TR4/4A TR3/4 Gearbox Input Shaft

[CJD]

Anyone know if the TR3 tranny input shaft is the same as the TR4? It looks identical to me, but just wanted to make sure I wasn't missing anything.

 

[TR3driver]

According to the SPC, TR3 from TS27063 onwards used the same input shaft as TR4, 204215. Looks like the change at that point (and also TS26825-TS27051) was to use the needle bearing between it and the mainshaft, instead of the earlier bushing. The mainshaft changed at the same time.

 

[CJD]

Thanks, Randall!

 

[TRTEL]

And that design carries into the six boxes till they changed the mesh angle on the teeth. There use to be a lot more of the NOS bushing type available. Purchased one a dozen years ago and had a shop drill, polish and press in the needle bearing. Do remember they complained mildly about the toughness of the steel to work with (it was about a '57 date on the box) and is still in a 4A daily driver.

 

[CJD]

Interesting, Tom! I guess I was assuming the needles would be the same ID and OD as the early bush. Apparently that's not the case.

 

[TRTEL]

No, that right. It was a cost saving measure, without sacrificing reliability (sort of). Though I do remember working on at least one failed bearing back then (when the gearboxes weren't all that old). Never did see a failed bushing. Just a lot fewer man hours in production. The early bushing and mating mainshaft required a good bit more machining. They just went up to an 'off the shelf' bearing size till they felt there was adequate safety margin for the load transfer.

 

[CJD]

I finally got home and had a chance to take some measurements. The TR2 through TR3A input shaft has a mainshaft bearing ID of .91" The TR3B-TR6 early has the hole for the needle bearings that is 1.12".

Of note, the bearing surface of the mainshaft is the same size for both. So...it appears the input shaft for a TR2/3A will work with the TR4 box, so long as you use the bushing instead of the newer needle bearing. I would imagine the TR4 input shaft will work backwards to the TR3 also, so long as you use the needle bearings.

This may become important, as the later input shaft is becoming scarce! That seems interesting to me, as there were a lot more cars with the later shaft built. I guess those cars are getting rebuilt more frequently than the earlier cars?!?

 

[TR3driver]

Since the SPC shows the mainshaft changing with the input shaft and bushing/bearing; there must be some difference. I'm guessing it had to be specially hardened to live with the needle bearings. So, if I were going to try to use a later input shaft with an early mainshaft, I might take Bob Schaller's advice and find (or machine) a bushing to fit instead of using the needle bearings.

Using a custom bushing might also be a means to saving an input shaft where that needle bearing has failed; but I haven't tried it. I've got the "ruined" input shaft though (which I use to align clutch plates).

Your last statement seems like a non sequitor to me. If there are a lot more cars, but they are being rebuilt at the same rate, it would still consume a lot more parts. But my guess is that the shortage indicates a higher failure rate, since the input shaft normally doesn't get replaced unless that bearing fails. Kind of supports Bob Schaller's. theory that the bushing gives longer service life.

https://drive.google.com/file/d/0B2...MmJmLWFiZGItNTI5ZjI3N2NjZTIy/view?usp=sharing

 

[mikephillips]

Seems to me that the bushing would be much more tolerant of low oil levels in the transmission. If the rollers aren't getting sufficient splash lubrication they start running with too little oil and quickly heat and start to fail where the bushing would be porous and retain oil. So that is probably why there seems to be a difference and tougher time finding a good later input shaft.