So this has kind of been bugging me. I seem to remember that if you're going to raise or lower a car, it's fairly critical to keep the input to the differential parallel to the output from the transmission to keep the drive line from eating itself. Something about the nature of universal joints causing a sort of snapping motion that gets worse the farther off-axis they're aimed. The front U-joint sets up this snapping and the rear one is aligned to take the snap out.
With that in mind, and not being in my garage right now to look, what gives with the T? I'm fairly confident the drive shaft angles down out of the transmission but then goes straight into the differential. I get that the point is to save a U-joint in the assembly but it should be less than ideal. As a result, are any parts more strained than they should be? Is anything in the rear end prone to breaking or am I over thinking this?
Tim, that's a rule to consider on cars with open driveshafts. On Fords up to 1948 the driveshaft runs in a tube that holds the angle between the rear end of the driveshaft and the pinion constant - and the angle between the transmission output shaft and the driveshaft has to be flexible for the car's suspension to work. Usually no problems when lowering Model T's, the pan is so deep around the flywheel so you can't lower the rear until the trans output and the driveshaft is totally straight, U-joint's don't like to run totally straight for an extended time. (well, that's what I've been told).
Roger - A comment (for what it's worth) about the very last point you mentioned in your post above:
You said,...."U-joint's don't like to run totally straight for an extended time."
In my opinion, and to use your words, that is also "a rule to consider on cars with open driveshafts". And that is because most modern open drivelines use U-joints that use needle bearings. I don't think the "rule" applies to Model "T's because the U-joint does not have needle bearings, the bearing surfaces are just plain. And needle bearings need to flex at least a minimal amount in order to distribute the lubricant that protects those needle bearings from wear. Without just a bit of "flex" that occurs when a driveline is NOT perfectly straight, each needle bearing will fairly quickly wear a little groove in the spot where the needle contacts the cup that retains the needles, and also another groove on the opposite side of each needle where the needle contact the journal. I've seen the four little journals on the "X" member of a modern needle bearing U-joint worn enough to look almost like a splined shaft. Especially on a car that had a fairly straight driveline. When I was a kid, my Dad had a '51 Pontiac (straight-8) with a nearly straight driveline and we had to put new U-joints in that car several times in the 6 or 7 years that he had that car. FWIW,....harold
The flexed single u-joint of the model T driveline introduces periodic fluctuations in angular velocity of the driveshaft (for constant angular velocity of transmission. The driveshaft speed up and slows down relative to the transmission during each revolution of the U joint. Using two simple Cardon(non-constant velocity) u-joints with equal angles at transmission and differential (& DS yokes in phase), cancels the fluctuation at the differential input, only the shaft between the two joints experiences these fluctuations. The +/- velocity fluctuation is a function of the angle of the Model T driveline. This article gives a good explanation and data tables:
Yeah, what JB said.
I guess there's no appreciable effect on a T, otherwise it's something we would have heard about sometime in the last hundred years.
Unless... is there something that wears less in the rear end of a TT? They ought to have a straighter drive line on account of the drive shaft going to the top of the differential housing.
Can't really argue with a hundred years of success?