearing retainer on the back of the transmission. The 4 bolt holes in the middle plate (2nd plate) need to have a recess in them so when you bolt it down the bolt heads will not interfere when the third plate is up against it. Now that there are two plates bolted to the transmission you need to find a seal that sits nicely over the output shaft. After you find one get the center hole in the outer transmission plate enlarged to accept the new seal (red arrow in pic). Make sure the seal has to be tapped in so it will not be flopping around in the adapter. Now take your 3rd plate and put a hole in the middle of it so the output shaft will slip through. Then sandwich the plate with the 2 plates that are bolted to the transmission and the 6.5" adapter D20 adapter. Now that the transmission output is splined into the t-case input clock the t-case to the 5" yoke difference I explained earlier. Then mark where to drill the holes on the plate so you can send bolts through the t-case adapter to thread into the 3rd plate (blue circles in pic). Take it all apart and drill the holes in the 3rd plate which will need to be threaded to accept 3/8th" bolts. Next, you can bolt the 3rd plate to the t-case adapter and reinstall it back onto the transmission output shaft with the 2 plates still bolted to it. This is the tricky part…how to bolt the 3rd plate to the middle plate? By now you will see that the 1st plate (closest to the transmission) is a lot smaller than the 2nd plate but the 2nd and 3rd plate are about the same size. This is the important part - with the t-case clocked to the position you want it mark where the 2nd and 3rd plate overlap. You need 4 bolts in a square-ish pattern (green circles in pic). The 2 bolts on the bottom will go through the transmission side of the 2nd plate and then thread into the 3rd plate. The top bolts will be the other way around, meaning the bolts will go through the 3rd plate then thread into the second plate. Attaching the 3rd plate to the 2nd plate needs to be done like this because of the clearance problems. All this work needs to be done very precisely so I would recommend taking the transmission and t-case to a machine shop and get them to mate the two together, but don't forget to tell the machine shop about clocking it and having the seal recess machined. After you finish the adapter make some gaskets to seal it all up. You will only need a gasket between the transmission/adapter and the adapter/EB adapter.

All the other things you need

Clutch Slave Cylinder
In order to make your clutch work with the new transmission and bellhousing you will need to buy an external clutch slave for a 80-82 Jeep CJ that HAS a 4-cyl engine. You will need to modify the slave push rod in order to fully engage the clutch. Actually you will just replace the existing rod with a piece of stainless steel rod that is the same diameter but 2" longer. I rounded-off the ends so the longer rod looked like the one I pulled out of the slave. The internal slave that my Jeep came with does not thread onto the hydraulic line that connects the clutch master cylinder. To get around this I used part of my old slave. I cut off 4"s of tubing that contains the little nipple that pushes into the line coming from the clutch slave. Then I simply got some break line fittings and flared a male end onto the 6" piece. This enabled me to thread the line into the new slave and also attach it to the clutch line the same way the old one did. Cool hey?

Bellhousing and CPS
The bellhousing that you will need is off a CJ with a T-150 or T-176 transmission (make sure you try and get the shift fork, ball and spring because you will need it after). Both of these bellhousings are exactly the same so don't stress about which one to get. The cool thing about this bellhousing is it will bolt up to your 4.0L and it will also bolt up to the NP435. The reason for this is Jeep did use a T-18 transmission in some Jeeps and the T-18 contains the same bolt pattern as the NP435. How lucky is that? The most important thing about the bellhousing is to machine a spot for the CPS (crank position sensor) to be anchored in (blue circle in pic). The CPS must be the same distance away from the flywheel as it is in the AX-15 bellhousing. I did my machining with an angle grinder and a steady hand. No special tools are necessary to get it to work. With the bellhousing all machined it is time to bolt it to the transmission. After you bolt it down you can bolt on the new clutch slave and assemble the shift fork, spring and ball. The throw out bearing that you will need to use is one for an 85 CJ.

This is a later version of my CPS mount which is adjustable.

 

