Installing the NV4500 Overdrive Transmission

Installing the NV4500 Overdrive Transmission

By CeetWarrior

I installed a New Venture Gear NV4500 HD 5 speed manual transmission in place of the stock T18 4 speed manual in my 1967 F100 2wd. The NV4500 closely matches the gearing of the original 4 speed, plus has a 0.73 overdrive for a fifth gear.

My freshly rebuilt 390 V8 provides awesome power around town and would motor powerfully down the highway, but was turning high revolutions at highway speeds. The addition of the fifth gear gives me a more comfortable cruise. I was turning 2800 RPM at 60 MPH; with the NV4500 I now turn 2050. This is roughly equivalent to changing a 4.11 rear end ratio to 3.0 without sacrificing the low end power provided by the 4.11. It should provide better fuel mileage and make my engine last longer.

The transmission is a joy to drive, with tight, short-throw shifts.

I installed it in a 67 pickup with a FE engine; however, I am told that kits are available to install it in any Ford pickup with almost any manual transmission. It is not quite a bolt on sort of job as a new rear transmission mount needs to be built but this should not be a problem for most home shops.

I purchased my NV4500 from a rebuilder in Denver. It was the heavy duty model used by Dodge in their V10 and Cummins Diesel trucks. To make the installation work with the adapter I purchased I had him change the input shaft to the standard duty shaft used by Dodge. The overall length of the standard shaft fit my bell housing and the adapter plate I used. It also allowed the use of a GM clutch plate.

I purchased a new slip yoke to fit the heavy duty output shaft, and had a new driveshaft built, sleeved, and balanced with a Cummins size U joint yoke installed on the front and a standard F100 U joint on the rear. The driveshaft needed to be shortened as the NV4500 is 8 inches longer than the stock T18.

They make a tail shaft for the NV4500 that has provisions for a speedometer gear, but they are scarce and I could not find one. I plan on adding an electronic speedometer to my truck.

The NV4500 will not bolt to the Ford bell housing, so I bought an adapter plate from Advanced Adapters (their part number 712551.) This is a nicely machined aluminum plate with perfect fit bolt holes. The kit included all necessary bolts and a new pilot shaft bushing. The bushing did not fit my 390 so I reused the original, drilling it out to � of an inch so it would fit the slightly larger input shaft of the NV4500.

I used the stock flywheel, pressure plate, and throw out bearing. This meant that the stock clutch linkage did not require any modification. I did need to change the clutch plate for one with 10 splines that will fit a 1 1/8 inch input shaft. I also replaced the throw out bearing and pressure plate with stock parts. This was not strictly required as I could have reused the old parts, but it seemed a good time to replace them.

The installation can be done over a long weekend, not counting the time it takes to have the driveshaft modified.

After buying various bolts and shop supplies my total cost for the install was around $700. With the $1100 the transmission cost me the total cost for my project was around $1800.

The actual installation required a new transmission mount be fabricated, the hole in the transmission tunnel for the shifter to be relocated, and modifications to the GM clutch plate.

The modification for the transmission mount took some thinking, but turned out simple to do. I took the original crossmember and flipped it over where the front became the back, and the bottom became the top. I used an FE motor mount as my rubber mount. The holes are 4 inches center to center, which is perfect for the NV4500. I then measured height and chopped accordingly.

Modifications to the GM clutch plate were required because the front of the hub would grind against the pilot bushing. I removed � inch from the front of the hub.

As you can tell from the picture below, the shifter for the NV4500 sits further back in the cab than the original T18, but no so far back as to cause any clearance problems with the seat.

I simply relocated the hole for the shifter, and patched the original hole. The pictures below show the patched transmission tunnel. The one on the left is the top, the right one shows the bottom.

And, of course, the addition of new carpet completes the job, and makes it look like the transmission was stock to this truck.

I have included my cost of this installation as a reference but your mileage will vary. The major cost I incurred was the transmission as I chose to buy a rebuilt unit from a rebuilder I trust. A good used transmission may be a considerable savings, as will a used slip yoke. I bought mine from the local driveline shop as it was the one item I forgot to get before I started the installation. The Dodge dealer wanted more than $230 for the same slip yoke.

One item we should discuss is the type of oil used in the NV4500. When this transmission was designed the manufacture was a wholly owned subsidiary of Chrysler. They specified that only Dodge brand oil be used in the transmission.

When GM started installing the NV4500 into their truck line GM specified that only GM brand oil be used. It could be the same oil Dodge is selling, just in a different bottle. Both companies claim the use of any other oil will void the warranty. I do not know the position of each company regarding the use of the other’s oil.

In any case I disagree with both companies. The Dodge brand is not synthetic and costs $15.55 per quart. I chose Royal Purple Maximum Life, a synthetic oil with better friction control and antiwear additives. It also cost 1/3 less than the dealer supplied oil. I did so not only because this oil exceeds the required GL4 rating, but also because I have family that has been running the same oil in their NV4500 equipped Dodge Ram with no problems.

Needless to say, the type and brand oil that should be run in the NV4500 is controversial. You should do your own research and make an informed decision as to the oil you choose to run.

One FTE member mentioned a problem he said was common to the NV4500. He claimed that the 5^th gear would come lose on its shaft, and eventually fall into the transmission case, causing catastrophic failure.

