• Do you tow or haul heavy loads and often encounter moderately steep hills that leave you shifting between 3rd and 4th gear repeatedly?
• Is your truck equipped with a stroker engine that doesn’t like to rev and tall axle gears that leave you in the slow lane on the freeway?
• Do you use your truck for a lot of highway driving (commuting perhaps) and would like to reduce your gas bill?
• Are you looking for an excuse to pull your transmission (fix oil leaks?) or balance your driveshafts?

If you answered yes to one or more of the above questions, like me, you will probably want to read more. Hopefully, the information in this tech article will help you decide if a Ranger Torque Splitter/Overdrive (or underdrive) make sense for you and your rig. If you decide to want one, the wisdom of my installation experience may help you too.

The Product:
Manufactured by Advance Adapters, Paso Robles Calif

Catalog description of what I bought:

Advance Adapters Ranger Torque Splitter for Ford 27% Overdrive with a 5.125" Index

These units are for Ford 4 speed transmissions and will bolt directly to the 4 speed and bellhousing with only minor modifications. Driveline and floorboard modifications are required.

This unit is cast aluminum, measuring 7-1/2". The gears are helical cut and the shifting mechanism is a short throw manual shift. The unit is built to handle 420 ft./lbs. of torque and has a GVW (Gross Vehicle Weight) rating of 25,000 lbs. This unit is ideal for towing applications or improving gas mileage by lowering the RPMs.

It has a 1-year unlimited-mile warranty from the date of shipment.

The items I received in my order from High Impact Gear:

• Ranger overdrive transmission
• Shift stick (handle) with bolts
• Oval shaped boot for shifter (looks like NPD part F-7277-2)
• 2 quarts synthetic transmission oil
• Instructions, parts list and warranty
   

Fig. 1

Fig. 2

Fig. 3

Models available:
Based on the marketing information I found, there are 5 overdrive models for Ford, Chevy and Toyota and 4 underdrive models for Ford and Chevy. There are several online suppliers to choose from in addition to buying directly from Advance Adapters.

How it works
It’s a manual-shift, synchronized 2-speed transmission. Engage the clutch, push the lever forward for overdrive, or pull it back for 1:1 ratio – in any gear that the 4 speed may be engaged, including reverse. There seems to be a (very small) neutral position in the middle of the shift stroke but I can’t think of a reason to actually use it. In fact it would be a really good idea to be sure the OD is firmly engaged in (either) gear if parking the truck on a hill just in case the parking brake doesn’t hold. I don’t know if the underdrive version is the same for lever positions or not.

Why I did it:

Highway Driveability
The 300 CI 6-cylinder engine in my truck does not like to run at high RPMs (2500 to 3000), consequently sustained highway driving at 60 mph or more was just not working well. I originally had a 240 6-cylinder with 4.10 gears and that worked OK. But the 300 CI 6-cylinder does not like to run at fast RPMs (above 2500) for long periods of time. So I changed to 3.54 gears which helped quite a bit to reduce engine RPMs at 60 mph, from 2600 to 2250. Adding the Ranger OD reduces engine rpm even further to only 1650 at 60 mph.

Save on gas costs
Prior to installing the Ranger OD I was getting about 17 MPG with a mix of highway commute driving and some in-town miles. Based on somewhat limited data (I’ve used only a couple of tanks of gas so far) I now get about 20 MPG for the same type of driving.

More gears useful for some driving conditions
Although the NP435 is a good transmission, there often seem to be situations where some in-between gears would be useful – I’m sure you’ll agree. The Ranger torque splitter turns your 4-speed into an 8-speed transmission (2-speed reverse) and a 4WD truck with a 2-speed transfer case would actually end up with 16 different forward gear combinations. Here’s a graphic summary of the gear combinations for my NP 435 and the 27% Ranger overdrive.

Fig. 4

Drive shaft needed rebalance
I had a single-piece drive shaft with some home-made welding modifications on the slip joint. It is not a standard driveline setup because I have put F250 2WD suspension under an F100 shortbed. For a long time, I had some minor but annoying vibration in the driveline and have been looking for a good excuse to get the driveshaft professionally re-done and balanced. Installing the Ranger OD required that I shorten the drive shaft by approximately 7½ inches. If you have standard driveshafts, the length may indeed be exactly 7½ inches, however I opted to wait until I had the Ranger OD fully installed and positioned so that I could measure the distance between the yokes on the transmission and the rear axle. I let the driveline shop figure out the appropriate length because the spline units had to be replaced in addition to shortening it. If you have a 4WD, the front drive shaft needs to be lengthened about 7½ inches also.

