NV4500 Transmission Repair Solution

The otherwise reliable Dodge NV4500 4x4 manual transmission has one fault, a tendency for 5th gear failure, we have the solution.

The Fifth Gear locknut retainer locks the nut to the spline on the main shaft. By doing this the retaining nut can’t back off. We have been installing this on our rebuilt units and have not had any failures to date. We have also installed this on updated main shafts that have had repeated failures and this has fixed the problem. Some customers have complained of as many as five failures until this retainer was installed. After installation of the lock nut retainer there have been no known failures. The retainers cost is little more than the lock nut itself.

This lock nut retainer is designed for the Dodge NV4500 4x4 transmissions with a 29 spline and 1½” main shaft. It is very simple to install as it slides over the output shaft spline and is easily indexed to the retaining nut. No special tools are needed to install and no costly transmission costs to pay. The unit should be installed by a competent mechanic but it’s very easy to do. If installing this retainer because of 5th gear failure, be sure to inspect the main shaft splines to make sure that no damage has been done by the break down. If damage has occurred be sure the transmission is repaired properly first.

Inventing this Fifth Gear Lock Nut Retainer did not happen overnight. Having more than 30 years in the transmission repair business and working with both standards and automatics transmissions our company recognized an opportunity to help with the pressing needs of the heavy duty and high performance transmission market. We saw the Dodge NV4500 5-speed transmission come into our shop on a regular basis with the same problem and realized it needed a better and more reliable fix. The fix was simple, lock the nut into place so it won’t back off!

In our opinion the NV4500 is one of the best transmissions on the market. We have worked on many different types of transmissions, including ZF 5-speed and ZF 6-speed and the NW5600 6-speed and in our opinion the NV4500 is still a better, more durable and smother shifting transmission than any these. With the number of trucks on the road with the NV4500, we realized there was a need for a simpler, more effective repair. After studying the main shaft and fifth gear lock nut configuration, we came up with the idea of locking the nut to the main shaft spline, thus the creation of the Fifth Gear Lock Nut Retainer. By locking the fifth gear nut to the splined main shaft the nut is securely locked in place and can’t move. Since we started installing these retainers in all of our rebuilt Dodge 4x4 units, we haven’t had a single 5th gear lock nut failure.

The NV4500 5-speed manual transmission often fails in fifth gear, even after installing a mainsaft update kit. In some cases the same transmission can fail over and over again. That's why Active Transmission & Gear's owner designed a new locknut retainer that makes it impossible for the fifth gear nut to back off.  The new retainer locks the nut into the mainshaft spline.


The Invention

"I've seen this problem with the NV4500 since 1994.  The fifth gear comes loose.  My lock nut retainer corrects this issue"
From the inventor

Fifth Gear Lock Nut Retainer (Patent Pending)

Lock nut retainer prevents fifth gear failure in the Dodge NV4500 transmission.


  • No need to purchase a mainshaft update kit or a new lock nut (works with original nut or any after market nut).
  • No special tools needed (just index the retainer on the spline and into your existing locknut).
  • Ensures that the fifth gear isn't lost.
  • Helps to keep the transmission running smoothly.
  • Make it a regular part of all your NV4500 rebuilds.

Features and Specs

  • The lock nut retainer is made of durable Chromoly steel.
  • Steel lock nut is cylindrical and measures 1½” tall and 2 ½” in diameter.
  • There are four posts on the bottom measuring ½” tall and 7/40” wide.
  • The inner hole is lined with 29 splines that are ¼” thick; hole measures 1½” in diameter between the spline and 3/8” in diameter from spline to tip.
  • Mechanic installs the lock nut on the transmission to keep fifth gear from coming loose.

For more information, or to order your locknut retainer, contact Active Transmission & Gear at 303-422-1465

Installation Instructions

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