Driveshaft to Transmission Engagement

[JimKueneman]

Yea this is for my daughters Duster but would like some other opinions. We put a 318/904/8.75" rear axle in it. After a lot of research I found the correct part number for the driveshaft for this combination in 1972 is 2996157 which was 48.89" long. I have a driveshaft that is 48" long. If I do the rule of thumb math it is 51.75" from tail shaft to pinion yoke bearing face so 51.75"-2.5" (rule of somebodies thumb) = 49.75" so the quandary begins the factory shaft is 1" shorter than the rule of thumb.

The full engagement of the yoke is just short of 6" onto the transmission shaft so another rule of thumb is bottom out the yoke then back it off 1" so that is 5" of engagement. If I used the factory 1972 shaft with the exact power train combination that gives me an engagement of about 4". My shaft will give me just about 3" of engagement onto the transmission shaft.

Bottom line is 3" of engagement enough? This is a cruiser so we are not planning on drag race starts so things get wound up and pull out a lot. It will be 2.76 gears and a road car taking it to shows and trips to town on the interstate at 75+ MPH.

Thanks,
Jim

 

[WileERobby]

You have to account for suspension travel. What is the amount of spline engagement at maximum suspension travel ?

 

[JimKueneman]

You have to account for suspension travel. What is the amount of spline engagement at maximum suspension travel ?

I am assuming by geometry class (which I sucked at) this would be at maximum spring extension?

 

[NOSTRT980]

https://sep.yimg.com/ty/cdn/chucker54/orderformDS.pdf

 

[WileERobby]

Yes, think of a triangle. The top line is the horizontal shaft, the back vertical line is the rear axle travel. And the line from the Trans slip yoke to the rear axle at its maximum travel points.

 

[steve340]

I have always worked on while the car has load on suspension and is at ride height the yoke can enter the trans 1 more inch before bottoming.
The yoke needs clearance but they do not move that much.
I think 3 inches of engagement is not enough.

 

[JimKueneman]

I have always worked on while the car has load on suspension and is at ride height the yoke can enter the trans 1 more inch before bottoming.
The yoke needs clearance but they do not move that much.
I think 3 inches of engagement is not enough.

I am thinking the same thing. Thanks.

 

[Dipstick]

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