Fix Transmission Oil Leaks
My NP435 had a lot of miles on it after 40 years of (very reliable) service and had developed some minor – well OK – real messy oil leakage. As part of my overall truck restoration, I wanted to fix all oil leaks before doing any underbody or frame painting. The tailshaft seal was probably the worst leaker, however some oil was also seeping from the top cover, PTO cover and rear bearing retainer. The Novak master rebuild kit has plenty of gaskets, shaft seals and I also used gray Permatex on gaskets for final assembly.

Preliminary work

Measure the transmission
Before ordering the Ranger OD I temporarily removed the transmission so I could accurately measure the index diameter, the clutch bearing sleeve diameter and confirm the input shaft spline type and stickout length. There are a couple of different versions available depending on year, and I didn’t want to be guessing or assuming on which one I had.

Overhaul the 4 speed (seals, bearings, synchros)

I purchased a master rebuild kit for the NP 435 from Novak which came with a really good set of instructions and plenty of new parts for a really comprehensive overhaul. The old main bearings were actually in very good condition so I reused the front (taper type) bearing and race and only replaced the rear main bearing (roller type). Replacing the front bearing and race requires some machine shop work (milling, pressing etc.) and I was too impatient to take time out for that. The old synchronizers definitely needed replacing and the new gearbox shifts much smoother now.

Fig. 5

After stripping the transmission completely, I did a lot of cleaning and scrubbing in order to get it ready for a coat of paint and reassembly. Enough said....a complete summary of this transmission rebuild should probably be done in a different technical article.

Cut off piece of front bearing retainer This minor surgical procedure is covered in good detail in the manufacturer instructions and turned out to be easier to do than I thought. I used a high-speed, pneumatic tool with cut-off wheel (see Fig. 6). The Ranger OD has an input shaft with a sleeve (snout) for the release bearing that is essentially identical to the one on the 4-speed transmission. The instructions emphasize that ¾" is the maximum amount that the input shaft retainer can protrude beyond the transmission front face otherwise it would conflict with the internal stuff in the Ranger OD and bad things would happen. On my transmission, there seemed to be plenty of clearance after cutting off the snout.

Fig. 6

A key item about this task is that all of the gaskets under the front input shaft bearing retainer must be reused in reassembly. Don’t damage any of the gaskets, or if you do, replace them with new ones having exactly the same thickness. The end-play clearance between the input shaft and the main shaft inside the transmission is adjusted by stacking these gaskets. The end-play clearance for the NP435 is 0.001 to 0.005 inches. If there is any doubt about the transmission input shaft end-play clearance, it would be a good idea to measure it with a dial indicator and put in the proper stack of gaskets before proceeding further. Also make note of the orientation of the retainer, there is a small oil passage cutout on the internal side that should be positioned at the top (I think).

Clutch inspection, service or replacement
My clutch has been working fine and was replaced not too long ago (5 years ago I think) so I didn’t do much other than just wipe off any excess grease or dirt. I did clean and regreased the clutch release bearing though.

Paint the Ranger OD (?)
This is a personal preference issue. Although the stock aluminum finish is very handsome, I decided to paint it, which I think will make it easier to keep it cleaner. I figured it’s better to paint it now while it is clean. I was painting the cast iron case NP435 anyway so I had plenty of paint to use up.

Lubricate OD shifter and replace grease fitting with plug
This is a relatively minor item, but it was something that came up unexpectedly. The Ranger OD comes equipped with a grease fitting (zerk) on the shifter pivot on the drivers side. Upon installation in the truck, that grease fitting conflicted with (rubbed) the tunnel/floorpan in a big way. Consequently, I had to remove it and replace it with a plug. I did squirt in a tiny bit of grease to make sure it was fully lubricated. The instructions don’t mention any need to re-grease this fitting so perhaps it is lifetime lubricated. I’m planning on checking it and perhaps re-greasing it any time I remove the transmission (for clutch service most likely).

