Clutch Slippage On 1968 Cf-600 With 5 Spd. Manual Trans

[AvantiBob]

Hello All,

I am having problems with the clutch on my 1968 Mack CF-608 Fire Truck with 5 speed manual transmission. It is slipping and all of the adjustments seem to be "all the way out". The clutch assembly lever is actually hitting the transmission mount and there is a grove that has been cut into this mount. I was hoping I could loosen this lever from the clutch release shaft, move it a few degrees (counterclockwise)and use the clutch adjustment lever to fix this problem (or is the fact that this clutch assembly lever is hitting the trans mount telling me it is time for a new clutch?). The truck will be used for a ranch fire truck, water delivery truck and will rarely see action on the open highway. The fear I have is releasing the clutch assembly lever from the clutch release shaft (in the trans) and not being able to reposition it. There seems to be tension on this clutch release shaft (tension I believe is coming from springs in the pressure plate). I can adjust the lever to remove most of that tension, but again do not want to remove the lever and not be able to replace it back onto the clutch release shaft or have some internal springs explode, creating a bigger problem. I am also fearful that since this adjustment is all of the way out and the lever is hitting the trans mount it is telling me time for a new clutch (did Mack put some type of fail-safe into this clutch adjustment to prevent people from adjusting a clutch that needs to be replaced, before the rivots hit the flywheel?

Last question, how much would I expect to pay for a clutch, pressure plate and other components needed for this repair. The person buying this fire truck is a boat expert, I restore classic cars and together can do the work. Any idea on the cost for parts and what parts should be replaced (since we have the trans out).

Your help would be greatly appreciated!! Thank you in advance!!

[Firemack]

Bob,

I replaced my clutch pressure plate and throwout bearing last year (I actually had them relined etc. as they don't build new ones or rebuilt for 1954 trucks!). That cost was about $600. However if your trans is similar to mine- the clutch cross shaft has a fork on the throwout bearing that has and grooved shaft at the end of the shaft and a adjustable fitting with a pinch bolt to hold it in place, you can loosen the pinch bolt, slide the fitting off and move it one or two grooves in the direction needed to get the shaft to move the throwout bearing closer to the pressure plate and that could solve your problem as it may have been adjusted incorrectly. It could be that after you adjust the position of the fitting there is no more play and then you know you need to replace the clutch.

I would recommend that you also get a copy of the drivers manual for a CF that will provide proper adjustment for the clutch. ( this is explained better in the driver's manual than in the shop manual). This way you can see where the fittings are in the original factory settings and make sure that they are installed correctly to start.

There is also an adjustment bolt on a roller bearing that also needs to be adjusted so you have both a rough (move the fitting) and fine adjustment (adjust the bolt) that can be used to get the clutch to work nicely.

Good luck and keep us posted on your progress,

Firemack

[chris88]

How much free play in the clutch pedel do you have on the truck now?

[AvantiBob]

Answer to Chris,

The adjustment lever is hitting the transmission mount, so the clutch is actually not fully engaging. We have tried to adjust the clutch play, and still cannot get it fully engaged due to the problem with this lever. When the clutch is adjusted fully out, there is a little play, although the clutch engages when the pedal is almost completely out. With the lever hitting the mount, we cannot actually do anything with the clutch play, since whatever we do in the correct direction to adjust it is nullified be the lever hitting the mount (there is not enough room to fully engage the clutch). The question is can we move that adjusement lever a few degrees, giving us room to fully engage the clutch plate, then the pedal adjusment (play) can be dealt with. I hope this better explains the problem

[Rob]

Answer to Chris,

The adjustment lever is hitting the transmission mount, so the clutch is actually not fully engaging. We have tried to adjust the clutch play, and still cannot get it fully engaged due to the problem with this lever. When the clutch is adjusted fully out, there is a little play, although the clutch engages when the pedal is almost completely out. With the lever hitting the mount, we cannot actually do anything with the clutch play, since whatever we do in the correct direction to adjust it is nullified be the lever hitting the mount (there is not enough room to fully engage the clutch). The question is can we move that adjusement lever a few degrees, giving us room to fully engage the clutch plate, then the pedal adjusment (play) can be dealt with. I hope this better explains the problem

I believe the end of the "throwout shaft" should be splined, or indexed for proper mounting of the arm you speak of. It sounds to me that someone placed the arm into the wrong set of splines, or the arm or assembly is incorrect for the application.

Rob

[Firemack]

Rob,

I agree, I think that is the problem. If he loosens the pinch bolt and adjusts the end so it is in the position to allow it to engage without interferance then he can adjust for the proper freeplay.

Firemack