Friction and Reaction Units Flashcards

A technician measures clutch pack clearance with a feeler gauge between the pressure plate and the snap ring and finds it greater than specification. Which correction is appropriate?

Answer: Install a thicker selective snap ring or pressure plate

A thicker snap ring or pressure plate takes up space in the stack and reduces clearance. A thinner one would increase it.

When air testing an assembled clutch drum by directing compressed air into its apply passage, which result points to a failed piston seal?

Answer: Air escapes with a hiss and the piston moves weakly or not at all

If the piston seals leak, air escapes and the piston cannot build enough force to move. A good clutch applies with a dull thud and releases when air is removed.

A technician disassembling a clutch pack finds the steel plates blued and the friction plates dark, glazed and flaking. What is the most likely cause?

Answer: Prolonged slippage that generated excessive heat

Blued steel plates and burned friction material result from heat produced by a slipping clutch.

Why must new clutch friction plates be soaked in the specified ATF before assembly?

Answer: To saturate the lining so it does not scuff or burn on its first engagements

Soaking saturates the lining with fluid so it is lubricated and cooled from the first apply. Dry plates can scuff or burn before fluid reaches them.

A technician checks an installed one-way roller clutch by turning the inner race by hand. Which behavior is correct for a good unit?

Answer: It locks in one direction and freewheels in the other

A one-way clutch must hold in its driving direction and overrun freely in the opposite direction.

During air testing of a band servo, air is applied to the apply passage. Which result indicates a servo in good condition?

Answer: The piston moves the apply pin smoothly and returns when the air is released

A good servo moves smoothly with no audible leakage and returns under spring force when air is removed.

After installing a band with an external adjusting screw, what is the correct adjustment procedure?

Answer: Torque the screw to specification, then back it off the exact number of turns specified and tighten the lock nut

Bands are adjusted by torquing the adjusting screw to specification and then backing it off the specified number of turns before locking it.

During inspection of a clutch drum, a technician finds that the check ball in the piston area is stuck in its seat. What problem can this cause?

Answer: The clutch may drag because residual fluid is not released from the apply chamber

The check ball opens to dump trapped fluid when apply pressure drops. If it sticks, centrifugal pressure may keep the clutch partly applied.

Which condition most likely results from too much clutch pack clearance?

Answer: Delayed or slipping engagement because the piston must travel farther before clamping the plates

Excess clearance means the piston has more travel before clamping, so the clutch engages late and may slip.

A technician checks steel clutch plates and finds one that is dished and warped. What should be done?

Answer: Replace the plate, because warping causes uneven clamping and hot spots

Warped steel plates do not clamp evenly, which causes hot spots, drag or slip. They should be replaced.

When installing a lip-type seal on a clutch apply piston, how should the seal lip face?

Answer: Toward the apply pressure side, so fluid pressure presses the lip against the bore

Lip seals are installed with the lip facing the pressure, so hydraulic pressure expands the lip against the bore and seals it.