Differentials: Identification, Restoration & Repair

by Jim Allen and Randy Lyman

Part history book, part school book, part mechanics manual, part encyclopedia, and part sales guide for aftermarket alterations, this 394-page 8” x 11” softcover book is a gearhead’s dream . . . if you want to dream about differentials, that is. If not, it could be slow going.

The 422 clear and well-placed photos are the main strength of this book. They show in excellent detail, much like a high-quality coffee table mechanics manual, what is being discussed at any specific point in the text.

The book tells you what you need to know in a clear, concise way. By the time you reach the end, you feel like looking around for a differential to take apart just for the fun of doing it.

All sorts of limited-slip and locked differentials are talked about, pictured, and illustrated from the traditional Detroit-supplied units to established aftermarket manufacturers. Differentials used by the performance industry from Ford, GM, Chrysler, Dana, Eaton, Visteon, Auburn Gear, ABR, Torsen, Detroit Locker, Yukon, Spartan, Ox, KAM, Quaiffe, and others are covered.

This comprehensive book was written by Jim Allen, the author of seven books and approximately 1,500 magazine articles, and Randy Lyman, who has personally rebuilt 2,200+ differentials on his path to becoming the CEO of a differential parts distribution company. Although the book does promote the products carried by Lyman’s company, only two unobtrusive advertisements interrupt the smooth flow of information about everything from the early history of differentials, axles, lockers, and limited slip designs, through a 139-page axle identification encyclopedia describing the strong and weak points of 44 different differentials used by folks involved in street performance, drag racing, four-wheeling, towing, and performance traction in general. How to repair and modify differentials for all of the above is also detailed clearly and concisely.

The books comes complete with a Dedication, Introduction, Acknowledgements, Table of Contents, and two Appendices covering Terms and Formulas. No Index, but it’s really not required as the seven-page Table of Contents is comprehensive enough to act as an index. Composed of seven chapters, the book is broken down into: Axle 101, Axle Encyclopedia, Building Blocks, Light Repairs, Major Repairs, Modification 101, and Upgrade Potpourri. In addition to the photos there are 29 illustrations and 16 exploded views of various sorts of standard and limited slip differentials.

The basic idea behind the book is to encourage you to tear your differential apart and buy the parts you need to put it back together from Lyman’s company. That being said, the book is an excellent read if you are interested in learning, as I was, about the current state-of-the-art in differential design, at least as it relates to the US aftermarket. I’m sure there must be more material about this topic out there but I haven’t found it! If you have an interest in transmitting power to the ground using domestic US OEM differentials, then this book is a good starting point.

High-quality paper was used to print this book and as a result, the photo reproduction quality is excellent. On the downside, there are typographical errors that are so obviously wrong it brings a smile. The backlash setting for a differential gear set, for instance, is generally in the .010 to .016 range. When the backlash is listed as 11 to 16 inches, which it was for one application, then you know something is not right. Given the number of differentials described, a misstep here and there is easily overlooked and does nothing (much) to detract from the book’s value.