Frequently Asked Questions

In many cases the noise is not caused by the release bearing, in fact, it may not be a bearing in the clutch system at all. It could be coming from the transmission. There is a simple inspection that can assist you in determining where the problem lies before you begin to pull the transmission. Once you understand at what point certain bearings are rotating you can identify which bearing is creating the noise.

Start the engine and place the transmission in neutral. Place both feet on the floorboard. If you hear the noise at this time there are two possibilities. The noise is coming from the transmission, or the clutch release bearing is in constant contact with the diaphragm of the cover and it is creating the noise. Shut down the engine and inspect the free play adjustment of the clutch release bearing. Generally, the free adjustment is between ½ inch to one inch, but it is best to refer to your vehicle manual for the exact specification. If the bearing adjustment is correct, or after readjusting the free play setting the noise remains while the engine is running and the transmission is in neutral, the problem is not in the clutch system at all. Most likely in this event, you should look toward the transmission as the culprit.

If after the engine is running and with the transmission in neutral you do not hear the noise, place your foot on the clutch pedal and partially depress. If after depressing the clutch pedal you begin to hear a noise, the problem is the clutch release bearing. It is at this point the release bearing begins to rotate as it comes in contact with the diaphragm of the cover.

If you do not hear a noise at this point, depress the clutch pedal to the floor. If you now hear a noise, then the problem is in the pilot bearing. The pilot shaft of the transmission does not rotate in the pilot bearing until the clutch pedal is fully depressed and the engine and transmission are rotating independently of each other. Once the clutch pedal is released the pilot shaft and the pilot bearing are locked up together and there is no rotation of the shaft in the pilot bearing.

Not always, sometimes the problem is the adjustment of the mechanical linkage or cable, especially if the clutch system in the vehicle has very low mileage. If your customer is complaining of clutch slippage, usually they have prepared themselves for a $300 to $700 dollar repair bill. If you can solve the problem with a simple adjustment, you have saved them money, and added a value that they will not soon forget, "trust in your product or service to them."

When a new clutch cover and disc are installed, the disc varies from 3/8 to 1/2 inch in compressed thickness depending on application. As the cover assembly mounting bolts are tightened, the diaphragm (or levers) move closer towards the center of the clutch disc. As the vehicle is driven, the friction material wears and becomes thinner. As material becomes thinner, the diaphragm (or levers) of the clutch cover moves away from the center of the clutch disc toward the clutch release bearing. If the free play adjustment is not maintained the diaphragm (or levers) will come in contact with the bearing and pressure will be applied to the diaphragm. This will reduce the clamping pressure applied to the clutch disc and will allow the disc to slip under a load. Depending on how long this condition has existed a simple adjustment can correct the problem.

If the vehicle has a hydraulic release system the same condition can occur. However, in this case a simple adjustment may not solve the problem. Some hydraulic systems have an adjustment and some do not. If the hydraulic system does not have an adjustment on the slave cylinder, that system is designed so that when the diaphragm moves closer to the clutch release bearing the fluid is forced back into the master cylinder reservoir. The master cylinder has special valves, which permits this fluid to return.

If the master cylinder is not allowing the fluid to return to the master cylinder reservoir, pressure is applied to the diaphragm and the disc slippage will occur. A quick check can determine if this is the problem on vehicles with an external slave cylinder. Unfortunately with an internal slave cylinder system removal of the transmission and bell housing are necessary.

To complete this test you will need some assistance. If the hydraulic release system has an external slave cylinder, you can push the rod inward toward the slave cylinder. Have someone remove the top of the master cylinder reservoir and look for the fluid to return to the reservoir. If no fluid returns to the reservoir the master cylinder should be replaced.  

I have seen defective returns to the manufacturer where the cushion segments of the clutch disc have completely broken off of the disc hub assembly, and the failure occurred almost immediately after installation. Most of the time this is an alignment problem, not a defective unit. The rotating axis of the clutch disc does not match the rotating axis of the flywheel and pressure plate. The disc is rotating in an elliptical pattern, placing stress on the very thin cushion segments attached to the disc hub. As the disc rotates, on each side of the elliptical pattern the cushion segments are bent forward and then backward. In a very short time they break.

If you can imagine taking a piece of tin bending it one way, then the other, back and forth until it breaks. This is the same condition caused by misalignment.

The causes of misalignment are several. The most common cause is related to the transmission input shaft not being supported correctly. A worn or missing pilot bearing will allow the input shaft to wobble side to side and up and down creating the elliptical rotation pattern. A worn transmission input shaft bearing creates the same condition by not supporting the shaft on the opposite end.

We see this condition frequently with vehicles that were not equipped with pilot bearings, such as some Honda and Mitsubishi applications.

In some cases, the transmission is not in alignment with the engine. Broken motor mounts or transmission mounts can create this condition.

What you are experiencing is a partial release of the clutch system. As you depress the clutch pedal and push it to the floorboard the clutch disc is in slight contact with either the flywheel, or the pressure plate, or both. There are several causes of this condition.

Here again, alignment of the engine and transmission can cause this problem. Check the engine and transmission mounts. A warped bell housing will create misalignment of the engine and transmission.

Excessive free play adjustment can cause this condition. If the position of the clutch release bearing is too far away from the diaphragm of the cover when the clutch pedal is depressed, there is not sufficient travel to fully release the clutch disc.

If the vehicle has a hydraulic release system, there could be air trapped in the hydraulic lines. Because the placement of some clutch master cylinders are mounted in a downward angle, it is very easy to have air bubbles trapped in the reservoirs. Ford has issued technical service bulletins on this subject. Bleeding hydraulic systems is becoming more difficult, and we are seeing more hydraulic systems on vehicles in each model year. The best technique to bleed the clutch hydraulic' that I've used is the new "Reverse Fluid Injector" systems. Almost all of the new clutch manufactures are offering these tools as part of the product line. If you are a professional installer it is a good investment.

If you are putting a clutch in your own vehicle and do not have access to one of these RFI tools, here is a "Tech Tip" that may help you bleed your system. Depending on the position of the master cylinder on the vehicle, raise either the front of the vehicle or the rear of the vehicle. The purpose is to raise the slave cylinder higher than the master cylinder. When you bleed the system with all wheels on the ground you are attempting to force the air bubbles downward through the hydraulic lines and out of the slave cylinder. Air bubbles; naturally want to rise to the surface. You are working against nature to attempt to force air bubbles downward. By raising one end of the vehicle so the slave cylinder is higher than the master cylinder you are forcing air bubbles upward.

Another potential cause of this condition is firewall flex. In some applications the mounting position of the master cylinder on the firewall has created a problem with the firewall flexing as the clutch pedal is depressed. Any flexing of the firewall will reduce the amount of pressure applied to the master cylinder, reducing the travel of the release bearing. The only solution is reinforcement of the firewall area.