Twin Sticks and Shifter Linkage
The transfer case shift linkage needed to be made next. Since I was going to have the twin sticks to control each axle independently I needed two shifters that would not interfere with each other when placed right beside each other. I chose to use a pair of twin sticks that came stock on a old Spicer 18 transfer case out of a mid 40's CJ. Since the Spicer 18 came with the two shifters I was able to eliminate all the chances of the sticks hitting each other as they were made to work together. The sticks originally had a hole about 4" from the end just before the stick bent to the side. I cut this piece off so I was left with only a hole then the top part of the shifter (see pic below). In other words the shifter originally acted as a class 2 lever but I would now act as a class 3 lever because of the fulcrum location. Now for attaching the shifters to the transmission all you need is a welder and a ½" bolt that is around 4" long or so. I used my angle grinder to make a flat part on the case that was in line with the shift rails on the Dana 20. Then I welded the bolt to the case and slipped the shifters on with plenty of grease. To make the linkage I used a little heim joint at the shifter end and a rod end at the t-case end with a piece of cromoly connecting them. Both the heims and rod ends had a female ¼" fine thread which allowed me to make a connecting rod that could be adjusted in length by turning it. I picked up four ¼" fine thread bolts that were around 3" long and I cut the heads off them. I then took the bolts to my local metal shop and bought a foot of cromoly that had a slightly smaller I.D than the diameter of the bolts. This way the smooth part of the bolt would have to be tapped in for a nice tight fit. After I figured out the right length for the rods I cut them to size, tapped in the bolts and welded them in place. Now there was about a 1.5" threaded end sticking out of each end of the cromoly I threaded on a nut that would act like a lock nut. The heims and rod ends were then threaded on. To connect the heim to the shifters I wanted to use a little ¼" bolt instead of welding to the shifters so I put the shifters in a drill press and drilled a ¼" hole in them about 3" above the hole at the bottom. It was very convenient that the Dana 20 shifter rails had a ¼" hole in the end of them already. I just put a little nut in between the little fork on each of the shift rails and threaded the rod ends in from the top. After everything was attached I figured out where I wanted the shifter to sit in neutral, high and low range and adjusted the rod lengths to achieve this. I ended up doing all of the adjusting when the tranny/t-case was installed in my Jeep so I could see their orientation to the driver's seat.

Pilot Bushing
After you have removed the old transmission you need to replace the pilot bushing that is in behind the clutch. So remove the clutch and try to pry it out. Mine was a real PITA to remove so I just welded a nut to the pilot bushing and then threaded in a bolt. The bolt will hit the block and after a few more turns it will be forced out. The pilot bushing that you will need can be had from Advance Adapters (part number 716156) and it costs around 25 bucks. You will also notice that the old bushing you pull out contained roller bearings and the Advance Adapters one does not. Don't worry; it is not supposed to have any. After you carefully tap the new bushing in DON'T grease it. All of Advance Adapters' pilot bushings are self-lubricating so nothing is needed. After this get out your clutch alignment tool and reinstall the clutch.

Skid Plate
You will need to trim the front of the skid plate a little to make room for the transmission. This was accomplished with a cut off wheel and my angle grinder. The skid plate only needed to be lowered ½" or so. All I did was place six 5/8" nuts between the skid plate and the frame and threaded in some longer bolts.

Transmission/T-case Mount
The transmission mount that needs to be fabbed up must have a bushing in it to allow a little movement. The reason for this is the engine will twist when gas is added and the transmission needs to shift with the engine otherwise you will be binding the transmission and you will most likely crack the bellhousing as it is only made out of aluminum. There is no real place to bolt anything to the transmission so I chose to make a mount for the t-case. The mount is fairly simple but does require welding so hopefully you have access to a welder. The mount bolted to 4 of the holes on the bottom cover of the t-case and then went through the stock skid plate. As you can see from the picture I did a fairly sloppy job but hopefully it will hold up. (If you can think of a better design please tell me!!)

Transmission Hump Cover
To cover up the huge hole that I cut in the floor to make room for the transmission cover and shifters, I used a piece of 20 gauge steel cut to shape. The easiest way to figure out the shape is to get a piece of cardboard and cut and test fit it. After you are happy with the shape cut out the piece of metal. I then drilled quite a few holes around the edges so I could bolt down the metal.

Exhaust
You may or may not have to get your exhaust rerouted but I did. The reason for this is that I swapped in an EB Dana 44 in the front and if you are familiar with this diff at all you will know that the pumpkin is fairly centered. So this causes the front driveshaft to smack into the exhaust when your driver side tire is pushed up. So to fix the problem I got a nice custom piece so there would be no interference with anything.

Transmission Shifter
This was my least favorite part of the swap because I couldn't get the shifter in and that was the last thing I needed to do before I took it for a drive around the block. To get the shifter in you need to push down with a lot of force and try and turn the cup at the same time. Well after a lot of effort it was finally in and ready to fire up. Note: I swapped a CJ dash into my YJ before I did this swap so the shifter did not need to be bent, however keep in mind that if you have the plastic dash you may need to do a little bending with a torch to make room for the throw into first gear.

Drive Shafts
Well if you don't already have a 'CV' type shaft in the rear you will now. My rear shaft is actually the front CV shaft out of a 90's explorer. These are perfect shafts because they're original Spicer units and are only 6 inches longer than the one you need. So after spending 80 bucks for my shaft I paid another 40 to get it shortened. The yokes on both the front and rear output of the Dana 20 are made to accept a u-joint type CV head (same as explorer front shaft) and not the 4 bolt flange type that the Rubicon Express SYE uses. Since my rear was such a steep angle I chose to do a little modifying of a normal 1310 size CV to make it flex just a little more if it needed to. A stock 1310 CV head will bind at around 26 degrees but I needed my shaft to run up to 35 degrees without binding. After thinking it over and talking to a few people I decided to use a 1310 CV joint but use a 1330 CV case. The reason for this is the larger case will allow the head to flex more without any binding. Before I assembled the hybrid CV head I ground down a few areas to get a little more flex out of it if I needed it. To make the case work with the smaller CV parts I used 1330-1310 u-joints. This way everything went together very smoothly and in the end the joint actually topped out at around 40 degrees. Not bad, hey?

