15 Oct Clutch Adjustment Tips

There are a few things to keep in mind when doing a clutch job on your heavy-duty truck. When you remove your old 15.5″ clutch and find that it’s an 8 spring, measure the flywheel bore, if it’s 8.5″, stick in a 10 spring in its place. I always go for the 10 if it will fit, on some flywheels the bore may only be 7.25″ and you’ll have to stay with the 8 spring clutch.

If you find the flywheel bore to be 10″ and you pulled out a 10 spring, install a 7 spring in its place. Mack engines will often have a 9 spring, so check for that. Count the paddles on all clutches, if you take out a 6 paddle, install a 6 paddle. The 6 paddle is often run in the higher horsepower, higher torque motors. Some may have a 6 spring, 6 paddle VCT clutch, if that’s the case replace it with the same VCT 6 spring – 6 paddle.

And remember to resurface the flywheel, replace the rear engine seal if seeping or leaking is detected, you may want to pop the seal on your new pilot bearing and see how much grease is inside, it really varies from bearing to bearing, sometimes there’s very little inside and it will fail within a years time, if low top it off with synthetic grease. After installing the flywheel, measure the distance from the friction surface to the bolt flange on the bell housing to determine which clutch brake to install the standard or .500 thick brake.

Replace your cross shaft bushings and fork, replace the cross shafts if you can see or feel wear, check the input shaft at the pilot bearing end with a new pilot bearing for wear, check the splines for torsion grooves, replace if needed. If grease tubes are not already installed on transmission, install them right and left, install one on the clutch release bearing and any of the clutch linkage pivot points that have zerks. Also, inspect the clutch linkage system and replace any worn components.

Some things to keep in mind about your clutch, always maintain your clutch pedal freeplay. Keep your left foot from resting on the clutch pedal. Always start the vehicle in the proper gear.

Use the proper gear shifting procedure and avoid slipping the clutch. Excessive rpm created by coasting will destroy a clutch. Never engage the clutch while coasting.

How Often Should You Check Your Clutch?

Save yourself downtime and costly repairs, have your clutch checked out every 30,000 or once a year whichever comes first and have the ring adjusted, even if it doesn’t need it, do it anyway don’t wait till the free pedal is gone. This is very important on the easy-pedal because of the tooth type adjuster.

Don’t Abuse the Clutch Brake

Used only for initial takeoff, many push the clutch pedal too far when coming to a stop or when shifting and eat the clutch brakes up, a lot of trucks have a removable brake in them because the ratcheting type you have to torch out.

Avoid vehicle – clutch overloading, and never use the clutch as a brake. Never apply the clutch brake while the vehicle is moving. Report erratic clutch operation promptly.

If you are running more than 400 horsepower make sure you have at least a 10 spring clutch installed, better than that is to always replace with the manufacturers’ specs to save yourself downtime and breakage.

And remember: always have your flywheel resurfaced during a clutch installation.