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[date: 2014-06-15]
Final teardown occurred today, on my 1943 Farmall M.
The final stumbling block was the nut on the countershaft. This nut keeps the countershaft correctly positioned front-to-back in the transmission, and due to the slot cut in the nut, it drives the hydraulic pump. However, what worried me was that as the pump is driven, the nut is torqued tighter and tighter. This tractor is 70 years old -- how stuck might this nut be? I'd already tried to remove the nut by slipping a long 3/8" driver extension in the slot and jumping on it. (As an aside, it is possible to slide several of the upper sliding gears so that it binds the countershaft and prevents it from rotating. This is very useful when the tractor is mostly disassembled, when it's not possible to use the engine or brakes to prevent the transmission from turning.) But regardless what I did, the nut refused to budge. The extension wanted to pop out of the slot, or bend.
I was tempted to weld a nut onto the countershaft nut, and use an impact on it. However, I prefer to not destroy components while disassembling. With a 70-year old tractor, it's not always possible to replace parts with new.
Instead, I modified a socket to have a 1/2" wide "paddle" on it, which engages with the slot in the countershaft nut. The sacrificial socket was a 1/2" drive, Chinese-made 10mm socket. For once, the fact that a tool was Chinese-made worked to my advantage! The sockets in this set were all cut from the same diameter stock (rather than stepping down like my Craftsman set, which enables them to fit in smaller places). The relatively small nominal size, combined with the large diameter socket stock material, left some very thick walls. This gave a lot of material to weld the 1/2" paddle into.
After the nut is removed, pound the countershaft towards the rear of the tractor with an aluminum drift, until both bearings disengage. To get the countershaft out, the rear bearing must be pulled off the shaft, then the front of the shaft can be lifted up and out.
If the rear bearing can't be eased off, try using a gear puller. Certainly, I wouldn't want to simply pull on the bearing unless you intend to replace it anyway -- you will likely strain it until it is out-of-round. But if the inner race is not frozen, you may be able to spin the bearing off with a gear puller, which is gentler than beating on the inner race. Snug up the gear puller by hand, then spin the bearing and puller arms so that it "climbs" up the gear puller's main shaft. This is applying even pressure so no single ball and no single spot on the race is overly stressed.
This worked for my 70-year-old tractor which appears to have had the transmission opened only once, and has had water in the transmission. Still, it came off. If yours won't budge with gentle coercion from a puller, try tapping around the inner race with a long screwdriver.
While disassembling my tractor, I briefly (and foolishly) considered whether it was worthwhile to remove the reverse idler. **Yes, remove it.**
The idler spins on a stationary shaft. The idler is lubricated internally with a brass lining. The brass lining has channels groved in it that pull oil towards the center of the shaft.
Interestingly, the oil is fed into the idler shaft from channels forged into the side of the frame, which are in turn fed from what the main gears throw off. One might hope this is the cleanest possible oil, because the sediments ought to sink rather than get flung. And yet, if trash does get flung into these channels, there is _no escape_. It will get fed into the reverse idler oiling system, for better or worse.
The oil collector bore in my tractor's idler shaft was **packed with gravel**. Seriously, look at this image. The largest rock was the same volume as a misshapen pea.
Gravel from oil collector bore
If the trash fed into the oiler bore is small enough to get pulled into the channels in the brass, it will eat away at the brass. If it is too large, then it will constrict the oil flow and the brass will wear due to oil starvation. Either option is bad. You _must_ clean the trash out.
Remove the bolt holding the shaft in place, then pound the shaft forwards. Remove the idler, and clean everything.
