Why does my car have a clutch?
As you let out your clutch pedal, you are rubbing the clutch disc surfaces between the flywheel and the pressure plate until the car starts to move, and then fully clamps down when you let the clutch pedal out completely. A tremendous amount of heat is generated in the clutch, pressure plate, and flywheel. This happens each time you start moving and to a lesser degree, when you shift. As time goes by, you will eventually wear the friction surface thinner, and it will get to a point where it is too thin to transmit enough torque to move the car normally.
The pressure plate is normally closed, clamping the disc between the pressure plate and the flywheel. When the clutch pedal is depressed, the pressure plate is forced open creating a very small space between the disc, flywheel and pressure plate. When the disc moves away from the flywheel, power flow from the engine to the transmission is interrupted. When the clutch is engaged, the disc slips briefly to provide smooth engagement and clamps the pressure plate and disc against the flywheel. This causes the input shaft of the transmission to turn, transmitting power to the transmission and then to the driveline and wheels.
Disc (or Clutch Disc)
The disc hub is splined to fit the input shaft, providing smooth engagement and dampens engine vibrations via torsion springs in the damper assembly. It is rides on the input shaft between the flywheel and the pressure plate. It can slide forward and backward on the input shaft, but cannot rotate without rotating the transmission input shaft.
Pressure Plate (or Clutch Cover)
The pressure plate clamps the disc against the flywheel during engagement. During disengagement, it releases pressure on the disc, creating a gap large enough for the disc to move away from the flywheel and enable the driver to shift gears.
A typical diaphragm spring clutch consists of a pressure plate, diaphragm spring, pivot ring, drive straps, and a cover. When the release bearing contacts the tips of the diaphragm spring fingers, it moves them toward the flywheel. The outside diameter of the diaphragm spring pivots on the pivot ring inside the cover. This action lifts the pressure plate off the flywheel through the drive straps that connect the cover to the pressure plate.
Lever style clutches produce clamp load by pressure from coil springs. As the friction material of the disc wears, the springs expand, reducing their clamping force. At the same time, pedal effort remains high. As a result of these disadvantages, passenger cars and light trucks are now almost exclusively equipped with diaphragm spring clutches.
Diaphragm spring clutches maintain higher clamp load than lever style clutches throughout the service life of the clutch. As disc friction material wears, clamp load increases during the first half of clutch life before decreasing gradually to its original level. Diaphragm spring clutches require less pedal effort the further the pedal is actuated, reducing stress on release system components.
Bolted to the end of the crankshaft, the flywheel provides the mounting surface for the clutch. During engagement, the disc is clamped against the flywheel by the pressure plate.
In addition to its other functions, the flywheel acts as a heat sink, dissipating heat and moving it away from the clutch pressure plate and disc friction material. The flywheel must provide a smooth, flat surface in order for the clutch to operate properly. Every clutch change must include either a new or resurfaced flywheel.
Release Bearing (or Throw-Out Bearing)
When depressing the clutch pedal the fork movement causes the release bearing to move along the transmission-bearing retainer forcing the diaphragm spring fingers to open the pressure plate. The internal bearings in the release bearing enable it to turn while applying pressure to the diaphragm spring fingers. The bearing retainer must be parallel to the input shaft and provide a smooth surface for the release bearing to function properly.
Angular-contact bearings, found in hydraulic release systems and self-adjusting cable systems, are in constant contact with the diaphragm spring fingers. Self-centering bearings are designed to compensate for slight misalignment, it is normal for these bearings to be "off center" until they contact the diaphragm spring fingers.
Some vehicle designs utilize a concentric or hydraulic slave cylinder. It eliminates the need for a number of release system components, including the release fork, pivot ball and bearing retainer. They are located inside the bell housing and should be replaced when replacing the clutch to avoid rework and additional labor cost.
The pilot bearing/bushing supports the end of the transmission input shaft and centers the disc on the flywheel. Types of pilots include conventional ball bearings, needle bearings and sintered bronze bushings.
A small and relatively inexpensive component, the pilot bearing, or bushing, should always be replaced during clutch installation. The variety of problems caused by a worn or defective pilot bearing or bushing are not worth the risk of having to remove the transmission to replace this component later.
Hydraulic / Mechanical Operation System
Clutch operation is either mechanical or with a hydraulic pressure system. If a vehicle has a mechanically operated linkage, it will incorporate either a shaft-and-lever linkage arrangement or a cable.
Linkage / Lever System
Systems that are made up of linkages, levers and pivot points are found primarily on older vehicles. These systems require regular lubrication and can only be designed to fit a limited range of configurations.
