VCCA Home Forums TECHNICAL - GENERAL Trucks and Vans 1941-1946 1/2T & 3/4T pickups, understanding gearing for highways

I would like to understand gearing on the rear ends.

I've seen mention of gears changing from spiral bevel gears to hypoid in 1940.

Alan,
The meaning of 3.55 as a reared gear ratio is that the driveshaft turns 3.55 times for every single turn of the rear axle. Any standard transmission, except for one with overdrive, is 1 to 1 in high gear meaning the driveshaft is turning the same speed as the engine when the trans is in high gear. The trucks you refer to will always?? have a 4.11 rear end ratio. So, in high gear the engine is turning 4.11 time to every revolution of the rear axle.
These low speed gears were needed when the trucks were earning a living carrying heavy loads. Now days we mostly want to drive around and look cool and not get run over by other people. as a rule we will not have a load of hogs on board so we don't need as much pulling power as was provided by the 4.11 gears.
I installed 3.55 gears in a '51 pickup and they worked great and allowed me to drive close enough to the speed of other traffic so as not to be a nuisance to others and risk my own life as well.
It is likely the 3.55 gears are offered as a direct fit upgrade for a '41 - '46 pickup. I hope this is helpful.

Mike

This makes sense.

The step from 4.11 to 3.55 is a big difference,it maybe too big a change for the 216 in steep country but out on the highway or flat area would certainly keep you rolling along nicely.
Counting the driveshaft revs is a bit difficult with the enclosed drive but the later models with open shaft it is a lot easier. Jack and support the rear end and turn the rear wheels by hand (make sure both wheels turn at the same speed) for 1 full turn while you count the number of turns the driveshaft does.
Tony

Thanks.

Or you could leave one wheel on the ground and turn the wheel you jack up 2 turns instead of 1.

The trouble with the old Chevys is the enclosed driveline, you can't see the driveshaft. But what you COULD do is remove the spark plugs, and put the transmission in high (direct). Jack up one wheel, make a flag of tape and put it at the top of the crank pulley. Make a similar flag on the top of the wheel you jacked up.

Have a friend watch the crank pulley and count the turns while you turn the wheel you jacked up exactly 2 turns in the direction that would make the truck go forward. Mind the backlash and take it out before you start counting your 2 turns.

Never thought of that.