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New Sprung Clutch Installation

PostPosted: Tue Jul 02, 2019 2:32 am
by brichardson
The GEN3 clutch is a racing clutch and isn’t just a plug and play. Conducting pre-installation testing can reduce issues like slipping and no disk engagement. A few simple tests can increase the odds the clutch will work properly after installation.

Step 1 - Disengagement Testing
Install the clutch cover (pressure plate) with the disk on the flywheel off the motor. Place the assembly in a hydraulic press on a scale pad and displace the clutch until the pressure plate releases the clutch disk. Use a dial indicator to measure the displacement. (See figure 1)

The hydraulic throw-out bearing has limited travel and might not be able to displace more than .250”. If the displacement required is or over/close to or over .250” check the displacement of the throw-out bearing. Remove the bearing from the transaxle, reattach it to the hydraulic lines, bleed the clutch, and then push the clutch pedal to the floor while using a dial indicator to measure the displacement. If the throw-out bearing travel Is less than the required finger release distance, the clutch will not release when installed in the car. You can either adjust the pedal stop or add shims between the clutch cover and the flywheel. Just make sure the displacement of the throw-out bearing is larger than the distance necessary to disengage the clutch.

Step 2 – Force Measurement Testing
After getting the clutch setup with the correct deflection measure the amount of force that is generated by the throw-out bearing. The peak force required to release the disk at the throw-out bearing contact should be over 400 lbs. If it is less than that the clutch cover, the diaphragm spring may need to be replaced.

If this force is too low, the clutch might slip when hot.


Release Test - If the clutch assembly released in a hydraulic press and the throw-out bearing displaces less than .250” the clutch should release when installed in the car.

Throw-out Bearing Displacement – If the measured displacement of the throw-out bearing is greater than the distance required to release the clutch disk, the clutch will release when assembled in the car.

Clutch Disk Upgrade – If when you displace the throw-out bearing enough to release the clutch the force is over 400lbs the clutch should not slip under most conditions. If the driver either speed shifts or doesn’t do a good job of matching RPM’s on downshifts a higher force clutch cover might be considered. The clutch cover can be upgraded to the “Buff” spring to increase the holding torque by about 20%. When using the higher force spring failures of the thrust bearing in the motor have occurred. It is recommended that the motor be started without the clutch being engaged, in neutral, to get oil on the thrust bearing surface. This only needs to be done when the car has been sitting for over a week or so.

Appendix - Torque Calculations & Key Specifications

The GEN3 clutch key specifications are:
Disk Material Kevlar
Torque Rating (with ceramic Tilton disk) 200 ft-lb
Throw-out Bearing Travel +2.50” typical
Disk Diameter 7.25”
The force to displace the throw-out bearing for a given displacement measured in a hydraulic press using a scale pad.

The force at the pressure place can be calculated along with the theoretical maximum torque:
Force at the Pressure Plate = (Lever Arm Ratio) X (Force of the Throw-out Bearing)
Lever Arm Ratio = 4.3 (calculated from measurement on the clutch plate)

Force at the Pressure Plate = 4.3 X 400
Force at the Pressure Plate = 1,722 lbs
The maximum clutch torque is:
Torque Max = (Force at the Pressure Plate) X (Radius of Contact X Coefficient of Friction)
Radius of Contact = 3.4” (the radius of center of the friction material)
Coefficient of Friction = .35 (published data for Kevlar® clutch material)

SCCA Material
Torque Max = 1,722 X (3.4”/12”) X .35 = 170 ft-lb

Tilton Clutch Material
Torque Max = 1,722 X (12/3.4) X .5 (published data for Tilton ceramic clutch material)
Torque Max = 243 ft-lb

The stock clutch supplied by SCCA-E is the “White” diaphragm spring. This spring is marked with a “W” and has a torque rating, with a ceramic disk, of 200 ft-lbs. The coefficient of friction for the ceramic disk material is about .50 and .35 for the Kevlar clutch material. The adjusted torque rating for the SCCA-E material reduces the rating to 130 ft-lbs., close to the torque of the motor.

AccelRaceTek can setup and test your clutch assembly, just give us a call at (669) 232-4844