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Drive Shaft? Drive Shaft

So, I’m watching the commercial for the new Tundra…You know, the one that is so strong, so tough, so much better…



And there is the shot of the two-piece drive shaft, one of steel for strength, and the other of Aluminum to save weight.



And I think to myself; “Hmmmmm…”



My old Generation Numero Uno Tundra has exactly the set-up they say is new and better.



But my two part question is: why two sections and why two different metals?

two part driveshafts with a carrier bearing in the middle are as old as the hills.

The reason for two parts is simple. Driveshafts are heavy. When the start to get long, they need to be supported in the middle. The only way to do that is two shafts with a U joint and a carrier bearing.

On trucks there’s a second reason as well. As the angle between the tranny outputs shaft and the differential input shaft becomes greater due to the chassis becoming farther and farther away from the axle due to the truck being placed higher and higher, the angle becomes too great for a universal joint to operate smoothly. U joints do not operate well at high angles of articulation. The common sloution is to use two U joints, each articulated to 1/2 of what will be the total angle, and support the center with a carrier bearing.

Saavy?

The aluminum simply saves weight. in today’s world with it’s mandates to improve mileage, every pound counts. High performance cars have been using aluminum driveshafts for years. The lower the weight, the better the launch. I suspect Toyota’s only sticking with steel for part of the driveshaft to keep the cost down a bit. Everything is a compromise.

In fact, I think it is a little more complicated than that. The driveline has “critical speeds” at which it resonates. When that happens, they can start to do what might be called “whip”. Generally speaking, you need to stay below the first critical speed. The critical speed is reached faster as the drive shaft is lengthened, as in a truck, and as the axle ratio is increased to increase hauling capacity as in a truck. The least expensive way to increase the critical speed is to articulate the drive shaft. You can also lighten the shaft by making it out of aluminum or metal composite, but that costs a lot more. Of course you are correct about the angles requiring another articulation on some trucks. Here is some data I dug up on another forum reputed to be from Ford concerning police cars:

Here is Ford Data on the Shafts:
maximum Critical Speed (16 inch wheels)

CVPI Amuminum Driveshaft 4.10 = 116mph
CVPI Amuminum Driveshaft 3.55 = 132mph
CVPI Amuminum Driveshaft 3.27 = 145mph
CVPI Amuminum Driveshaft 3.08 = 154mph
CVPI Metal/Matrix Driveshaft 4.10 = 133mph
CVPI Metal/Matrix Driveshaft 3.55 = 154mph
CVPI Metal/Matrix Driveshaft 3.27 = 167mph
CVPI Metal/Matrix Driveshaft 3.08 = 177mph