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379 Clutch Adjustment

69K views 33 replies 10 participants last post by  Mr. Haney 
#1 ·
Just had a new clutch installed (buddy couldn't find the time to help me do it). The shop didn't completely adjust the linkage because the cab was sitting crooked due to bad cab mounts (which I replaced). The clutch is already within spec in regards to proximity to the throwout bearing (about 1/2" between the two with pedal released according to my service manual). All I need to do now is the linkage, but I want to make sure it's done right. Am I supposed to adjust the linkage ends or just set screw and jam nut near the cross shaft? Any suggestions are welcome.
 
#2 ·
Loosen both lock nuts and turn the long hex adjusting sleeve. It has reverse threads on one end. Every Pete I ever adjusted seemed like the sleeve was almost too short. A longer hollow pipe with welded nuts on either end worked great.....have to find one left thread nut though.
You'll be lucky if the threads are not siezed on the alum sleeve.
 
#3 ·
Sled got it down right, but it you are having to adjust linkage then the clutch is not adjust right. You should never have to move your linkage to make a new clutch work.
 
#4 ·
:whs

The only time to adjust the linkage is for setting the brake....which is usually not touched after the factory. But if you must, adjust brake first, then set the free travel with the pressure plate.
 
#6 ·
You adjust the linkage to stop the pedal about 1/2 inch off the floor to touch the brake. Then you adjust free travel with the pressure plate to gain 2-3". Not sure what you mean by set screw/jam nut. You have to roll the engine around until the adjuster on the pressure plate is at the inspection hole on the bottom of the clutch housing.

Depending on what type clutch you have, some have a bolt holding a lock in place, or it could have a 5/8" spring loaded bolt you have to push and turn to adjust free travel. ALL pressure plate adjustments are made with the clutch pedal depressed.
 
#7 ·
Yes I had a truck with the set screw/ jam nut on the clutch arm and I used that for the free travel adjustment if needed after setting the 1/2" gap with the pressure plate. If the clutch brake isn't set at the height you want it you will have to adjust the linkage, but after you get it set you should never have to touch the linkage again.
 
#12 ·
Being sure there is free play at the bearing is why there is a spring on the linkage, to take out all, the slack.
First be sure the clutch break is working, The tangs are not broken and the clutch is not dragging. I set the bearing clearance to 1/2 to 9/16 on a Pete. 1/2 on a Freightliner conventional. I reposition, drill new holes, the linkage on the Cab overs to get the correct settings. Then I set the clearance to the floor. The free play is what is left, as long as it is not extreme. 1.5 to 2 inches is normally left.
 
#13 ·
Still not sure why you would adjust the linkage, if the clutch is adjusted properly there should never be a need to move the linkage from the factory setting, and if you have to it is most likely time for a new clutch.
 
#14 ·
Many Many people play with the linkage and except for wear you should not have to adjust it except to repair a faulty unit.
Their is also a lot of things that need inspecting If the linkage is out of adjustment cab mounts, motor mounts, bushings loose pieces.
Same if the clutch needs a lot of adjustment. That is usually caused by a driver that keeps his foot above the clutch, their is a fix for that also, remove the rubber, drill the pedal and put a 1/2 inch bolt in it with about 1/2 inch of thread sticking up normal clutch operation the driver will not have a problem. If he leaves his foot on the pedal it will feel like it is burrowing a hole in his foot. In a week he is cured.
 
#15 ·
I'm still lost on this one fellas. The clutch is brand new, as is the clutch brake. If the clutch and brake need no adjusting being that they're new, then why does the pedal sit almost halfway down to the floor? What should I be doing to address this?
 
#16 ·
It does not mater if it is new you first adjust the clearance between the bearing, brake, and cover, Then you adjust the linkage. If the linkage is away out of adjustment you will have to adjust it first to get the pedal travel to adjust the clutch. When all is right you should have 1/2 to 9/16 clearance. around 2 inches free play and with the brake fully compressed about 1 inch to the floor.
Some linkages you have to pull the pin and adjust the linkage, some have the adjuster at the cross shaft. That has a 3/4 inch lock nut and a 1/2 inch adjuster bolt.
Be sure you grease the cross shafts, linkage, and bearing.
 
#19 · (Edited)
I disagree.... You adjust the linkage FIRST....for the brake.....THEN adjust the presure plate to achieve the proper free travel. Pay attention people......if his pedal is stopping off the floor 1/2" and is hitting the brake, but he has half a pedal of free travel, it was simply adjusted wrong. Hold the pedal down, push in the 5/8 bolt and turn it counterclockwise about 2 turns and check the free travel.... John if you adjust free travel first, then the linkage, it will change what was just adjusted for free travel.

