DISCLAIMER

This document is a description of the limited-slip units used in Datsun/Nissan H190 and R160/180/200 differentials AS I UNDERSTAND IT! I am not an engineer nor do I claim to have a full and complete understanding of these units. There seems to be no published information on these units and I have been unable to find anyone who can explain them to me.

In order to understand these things, I have done some research into the theory and parts, and have successfully rebuilt a few of them. My experience has been exclusively with the H190 unit, but the R-type units operate on the same principles. Please view this document in that light. It should be considered an introduction to the workings of these units, a base from which to do your own investigations. I make no claims to total accuracy. If you find mistakes in either the theory or practice, I would appreciate hearing from you so I can learn, too.

I also assume that the reader already has an understanding of a regular differential and how it works.

STRUCTURE OF THIS DOCUMENT

This document begins with a general description of some types of limited-slip differentials. It then defines the part names as they are used in the Nissan Competition Catalog and gives a brief description of each part. Following that is a section showing the relationship of the parts as they are assembled inside the unit. The next section is a description of how this unit functions. The final section provides information on rebuilding and testing techniques. The Appendices contain cross-references of part names to part numbers for the H190 and R160/R180/R200 units along with some interchangeability information. I make no claims of completeness for this information; I have done the best I can to cross-reference part numbers from the numerous Nissan Comp catalogs in my collection.

GENERAL INTRODUCTION

In a standard differential, if one wheel loses traction, it will get all the power and will spin, while the wheel with traction gets nothing. The idea of a limited-slip differential is to prevent all power from being applied to only one driving wheel when traction is lost. There are numerous types of limited-slip, positraction, locker, etc. units.

Lockers

This term can refer to two types of differentials. The simplest is a regular differential that has had the spider gears welded to the side gears, resulting in a completely "locked" assembly that has no differential action. The circle-track people often use a specially built unit that has no spider or side gears at all, just a carrier for the ring gear that has splines for the axle shafts. This unit is also referred to as a "spool."

A second type of locker is the "Detroit Locker" which is the brand name for a ratchet-type unit. When no power is being applied, there is full differential action. As soon as power is applied, the ratchet mechanism effectively locks the axles together. It is an all-or-nothing deal. Nissan supplies Detroit Lockers for the pickups that run H190 rear ends, but I don't know about interchangeability into other Datsun applications nor will they be discussed further in this document.

Limited-Slip

The feature which distinguishes a limited-slip from a locker is its progressive action. It provides some degree of differential action even as power is applied until at some point it may lock up completely, depending on how it is set up. I have heard the terms "limited-slip" and "positraction" used interchangeably and I have heard other people claim there is a difference. No one has been able to explain the differences, if any, to me. The biggest difference seems to be that "Positraction" was a particular brand of limited-slip.

The Nissan limited-slip is a Salisbury-type unit consisting of a set of discs and clutches inside a housing that provide a friction coupling between the two axles. This same type of unit has also been used in E-type Jaguars and Cobras.

Note: at one time, another type of limited-slip unit, called a Gleason-Torsen, was available for the R200. At last report it is no longer available, which is a shame, because it had all the advantages of a limited-slip with none of the drawbacks. It was a very unusual design, using worm gears, worm wheels and spur gears to limit wheelspin while still providing full differential action. Like the Detroit Locker, it will not be discussed here.