I researched this on the Internet and found that there were a few such instances on trucks that regularly pull or haul heavy loads. The consensus was that when lugging the Cummins diesel below 1500 RPM while in fifth gear the power pulses from the engine would loosen the retaining nut for the overdrive gear.

Dodge addressed this problem in two technical Service Bulletins, TSB 21-09-95 and TSB 21-10-98. They put an adhesive pad on the face of the retaining nut to glue it in place. There are also other aftermarket solutions to the problem.

The first symptom of such a failure is that the operator has trouble shifting into fifth gear.

I do not consider this to be a common problem, nor do I lug my engine. However, should I ever experience difficulty in shifting into 5^th I will check this nut before I drive very far.

Research on the Internet has yielded a wealth of information on the NV4500. I have posted some of this below. I consider this information to be reliable; however, I encourage you to do your own research on items critical to your conversion.

The NV4500 was first introduced by both Dodge and GM in 1992. It was an option for  and 1 ton GM trucks, while Dodge offered a standard duty NV4500 for  ton and larger trucks equipped with the 5.2 and 5.9 liter engine, and a heavy duty unit for use behind the Cummins diesel and their V10 gas engine. The NV4500 is rated for 450 foot pounds of torque.

There is also a NV3500 which was offered in the � ton trucks. It too is a 5 speed overdrive; however, it is only rated for 300 foot pounds of torque, and has a much faster intermediate gear set. I didn’t think it would handle my 390 FE.

The top-loaded transmission has a cast iron case, with an aluminum shifter housing. It has PTO ports on both sides of the transmission. Gears are helical cut, in constant mesh, and fully synchronized. The 1-2 synchronizer uses a set of spring loaded flyweights in the synchronizer hub to govern shift speeds; thus avoiding over-revving the engine when down-shifting from second to first.

The case and internals are identical in all NV4500 (except early GMs) with the difference between the Dodge standard and heavy duty units, and the GM units, being the input and output shafts. You can mix and match the different input and output shafts as needed for your application. In my conversion I used a Dodge standard duty input shaft and a Dodge heavy duty 2wd output shaft.

The chart below can be used to find the best combination for your conversion.

Please note that Dodge did offer a 13" tail shaft housing and output shaft that had provisions for a speedometer drive, however, this is no longer available. Unless you are lucky enough to find a used unit you will not be able to use your stock speedometer.

Also, there is some question as to the Dodge standard duty output shaft being 30 or 32 splines. My transmission has the heavy duty 31 spline 1 5/8" output shaft so I was unable to verify anything about the standard duty output shaft. You should verify exactly what you have for an output shaft before you order a slip yoke.

The main function of a transmission is to match the engine speed (RPM) to the over the road speed (MPH) of the vehicle. When towing or hauling heavy loads you use the gears to keep your engine RPM within its power band, while for normal daily driving most of us want to operate the engine at its most fuel efficient speed.

Generally speaking, high gear in all transmissions is a direct 1 to 1 ratio, that is, for each revolution of the input shaft the output shaft will also rotate one full turn. This means that when the engine is turning 2800 RPM, the driveshaft is also turning 2800 RPM.

In overdrive transmissions such as the NV4500, there is an extra gear (fifth) which drives the output shaft faster than the input. In fifth gear (overdrive) the NV4500 has a ratio of 0.73 to 1, that is, for a 0.73 revolution of the input shaft the output shaft will rotate one full turn. This means that when the engine is turning 2044 RPM, the driveshaft is turning 2800 RPM.

The low and intermediate gears work the same, except in those gears the input shaft is turning faster than the output shaft. For instance, in third the NV4500 input shaft must turn 1.67 times for one revolution of the output shaft. This means that when the engine is turning 2800 RPM, the driveshaft is turning 1677 RPM.

Second and third gear ratios in the NV4500 are a very close to the ratios in the T18 four speed used in the ’67 to 72 pickups, as shown in the chart below. The T19 four speed transmission used in later pickups had three different gear ratio setups. I have shown all three in the chart, however, I do not know how to identify which gear set you may have.

Low gear (sometimes called "granny low") in the NV4500 has a ratio of 5.61 to 1. This is a faster gear than the low in the T18. The NV4500 transmission installed in the ’93 and ’94 GM applications had a low gear ratio of 6.34, but those transmissions require the use of the GM input shaft that is too short in length for an easy conversion into a Ford bell housing.

The reverse gear on the NV4500 is quite a bit faster than the reverse in the T18. In 1998 the gear ratio for reverse was changed to 5.04.

The chart below shows the RPM and the over the road speed in the different gears of the NV4500. It is calculated for a truck with a 3.54 rear end ratio and 29 inch in diameter tires.

The chart above shows the over the road speed for the different gears. As you can see, I can keep my engine between 2000 and 3500 RPM for any road speed over 7 MPH.

Would I recommend this conversion? You bet! I love this swap. It is worth the money to me. Cruising down the highway in overdrive and actually being able to talk to my passengers is great. But besides the overdrive, the overall smooth shifting is great, short throws, and a nice spring loaded action like a transmission should have.

Plus no one can believe I put a 5 speed in a 37 year old truck!

CeetWarrior 2005