So.... why? It's not like I spend hours in reverse, but I would rather not have my teeth shaken loose every time
Contaminated or dirty clutch friction surfaces plus sometimes a clutch disk with soft or worn center springs with let the old glazed or lightly contaminated clutch facings chatter and grab-slip, grab-slip, grab-slip at a very fast rate even tho it doesnt look like a wornout disc. Ive seen soft center springs make probs. It can really hammer the whole car no matter how much you try to feather it. that can happen in either direction or only one. Since reverse gear has the lowest gearing of all the gears, it often shows up there first, or at least hammers the worst. I cured a few of my cars with a fresh disc with heavy duty rating, which usually means simply stiffer center springs try to keep them clean and dry, or that could change the friction characteristics and encourage a return of the prob sooner than you want. and oh yeah... I've been rough enough in the past to collapse the center springs on fairly low mileage standard discs on a dirty flywheel , and sometimes no matter how careful I was, it acted like it was going to knock out the back window when I carefully tried to back up. out comes the clutch again for a new disc with stronger springs, and a thorough clean up and degreasing of everything... then I'd go for years without it coming back. WHY BE ORDINARY ?
broken brake hardware? shoe wrapping drum. does it have a center driveshaft carrier bearing? I have seen them do that when worn/broken.
Could be a leaking rear main getting oil on the clutch, could be motor mounts, could be rear spring bushings. You need to put it up on jack stands and get under it and look. It amazes me that you post and never mention that you checked anything. It sounds like clutch chatter. Does it only do it in reverse? Have you checked to see if the frame isn't cracked somewhere. It sounds crazy , but when I worked for the Govt. we had a bunch of 1986 Caprice police cars that the frames cracked right in front of the right rear wheel and we had to cut a section of floor out to weld the frame. Then weld the floor back in. Have you checked the body mounts ?
RE: never mentioning checking stuff: yeah, I work second shift and usually don't spend any daytime hours during the week doing anything but staying out of the sun until it's time to clock in! Weekends are when I do stuff on the cars, and, unfortunately, this weekend is pretty much ruined for that. Frame doesn't show any of the damage you mentioned, I have spent a lot of time poking around under it. Haven't checked the motor mounts, and, no, it only does it in reverse. Springs, bushings, etc look good. Idles kind of high IMHO and that might add to the mystery. I don't like the floor shift at all; it's too far away from my hand when the seat is comfortably adjusted. I'd rather put the levers back and have 3 on the tree, but the PO shitcanned those parts.
one of the clutch disk I've broken was doing this in reverse and sometimes in 1st, but mostly reverse. Made a clock out of it, haha!
I did damn near the same thing in my old Power Wagon , it has a 4bt Cummins , they do not stop as soon as the key is turned off . I would have it in 1st gear turn the key off and let out on the clutch to stop the engine . This abuse blew 3 out of the four hub springs out . Never saw this happen until mine , but I guess it must happen more than I have known . About the chatter , as stated , worn springs are not your friend on a heavy car or truck . Lots of clutch issues can be traced to weak springs and shocks , bad bushings maybe all the previous thinking . Have someone watch to see if you are wrapping the rear suspension terribly while backing is where I would start .
If it's as severe as you indicate, I'd bet motor mount too. Then I'd get under there, pull the cover, and get an eyeball on things. If there's signs of seal leakage, you know what eventually has to be done. Brake-Kleen & Ajax can band-aid it for a while. If it's dry, probably time for a clutch kit.
Last car that I had that did this was fixed by resurfacing the flywheel. Now when going to that much trouble you put in a new clutch also so cause and effect? I don't know. It's an old car........if you can find nothing broken, I'd do the above.
May be a stretch but check for loose or missing spring clamps on the backside of the spring while your looking around. Just a thought.
Weak rear springs. add a leaf or two and cure your trouble? I drove a 62 that wheel hopped and it was the rear springs. You might want to check the pinion angle possible that the rear U joint is binding?
I put a turbo diesel in my 46 Willys as well, 2.3L Kubota. Since then I've broken 2 clutch disks, but the motor always turns off instantly. I have a larger pressure plate and clutch disk ready to go on there, hopefully that fixes it. That little factory style clutch disk wasn't meant for diesel torque, haha!
Mine was a 12 inch Disc , Borg and Beck Pressure Plate from a 440 gas engine . Second clutch is fine now that I have stopped using the clutch to stop the engine , monetarily running on is Cummins issue . Later models than mine have a chirp from the alternator once the key is turned off .