Model A rear axle and the Pythagorean theorem

[nosoup4u]

How does the model A, or any other torque tube rear axle, allow for up and down movement? When the car is loaded, the hypotenuse, that being the drive shaft should get shorter. I don't see and "slack" on a model A driveshaft.

[texas webb]

I'll watch this.

[wmws]

I think the difference is so mynute that the rear spring easily takes up the slack. Maybe you could figure out mathematically how much shorter it would be if the rear axcl moved up say 4 inches.

[katy]

The minute difference in length is allowed for by the rear spring shackles.

[nosoup4u]

Originally Posted by wmws

I think the difference is so mynute that the rear spring easily takes up the slack. Maybe you could figure out mathematically how much shorter it would be if the rear axcl moved up say 4 inches.

Just guessing that the driveshaft is 60" and the frame is 12" above the driveshaft. The rear axle moving up 4" would change the driveshaft only about an inch.
Thanks to the PT calculators on the internet because I slept through geometry class.

[Licensed to kill]

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Originally Posted by nosoup4u

How does the model A, or any other torque tube rear axle, allow for up and down movement? When the car is loaded, the hypotenuse, that being the drive shaft should get shorter. I don't see and "slack" on a model A driveshaft.

In other words, how does a torque tube setup deal with the lack of, or not need, a slip yoke?. I've thought about this myself and the only thing I can think of is that the use of a transverse spring allows the spring to "rock" or pivot slightly on the upper mounting bolt so the diff moves for and aft slightly as the spring compresses under load. This can't happen with springs running perpendicular to the axle but can with the spring parallel to the axle. Just a guess.

[nosoup4u]

Originally Posted by Licensed to kill

In other words, how does a torque tube setup deal with the lack of, or not need, a slip yoke?. I've thought about this myself and the only thing I can think of is that the use of a transverse spring allows the spring to "rock" or pivot slightly on the upper mounting bolt so the diff moves for and aft slightly as the spring compresses under load. This can't happen with springs running perpendicular to the axle but can with the spring parallel to the axle. Just a guess.

Just did some reading on wikipedia. Apparently a big reason for use of the torque tube (perhaps not with the A Ford) was to be able to use coil springs for a softer ride, which I guess would give that slack. On a torque tube vehicle the wheels push against the transmission, instead of the suspension as on most other vehicles.

[Jim Brierley]

Hey guys, put your brain in gear! The torque tube locates the rear end. The ball at the front of the tube allows for movement and the U-joint is directly centered in the ball. The rear hardly moves, not near an inch! On late model cars, and especially pickups, there is often a 'clunk' when taking off from a stop, this is the slip-joint moving in, after moving out during braking. On open drive shaft vehicles the movement is mostly caused by the springs 'wrapping up' caused by braking action.

[nosoup4u]

Are you saying that the rear axle moves up and down less than an inch?

[Jacksonlll]

Here is an 8 minute video I did on my car. It shows the excursion of the suspension components. https://www.youtube.com/watch?v=LeSE...cz4R0&index=47

[Y-Blockhead]

Nice video. I miss my Flip Camera.

[Jacksonlll]

That is the video that is upside down. Somewhere I have it flipped so it is up right. I'll look for it.
On the flip camera, I have a few. I got my last one on ebay for $12. Still a good deal. jack

[Jacksonlll]

Here is the right side up video. jack
https://www.youtube.com/watch?v=ry29zQZ3E5Y&t=374s

[nosoup4u]

Neat video. I'd say that's way more than an inch.

[MAG]

How does the model A, or any other torque tube rear axle, allow for up and down movement?
On a Model A the spring shackles allow the chassis/body to move up or down.

When the car is loaded, the hypotenuse, that being the drive shaft should get shorter. I don't see and "slack" on a model A driveshaft.
On a Model A the drive shaft length is "fixed". There is no forward movement of the torque tube therefore the drive shaft does not get shorter.

In the video if the camera had been placed on the axle housing you would have seen the body going up and down instead of the axle and wheel.

[Pete]

Originally Posted by nosoup4u

Just did some reading on wikipedia. Apparently a big reason for use of the torque tube (perhaps not with the A Ford) was to be able to use coil springs for a softer ride, which I guess would give that slack. On a torque tube vehicle the wheels push against the transmission, instead of the suspension as on most other vehicles.

Leaf springs can be made to ride as soft as any other type spring.
Any automotive spring is part of the suspension package. It has to fit the design parameters of the package. It has to have a certain rate of travel, amount of travel and physically fit in the available space.
On a model A, the fore and aft travel of the rear end housing in relation to the frame is absorbed by the spring leaves and shackles. It is not very much, but enough to let the system work. Cost, was the reason Ford used this type of suspension system.
The car is NOT driven through the transmission. IT IS 90% DRIVEN THROUGH THE CENTER CROSS MEMBER. The other 10% is through the spring into the rear cross member. If it was driven through the transmission, the fan would bore a hole through the radiator.

[5lugnuts]

How does the model A, or any other torque tube rear axle, allow for up and down movement? When the car is loaded, the hypotenuse, that being the drive shaft should get shorter. I don't see and "slack" on a model A driveshaft.
……………..
The subject of the solution is not a triangle, it is an arc. The rear axle is free to move up and down but it cannot move fore and aft more than the distance between the "ball" and the clamshell. The two splined ends of the u joint will take up any for and aft vibrations of the driveshaft which does not move for or aft either if everything is working as designed.

The torque tube is like the radius of a circle -- the distance from center to circumference. The circumference of a wheel is the same distance from an axle at all times. When the rear end goes up and down it does not move fore and aft because the ball, clamshell and torque tube will not let it. Yes, the rear spring does compensate for the small degree of arc but that is so small we can't easily see it.

But then, I remember being wrong once so now I'm not sure?

[Dick Steinkamp]

Originally Posted by 5lugnuts

But then, I remember being wrong once so now I'm not sure?

Was that the time you thought you were wrong, but it turned out you were right? So you were wrong to have thought you were wrong?

[Synchro909]

Originally Posted by Dick Steinkamp

Was that the time you thought you were wrong, but it turned out you were right? So you were wrong to have thought you were wrong?

That's right!

[31 Woody]

The torque tube is a solid part and does not expand nor contract. As the torque tube is solidly attached to the axle and clamshell—the axle is fixed to the transmission output clamshell. Therefore, assuming the clamshell pivot point on the end of the torque tube and the universal joint on the driveshaft are perfectly aligned, the driveshaft does not expand nor contract either. The spring must provide the fore/aft ward movement necessary for the axle to move up and down.