Commonly, multi-disc racing clutches vary from 4.25in to 7.25in. Racers often favor the smallest diameter clutches available because they believe an advantage can be found in its lighter rotating mass. Yet experience demonstrates that smallness rarely makes an appreciable difference—except in diminishing the clutch’s durability.
Some clutch makers fervently believe that the slightly larger diameter clutch with thicker friction materials can withstand much more abuse than its smaller counterpart. Constant racing starts, for example, on a small unit can result in severe wear. Such doctrine is firmly held by Ram, the Columbia, SC long-time racing clutch maker. Monitoring the condition of the multi-plate racing clutch is an essential yet simple operation.
When replacing the friction discs during servicing, renew the full pack and ensure the pads are in vertical alignment to apply the clamp load evenly down though the pack. Also, oils and grease cause slippage and damage to clutch components. Always check the oil pan and main seals.
Here is how Ram checks their 6.25in Assault Weapon.
The most critical dimension on the multi-disc racing clutch is the pre-load, which provides the clamping force on the clutch pack. If this gap averages 0.060in or less, remove the shims from the studs. When the gap eventually reduces to 0.060in (without shims) replace the disc pack.
The second check involves measuring the flatness of the flywheel, using a straight edge and a feeler gauge. Wear on this flat surface should not exceed 0.005in. Observe the surface for shiny areas or severe bluing as such condition would indicate severe slippage. If present, it’s likely that warping would be higher than the prescribed minimum.
Ram uses thick, sintered bronze metallic pads to withstand heat and abuse—they better dissipate hot temperatures without distorting the discs. Measuring approximately 0.200in., they should be replaced when they reach 0.010 to 0.015 undersize. When loading race cars on trailers without a winch (never recommended), thin small discs often fail prematurely.
Racing clutches are available with either 10- or 26-spline hubs. Inspect the splines for wear and ensure there is no perceptible deterioration. Over time spline hubs wear from constant engagement and disengagement.
Neither the steel floater plates nor the pressure ring sustain much wear. However if they suffered from warping the preload dimension would vary and the clamping potential of the clutch would be impaired, reducing its ability to transmit full power.
As long as the steel floater plates and the pressure ring are flat they can be re-used. Warping of either component should not exceed 0.006in.
Check for wear on the finger tips of the cover plate. If the release bearing is adjusted too close to the fingers, the tips will suffer severe wear. Also these units require a release bearing with a rounded face. A flat-face bearing can result in a hard pedal and clutch release difficulties.
Finally, the diaphragm spring should be tight on the rivets that hold it to the cover plate. If the spring is loose the clutch will not disengage properly.
Source RAM Clutches 201 Business Park Blvd. Columbia, SC 29203 Telephone (803) 788-6034 www.RamClutches.com