Transmission rear support
The manufacturer’s instructions say to drill new holes in the frame for the rear transmission support cross member that are 7½ inches back of the existing holes. I did that and found that it would have been a better fit to make the new holes only about 7 inches back. This is because the method of supporting the rear of the transmission changes (rear insulator gets eliminated). See discussion below on transmission rear support modifications.

Test fit the OD to the 4 speed
Slide the Ranger OD onto the input shaft of the 4-speed and hopefully it will seat smoothly and tightly to the transmission front face. If it does not fit together properly, the following problems might be present:

• Input shaft splines mismatched

• Index diameter wrong

• Input shaft snout is too long

• Transmission front bearing retainer bolts protruding too much

If it fits properly, thread in a couple of bolts, attach the Ranger OD shift stick and do a quick bench test of the unit. (see Figs 7 and 8) Put the 4-speed in gear (4th gear would be 1:1 rotation) and rotate the Ranger OD input shaft while gently shifting the unit. If the Ranger OD is engaged (OD stick in forward position) and the transmission is in 4th gear (1:1 ratio), the output shaft should rotate about 5 times for every 4 rotations of the input shaft. If Ranger OD is disengaged (OD stick in rear position), the shafts should turn at the same rotation rate. An underdrive would function similarly.
 

1. Bolt the Ranger OD to the transmission and then install them as a set on the truck, or
2. Bolt the Ranger OD to the truck bellhousing and then install the transmission into the Ranger OD.

I have set up my floor jack with some metal straps and bolts to hold the NP 435 firmly on top of the jack pad so option #2 works much better. The Ranger OD is only about 80 pounds so it was fairly easy to simply grab the OD unit and manually put it place on the bellhousing in the truck (see Fig. 9). The input shaft went through the clutch plate and into the pilot bearing very easily and the bolts lined up easily. The Ranger OD comes with bolts for attaching to the bell housing and two of those bolts are “captive” on the unit. The instructions call for putting a small bead of silicone sealant between the Ranger OD and the transmission. Consequently it’s important to accomplish the transmission installation and bolt tightening fairly quickly and smoothly (see Fig. 10).

Transmission Rear Support Modifications
This step turned out to be more complicated that I expected. Once the Ranger OD and transmission are both bolted firmly to the bellhousing, it is necessary to figure out what the correct position is for permanent mounting of the rear of the transmission. The extra 7½ inches of the Ranger OD definitely pushes the 4-speed transmission down a couple inches lower than the stock location. This would apparently be due to the power train having a centerline angle that slants downward toward the rear of the truck. The best guide for correct position seemed to be making the clutch bellcrank (z-bar) perpendicular with its pivots on the engine and the body. Putting the power train in this orientation results in the rear of the transmission tailpiece resting directly on top of the cross member. The transmission rear insulator (mounting bracket between the crossmember and the tailpiece) does not fit as it did before. I figured there are two choices:

1. Eliminate the rear insulator and just position the tailpiece pad on the top of the cross member, or
2. Fabricate a new custom cross member that will permit reuse of the standard transmission rear insulator.

I decided to go with option #1 and that necessitated drilling a couple of more new holes in the cross member that would allow me to bolt the transmission tailpiece directly to the stock cross member. However, I recognize that I need to have some flexibility in this connection so that the engine and transmission assembly can rotate slightly in reaction to torque under acceleration or deceleration etc. So, I inserted a ¼"-thick slab of neoprene rubber between the cross member and the transmission tailpiece mounting surface and I also put heavy duty rubber grommets (about ¼" thick) with washers under the heads of the bolts. I’m hoping this provides sufficient flexibility and seems to be reasonably solid (see Figs. 11 and 12). The new location for the cross member does tend to crowd the exhaust pipe (some rubbing) however I plan to re-do the exhaust system soon anyway and will correct that problem later.

Measure and shorten drive shaft (balance too)
Once the powertrain is in the best and final position, it is possible to make a measurement between the transmission output shaft yoke and the rear axle pinion yoke. I consulted with the driveshaft machine shop to get instructions on how to correctly make the measurement. Depending on specific shaft angles, it is sometimes appropriate to add some payload so the measurement is taken with the suspension loaded. I did not add payload, because the shaft angles are small. The driveshaft re-work took only a couple of days.

