Hey Guy's we are upgrading our 2 door '65 Valiant to a 8 1/4 rear and changing over to a '66 and up style tranny with the slip yoke. I looked up a drive shaft for a '66 valiant on car-part.com, but the question is does the 8 1/4 use the same size u-joint as the 8 3/4? Or will I have to get a driveshaft made, which is what I'm trying to avoid!

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To each his own (so what if I wanna build a 450 horse MPFI turbo /6 instead of using a V-8!)

Driveshaft length is what will make you have to fab up a new one. The yokes should be the same.

Here is what works for me. Get the rear end in the car . With the rear tires under the weight of the car ....and the trans yoke in the trans ...measure to the centre of the yokes.

Go to the wrecking yard and look through their driveshaft pile till you get a nice shaft exactly the right length with the correct yokes.

If you dont find one exactly the right length ....get one 4-6" too long and get that one machined to exactly the right length. This is cheap and easy.

My 65 Valiant with Ford Explorer 8.8 and Mustang 5 speed is using the factory shaft for a 3speed manual / 7.25 axle. Crossover Ujoints are used. Coincidence or serendipity?

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Yeah....Im the one who destroyed this rare, vintage automobile.....

An 8-1/4 will in all probability have the 7260 U-joint in it.

The 8-3/4 can have a 7260, 7290, or a 1350 depending on what yoke is on it.

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Official Cookie and Mater Tormentor.

I'm not sure if this well be helpful, but here goes:
My '78 Volare came with a 7 & 1'4 differential. Years ago, when I swapped in an 8 & 1/4 differential into my Volare, I'm pretty sure that the u-joints were the same part number. I did have to get the driveshaft shortened and rebalanced at a shop, which cost $80 bucks.

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"Ja, Ich fahre ein altes auto."
'78 Volare 225
'67 Charger 318