REPLACING A FRONT-DRIVE CAR'S CLUTCH
BY JOHN DECKER

The problem was almost imperceptible at first: Going up a slight hill at highway speeds, you noticed that the engine was revving higher even though your car wasn't going any faster. Backing off the gas or dropping into a lower gear made the problem go away each time.

But that was a month ago. Now you spend your days looking for routes that have no hills, because even a slight incline causes the engine to rev wildly while the car slows down. There's also the smell of burnt buttered popcorn in the air as you downshift in a feeble attempt (the semi driver on your bumper is blasting his air horn) to reduce the engine load and get the car going again. Your biggest fear is that you'll end up backing down the hill. The problem isn't in the engine or transaxle. All that slipping is caused by a worn-out or misadjusted clutch.

Compared to other automotive devices, the clutch is decidedly low-tech (see How It Works, above). And while replacing and adjusting the clutch doesn't require exceptional skill or high-tech equipment, there are some things you should look out for.

Please release me

It couldn't be simpler: Push the clutch pedal in and the clutch should disengage. However, if the clutch doesn't fully disengage, you'll hear a lot of grinding during shifts or when you try to put the car in gear. "A lot of people immediately think there's a problem with the clutch disc or pressure plate when the clutch doesn't disengage," says Gabe Vajda, a technician with LuK, a maker of clutch parts.

"Any play in the clutch-pedal parts soaks up travel, so the clutch won't fully release," Vajda cautions. He says that before you remove the transaxle and clutch, it's wise to check the pedal-arm bushings and the actuating cable, or, on cars with hydraulic systems, the slave and master cylinders. Also, a nonreleasing clutch could even be caused by something as simple as carpeting under the pedal that's too thick, which has been the case with some 1988-90 Chevy Beretta and Corsica models. Trimming away insulation under the carpet will restore full pedal travel.

If a clutch isn't releasing, start by manually prying the release arm at the bellhousing with a screwdriver. If the arm moves freely and the clutch releases there, chances are good that the problem lies outside the bellhousing. On cable-operated clutches, there could be too much play in the cable, which can reduce travel. To reduce cable play, find the adjusting nut at the top or bottom of the cable and adjust the cable to the proper specifications. On hydraulically operated clutches, air in the lines, or a worn master or slave cylinder, can result in reduced travel. To bleed the air, top off the master cylinder reservoir with brake fluid. Place a piece of hose on the slave cylinder's hydraulic vent, then place the other end of the hose into a partially filled glass bottle. Open the vent, then have an assistant repeatedly depress the clutch pedal slowly until bubbles coming from the end of the vent line disappear. After tightening the vent, clutch travel should return to normal. If it doesn't, then the slave and master cylinders should be replaced.
The clutch is readily accessible–but only after removing the transaxle from the engine. You'll need to remove or unhook the axles as well.

Removal and inspection

Barring adjustment, the only way to fix a slipping clutch is to replace it. Installing a new clutch is very straightforward. But you have to make sure the work is done right, since fixing any mistakes usually means removing the transaxle-something you don't want to do more than once. It's best to consult a service manual for instructions specific to your vehicle. The following is a general procedure for replacing a clutch.

Start by disconnecting the battery positive cable. Then, while working under the hood, prepare the transaxle for removal by disconnecting the clutch cable or hydraulic slave cylinder. Also, remove or disconnect items that prevent the transaxle from being removed, such as backup-light wires, air-cleaner ducting, exhaust pipes, the starter motor, speedometer cable and other items. If you are in doubt as to exactly what needs to be removed, consult a manual.

Next, chock the rear wheels and jack up the front end of the car and support it with stands. Working from under the car, remove any additional parts that you couldn't reach from under the hood, including the bolts that hold the axle shafts to the transaxle.

To remove the transaxle, you normally have to remove one or more engine mounts. But before you can start removing them, you'll have to support the engine. With many cars, it's possible to support the engine from underneath by placing a jack under the oil pan. But on other cars, a special engine-support rod that allows the engine to hang while the transaxle is out must be installed under the hood. Again, consult a manual for the proper method.

To disconnect the transaxle from the engine, support the transaxle with a jack and remove the bolts from around the flywheel bellhousing. Next, slide the transaxle away from the engine until the transaxle input shaft clears the pressure plate, then lower the transaxle to the ground and roll it from under the car and out of the way.

Once you have removed the transaxle, you will then be able to access the pressure plate and clutch disc. Remove the bolts from around the pressure plate, then remove the plate and clutch disc. Inspect the friction surface of the flywheel. If it is scored, checked or shows signs of hot spots, it must be removed, machined at a machine shop and then reinstalled. Keep in mind that it's good practice to have the flywheel machined so the clutch disc has a proper surface to break in on. If you don't have the flywheel machined, sand it lightly with medium-grit sandpaper wrapped around a small block of wood.

