Clutch Service

Manual transmissions are becoming rarer in daily-driven automobiles, even in economy cars, but there are people out there who still enjoy shifting gears. And there are enough vehicles using manual gearboxes that understanding the operation and service of these transmissions is still an important skill.

In particular, clutch service will be the focus of this article. Rear Wheel Drive (RWD) vehicles, such as light trucks, do not present any significant challenges. On the other hand, Front Wheel Drive (FWD) vehicles can test your patience. The clutch operates in the same manner on both styles of vehicles, but access to the FWD transaxle, such as a PT Cruiser, along with driveshaft removal, can make this job a tough and lengthy task.

CLUTCH BASICS

The clutch assembly is a mechanical device (friction disc and pressure plate) that locks the flywheel to the input shaft of the transmission. As a result, the engine and transmission rotate as one unit, with no slip, to transfer power to the drive wheels. In an automatic transmission, fluid in the torque converter connects, so to speak, the flywheel to the transmission. There’s always some power loss in the fluid, making the clutch connection more efficient than the fluid one.

In order to shift gears, the clutch must be released. This is done mechanically with the clutch pedal. Depressing the pedal starts a chain reaction of events by building fluid pressure in the clutch master cylinder (not to be confused with the brake master cylinder) that is transmitted to a slave cylinder. The slave cylinder is connected to the release lever that moves when fluid pressure is applied. Then the release lever pushes the release, or throwout bearing, against the fingers on the pressure plate to release the clutch. On some older vehicles, a cable was used instead of hydraulic fluid.

CLUTCH PROBLEMS

Problems with shifting gears can be a sign that there is a problem with the clutch. If the clutch cannot release (or disconnect) from the flywheel, shifting gears can become difficult. It is best to test drive a vehicle that is suspected of having clutch problems to verify the condition. What your customer might think is a clutch problem could be a problem with the transmission or other driveline component. Drive the vehicle at normal speeds and shift through all the gears. Pay attention to the clutch action and take note of any chatter, grabbing, slipping or improper release of the clutch. If any of these conditions are noticed, you’re going to have to remove and inspect the clutch components.

After an extended length of service (more than 100,000 miles), much of the friction material, or lining, can be worn away, causing the clutch to slip on the flywheel. This is a very common problem. Premature wear of the clutch lining can occur from extreme service operation (racing), riding the clutch (resting the left foot on the clutch pedal), or improperly using the clutch (an inexperienced driver). All three of these modes of operation can result in excessive wear and clutch slippage.

In extreme cases, some or all of the clutch assembly components can break. Just ask someone who drag races or drives the vehicle very hard. For example, fingers on the pressure plate can break or the hub can separate from the clutch disc. When this happens, the clutch is inoperable and must be replaced.

TRANSMISSION REMOVAL

Regardless of whether the vehicle is RWD or FWD, replacing the clutch is a rather straightforward procedure. Getting to the clutch can be laborious. In all vehicles, the transmission must be removed. It’s just a bit tougher on FWD cars. Let’s take a look.

The challenge that is encountered is limited access. On FWD cars with manual transaxles, such as PT Cruisers or Neons, access is restricted. If you look in a Neon service manual for clutch replacement 
instructions (Section 21), the removal procedure covers 2½ pages with several illustrations. A review of the highlights is in order.

The air cleaner/throttle body assembly, the air cleaner assembly and the accelerator and shift cables must be removed. Then the vehicle is raised and the transaxle oil is drained. Next, remove both axle shafts (driveshafts) and remove the engine braces. Lower the engine and transaxle on a screw jack until proper clearance can be obtained. Finally, with the help of an assistant, remove the transaxle-to-engine mounting bolts to remove the transaxle. Now we can service the clutch.

On a RWD vehicle, such as a Ram pickup, the task is much easier. In general, disconnect the shift and clutch linkage, remove any exhaust pipe and transmission braces (be sure the gearbox is supported before doing this), then remove the transmission-to-clutch housing bolts. Slide the tranny rearward, lowering it to remove it from under the vehicle. On 4WD trucks, the transfer case must be removed. Now we can service the clutch.

CLUTCH REPLACEMENT

A typical clutch assembly is shown in Figure 1. Mark the position of the pressure plate on the flywheel, then remove the pressure plate-to-flywheel bolts. Closely inspect the surface of the flywheel. If there are signs of damage, such as scoring or deep scratches, the surface must be refaced. Also, place a straightedge across the flywheel to check for flatness. If the flywheel face is warped, it must be refaced, too. In either case, remove the flywheel-to-crankshaft bolts and remove the flywheel.

Inspect the clutch disc for damage. Such damage can be an indicator of other problems. For instance, if the flywheel contact face shows alternating wear patterns, the flywheel might be warped. Friction material worn down to the rivets will most likely damage the flywheel.

Before installing the new clutch, inspect the release lever and release bearing (Figure 2). Be sure the bearing is not excessively worn (it should rotate smoothly if it is good). Also, if the flywheel has not been refaced, clean its surface. Clean the surface of the pressure plate, too. Neither surface should have any signs of oil, grease, dirt or rust. This is just as important as it is with brake rotors and drums. If the flywheel had been removed, re-install it, properly torquing the mounting bolts. Remember to crisscross tighten the mounting bolts to prevent distortion.Now we can install the new clutch. First, apply a very thin film of grease to the splines of the clutch disc hub. Next, position the clutch disc on the flywheel. Be sure that the flywheel side of the disc is facing the flywheel (often, the disc will be marked, Flywheel Side). Install the clutch pressure plate on the flywheel and finger tighten the pressure plate-to-flywheel mounting bolts (be sure to align the mark on the pressure plate with the mark on the flywheel). Use a clutch alignment tool to align the center of the clutch disc with the center of the flywheel, as shown in Figure 3.

After the clutch disc has been aligned, tighten pressure plate bolts. It is very important to tighten these bolts evenly and to the specified torque. Failure to do so can distort the pressure plate. Use a crisscross pattern when torquing the bolts.

After the bolts have been tightened, remove the clutch alignment tool. Apply a light coat of Mopar® High Temperature Bearing Grease, or equivalent, to the splines of the clutch hub and transmission input shaft. Be careful when applying the grease. Excessive amounts of grease can contaminate the clutch disc, resulting in clutch slip problems.