Mr. Bill Posted July 28, 2007 Share Posted July 28, 2007 I am new to Mack and big trucks. I purchased a 1968 R 685T last year and finally got time to work on it now. It needs a clutch so I have pulled the transmission (5 speed) back and removed the pressure plate. I was surprised to see two clutch plates in there. How does that set up work? There is still only one clutch face pressed against the flywheel.The clutch shop says they need the pressure plate, middle plate, two clutch plates, and the flywheel. My problem now is the flywheel. I am not sure what they want. There are bolts around the outside of the flywheel and also in the middle there are 6 castle nuts. I tried the castle nuts but could not get them loose. Can anyone tell me what I need to remove so they can turn the clutch face? Quote Link to comment Share on other sites More sharing options...
MACKS Posted July 29, 2007 Share Posted July 29, 2007 The six nuts in the center, you might have to heat them a little if there is thread lock on them, be ready when you pull it off, it's a heavy hunk of steel, as for the clutch and pressure plate I would buy a new one get the easy peddle. Quote Link to comment Share on other sites More sharing options...
Bollweevil Posted July 29, 2007 Share Posted July 29, 2007 The six bolts in the center retain the flywheel to the crankshaft. The easy way to get them out would be with an air wrench. If you have to resort to a pull handle, you will have to find a way to block the wheel to keep it from turning. You won't realize just how heavy the flywheel is until you have to handle it. Don't get under it. For the cost differential I personally would not use a rebuilt clutch no matter who rebuilt it. A new Spicer soft pedal clutch would be my choice. A single disc clutch is just not heavy enough to stand the torque load generated by a class 8 truck. Thus you find a second disc sandwiched in the assembly. Keep in mind that both disc's have to be in alignment during reassembly. A new assembly is usually packaged in the order that it needs to be installed. Each disc has a front and rear side. With the clutch and flywheel removed go ahead and replace the pilot bearing. You will be working with some heavy parts, with sharp edges, so be careful. I use a couple of bolts with the head cut off to act as dowels until I can get the clutch mounting bolts started. Most mechanics use an old transmission input shaft to to align the clutch. Let us know about your progress. James Quote Link to comment Share on other sites More sharing options...
chris88 Posted July 29, 2007 Share Posted July 29, 2007 It seems that most new clutchs are somewhat idiot proof. The friction plates can be installed either way. If not they should be marked but just to be safe keep track of how it came in the box and put them back in the same way. When your putting it in make sure the two friction plates are lined up with each other. The hardest part of the whole thing is physically lifting the clutch and holding it up there, after that it shouldnt take much to finish up. Just pay attention to how it comes out of the box. Quote Link to comment Share on other sites More sharing options...
Mr. Bill Posted July 29, 2007 Author Share Posted July 29, 2007 The flywheel was removed safely today. Thanks to everyone who replied with information and cautions. It took about 5 minutes. The best thing was that I got to get a 3/4 inch impact. That made short work of the castle nuts. The clutch shop mentioned something about an easy pedal. I will go with that even though it costs a bit more. They will turn the flywheel and assemble the new clutch plates, middle plate and pressure plate to check for proper clearances. I will have to get the new pilot and throw out bearings.Does anyone know how these clutches work? It seems that that there is still only one surface of a clutch plate connecting with the flywheel and the second one doesn't do anything. I am missing something here so could someone please explaing.Thanks again to everyone and I am sure I will have more situations that I need advice. Quote Link to comment Share on other sites More sharing options...
HK Trucking Posted July 29, 2007 Share Posted July 29, 2007 Does anyone know how these clutches work? It seems that that there is still only one surface of a clutch plate connecting with the flywheel and the second one doesn't do anything. I am missing something here so could someone please explaing.Based on the fact that it is a 1968 R685T, I'm assuming you have the 14" pull type clutch with the "pot" type flywheel.The center plate has notches which engage with the drive pins in the flywheel, enabling the center plate to also transmit torque to the clutch discs, therefore you have twice the friction surface as you would with a single disc clutch of the same diameter.Incidentally, when you have the flywheel machined the drive pins have to be removed. When you reinstall the drive pins, use a small machinist's square and be sure the drive pins are installed perfectly straight, or the center plate will bind on the pins and your clutch may not release properly. Quote "If You Can't Shift It Smoothly, You Shouldn't Be Driving It" Link to comment Share on other sites More sharing options...
Mr. Bill Posted July 29, 2007 Author Share Posted July 29, 2007 Incidentally, when you have the flywheel machined the drive pins have to be removed. When you reinstall the drive pins, use a small machinist's square and be sure the drive pins are installed perfectly straight, or the center plate will bind on the pins and your clutch may not release properly.Thanks for the info. I guess I didn't look at it close enough to figure that part out. Makes sense though. I do remember the center plate being locked in place. Quote Link to comment Share on other sites More sharing options...
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