Skip over navigation

Clutch 2013

Andrew Hanna, Dan Taub, Danny Zirkel

What is it?

Clutch (n) -- a device that enables two revolving shafts to be joined or disconnected as required, esp one that transmits the drive from the engine to the gearbox in a vehicle

Exploded View

From the Tiger Cub Bible

Exploded View

Our Exploded View

Photocreds: Dan Taub

Back Plate

Purpose: Connected to main shaft; transfer rotational energy from clutch basket to transmission

Clutch Basket

Purpose: House the clutch plates; connected to primary chain

Specs: 48 teeth (vs. 18 on engine sprocket) Ratio: 2.67 / 1

Driven vs. Friction Plates

(Image is a friction plate)

  • Friction plate: connected to clutch basket
  • Driven plate: connected to inner hub
  • When clutch depressed: both spin freely
  • When clutch not depressed: surface friction prevents slippage (allows transfer of energy)


  • Thickness: 1/8 in
  • Diameter: 4.95 in



Compress the clutch plates together when clutch is not engaged.


Free length: 1.4 in

Compressed length (for testing): .77 in

Force applied during testing: 40lbs=177.93N

Spring constant: 761lbs/ft = 11,120.55 N/m



Utilize mechanical advantage to lower the force needed on the handle.


Distance from pivot to push rod: .25 in

Distance from push rod to applied force from cable: 2.5 in

Mechanical advantage: 5:1


Not listed here: Primary Chain, Push Rod

The Science Behind

How much force is required to depress the clutch?

(Measurements based on ’58)

Force to release clutch without any mechanical advantage: ~200lbs

Divide by mechanical advantage of lever (5:1): ~40lbs

Divide by mechanical advantage of clutch handle (2.5/.6 =4.2:1): ~9.5lbs (with no friction)




Symptoms: Engine revs but no corresponding acceleration.

How: Clutch slippage is when the clutch plates are slipping across each other, rather than engaging and transferring engine torque to the drive train.

Why: The cause can be a poorly adjusted clutch, or worn springs, or worn plates.

Our clutch slips at between 6 and 9 ft lbs with well-compressed springs.

Working With the '58

Clutch was heavy, noisy

**During testing, clutch cable “snapped”

Solution 1: We used emory paper to smooth out the teeth on the driven clutch plates, then buttoned up and attached new cable

Consequences: “Oh, well that’s just awful.”


Solution 2: We lubed cable to stop noise; tightened adjustment screw for better push-rod connection

Consequences: "...still worse than it's ever been."

Solution 3: Run cable along a straighter path (reduce friction)

Consequences: “The best this clutch has ever felt!”

Reassembling the '59

The assembled clutch basket, complete with driven plates, friction plates, cups and springs.

The assembled clutch in the engine casing, including the primary chain, lever and push rod.

Size: 5.1M bytes Modified: 13 May 2013, 10:20