Re: towing the Model A

Posted by Joe on March 30, 1998 at 10:29:38

In Reply to: Re: towing the Model A
posted by geo. shebley on March 30, 1998 at 09:04:25

: The test showed that while being towed the gearsin the transmission that normally turn and sling the gear grease around the transmission are idle. Unless you overfill the transmission during towing, it is NOT being lubricated properly.

George and Dick
This makes a certain amount of sense.When the shift lever is in the Neutral position, the gears are lined up such that the "custer gear" is not being driven from the rear shaft.When this occurs, no oil is thrown to lubricate the bearings.
This is problematical for the center needle bearing and the rear ball bearing, but not chronic.
First, you have to remember that the rolling friction between the mating surfaces of the ball & needle bearings is directly related to the power transmitted by the transmission.The bearings normally only resist the couple-forces of torque and the tendency of the transmission shafts to separate from each other when under load.(This is related to the "pressure angle" of the gears)
In the case of a Neutral gearshift position, there is no torque or gear tooth loading to deal with, thus we have only the force of gravity downwards on the spinning gear assembly being resisted by the bearings.
"Normal" Model A rear shaft bearings probably have enough lubricant present to last for a short to medium term of session of towing under these no load conditions.How to be entirely sure of this is the question, however.I don't think I would tow at high speed for hours on end.I would give it perhaps an hour or two at most.
It may be possible to stop periodically with two people for a short "lube pull" by the towing vehicle and lubricate the Model A transmission.In this case Driver #2 in the Model A would depress the clutch pedal and put the transmission in gear, probably 3rd gear, and on signal, Driver #1 in the towing vehiclewould carefully tow the Model A for a short distance.This action spins all the internal components of the transmission (including the clutch disk) and gives everything a good bath.The question here is "how much of a pull" and "how often".
Another solution I have thought some about would be to replace the filler plug on the side of the transmission with a short length of 3/4 inch pipe and a pipe cap.This would allow you to carry a slightly higher oil level which would contact the two sliding gears of which the rear one is the larger in diameter.The trick here is to study out the transmission case level required and provide a length of pipe such that your maintained oil level is not too high and cause a problem with leaking of the seals on the tranmission main shafts.Err on the side of conservative with too much oil here and you create a mess!
To counter leakage of this kind, one trick which I have taken advantage of in my ordinary tranmission rebuilds is to utilize a "sealed" modern bearing at both front and rear of the transmission.In this case the normal "oil shields" are not used and the integral bearing seals on the modern bearings are used to prevent oil from leaking from the transmission.This prevents the mechanic's nightmare of the "dreaded unsightly drip of oil" and makes a transmission a lot tighter than it was originally.
A tranmission sealed in this manner would be good for modification to include towing but to do it of course involves some thought about it from the "ground up" in a rebuild situation.I confess to not having gone the whole route to actually create a "towing modification" to my transmission.
I wish I could give you some "really definitive" answers to your questions concerning towing the Model A.I don't think there is that kind of answer in this case.Perhaps what I have indicated will help you make up your own mind about "how far to push the envelope" with towing or modifications to allow it.
In any case I'm glad I was able to give you something to think about.
Best regards,
Joe

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