This week at Bowers Automotive of Colorado Springs, we want to talk about the basics of replacing a clutch. Understanding the basic inner workings of your vehicle and getting it to an automotive professional on time can make a huge difference in the cost and simplicity of a repair job.
A failing clutch is a common enough problem that usually occurs when the clutch ‘slips’ or completely fails to engage or disengage. This issue can occur for a number of reasons which we will discuss in more detail, along with an explanation of the method used to replace the faulty components in a failing clutch.
How Does the Clutch Work?
The clutch in manual transmission vehicles is used to allow the driver to change gears. To understand how the entire system works and be capable of repairing or replacing a clutch, you must have a basic understanding of the different components and how they interact with each other. The clutch pedal, when pressed down by the foot of the driver, will disengage the clutch and allow the car to freewheel from the engine. Slowly easing off the clutch pedal engages the engine to the transmission and allows the transfer of engine power to the wheels.
When the clutch pedal is pressed, the clutch master cylinder produces hydraulic pressure using brake fluid from its reservoir. The hydraulic pressure created controls the movement of the clutch slave cylinder which is located on the bell housing of the transmission. The clutch slave cylinder is responsible for pushing the throwout bearing against the clutch pressure plate. The clutch pressure plate is in turn connected to the engine’s flywheel and crankshaft. Between the pressure plate and flywheel, there is located an asbestos-lined clutch disc which is used to create the necessary friction.
The pressure of the throwout bearing causes the clutch disc to engage or disengage with the flywheel, allowing power to be transferred to the transmission input shaft. When the clutch pedal is engaged, and the engine is running, the clutch disc is stopped, while the flywheel and pressure plate are rotating at engine speed. This allows you to shift gears without grinding. It is the wearing down of the clutch disc surface that eventually causes the whole clutch to start ‘slipping’ over time. Other reasons for a faulty clutch include brake fluid leaks from the hydraulic components or faulty seals around the master and slave cylinders.
Servicing and Replacing the Clutch
The most common reason for your vehicle to need a clutch service or replacement is a worn out clutch disc. The replacement components needed for this service include a new clutch disc, pressure plate, and throwout bearing. The first step in servicing the clutch is to jack up the vehicle and support it securely on jack stands. To reach the clutch system, the transmission must be removed first. In some models, it is also necessary to physically remove the exhaust system and drive shaft to access the transmission and clutch.
Once there is clear access to the clutch, the pressure plate can be removed from the flywheel. The pressure plate is securely bolted to the flywheel, and the clutch disc is held in place between them. As the bolts are undone, the pressure plate will move away from the fly disc, and the clutch disc must be supported to prevent it from falling out unexpectedly. When both the pressure plate and clutch disc have been worked free, it will be possible to inspect the surfaces for wear.
Inspecting the abrasive surfaces of a clutch disc usually reveals obvious signs of wear. Often, the asbestos or brake pad material used to coat the disc will be worn very thin, showing exposed metal. The surface of the flywheel can be examined for cracks and hot spots which may have appeared due to the intense friction. One important part of the clutch service is to re-machine the flywheel if it is not going to be replaced.
The next step in replacing a clutch is to replace the pilot bearing. Over time this bearing can get worn out or lock up. If this happens, it is likely to allow the transmission’s input shaft to wander too much and make it difficult to disengage the clutch. After replacing the pilot bearing it is time to match up the new clutch. Placing the old clutch beside the new clutch disc and line them up to check that they have the same diameter and that the surface area of the abrasive material is similar. If there is a significant difference, there may be trouble engaging or disengaging the clutch with the replacement disc.
When it comes to replacing a clutch, the flywheel and pressure plate contact surfaces should first be degreased with brake cleaner. The clutch disc has one side that protrudes more than the other. The protruding side must face the pressure plate. The pressure plate and clutch disc can then be lined up with the alignment dowels of the resurfaced flywheel and bolted in by hand. Before tightening the bolts, a clutch alignment tool can be used to ensure the disc lines up perfectly with the pilot bearing.
The bolts can then be gradually tightened in a star pattern to add pressure evenly and gradually. Before finishing the job, it is recommended to replace the throwout bearing, as this component has a high rate of failure. If the throwout bearing is attached to the clutch slave cylinder, then both should be replaced as one unit. The transmission and other components can then be replaced in the reverse order to how they were removed. When driving the vehicle straight after a clutch service, shifting gears can feel a little clunky over the first few miles as the clutch goes through its ‘breaking in’ period before smoothing out.
Knowing the basics of replacing a clutch can be useful, especially for car enthusiasts. To do the job yourself, you will need the right tools and suitable protective clothing and a mask for working with asbestos. To save yourself time and possible frustration, it is recommended that you allow our team at Bowers Automotive to take care of your car for you. We offer a full range of high quality and affordable auto repair services to the drivers of Colorado Springs. Come see us!