Annular Clutch Systems


January, 2010

As you are all aware, the auto industry is attracting new technology at a very fast pace.  The Birkin factory is utilizing this technology in much the same way as other manufacturers do.  In the past couple of years the Birkin factory and Birkin America/Texas Motor Works have cooperated in changing over to new products such as the Ford Duratec Engines, Wide Track Front Suspension Systems, IRS Rear Suspension Systems, Haltech Computers for engine management, and AT Power Throttle Body Intake Systems to name a few.  These changes have proven to be highly successful and more are on the way.  It is obvious that Seven cars are going more upscale in sophistication and design to the delight of most folks.  Yet, for those who would rather stick with more basic versions of the car, these are also available.

At this point I would like to address the subject of annular clutch systems.  Over many years, this technology has been so successful that it has been adopted as the favored standard by most people in the racing and production car communities, and the Birkin factory now offers all cars with annular clutch systems.  How does an annular clutch stack up? Where engineering design is concerned, there is never just one answer to any question; pros and cons exist in any design change.  Our concern is the "net" best design for a given application and objective.  I am certainly not an engineer and cannot design these products; that is best left to Birkin.  My goal here is to present some of the ideas and opinions being discussed in the industry, to the best of my understanding.

Let's look at some advantages:

1. Most of the problems with the lever-type clutch release systems are caused by the linkage itself, and not failures of the cylinder.

2. This design places the slave cylinder directly behind the throw out bearing. Therefore the need for a linkage system has been eliminated.  As a result there are fewer working parts and a sharp reduction in friction surfaces.  The force needed to actuate the throwout bearing is reduced.

3. A sharp reduction in clutch pedal travel.  As a result, the driver can change gears a bit faster.  In the older systems there may be a need for moving the clutch pedal approximately 1 ½ “ before actually beginning to move  the clutch release bearing.  With the annular system the pedal  travel can be as little as 3/8” before the clutch release bearing begins to move.

4. The driver will also notice a sharp improvement in the FEEL of the clutch.  One can shift with greater confidence and precision, as the stiction and friction of the  mechanical linkage is eliminated.  The modulation of the clutch is improved, allowing the precision starts that are required in solo and racing.

5.  The annular system is self adjusting as the clutch wears, so the pedal position and feel remain constant as the clutch discs wear.

6.   The more recently designed annular systems are longer lasting than the older systems. The Tilton-based annular systems used by Texas Motors Works are hard anodized for nearly infinite life. Additionally, only one seal performs the task of as many as four in earlier systems, increasing reliability. The Tilton annular cylinders are specified by most NASCAR teams because of their reliability. Always be aware that not all annular systems are of the quality we desire for Birkin Cars.  So, as is the case with any purchase, we need to select quality components. Therefore, the race-proven Tilton-based system is what Texas Motor Works specifies for any installation designed for racing.  A collateral advantage of this 7” clutch package is that is saves 11- 15 lbs of weight   This is a big deal when the difference in static inertia is measured.

 7.  We have two systems available.  One is for normal road use with stock based clutches, such as the heavy duty clutches supplied by Texas Motor Works. The other is the above-described Tilton based system specifically designed for us.  We also have a pedestal system available from Taylor Racing which can be set up to work with virtually any clutch system need.

As with any design there are also disadvantages:

1.   It is necessary to remove the engine to replace a slave cylinder.  We consider this to be an acceptable risk given all the advantages and the longer lasting qualities of the annular system. 

2.   In order to work successfully, the annular system must be designed to work with a  specific flywheel, clutch, and bell housing combination. Conversion requires some measurement to be provided for the design, and the installation of a positive clutch pedal stop to prevent over travel of the clutch spring.

So, lets all keep learning together!  The Seven Community does an outstanding job of keeping up with progress.  We appreciate your assistance!

Dick Brink

Texas Motor Works/Birkin America