How to Adjust a Clutch in a Semi Truck

The first thing you need to do is remove the inspection cover plate from the bottom of the transmission's clutch housing. Take a rag and wipe the loose grease out of the housing. Now check the grease clumps for any pieces of metal(clutch springs).

Hopefully you didn't find any metal in the grease of clutch housing, but it you did that means you need a new clutch!! Lets say the clutch is ok. Your next thing to look for is the adjuster bolt on the clutch. Make sure the adjuster is at the bottom were you can reach it with a socket and ratchet.

With your buddy in the truck, have them push the clutch pedal all the way down to the floor and hold it there. Take a 5/8" socket and put it on the adjuster bolt head. Push on your ratchet with a screwdriver or pry bar. While pushing in turn the adjuster bolt to the right(follow the arrow on the clutch plate). Just turn a couple of turns at a time. NOTE: once you start to turn the bolt stop pushing on it so it can lock at the next lock position.

After making a couple of turns and the bolt has "popped" back out to the lock position have your buddy let off the clutch pedal. Take a long(about 3 of 4 inch long) bolt with a 1/2" head on it and put it between the clutch brake and throw out bearing. If the bolt head fits in there loosely then the clutch brake adjustment is were it needs to be.

Now you need to check for "free travel" in the clutch pedal. On a Peterbilt 379 it should be about 2 to 2 1/4 inches of movement before there is pressure on the pedal. On all the other trucks out there you will need to measure it at the throw out bearing and clutch fork. There should be about 1/8" between the bearing and fork.

If you need to adjust the free travel in the pedal all you need to do is adjust the clutch linkage under the cab or at the firewall.

Now you are finished and ready to go trucking!!!