Clutch Repair and Replacement
By Mike Bumbeck/autoMedia.com
Degree of Difficulty
Repairing the On-Again-Off-Again Engagement -
Think of the clutch as a switch between your engine and the transmission. Every time you press on the clutch pedal, you turn the switch off, and no engine power gets to the transmission. Light goes off. When you let the pedal back out, the switch turns back on and away you go. Light goes on. If you let the clutch pedal halfway out, the clutch transmits roughly half the engine power to the transmission and acts more like a dimmer switch.
The clutch is able to perform this on-and-off delivery act by way of four major component parts – the flywheel, the clutch disc, the pressure plate, and the throw-out or release bearing. Since the average clutch is engaged and disengaged thousands of times over its service life all these parts will eventually wear out. Oddly enough that's what they are designed to do.
Caught in Between The clutch disc takes most of the abuse over the service life of a clutch assembly. The clutch disc is one of those parts designed from the start to wear out as it does its job. Like a brake pad, the clutch disc wears out a tiny bit each time it is engaged. The clutch disc lies in wait and endures extreme pressure as it is sandwiched between the two steel surfaces of the flywheel and pressure plates. The material of the clutch disc absorbs friction and allows for the smooth transition of engine power to the transmission from the flywheel through the pressure plate. Dampening springs in the center hub of the disc absorb vibration from engagement to prevent damage to the drivetrain and transmission. Eventually the clutch disc material will wear too thin and the clutch assembly will no longer be able to hold the torque, or twist, created by the engine and will slip. The heat created by this extra slipping will quickly make things worse, and soon the switch will be off for good. Light goes off. Vehicle goes nowhere. How to Steps
Unit, Not Parts
While the clutch disc is usually the part that wears out first, all components should be inspected or replaced when servicing the clutch. The flywheel should always be resurfaced for chatter and vibration-free engagement. Pressure plates should be replaced if worn. The throw-out or release bearing can also raise a ruckus and start howling as it wears out. Since this bearing handles the load of disengaging the clutch and allowing the assembly to spin freely while disengaged, replacement is usually a safe bet. The pilot bearing should also be inspected as it centers the transmission input shaft in the flywheel and allows it to spin. For these reasons, it is a smart strategy to replace the entire clutch assembly as a unit. Readily available kits, complete with alignment tool, are a great way to get everything required for the job in one box.
Opening the Can
The clutch is one of those parts, like a cylinder head gasket, or a timing belt, that while not prohibitively expensive by itself, can be a real chore to access. On a rear-drive vehicle, getting down to the clutch requires removal of the driveshaft and transmission. On a front-wheel-drive vehicle, the task becomes more complex. And on an all-wheel-drive vehicle, a true maze of components must be removed to get down to the clutch assembly. While replacing the clutch assembly itself usually takes a matter of minutes, getting the transmission and everything else out of the way, and then put back in again can take many hours.
There is no possible way in this short space to outline removal and replacement of all the different configurations of transmissions and drivetrains. Consulting a service manual for procedures, torque specifications, and final adjustment is the only way to go before tackling a clutch job.
How to Steps
Disconnect the negative battery cable. Secure the vehicle on jack stands. Drain the transmission oil. Remove the clutch and shifter linkage. Remove the driveshaft and the transmission.
Remove the pressure-plate bolts a little at a time in a circle in order to slowly release the pressure plate from the flywheel.
Remove the clutch assembly as a unit. Do not breathe the clutch dust or use compressed air to clean.
This clutch disc was slipping. The now glazed, thin surface was worn down to the rivets and about to give up completely.
Remove the flywheel bolts with an impact wrench. Remove the flywheel. Be careful, it's heavy! Always resurface, or replace the flywheel when installing a clutch.
Clean the bell housing and input shaft of dust and grease. Install and lube the clutch fork and throw-out bearing. Test for proper operation. Test for pilot bearing fit on the transmission output shaft.
Install the new pilot bearing flush with the transmission side of the flywheel. Drive it in with a drift or a socket that lines up with the outside of the bearing. Install dowel pins if required.
Use a torque wrench to install the new flywheel on the crankshaft. The cheater bar prevents the flywheel from spinning.
Alignment of the clutch assembly is key. Use the alignment tool to first center the new clutch disc onto the flywheel. Keep the disc centered as the assembly proceeds.
Install the pressure plate evenly. Tighten the bolts a little at a time in a circle, first one, then the furthest from that, and so on. Use the alignment tool to keep the clutch disc centered as you go. Torque the bolts to specification.
Remove the alignment tool. Measure to see if the clutch disc is centered in the assembly. If not, start over!
Reinstall the transmission. The transmission should mate up correctly with little effort. Do not force the transmission into place in an attempt to overcome misalignment. Do not allow the transmission to hang from the input shaft.