A cable operated clutch mechanism is relatively simple. A cable connects the clutch pedal directly to the clutch release fork. This simple design is flexible and compact. There is however, a tendency for cables to gradually stretch and eventually break due to age and wear. Cable systems require regular adjustments, every 6 months or 6,000 miles!
On a hydraulically operated clutch, a master cylinder is usually directly operated by the clutch pedal assembly. A slave cylinder at the transmission is connected to the master cylinder by high-pressure tubing. The slave cylinder pushes either an operating lever or directly on the release bearing. Hydraulic systems require less pedal pressure and provide a smooth feel throughout clutch engagement.
Wear in hydraulic components causes clutch release problems. Due to the gradual nature of this wear, problem diagnosis can be difficult. Internal slave cylinders are prone to early failure due to the conditions inside the bell housing. To prevent premature failure and added labor costs later, always replace internal slave cylinders when installing a new clutch.
Clutch Fails To Release
Hard Going Into Gear
Squeals When Clutch Is Engaged
Pops Out Of Gear
Noise In Neutral W/ Engine On
Noise In Reverse Only
Noise In All Gears
Noise In Any One Gear
If any of these symptoms are present, call or bring your car into Clutch Mart today for a free adjustment / evaluation / diagnostic test.
Below are some clutch life averages that Clutch Mart has observed:
Avoid excessive downshifting, especially into 1st and 2nd gear, if you need to slow down use your brakes.
Whenever you downshift, you subject the clutch to unnecessary wear which is removing miles from the life of your clutch. Remember, you have one clutch and four brakes on your car. Brakes are engineered specifically to stop your car. The clutch is engineered to transfer power from the engine to the transmission, enabling the car to move.
Left Foot Placement
When the car is in gear and moving, take your foot left foot off the clutch pedal.
If you even slightly rest your foot on the clutch pedal after shifting you are causing unneeded wear to your clutch components. Take your foot off of the clutch pedal after shifting; this will extend the life of your clutch, saving you time and money.
When you come to a traffic light put your car in neutral and take your foot off the clutch pedal
Even though you have the clutch pedal depressed, your clutch will still wear because the clutch components are engaged. Each time you sit at a traffic light with your foot on the clutch pedal you are removing miles from the life of your clutch.
Entering a Parking Lot – Feel the Shakes?
When entering a parking lot always be in the proper gear for the speed you are going. When traveling at less than five miles per hour, you should be in 1st gear.
If you are in a higher gear than what the vehicle is designed for you will feel a “shake”. When you feel that “shake”, your clutch is hammering against itself take miles off of your clutch system.
When you start out in 1st gear you “feather” the clutch pedal for a smooth start. When shifting through the rest of the gears, do not “feather” the clutch. The clutch pedal should be “in” and “out” in gear 2nd, 3rd, 4th, and 5th.
If you “feather” (letting the pedal out gradually) the clutch between gears you will cause excessive wear to the clutch components. When shifting between 1st & 2nd, 2nd & 3rd, 3rd & 4th, and 4th & 5th, the pedal should be “in” and “out”.
Hill Holder – Traffic Light or Stop Sign
When you are on an incline (up hill) waiting for traffic to clear or a light to change, do not use your clutch as a hill-holder. Hill- holding is keeping the car in 1st gear, feathering the clutch to hold your position, while at a light or for traffic to clear.
Using the clutch as a hill holder you can wear the clutch equal to 5,000 miles in just one intersection.
At Clutch Mart, we only use OEM (Original Equipment Manufacturers) parts. It is our belief that clutches, in particular, should be replaced using the same parts that the vehicle came with from the factory.
We recommend that you don’t accept aftermarket clutches from non-OEM manufacturers. The only exception might be a high performance or heavy duty clutch package.
Major OEM manufacturers for American cars include:
Major OEM manufacturers for Japanese cars include:
Major OEM manufacturers for European cars include:
All Clutch Mart package (disc/cover/release bearing) replacements are with OEM parts and come with the Clutch Mart Lifetime Parts Warranty (see warranty page additional information).
Clutch Mart offers the best warranty in the industry. Under normal, non-commercial use, Clutch Mart installed parts are warranted for as long as you own your car.
Yes, a lifetime parts warranty! Replacement clutch parts cost you nothing.
Our normal use (non-commercial) warranty is simple:
All warranty work becomes the top shop’s top priority – fix the problem fast
Simple, fast, expert technicians, and low prices – your Clutch Mart advantage!
Selecting your clutch and transmission repair expert may require different criteria than selecting the shop to do your 60,000 mile service, air conditioning, or oil change. Clutch and transmission services require specialized skills and equipment. Clutch and transmission prices can vary a great deal from shop to shop depending on expertise.
When selecting your clutch expert, please consider Clutch Mart: