ASE PS2 Test Preparation Guide: Manual Transmission/Transaxle Parts

ASE PS2 Test Preparation Guide: Manual Transmission/Transaxle Parts

● CLUTCH — Used with manual transmissions to engage and disengage the engine from the transmission and when shifting gears. The clutch is bolted to the flywheel on the back of the engine, and clamps the clutch disc against the flywheel when the clutch is engaged. When the clutch pedal is depressed to disengage the clutch, the pressure plate pulls away from the flywheel and disc, releasing the disc.

The clutch is a spring-loaded pressure plate assembly. Most vehicles have a diaphragm spring clutch, but some older vehicles have a coil spring clutch.

If the clutch disc is worn or contaminated with oil, or if the clutch linkage is not adjusted properly, the clutch may slip. Slipping is most noticeable when the engine is under load, as when lugging at low speed in a high gear, when driving up a hill, when accelerating to pass another vehicle or when towing a trailer.

If a newly installed clutch is slipping, the most likely causes would be oil or grease contamination, incorrect release system adjustment, a defective cable adjuster, a blocked clutch master cylinder port or binding slave cylinder, a misaligned or improperly installed release bearing, or improper flywheel machining of a step or cup flywheel.

Because of the labor involved to replace a clutch, recommend replacing all the major clutch components at the same time: the clutch, disc, release bearing and pilot bearing/bushing (if equipped). A complete clutch kit will provide all the parts your customer needs. A kit also means the parts are properly matched for the vehicle application.

For towing or performance applications, larger, stronger clutches are available to upgrade driveline reliability and performance. Recommend upgrading to a performance clutch if your customer has had repeated clutch failures or is heavily modifying his engine.

● CLUTCH DISC — A flat plate with friction facings on both sides that allows engine torque to drive the transmission. The disc is mounted between the flywheel and pressure plate, and is connected to the transmission input shaft with a splined hub. The hub may be rigid (no springs) or have five to eight springs to help cushion clutch engagement. The disc facings provide friction and grip as they rub against the flywheel and pressure plate. Over time, the facings wear and reduce the clutches ability to hold under load. Eventually the clutch starts to slip and must be replaced. Slipping or chattering (jerky engagement) also can be caused by glazed or burned facings, or oil contamination. Oil leaks must be fixed before installing a new clutch disc. A “pilot tool” is required to center the disc when it is replaced.

● RELEASE BEARING — A bearing that slides around the transmission input shaft and pushes (or in some cases pulls) against fingers or the spring in the pressure plate to disengage the clutch. The bearing is held by a yoke lever attached to the clutch linkage and clutch pedal, or a telescoping hydraulic linkage inside the bellhousing. When the pedal is depressed, the clutch linkage pushes the release bearing forward against the fingers on the clutch plate. This relieves spring tension, allowing the pressure plate to release the clutch. Adjustment of the linkage is important for proper clutch engagement and release, as well as bearing life. A chirping noise that intensifies when the pedal is slowly depressed usually indicates a bad release bearing.

● PILOT BEARING/BUSHING — A small bushing or bearing located in the end of the crankshaft that supports the transmission input shaft. Used primarily on rear-wheel drive vehicles. Failure can cause noise or clutch release problems. Replacement is recommended when servicing the clutch or flywheel.

● FLYWHEEL — A large heavy wheel bolted to the back of the crankshaft that helps maintain engine momentum and serves as both a friction surface and heat sink for the clutch. The face of the flywheel must be smooth and flat for proper clutch engagement. It also must be free from cracks, hard spots or oil contamination. Resurfacing the flywheel is recommended when the clutch is replaced to restore the friction surface.

Some engines have a “dual mass” flywheel, which is like two flywheels in one. A dual-mass flywheel is supposed to dampen engine vibrations and cushion clutch engagement for smoother operation. If a dual-mass flywheel is cracked, damaged or the internal springs have failed, it needs to be replaced. Some dual-mass flywheels (Ford) can be resurfaced, but others (GM, BMW and Porsche) should only be replaced. Dual-mass flywheels are very expensive. One alternative is to replace them with a conventional one-piece aftermarket flywheel. These are available for Ford and GM, but they require a different clutch set than the OEM dual-mass flywheel. Replacing a dual mass flywheel with a solid flywheel may increase drivetrain harshness and vibration.

The flywheel also is used to start the engine. Gear teeth around the circumference of the flywheel are engaged by the starter to crank the engine. Missing or damaged teeth can interfere with reliable starting. If the gear is damaged, the ring gear or flywheel should be replaced.

When removing a flywheel, the flywheel’s index position on the crankshaft should be marked so it can be reinstalled in the same position as before. This is necessary to maintain proper balance on some engines.

● CLUTCH MASTER AND SLAVE CYLINDER — The master clutch cylinder is attached to the clutch pedal, and pushes fluid through a hose to the slave cylinder, which is connected to the release bearing or bearing yoke. Failure of the master or slave cylinder or a loss of fluid will prevent the clutch from releasing. Replacement is required if either is component is leaking.

● CLUTCH CABLE — Used on some older vehicles to connect the clutch pedal to the release bearing yoke. Most cables have an automatic adjuster that maintains proper clearances between the release bearing and clutch. If the cable breaks, the clutch cannot be released. If it sticks, it can prevent proper engagement. Replacing the cable is recommended when changing the clutch.


Cooling System

Electrical System

Exhaust Parts

Ignition System

Manual Transmission/Transaxle Parts

Suspension & Steering Parts

Fuel System

Engine Parts

Emission Controls

Driveline Components

Heating, Ventilation & Air Conditioning (HVAC)


Automatic Transmission/Transaxle

You May Also Like

Do You Suffer From CED? Good News – It’s Curable

The creep of Customer Experience Decline can take hold if you allow your shop to lose focus.

In business, as in life, mistakes WILL happen. How you respond will make the difference in whether your customer will remain loyal and continue to do business with your store. Customer relations are easy as long as things go well – when they don’t, you and your team have the opportunity to shine or look like the proverbial pile of…well, you know. 

Tool Time Podcast: CTA Tools

Nadine Battah and Eric Garbe learn about CTA Tools’ history and innovative technology.

The Purge: Flushing & Filling the Coolant

This job isn’t needed as often as it used to be, but it’s still important.

ADAS: Coming of Age

Driver-assist systems are categorized into levels, determined by the amount of automation for any given system.

Minding Your P’s And Q’s

Price and Quality are two of the most important considerations for customers purchasing from you.

Other Posts

Cummins, Daimler Truck and PACCAR Form Joint Venture

The completed joint venture is now known as Amplify Cell Technologies.

MEMA Aftermarket Suppliers’ BMC to Host Summer Meeting

The Brake Manufacturers Council meeting will be held on May 31, in Naples, Florida.

Tool Intel – Understanding Air Tool Fittings and Couplers

Why don’t air tools come with fittings installed? Here’s why customers need to buy what they actually need.

Read the April Digital Edition of Counterman

The April issue contains article designed for technical training, management efficiency and store profitability.