Re: Slipping Snapper
"If I turn the wheel close to the differential the opposite one turns the other
"If I start the motor with tires removed one sees that the axles slightly
turn but can be stopped easily by hand."
The ONLY link in that drive train which should be capable of soft-slipping is contact between the rubber power-collection driven disk and the motor-attached driving aluminum disk. If you can verify that you are observing soft slippage somewhere else in your drive system, that slipping link must be identified and locked back together.
Chains may jump off their sprockets, but they don't soft slip as you've described. Splined shafts don't soft slip inside steel driven rotating parts unless that section of splines has broken off from either the driving shaft or the driven part. I have a Kubota B5100D tractor with spline-shaft driven front Power Take Off shaft which slips inside the broken spline area of its cast iron driven shaft. Failures like that are EXTREMELY uncommon, so it's unlikely that you're experiencing one of those failures. Kubota was not stupid enough to select cast iron when fabricating that driven shaft, but the American subcontractor which made them so those excellent little tractors could drive belly mowers to US market buyers did make that stupid materials selection. Kubota failed to spot the error, sold mowers with those failure-prone cast iron splined shafts and never stood up and replaced every one of them as they should have done. Even that premium-priced brand sold at least that one junk-quality part and failed to issue an honest parts recall & replacement program despite the fact that they have long known those internal splines are too brittle and fragile like "glass gears."
When you get to the bottom of this little mystery, please take some close-up photos and share them with others here so we can better understand future failure issues.
Soft slipping you described still sounds like a clutch - rubber disk interface surface problem to me rather than something within the transmission cases which should be filled with grease to their level-check holes.
Walt, we need your experience-based feedback about the following potential issue. Can low transmission-case grease levels cause high friction between the internal splined shaft and the sliding input gear's splined surfaces? Frequent Snapper owner complaints about difficulty in getting the rubber disk to slide over to the reverse-spinning side on the driving disk must either be caused by external linkage or by internal transmission friction along that splined shaft. I expect some of these difficult-to-shift transmissions haven't had their transmission grease levels checked for 10, 20, 30 or more years, yet still transmit power to their driven axles! If they are running without enough grease splashing around inside to keep those splined-sliding interface surfaces wet with lubrication, wouldn't that explain why they stick & jerk while resisting shifting-linkage load rather than sliding freely all the way from full reverse position through to full-speed forward and back? Being durable transmissions, many owners probably don't check their transmission grease levels for decades. They can usually get by failing to check grease levels in rear-wheel drive automobile differentials because most RWD rear ends don't seep enough lubricant through their seals to wet their outside case surfaces. But most Snapper transmissions that haven't been recently cleaned are covered with grease film which makes them behave like wet air filters so they form increasingly-thick grease and dirt wetted surfaces. The grease wets the dirt so the attached layer keeps getting thicker as the transmission becomes less filled. I assume Snapper transmission grease is typically slowly seeping out based on these observations. Does this analysis make sense to you? Do you think low grease levels may explain many ratio-shifting difficulties?