When inspecting the flywheel, also inspect the pilot bearing or bushing at the center of the flywheel. The needle bearings (if applicable) should be lubricated and show no signs of galling. If there's any doubt about the quality of the bearing, remove it with the appropriate tool and install a new one. You should also inspect the back side of the flywheel for signs of oil leakage at the engine's rear main seal. If oil reaches the surface of the clutch, chattering and grabbing will result. Some cars have "stepped" flywheels, which is when the clutch disc rides on one surface and the pressure plate bolts to a surface that's stepped above the clutch surface. It's important that both surfaces be machined the same amount, or slipping or failure to release could result.

If the flywheel is machined too much, it moves the clutch and pressure plate away from the release bearing. This can keep the clutch from fully releasing. You might be tempted to use shims between the crankshaft and flywheel to move the clutch assembly toward the release bearing. However, it's possible for a thin flywheel to burst at high rpm. The only safe alternative is to replace the worn flywheel with a new one.

Inspect the transaxle's input shaft seal to be sure it isn't leaking. (There's no need to inspect the clutch disc, pressure plate or release bearing, since you'll be replacing those.) If the seal is leaking, replace it. Next, look for leakage at the engine's rear main seal. If there's more than a hint of seepage there, this may well be the reason for the early demise of the clutch disc. Mark the flywheel so you can reinstall it back on the crankshaft in the correct index. Remove the flywheel and remove the old seal. Carefully install the new seal without gasket sealer by tapping it in with a seal installation tool, or at least a large socket or a piece of wood. Check the crankshaft's sealing surface for a depression where the seal has eroded the metal (this is particularly common in dusty areas). There may be a repair sleeve available for your engine, so check with your machine shop if you think you have a problem.

Installation

Before you install a new or freshly machined flywheel, make sure the crankshaft flange is clean. After placing the flywheel on the flange, tighten the bolts in a star pattern to the proper torque specification. There are two tricks to installing the clutch disc and pressure plate. First, the disc is designed to go on in one direction. If you look at the center hub, you'll notice a series of damper springs. On one side of the clutch, this damper hub sticks out from the friction surface. That side always goes toward the transaxle. Put it in the other way, and you'll soon be taking the transaxle out to do it all over again. Second, you'll need a "clutch pilot tool" to install the clutch disc so it aligns with the pilot bushing in the crankshaft. To install the disc, slide it onto the pilot tool, then securely stick the center of the tool into the pilot bearing. Install the pressure plate over the clutch disc, torque all bolts to specifications using a star pattern, then remove the pilot tool.

Before installing the transaxle, install the new release bearing onto the release fork, then make sure that the fork operates freely. Jack the transaxle into position and slide it forward so that the input shaft slides into the splined hole in the clutch disc. You may have to spin either the input shaft or the engine's crankshaft (and the flywheel and clutch along with it) to get the splines to align. Don't force the input shaft into its splined hole. When everything's properly aligned, the shaft will slide right in. If it doesn't slide right in, don't force it. Back it out and try again.

Never let the transaxle hang unsupported from the engine, since this can lead to damage to the pilot bearing, input shaft and front input shaft bearing.

After installing and torquing all the bellhousing bolts to spec, you can reinstall any motor mounts that you had removed, the drive axles, as well as any other components under the car. Once the underside work is done, remove the jack holding the transaxle and lower the car to the ground. Reinstall any underhood components.

You don't really have to replace the clutch cable at this time, but because it costs less than $50, replacing it is good insurance against trouble later on. In any case, adjust the cable to the proper amount of free-play.

Most hydraulic clutch actuators are self-adjusting and, therefore, have no free-play. Still, you'll want to make sure the self-adjusting action is working properly. To do that, simply push the slave cylinder piston back into its bore. If it moves, the system is working properly. If it doesn't move, it means the slave cylinder's pressure-relief orifice is clogged and the slave cylinder should be replaced.

Remove the outer stub axle from the hub, and then pull the entire axle free of the transaxle. You may need to plug the inner socket.
Regardless of method, depressing the clutch pedal will push the throwout bearing against the pressure plate. There should be some adjustment mechanism as well.
A support bar or a stout piece of timber will be necessary to support the engine while the tranny is out.

How It Works: Clutch Play

To get the clutch moving, the clutch pedal is connected to a sheathed cable or a hydraulic master cylinder and slave cylinder. The cable system works much like a heavy-duty version of the brake-caliper cable that can be found on a 10-speed bicycle-depressing the pedal pulls on the cable to release the clutch. With the hydraulic system, pressing on the clutch pedal moves a piston in the master cylinder, which displaces fluid, causing the piston in the slave cylinder to move. This, in turn, operates the clutch. Some older cars and trucks use a simple mechanical bellcrank linkage instead of a cable or slave cylinder, but the mechanical principle is the same: Depress the clutch pedal and the clutch is released. How?

Whether the clutch-pedal system is operated hydraulically or by cable, it moves a release fork that pivots on the bellhousing. The pivoting action moves the end of the fork toward the pressure plate. A throwout bearing (also called a clutch-release bearing) at the end of the release fork applies even pressure to the diaphragm spring and the pressure plate moves back, releasing the clutch disc. Let the clutch out, and the pressure on the spring releases and the clamping force on the disc returns.

–J.D.