Shift lever fitting (cut, drill, weld, bend)
This step also turned out to be a lot more complicated that I expected. Once I finished modifying the rear transmission support to get the powertrain in the final position (and the driveshaft was sent away for shortening and balancing), I was able start working on the shift stick installation. The Ranger OD has a heavy-duty steel shift lever positioned high on the driver side. It turned out to be too close to the floor pan/tunnel and would rub and bind. Although the shift lever is threaded so that the shift stick is simply bolted on vertically (2 bolts), that would put the Ranger OD stick within an inch of the gas pedal (way too close) and penetrating the floor on the side of the tunnel. I wanted the Ranger OD shift stick and the rubber boot to be pretty much on top of the removable transmission cover plate. I essentially positioned the cover plate and the rubber boot where they looked best and inserted a marker down through the hole in the rubber boot so that it left a mark on the Ranger OD. (See picture 10 or K.) That would be approximately where the shift stick would need to end up. The final arrangement for the shift lever boots ended up like this. (See picture J)

I decided to cut off a portion of the shift lever so that it would not rub on the floorpan or tunnel. (See Fig. 14) Next I made an adapter from a piece of 3" angle iron so that I could relocate the shift stick to a position approximately 4" to the right of the stock lever position. The angle iron piece is about 1¼ inches wide and ¼" thickness and one leg of the angle must be cut off to about 1½". Next I modified the shift stick by heating and bending the bottom section 90 degrees (where there are two mounting holes) so that it would mount on top of the angle iron, drilling and tapping two holes for the shift stick to bolt on and drilling a hole on the other leg to bolt the short leg of the angle iron piece to the shift lever. I determined that the connection of the angle iron to the Ranger OD shift lever (that was cut off slightly earlier) is virtually impossible to accomplish with bolted fasteners only. So I decided to just put one bolt in place to get the stick positioned correctly and then weld the connection so it is really solid (see Fig. 15). Before welding the connection, be sure the stick and shift lever move smoothly forward and back full-stroke without rubbing or binding on anything. I had to do a little bit of heating and bending on the shift stick during this step because initially it was bumping into the dash.

Shift stick modifications
Once the Ranger OD shift stick is permanently mounted, some modifications on the 4-speed shift stick are in order. Since the transmission has moved 7½" rearward, the shift stick tends to bump into the seat in reverse gear. Bending the stick to a more vertical position solves that problem, but then it is too tall. I decided to shorten the transmission shift stick by cutting out a section about 7 inches long and rewelding the threaded piece for the shift knob on top. (See Figs. 16 and 17) A little bit more heating and bending can be done to get the two shift sticks in a place where they look good, do not conflict and are at a comfortable height. Shortening the transmission shift stick does result in less leverage, which means somewhat more muscle is needed to make gear shifts. (See Figs. 18 and 19)

Tunnel cover plate modifications
Modifying the tunnel cover was fairly straightforward and simply involved some sheetmetal cutting and welding. The key is to make sure the cut-out is positioned correctly so that there is no rubbing or binding of the shift stick or transmission top cover and that the rubber boots fit properly. (See Figs. 20, 21, and 22). Although I have not yet done the final assembly of the tunnel cover plate, I think I will install some captive nuts on the holes through the tunnel so that installation would be easier (for one person to do) and put some stick-on gasket seals (like camper seals) around the perimeter for a good drip-tight weather seal.

Lubrication and break-in transmission and overdrive
The instructions for the Ranger OD call for initial operation using 30-weight motor oil for the first 15-30 minutes of operation. Then drain the oil and install the synthetic gear lubricant supplied with the unit. The Ranger OD holds about 1.65 quarts of lubricant. The drain and fill plugs are easy to access. Since I had also done an overhaul of the NP435, I’ve done the same thing for the transmission (putting synthetic lube in the NP435).

Summary of Costs:

Regarding the price of the Ranger OD: Advance Adapters and most other retailers list the unit for $1,495, which really is a fair price. I contacted High Impact Wheels / Transmission & Gear in California, 888-898-4331, www.high-impact.net and Greg was feeling very generous that day and offered a discounted price. The order got shipped quicker than I thought and the people at High Impact and Advance Adapters were very helpful and kept me updated regularly on the status of my order.
 

My project cost an extra $450 because I did the transmission rebuild and had to buy some new parts for the drive shaft and a new shift boot. The total for a Ranger OD and one drive shaft cut and balance for a 2 WD is only about $1500 to $1650. A 4 WD would have two drive shafts to cut and balance for a total of about $1600 to $1750.

Fig. 23 - Beautiful, huh?