On a recent show, I heard them mention that you shouldn’t rest your hand on the shifter of a manual transmission while you drive. They never explained why because they had apparently explained it on a show years ago.
Does anyone know why you shouldn’t do this? Or even better, do you have a link to a download of that specific episode?
The reason you should not do this is because the weight of your hand, and arm, is multiplied due to leverage. This can move the shifter rail slightly off the detent ball which holds the shift and fork in its proper position. The shifter fork fingers are then being rubbed against the rotating synchronizer sleeve (think of placing your thumb and forefinger inside the grooves of a small pulley).
Over time the shift fork fingers and the sleeve will wear down. Once the gap is excessive the force applied to the gearset in question (1/2, 3/4, etc) will try to slide the synchronizer inserts inside the sleeve. There is a point of no-return here and the synchronizer hub/sleeve assembly will then try to place itself in the neutral position; a.k.a jumping out of gear.
Hope that explained it anyway. 
I believe it’s more of a safety issue. You are supposed to have both hands constantly on the steering wheel while driving, except to shift only. If you have one hand on the steering & the other on the shifter while taking a driving test, you will surely fail.
My experience is with a Subaru GL wagon - I used to “ride the shifter” - what happened is that the synchronizer mentioned by ok4450 wore out and the gears would clash when I shifted - after a while of gear clash, they finally went altogther and the transmission stuck in gear. Thankfully it was in 2’nd gear so I could trash my clutch and drive it to the dealer for a transmission replacement.
I agree that the concern is wearing the synchronizers by putting pressure on them.
Besides, you need that hand free to talk on the phone.
Or eat.
Or drink some Tim Hortons coffee, and then use the same free hand to roll up the rim and win a new car!
…or try to do all those things at once while steering with left knee (like me).
I’m not disagreeing with the experts, but this seems to be something that can be fixed with the proper design. After all, the weight of the lever is a few pounds and that is pressing in the same direction.
The problem is that some people put sideways pressure on the shifter, it’s not the downward force due to the weight that causes the problem. You probably could design a shifter that was not susceptible to this problem.
Or the boat, I’ll take either!
I’ve got a large pile of Subaru manual transaxle parts. Will see if I can take a pic or two later to show what I’m talking about in relation to shift forks, rails, and detent balls.
The problem could be alleviated by installing stronger springs on the detent balls (which hold the shift rail/fork in position but the problem then will be that the shifter will be very hard to move and will feel like pulling a sandbag with a rope.
It is required to put your hand on the shift knob while driving…to look cool
after i read this post i see it applies to manuals…?
I don’t think a scenario like that will hurt anything at all. If someone made a chronic habit of it for weeks and months on end then it could.
The exception might be if this knee resting was heavy, went on for hours, and IF the transmission was very low on gear oil.
That’s stretching it a bit and not something I’d worry about. Hope that helps.
and a Starbuck’s coffee in the other
Yes thank you