Slipper Clutch Evolution
by Jim McFarland

It was late in the evening of December 30, 1967, and the phone call was akin to an unexpected blow to the stomach. "Jim, we lost Sorokin tonight. It was a clutch explosion at Orange County Raceway." Every word was problematic.

At the time, Funny Cars didn't exist at we know them today. Top Fuel "diggers" were the darlings of the drag racing sport, although Factory Experimental extensions of high-end Super Stock cars were heading in the direction of T/FC. For T/F cars, it was locked-up multi-disc clutches, "light the tires" the length of a quarter-mile, and a "stab and steer" driving technique. Spectacular, at the very minimum. But then, from all reports and quite by accident, something happened that changed the landscape of Top Fuel (and Top Gas) drag racing.

Among the more prominent T/F teams, the ones of Roland Leong (owner/crew chief) and Mike Snively (driver) were guided by master engine builder and mentor to many racers, Keith Black. Roland's mother, Teddy Leong, had mandated that if Roland was to be involved with his chosen class of drag cars, Keith was to be his "director of activities." In fact, Keith not only built the engines, he was almost always trackside when the car was raced. After all, Teddy trusted Keith with the fortunes of her son's interests and felt comfortable in so doing. Then came the unexpected.

Keith was also heavily involved in the racing efforts of Chrysler's marine division and often required to attend off-shore boating events. And so it was that on a particular weekend when Roland had planned to race the car at the renowned Lions Raceway in Long Beach, Keith was out of town. In his absence, Roland had gone through the time-honored process of disassembling, inspecting and reassembling critical components of the car, particularly the clutch package that consisted of a sintered-iron, two-disc and single "floater" unit matched to an aluminum flywheel. Here, you can take note.

There was a dimensional difference between the leading and trailing portions of the clutch disc hubs. Although slight, it was sufficient to prevent total contact of the sintered iron friction faces, once the pressure plate and centrifugal levers applied the clutch's total clamping force if either of the discs happened to be accidentally installed facing the wrong direction. Even when fully released, the clutch could not become totally compressed, resulting in a measure of uncontrolled slippage.

So, at the Beach, Snively makes his first pass of the afternoon. It's virtually smokeless and the elapsed time drops, accordingly The pits are in a flurry. As you would reckon, the belief is that Roland has taken away clutch pressure to produce the drop in time. Roland didn't even know why it had happened, at least for the moment. It wasn't until Keith returned, heard about the events and examined how the clutch had been assembled that the reasons became known. But neither he nor Roland wanted anyone else to become aware Racers are racers.

Almost immediately, T/F (and Top Gas) competitors began dropping spring pressure in their clutches. It was purely experimental. How much was enough? How much wasn't? And in the process, clutch packages quickly overheated and were short-lived. On more than one occasion, particularly during night racing, I saw white-hot clutch parts shoot high into the darkness. Cars were cut in half. Floaters and discs were thrown into spectator areas. Racers were injured or killed. By now, most knew what had been behind Snively's first smokeless run, but the genie was already out of the bottle. Clutch package experimentation was on the loose and leaving a trail of damage in its wake. The accident involving Mike Sorokin, driver for the then-popular Surfers T/F team, was the last straw.

Then I received another phone call. It was Paul Schiefer, owner of the company producing many of the clutches being modified by racers. In short he said, "Jim, we're losing our friends and I'd like to work with you to solve the problem." At the time, I was in the process of leaving Petersen Publishing Company to join Edelbrock, but a few months stop-off at Schiefer seemed appropriate. Besides, Paul was a very dear friend, genuinely concerned about racer safely and an innovator extraordinaire. Plus, Bruce Crower was also on the trail of a solution although, in reality, it wasn't about competition among clutch manufacturers but a matter of solving a widely-spreading problem.

During the course of the next few months, Paul committed considerable funds and time to developing a solution that would enable clutches to slip (in a controlled fashion) and stay in the cars. It was a herculean effort but the problem was eventually resolved, including the Crowerglide from Bruce's creativity. Meanwhile, Mike's death had spawned the Mike Sorokin Safety Foundation (created by the then-manager of Orange Country Raceway, Mike Jones) to conduct further investigations into ways for improving racer safety. It was a delicate time in drag racing's evolution, but it turned out that those who had contributed to the problem ultimately became part of the solution.

Schiefer Patent info below.


A "Long" type clutch cover has a plurality of windows for the release fingers utilized in disengaging the clutch's pressure plate from the clutch's clutch disc assembly. Each window has a pair of inwardly extending bearing flanges to increase the strength of the clutch cover to resist pressure plate imposed, rotational loads. The corners of the windows are radiused to reduce the likelihood of fatigue failure. Each pair of bearing flanges is engaged by upstanding bosses of a yoke on the pressure plate to provide the load coupling of the pressure plate with the clutch cover. The yokes also provide mounting of the release fingers to the pressure plate, the release fingers also being pivotally mounted to the clutch cover.

Patent Number: 3670859
Inventor: Schiefer et al.
Published: June 20, 1972
Application number: 05/000,117
Filed: January 2, 1970
Primary Examiner: Benjamin W. Wyche
Assistant Examiner: Randall Heald
Assignee:Schiefer Manufacturing Company , Monterey , CA
Paul Schiefer, Sherman Oaks, CA , James McFarlandJr., Chatsworth, CA

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