It's not brain surgery.....
 
#18 ·
The perfect clutch adjustment issssssssssss

1/2" -9/16" between the clutch brake and throw out bearing.

The second adjustment isssssssssss 1/8" between the clutch fork fingers and the throw out bearing

Here is a link to a video at RoadRangers website that shows you exactly how to install and adjust a clutch after an installation

http://www.roadranger.com/ecm/idcplg?IdcService=GET_FILE&dID=281970
 
#20 ·
The free travel of the clutch pedal in the cab has no correlation between whether the clutch is adjusted correctly or not.

Free travel is determined by each individual OEM truck manufacturers engineers in designing the clutch linkage between the cab and transmission. The free travel in the cab has nothing to do with whether or not the clutch and it's linkage is adjusted properly. Once the clutch is adjusted as done in the video, the amount of free travel left..........is...... what it is. If you have a problem after the inner and linkage adjustments are made correctly to achieve the measurements listed above then you have a problem in the truck(worn linkage, cab mounts)........not the clutch

Every Peterbilt 379 I've adjusted the clutch using the method shown in the Eaton/Spicer/Dana/RoadRanger video will have roughly 2 1/2" to 2 3/4" of free pedal travel in the cab with a new clutch, clutch brake, input shaft bearing housing cover, clutch fork cross shafts, cross shaft bushings, clutch release fork, clutch swing arms linkage, clutch swing arm cab pivot pins, military/aircraft spherical bearings on all rods and NEW flywheel. As you can see from my list everything is new with the linkage and internals inside the flywheel housing, so wear can't affect the measurements I've listed as pedal free travel in a 379 cab.

Watch the video, it was made to correct the problems with improper installations and improper adjustments made by supposedly trained mechanics everyday

John is correct in his method of adjusting
 
#21 ·
To each his own, I guess.
I've done the linkage first, then the pressure plate for over 20 years.....whatever works.
 
#29 ·
What I use as a gauge is two 5/16 bolts long ones held together with a nut.
It has worked for me for years.
 
#30 ·
There is only one way to do this properly. The first thing you do after the new clutch is installed is to verify there is 1/2" clearance between the throw out bearing and the clutch brake...don't worry about the linkage at this point. This insures that the clutch itself is physically adjusted properly. If it not 1/2" after installed, then adjust it so it is and leave it alone. Next would be to check the linkage. You should have 1/8 inch gap between the forks and the throw out bearing. If you don't then adjust the linkage to get this. If you do both of these things in this order everything will be right. Any time you adjust the clutch after this you will be putting it back to the 1/2" gap you originally started with. If you do the linkage first and then adjust the clutch to get the desired freeplay, you can't possibly know where the clutch is actually adjusted. Too tight and it could still want to drag a little and act like the clutch brake is not working properly. Too loose and it could slip. The 1/2" sets the proper spring pressure on the pressure plate, as is wears you get less freeplay and less spring pressure, that's why it slips. These instructions are directly from Eaton and is the way we do it at the truck shops where I am the shop manager.
 
#31 ·
That is right BUT with a Peterbilt doing it at 1/2 inch you end up with either a lot of free play or a lot of pedal from the floor clearance.
That is what you want but many different units need different settings.
 
#33 ·
That is what I said, but on a peterbilt that would give you a lot of clearance to the floor. On some cab overs you would have no clutch brake.
 
#34 ·
The measurements on the throw out bearing are the only way to properly adjust the clutch. Pedal free travel in the cab is a by product of the OEM truck builders design and how much leverage is built into the clutch linkage swing arms. The Peterbilt 379s has a design that gives you a large amount of free travel, but at the same time it has more leverage built into the linkage for a softer pedal effort. In a Pete 379 with a Spicer Easy Pedal clutch rated at 2050 ft-lb of torque, the pedal effort is so low that you can easily depress the clutch pedal with your hand while standing outside of the truck on the ground. Now KW doesn't have as much leverage built into the linkage and has a much higher pedal effort to depress the same clutch, while at the same time only less pedal free travel. The 379 will have roughly 2 5/8" to 2 3/4" of free pedal travel in the cab, there isn't anything wrong with this, if the clutch brake doesn't work properly after setting the measurements at the throw out bearing than you have issues with worn clutch linkage or linkage bushings, worn input shaft bearing cover or a flywheel that has been machined too thin
 
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