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Nylon Coupling Purpose?


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What is the purpose of the flexible nylon coupling (washer) on each end of the drive shafts? In other words, why is this setup used instead of automotive type universal joints? Cost perhaps?
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Those are fiberglass disks. They are cheaper, easier to install, have very little weight to eliminate balancing problems, they have no moving parts, no bearings to go bad, and probably a couple other reasons. The driveshafts run close to a straight line between the engine and transaxle. These disks have a smaller working range than a U-joint, but are capable of taking the torque of a garden tractor engine thru an angle of 5 - 6 degrees or maybe more without problems. This small amount of angular flexure keeps the disks below the bending threshold that would creating a low-cycle fatigue problem. I have run them with that much angle on applications in the past without any problems. In my opinion, an automotive U-joint would be a tremendous amount of overdesigning in this application. I like the flex disk setups and have never had a problem with one. I converted the rattle disk couplers from my 61 Wards to the fiberglass flex disks about 18 years ago, using well worn disks from an AC716H. They are still in use, even after two more engine changes and look the same as they did when I first installed them.
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Hi, The disc is a fiberglass product with excellent strength. Two issues come up with the cross type u-joints. One is they have a significant reduction in MTBF (Mean time between failures) when they are installed in an application that is in almost perfect alignment. When the shafts are out of line and the joints turn the needle bearings roll and the races remain smooth. If the shaft is in a straight application, the crosses never move and the needles wear indents in the cups and the cross shafts, because the needles never move. The joints become stiff and don't function. Regarding the rubber tire type joint, they need an extension on the shaft into a bushing to keep them centered, or the rubber lets the shaft flop around SHAKE and it will tear the rubber and fly out at 3600. I am working on a drive shaft problem right now because a vendor to Simplicity has ceased making a part. It is a critical problem to me, and when we get it resolved, we may provide a replacement solution for people that need the NLA part. Al Eden
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Back when I was growing up using a B-10 FDT, the coupler for the driveshaft was actually two metal disks with rubber sandwiched inbetween. One was mounted to the engine side, the other to the BGB side just like the fiberglass disks. How do I know this? During one day of cutting back in the 1970's, the old B-10 was making more noise than usual. At the time I went inside and got my old stereo headphones to cut down on the racket so I could finish the lawn. On my way back to the shed, the disk on the engine side let go. To say I was surprized was an understatement. Made one heck of a racket by the time I shut it down, which was almost instantaneously. When we went to order replacement couplers, they gave us a kit including the fiberglass disks and spacers to make up for the difference in thickness between the old style metal-rubber-metal coupler and the new fiberglass disks. So far, I've never had a fiberglass disk fail on me.
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