Reverse Lights
To get your reverse lights to work with your new transmission you will need to get a little wire and a some crimp style butt connectors. It worked out nicely that the old reverse light clamp that originally clamped into the AX15 also clamps into the NP435. All you need to do is extend the wires on it so it will reach to the little female end on the transmission cover.

Speedometer Cable
Well I am not going to be able to help you out here because I just used a stock EB speedo cable that I picked up for 10 bucks. The reason I was able to use this mechanical type cable that runs right to the speedo was that I had recently swapped in a CJ dash with the old CJ speedo, which accepts the EB cable. Lucky me, hey?

AX-15/NP231 Removal and NP435/D20 Install

I am not going to give you a very detailed description of how to remove the old AX15 and NP231 because a Haynes manual will do the job just fine. Before you start the removal you will need to go purchase a reversed torx E-12 socket. Jeep used two bolts on top of the bell housing that have a very different bolt head pattern so don't try and use any other sockets because you will strip the heads and then you are…well, screwed. I was able to remove everything by myself because I removed the t-case by its self then I lowered the transmission. It would have been nice and easy to take it all out as a unit but I didn't have anyone there to help at the time and I really wanted to take it all out to replace the pilot bushing.

After a long debate I chose to try and install the NP435 and D20 as one unit. The main reason I was a little apprehensive about doing this is because the two cases weigh a ton together. So with that in mind I filled the two cases with 80W140 gear oil and ran some straps around the cases. The unit was on a trolley so I wheeled it under my Jeep and got out the engine hoist. The put the engine hoist perpendicular to my Jeep so the hook part would lower through the large hole in the transmission hump. Keep in mind that you will need to do a fair bit of trimming of the floor to get the transmission and t-case shifters tucked up nice and high. Do not try and install the transmission shifter because you will not be able to move the transmission around to line up. I was able to line everything up and managed to install the unit in only around 45 minutes as the engine hoist allowed me to move the transmission around in any direction I needed to. I did this step by myself, too, so don't worry if you can't get anyone over to give you a hand. After it was lined up, I installed a few bolts to keep it in place and began to trim the floor to allow everything to be tucked up out of harm's way. I then reinstalled the starter and connected the clutch hydraulic line that needed to be bled. After bleeding the clutch I installed the skid plate and made some measurements for the mount. After making the mount it was installed and everything was double-checked. The last thing I did was install the transmission shifter and adjust the t-case shifters so the perfect amount of throw was achieved. After the shift linkage was the right length I tightened the little lock nuts and started looking for my keys. Then the true test was about to be performed, I put the Jeep in neutral just in case the clutch didn't work and turned the key. It started right up and everything looked okay. I then put it in reverse and drove it out to the street.

Driving Impressions

Street
After reading this write-up you might be thinking to yourself that this is the perfect swap for your Jeep. Well let me tell you something, if you like a nice and quiet drive with not much vehicle noise, then toss this article aside. This transmission is extremely loud and is no Civic when it comes to shifting. When driving, you will experience a loud gear hum coming from the transmission but don't be too alarmed, it is supposed to be loud. Shifting the transmission is not the friendliest thing either but I have driven worse. The throws between each gear are farther, take a lot longer to make, and require more effort than the old transmission. On the other hand I do experience more power out of each gear. The reason for this is the transmission is mainly a 3 spd with a low gear which means that the 2nd, 3rd and 4th have a wide ratio. Driving on the freeway is a little easier because of the added power of not having the overdrive. With the lack of a overdrive the engine usually runs at around 2800-3000 rpm instead of 2000-2200 like the old transmission. This does hurt the gas mileage but the added power with larger tires is nice to have.

Trail
I have not taken the Jeep off-road to test out the new drivetrain but as soon as I do I will update this article.

Parts Cost (Canadian Dollars)

The End

A special thank you must go out to Chris Waterman, Chad Loyd and Larry Soo for there assistance in choosing the best transmission/t-case combo and for answering my many questions as the swap was taking place. Without them, chances are I would have not figured out half the stuff involved in the swap.

Do you want even a lower crawl ratio?? How about adding another t-case between the NP435 and EB D20. Read about it here http://www.bc4x4.com/tech/waterman/waterman.cfm.

If after reading this write-up you still need some questions answered feel free to email me at andrew@bc4x4.com.