Eaton Detroit Truetrac install – 9″ Ford – PEM Racing

The Project: “Hot Rod Regal” has been upgraded with one of the coolest differentials on the market – the Eaton Detroit Truetrac differential.   Follow along as I share my research on the Eaton Detroit Truetrac and experience working with drivetrain industry expert Roy Teeter from PEM Racing in St. Clair, Missouri.  Roy shows us a comprehensive, step by step installation of the Eaton Detroit Truetrac into an aftermarket, nodular iron 9″ Ford third member. Hopefully these videos will show you why I went with the Detroit Truetrac and how easy it is to change one out in a third member design.

The Eaton Detroit Locker removal and Eaton Detroit Truetrac Installation.
The Eaton Detroit Locker removal and Eaton Detroit Truetrac Installation.


Nodular Iron, aftermarket third member waiting for the Detroit Truetrac differential swap.
Nodular Iron, aftermarket third member waiting for the Detroit Truetrac differential swap.


To begin with, the Regal had an aftermarket, nodular iron 9″ Ford rear with 31 spline axles, a 3.70 to 1 gear ratio, and an Eaton Detroit Locker differential.  The Detroit Locker is virtually a bullet proof differential and works by mechanically “locking up” the left and right side axles when power is applied. This style differential is one of the BEST off road, and drag strip use differentials made, especially for higher horsepower applications. The idea here is to apply power, lock up 100%, use both wheels to gain traction and keep going straight. The axles will remain locked even with one wheel off the ground. During cornering, the Detroit Locker will unlock the (faster spinning) outside wheel and use the inside wheel to power the car through the corner. This is not an issue for straight line or off road use, but for sharp cornering, may cause a “pushing” condition with the inside rear wheel exerting force on the outside front wheel, resulting in increased tire wear.

The Eaton Detroit Truetrac differential applies power to the wheel that has the most traction (which could be the inside wheel, the outside wheel, or both simultaneously). This performance differential maximizes traction with its helical-gear design by allowing one wheel to spin faster or slower as conditions require. The helical-gears transfer torque to the high-traction wheel until traction is regained on the other wheel. This is all done automatically, quickly and quietly. It has the best of all worlds when considering differential types and is the most versitile (see Eaton Quick Reference chart below). The Eaton Detroit Truetrac is also maintenance free, which is something I really like. As for power applications, it would be best to contact Eaton for warranty information, but I have personally seen one hold up behind a 555ci big block producing approx. 700 hp and 675 ft lb of torque (Greg’s El Camino)

How do you drive your vehicle?
How do you drive your vehicle?

I will mostly drive the Regal on the street in both wet & dry conditions as well as some auto crossing. This style of driving requires sharp cornering under power and will need to apply power to the wheel with traction. I found the Eaton Detroit Truetrac differential would be the optimal solution for my proposed applications. To help understand this even better, Eaton has produced several cool CGI videos that are very helpful – check out the one on the Detroit Truetrac.

Now that we have a basic understanding of why I went with the Eaton Detroit Truetrac, I would like to introduce Roy Teeter of P.E.M. Racing (636) 629-6200 St. Clair, MO). Roy has built thousands of rear axles for all types of motor sports and driving. I am extremely lucky to have a resource like P.E.M. Racing in my “backyard”, but this install is something that can be accomplished in one’s own garage.  As always, the right tools make the job easier though. Follow along as I document the removal of the Detroit Locker and installation of the Detroit Truetrac differential through these short videos.

Part 1: Disassembly.

Part 2: Differential/ring gear assembly & bearing installations.

Part 3: Third member final assembly, bearing preload, setting backlash, pinion/ring gear pattern.

Wow! How is that for instructional videos from an industry expert? “Seeing the man behind the curtain” definitely applies here. Hopefully you like technical data, because these videos illustrate exactly how the professionals at P.E.M. Racing assemble rear axles. Roy Teeter (a Marine Veteran with extensive Machine shop and Aviation experience) is a GREAT resource! I highly recommend considering P.E.M. Racing for any rear axle needs. Keep an eye out for another future article with P.E.M Racing for Project: LSX El Camino. Along with one of the best rear differentials on the market, the Eaton Detroit Truetrac, Greg will be installing a complete P.E.M. Racing axle.

As for the Hot Rod Regal, I can’t wait to get this center section back in the car! Adding an Eaton Detroit Truetrac is one of the best upgrades a person can do for their 9 inch Ford rear axle. I will have no issues with traction, slick spots on the road, and I will not need gear oil additives. These features along with the instant traction control, seamless and quiet operation, and durability of the Eaton Detroit Truetrac, make it the best rear differential for my application.

If you would like to perform similar modifications to your car, and need to know who to contact – try these links or contact numbers!

For Eaton:


For P.E.M Racing
(636)-234-0975 Sales
(636)-629-6200 Office



Leave a Comment