Changing from 7 1/4" to 8 3/4" rear end questions

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92b

92b

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I have an 8 3/4" rear end out of a 69 barracuda I want to put in my 69 barracuda with a small block and 904 transmission. I have the original sbm/904/ 7 1/4" driveshaft it measures 51 3/8" center to center. I saw in another thread that the driveshaft should be 49.27" are the driveshaft lengths different between 7 1/4" and 8 3/4"? Also is the 7 1/4" u-joint the same as 8 3/4"? Thank you.
 
92b said:
are the driveshaft lengths different between 7 1/4" and 8 3/4"?
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Yes, by approximately 1.5". The pinion "nose" of the 8.75 is longer.

92b said:
Also is the 7 1/4" u-joint the same as 8 3/4"? Thank you.
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Depends which yoke you have on the 8.75. Measure 'em up.
Also be aware that the axle tubes of the 8.75 are larger diameter than the 7.25- that means you will need different shock plates and U bolts, too.
 
It was my experience that the driveshaft lengths I found in charts weren’t correct for my car, even though the components were all the same. I suggest measuring at least twice and use the number you come up with.
 
the drive shaft from a stock 7 1/4 is probably a 2 piece shaft with a rubber dampener between the two halves. you would be better off having one made
 
Professor Fate said:
Yes, by approximately 1.5". The pinion "nose" of the 8.75 is longer.


Depends which yoke you have on the 8.75. Measure 'em up.
Also be aware that the axle tubes of the 8.75 are larger diameter than the 7.25- that means you will need different shock plates and U bolts, too.
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I was surprised to save the u-bolts. The nuts came right off. I also have the shock plates. I don't know how or where the measurements need to be taken for the yoke. Thank you.
 
Dana67Dart said:
the drive shaft from a stock 7 1/4 is probably a 2 piece shaft with a rubber dampener between the two halves. you would be better off having one made
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Mine is a solid driveshaft tube. I don't know if it is original. Thank you.

16352022283153614557096402949327.jpg
 
shove yolk in all the way. slide it out 3/4". measure from center of hole on slide yolk to center of hole on pinion yolk. car must be on wheels with full weight. take measurement to driveline place. done. if your re using current...take that too.
 
Why are there spring perches cut off????? tell me you did not cut up a stock A body 8 3/4 :(

92b said:
I don't know if it is original.
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are the balance weights are rectangular it is probably OEM, if round probably not. BUT the tapered ends makes me think it is OEM
 
The 7 1/4” U bolts and shock plates are different. 7 1/4” has 2 1/2” tubes. 8 3/4” has 3” tubes.
 
you can use the same yoke, may need a conversion U-joint but if your gonna get one made, just have it made to your 8.75 yoke. Get a Longer one and have them cut it. Probably under $100 here, but its been a while.
 
Dana67Dart said:
the drive shaft from a stock 7 1/4 is probably a 2 piece shaft with a rubber dampener between the two halves. you would be better off having one made
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No, not on a 67-69. It would be solid.

When I did this swap on my 67 Barracuda, I found the correct driveshaft at a wrecking yard (very unlikely today). I had to change u-bolts and plates. I did not have to change u-joints — this was a 741 case with SBP axles — your mileage may vary.
 
mvh said:
, not on a 67-69. It would be solid
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67 - 7 1/4 = 2 piece shaft. The outer tube (red arrow) is attached to the inner tube (green arrow) by rubber.

PXL_20211026_035225251~3.jpg


67 - 8 3/4 = 1 piece with tapers on each end like photo shown above.

I don't mean a 2 piece shaft like this

Screenshot_20211025-214137.png
 
I can say in all my years of working with A bodies, I have never encountered one with the two piece rubber inserted shaft. I know what your talking about and have seen them in the past.
 
SGBARRACUDA said:
I can say in all my years of working with A bodies, I have never encountered one with the two piece rubber inserted shaft
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My 67 dart is stock. 273, 7 1/4, 2.93

Note the last paragraph before the word diagnosis.

Screenshot_20211025-220353.png


Note (R) rubber isolated....

Screenshot_20211025-221216.png
 
clementine said:
shove yolk in all the way. slide it out 3/4". measure from center of hole on slide yolk to center of hole on pinion yolk. car must be on wheels with full weight. take measurement to driveline place. done. if your re using current...take that too.
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I don't have the motor/ transmission in the car yet. I was hoping to get all the parts gathered up to make the swap when I put the motor in. If I have to wait I will. Thank you.
 
Yes you need to wait till you get the engine and transmission installed. So you can get a accurate measurement.
 
Dana67Dart said:
Why are there spring perches cut off????? tell me you did not cut up a stock A body 8 3/4 :(



are the balance weights are rectangular it is probably OEM, if round probably not. BUT the tapered ends makes me think it is OEM
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Perches are off another rear end for my other 69 barracuda. Junk yard had it marked as coming out of a van. I plan to narrow that housing in the future. Thank you.
 
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