Heavy Duty Clutch

	One of the most interesting, rare and overlooked high performance options available for the early Camaro is the Heavy-Duty Dual Disc Clutch, Regular Production Option MA6. This heavy-duty (HD) performance option was first released for use on the high-performance optional engines during the 1969 model year. The intent was to offer a clutch system that would stand up to rigors of performance driving and, as it turns out, the design may have been overkill. The durability of this clutch is absolutely amazing; combinations similar to this were used as slider clutches in dragsters handling well over 1200 horsepower! The unit is especially well-suited for use with the Z/28-302 in conjunction with the M21-M22 transmission using the 2.20 first gear and any rear axle ratio numerically lower than 4. l 1: l . The combination of the 302 being relatively low on torque at the bottom end and the standard gearing being relatively stout requires higher revs and more slipping of the clutch to get rolling at a moderate pace. Even more revs and clutch slippage are required to get off smoothly and quickly. This action substantially reduces clutch life and the standard 10-1/2" clutch with its marginal performance characteristics was a compromise at best. In recognition of this, Chevrolet offered the optional HD dual-disc clutch. Unfortunately, the high cost of the option was a factor that kept it from being ordered on many cars. In fact, if a car was to see any real high-performance work, standard protocol of the day was to replace the stock unit with one of the lower priced high-performance aftermarket units. We know today in retrospect, however, that the dual-disc system was far superior.
	Here's a comparison of an 11" clutch disc with the driven disc from the MA6 option. The discs used in RPO MA6 are 10" in diameter, but the use of two greatly increases the amount of abuse the clutch system can take.

	CHARACTERISTICS: The HD dual-disc flywheel weighs 24-l/2 pounds and the diaphragm cover with two driven discs and a 10" center plate weighs 30 pounds, the total of which is approximately equal to the standard BORG and BECK unit at 33 pounds for the flywheel and 21 pounds for the cover and plate. It is important for the 302 to maintain momentum by using a heavier flywheel-clutch combination such as this, whereas the big block can use a lighter unit like the 15 pound flywheel developed for the L88. This is due to the big block's greater torque enabling it to pull through the lower rpm range. A heavier flywheel maintains the engine's momentum by keeping kinetic potential high which in turn requires higher revs to do so, and since the 302 powerband is found in the higher rpm range the dual-disc/302 combination works extremely well together. If, for example, you were to use the 15 pound flywheel with the 302, the decrease in kinetic potential would bring engine rpm down under load, out of the powerband causing a bog on takeoff and upon each subsequent re-engagement to the next higher gear. The dual-discs' biggest asset with regard to the big block is the abuse factor. It can easily stand up to the brutal punishment associated with the healthiest of 427s and has only about half the pedal pressure of the stock unit! Because of the greater total working area of the dual unit, 201 square inches (a 62% increase), it permits a reduction from the normal plate load of 2400-2800 pounds to 1600-1800 pounds with no loss of efficiency. As a result, pedal pressure is about one-half that of the conventional unit, clutch life is more than doubled and the abuse quotient significantly increased.
	Total disc face area is 201 square inches, or roughly double that of a standard clutch setup. This larger surface increases the amount of abuse the clutch can take, an important feature considering this unit was installed behind high-revving 302s and ground-pounding high-torque big blocks.

	The 11" disc on the left uses 5 springs to absorb shock, while the dual-disc plates use 6. In addition to the dual-disc's ability to take abuse, the pedal effort is light and the "action" is exceedingly smooth, reducing driver fatigue during endurance races.
	The decreased pedal pressure is most significant with regard to the reduction of fatigue associated with road racing commonly encountered in events such as TRANS-AM, CAN- AM and NASCAR racing. Basically, these are endurance events, testing both man and machine, with races that span 1-2 hours of extreme high-performance driving. Imagine how it feels getting stuck in traffic with a stick, and compare it to how it might feel to shift continuously, one thousand times in a two hour endurance event! The benefits of using the HD dual-disc system in drag racing begin with its ability to efficiently manage tremendous horsepower and torque loads allowing for a more controlled launch. In addition, using the smaller 10" diameter clutch housing and discs results in a decrease in centrifugal force which lowers the chances for explosion and promotes increased rpm usage. From racing experience, Chevrolet Engineering clearly knew the advantages of these HD units - and now so do you!
	HOW RARE? While no official numbers exist in Chevrolet archives, it could be said that it enjoys a place among the lowest volume high-performance options ever sold, if not THE lowest.
	RPO MA6 HEAVY-DUTY CLUTCH (DUAL DISC) TECHNICAL SPECIFICATIONS FLYWHEEL: 14" - 24.5 pounds Casting number P 8999 NF (Nodular Ferris - the material the flywheel is made of) Chevrolet part number 3992094 CLUTCH ASSEMBLY: Borg & Beck, 10" dual-plate diaphragm type Chevrolet part number 3959176 Total clutch/flywheel assembly weight: 54 pounds Total disc facing area: 201 square inches PERFORMANCE FEATURES Friction surface doubled greatly increasing coupling power and torque capacity. Much improved pedal modulation results in consistent, faster starts Extremely light pedal effort because great friction area allows lighter plate load with diaphragm spring. Special design and heat-treated high cone diaphragm for positive high rpm engagement - no pedal sticking. Triple strap design (cover to pressure plate) instead of two gives quick, positive plate lift for cleaner shifts. DURABILITY AND SAFETY FEATURES Heat dissipation doubled, greatly extending life and stamina. Ferric ductile iron pressure and center plates with high tensile strength. Heavy .140" cover stock for added rigidity. 10" diameter for less centrifugal force at high rpm.Integral design with center plate secured to cover assembly. Integral design with center plate secured to cover assembly.
	MA6 systems use a dedicated, 14" flywheel (casting number P 8999 NF) made of nodular ferris cast iron. Flywheel weight is 24 pounds. The pressure plate used in the dual-disc system is the typical GM diaphragm type. Total system weight, including flywheel, pressure plate and discs, was 54 pounds.
	CHEVY'S COMMENT "The dual-disc system is well suited for extremely heavy-duty use on strip or track, including road racing. Also suitable for street use creating a new driving experience."
	This is a copy of part of an order sheet for 1969 Camaros. The MA6 heavy-duty dual-disc clutch option is seen about 1/2 way down. The option was obviously overlooked by most people ordering a performance Camaro. The MA6 clutch is most probably the lowest production performance option offered for the Camaro in '69. Those were the days . . .
	This article originally appeared in the Summer 1996 Issue of YEAR ONE's Restoration Review magazine. Restoration Review is intended as a forum for and about the vintage automobile restoration hobby. For more information about Restoration Review or to subscribe please call YEAR ONE today ! 1-800-950-9503.