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Posted by Gordon Maney [208.126.138.206] on Wednesday, November 03, 2010 at 18:08:09 :
In Reply to: Re: 1970 Power Wagon Flat Tow Question posted by copey [206.80.248.91] on Tuesday, November 02, 2010 at 13:59:46 :
The spur gear transmission is a sliding gear transmission. [It is not a constant mesh transmission.] You choose gears by sliding gears in and out of engagement.
If you are towing it down the road, assuming the rear drive shaft is in place, the mainshaft will turn. Whenever the mainshaft [output shaft] rotates, all the larger gears splined to it rotate in the oil. If you look at one apart I think you will see that several gears on the mainshaft reach farther down than the lubricant fill hole, enabling them to throw oil when turning.
The mainshaft will be turning in the pilot hole of the main drive gear [input shaft]. There is a need for lubricant there, but it should be served by the throw-off described above.
A constant mesh transmission, however, is quite different. Any synchro mesh trans will be constant mesh. A constant mesh is not necessarily a synchro mesh, however. A constant mesh transmission will have multiple pairs of [typically helical] gears in mesh simultaneously. You choose a gear by locking a gear to the mainshaft, either with a synchronizer assembly or with a shift collar [such as some ag and construction equipment].
The collar shift trans is not synchronized, but is constant mesh. Constant mesh transmissions are stronger because of the helical gears, and also quieter.
If you tow a *constant* mesh transmission, the drive shaft turns the mainshaft as it runs inside the stationary gears. There is no gear rotation to throw oil and after a while you destroy the transmission because it is not lubricating itself.
I recall an IH dump truck being brought in to the dealership once, towed a considerable distance. It seized on the way. I took it apart and got to see quite a number of parts that were the most beautiful blue.
When in doubt, take out the rear driveshaft.
To pull with a towbar, you have to have a vehicle that is willing to follow you through turns and come back out of them, still happily following you. Not all are cooperative.
Some people would tow front-pump cars by starting the engine and letting it idle while towing.