Driveshaft length 8 3/4

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Eworth

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Hi Folks,

I own a 1964 Dodge Dart, put in a 318, 904 automatic (not pushbutton type) and it has a 7 1/4 rear. I am going to an 8 3/4 rear axle, 3:55 suregrip.

Does anyone know what length the driveshaft should be for this combination and exactly from what two points the measurement is taken?

Thanks in advance,
Mark
 
The one on my 68 Dart (904/8.75) is about 52" cup center to cup center or 49" weld bead to weld bead..... Not sure what if any difference there is in wheel base....
 
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Im finding in other posts 52" , 52 1/4 , 52 3/8 and
52 1/2. IF I do this blind without measuring, I think I'm good if I average the above.
 
Better a little short than too long. You don't want spring wrap bottoming out the yoke on the tailshaft. I ran a temp shaft of 50.25 / 47.25 respectively with no issues other than a lot of yoke exposed....
 
Cool, then I won't push it with length.
mguner said:
Better a little short than too long. You don't want spring wrap bottoming out the yoke on the tailshaft. I ran a temp shaft of 50.25 / 47.25 respectively with no issues other than a lot of yoke exposed....
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Going from a 7.25 to a 8.75 rear end will require you cutting your drive shaft down some. I dont remember what I figured it to be on a 66 Dart GT with 8.75 and 904 trans mission. I can get a measurement if you need. Just measured it, it is 54 inches from the center of the rear u joint to the center of the front u joint. It could stand to be little shorter but that measurement works for me.
 
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If you are cutting this shaft yourself I would certainly trial fit it before I weld. 54 sure sounds long for a 2 door. I was just measuring mine Sunday.
 
mguner said:
If you are cutting this shaft yourself I would certainly trial fit it before I weld. 54 sure sounds long for a 2 door. I was just measuring mine Sunday.
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It is what it is. Works no problem. An inch shorter would still work. You measured yours sunday, what did you get? And his is a early A body, not the same as a later A body.
 
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Post#2 and that left maybe 1/2" from the yoke shoulder to the seal without the boot.
 
I have an 833 with an 8 3/4 in my 64 and the drive shaft is 54 inches center to center on the U's
 
mguner said:
Post#2 and that left maybe 1/2" from the yoke shoulder to the seal without the boot.
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54 on mine left 1/2inch from the shoulder to the dust seal, the boot. The boot is another 1nch at least. Yoke is nice and snug. no vibration at all.
 
I was hoping you were right Tim. I wonder if we are measuring differently. Center of U- joint cup to center of U-joint cup (front of front cup to front of rear cup - same thing)? I had a 54" shaft laying around so I put a 904 yoke on it and since my 68 Dart was still up on the lift I tried it and took pictures.... Just no way it will fit my car with 904 and 8.75 rear. With the rear hanging it should have even more room.
20160524_194020-jpg.1714937353

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20160524_194241-jpg.1714937356
 
66 is longer then 68 A body. At least that part is. And I measured center of both U joints.
 
Mopar Tim said:
66 is longer then 68 A body. At least that part is. And I measured center of both U joints.
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I figured something like that, engine location etc.... The guys that say "any 108 inch wheel base shaft should work" need a little education. Definitely good to have clarification on this. I really was hoping the 54" would fit my 68 but alas the cut and weld was needed.
 
Here it is in the car. Taped one end to get the photo on the other 54 inches. 53 1/2 would be ok as well

009.jpg


010.jpg
 
trapster said:
There should be 1 inch of slack with the car at rest.
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As the car is loaded down the yoke pulls out of the transmission. I thought it would be the opposite. Support the car on jack stands and let Axel down and see what I mean. I was surprised. At least on my setup it does.
 
Ideally, so I have been told, the slip joint is the furthest in when the car is at rest on all four wheels. That is to say when cruising there should be no bends on the ujoints.
 
Found this in the search feature, hope it helps :)

A 108 wb with 904 & 7 1/4 to 8 1/4 swap the difference between 7.25 and 8.25 housings is 1.25 so what ever your original drive shaft measures minus 1.25.

Here is some other tech I've found from here:

108"wb with 440/727/8 3/4=46.5
904/8 3/4=49.25
add 2.25 for 7 1/4
subtract 4" for 727
8 1/4 D shaft is 1.25 shorter than a 7 1/4 D shaft
727/8 1/4 48.9 w/ 108 wb

111" wb w/ 904/8 3/4=51.99

Make sure your yoke isn't tight in the trans & leave about an inch out for play.

feel free to add your set ups so others have a quick reference
 
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