I took these photos a few weeks ago and thought I would add them to BigBills post.
This PTO was from a 154 that sat for several years. The PTO seemed to work well but I thought I would take it apart and give it a good look.
The PTO starts at the front side with the pulley and belts, a spherical cased self align bearing, shaft, drive cup. The clutch itself starts at the drive cup, a stack of friction discs, cam actuating mechanism, springs, rear self align bearing, splined shaft.
You can remove the clutch alone but I wanted to check the shaft bearings so I removed all the parts.
Loosen the 2 drive belts and remove from the pulley. Loosen the mower belt and remove the pulley. You may have to remove the sheet metal shield to get to the clutch. The clutch is held in place by three 3/4 inch headed screws, one 7/16 head screw holding the mount plate and clutch brake. There are two 7/16 head screws holding the stationary cam mount and a pin, spring, cotter pin for the moving cam. Once those are removed, the clutch should pull straight back and out. Loosen and remove the front bearing bolts, 9/16 inch head. Loosen the bearing cover/clamp. Take out the clamping bolt on the drive pulley, add some heat and it should slide off with some gentle tapping. Pull the shaft out from the back.
The front bearing can be inspected, if it needs to be replaced then some heat will aid the removal from the shaft.
Remove the 9/16 inch head bolts from the rear bearing and the splined shaft will slide free of the holder. If the bearing is good then leave it as is, if not, some heat will help it to slide off the splined end. I then clamp the splined end in a vise with some aluminum or a cloth towel to protect the splines, vertical, clutch upright. The clutch should be disengaged, rotate the cams to do that if needed. The top of the clutch shaft, the front, should have either a locking collar or a spiral external clip. Remove which ever you have. There should be a group of .003 inch 1 3/8 bore spacers under the clip or locking collar. Remove those. Next is a pressure plate, remove. Next is the stack of friction discs, wavy spacer washers, driven steel disc. Remove those, they should just pull off if not all rusted.
The friction disc are bimetal with a spiral groove and I believe 6 tabs. Inspect. Should be flat not bent. If you see spiral grooves then they are fine, no need to replace. If the grooves are worn smooth then time to replace. The wavy washers should have a distinct bend to act as spring spacers. Should be 2 wavy washers for each friction disc although the washers are overlapping so they may seem to be just one. Set all of that aside and pull off the lower pressure plate and the ring spacer under it. Next is the moving cam and bearing. It also should pull off but make sure you notice which way it goes on so you do not get it on upside down. Check the bearing and replace if needed. Take out the 3 steel balls and inspect. The rest is held on by an 1 3/8 inch external clip. You can spin the stationary cam which is held on by the clip. If the bearing seems OK then I would leave it as is. If not then remove the clip and the stationary cam will pop up slightly due to the large spring washers under the bearing. Remove the cam and bearing if needed to replace. There are two large spring washers concave to concave that function as the pressure spring. Under those washers is another 1 3/8 inch external clip and under that is nothing except the rear bearing and the spined shaft. End of the line.
Check the large spring washers and the two large cam bearings. It goes together in reverse order, two spring washers with the stationary cam on top. This has to be compressed for the next external clip to be installed. I slide the clip down as far as I can followed by the thick spacer. This is not where the spacer really belongs but I use it to push on the clip. A piece of pipe over that pushes on the spacer which pushes on the clip which pushes on the bearing that compresses the two spring washers. Compress with a large C clamp or gentle tapping on the pipe will eventially compress enough for the middle clip to pop into its groove. Remove the pipe and the spacer and squeeze the clip with pliers to make sure it is completely seated. Use a new clip, the old one will be ruined when you removed it. Make sure the cams are clean, place the steel balls in the grooves and place the moving cam on top. I do not lubricate since I do not want any grit being caught by grease. Thick spacer next followed by a pressure plate, wavy washer, bimetal friction disc with a steel driven disc. Keep stacking until done. Pressure plate on top, spacers, either a locking collar or spiral clip. I do not use the spiral clips but just use another external clip. Adjust by either moving the locking collar or by adding/removing the thin spacer shims. When done, the movement of the pressure plates from open to closed should be 0.05 inched. Measure with a caliper.
Inspect the drive cup. If the grooves are worn with ridges then file/grind until smooth. I place the drive cup on the clutch and inspect the bimetal disc tabs and the drive cup grooves. all the tabs of a disc should touch all the drive cup groove sides together so one tabe does not take all the load. If not, the remove the cup and file/grind as needed.
Make sure there is no grease in the area of the needle pilot bearings or the clutch will not slide fully onto the shaft. A thin coating of grease is needed on the needle pilot bearings but none on the shaft or hole.
Slide the shaft into the tractor without the clutch installed. Put the pulley on the shaft and do not froget to place the belts. Do not tighten the belts yet. Place the bearing into the carrier and loosely tighten the bolts to reduce front to back movement but still allow side to side and up to down movement needed for alignment. Slice the clutch into the end of the shaft, you will need to hole the bimetal discs to get them to align and slide into the drive cup. Install the rear mount 2 bolts, do not install the 3rd 3/4 head bolt or the 1/4 inch bolt on the PTO brake. The rear bearing carrier should be in position, loose not bolted into place. Now tighten the two 9/16 head bolts on the front bearing carriers. Pull and push the spined shaft forward and back. It should move forward and back 1/8 of an inch. The 1/8 inch freeplay keeps the PTO shaft from pushing against the inside of the clutch shaft. If you have the 1/8 clearance, the tighten the rear carrier bolts, If not, move, slide, the rear bearing as needed to obtain the clearance. Too much clearance and you may damage the clutch shaft, too little and the clutch will not release. You can then attach the brake plate. The clearance between the rear pressure plate and the brake puck when engaged should be 0.04 inches. Attach the lever, cotter pin, spring and you should be done. Clamp a pair of visegrips on the PTO shaft behind the pulley to keep it from moving. The splined shaft gets two 1/8 inch Allen wrench shafts in the spines. This will allow a 15/16 socket to fit over the spines along with a torque wrench. The clutch should not turn with 80 ft.-lbs. of force applied to the wrench. Tighten the belts and you are done.
Measureing difference 0.05 inches between locked and unlocked
Unlocked, the friction discs should be freely movable
All tabs touch the drive cup slots equally
The pilot bearings (2) are Torrington B1212 bearings, the support bearings are Fafnir RA 102, the cam bearings I believe are SKF 6007 2rs1n but we need to verify that number.
The support bearings are also stocked by the Surplus Center for around $6.00 each which is where I got mine.
1 3/8 external clips, 1 3/8 wavy washers, 1 3/8 spiral clips are all at McMaster-Carr.
Some key points:
The front to back free play of 1/8 inch is important.
Spiral grooves on the friction means the discs are usable, no need to replace.
The cam should lock hard, if you can easily pull and lock the cam then it is too loose.
Grease the fitting on the rear of the clutch shaft, it actually greases the pilot bearings but don't do it until you have already assembled the clutch on the tractor.
Alignment of the front and rear bearings is important, do not tighten the carrier bolts until aligned.
Do not tighten the belts until the last step. doing so early will affect the alignment of the support bearings.
The clutch will work with a little oil or greasy on the friction disc since it was made for either wet or dry so do not sweat some greasy finger prints on the facings.
The clutches are well made and if assembled correctly, adjusted correctly, they will work well. I expect most of the problems are from improper adjustment or assemble. Likely there is little true need to "rebuild" the clutches that were rebuilt.