____Driveshaft Question??

-
twister360

twister360

Well-Known Member
Joined
Mar 16, 2008
Messages
274
Reaction score
5
Location
Houma, La.
Ok,

I just changed the rear end in my '75 Dart Sport. It's a 318 904 a/t that 'HAD' a 7 1/4 rear (SBP). I changed to a 8 1/4 rear (BBP) that came out of a '73 Swinger. The the driveshaft is to long and does not fit into the rear. I measured the driveshaft from end cap to end cap and it is 52 1/2".

So my question is, is the drivehshaft longer in cars with a 7 1/4 versus an 8 1/4?

Thanks for your time and looking forward to some input!
thumbs.gif
 
I have not done the 7 1/4 to 8 1/4 swap, but I have done the 7 1/4 to 8 3/4 swap , and the 7 1/4 driveshaft is longer. I take the measurements and have my local driveshaft shop make a new one.
 
I had been running a 273/904 with a 7 1/4 rearend. Last fall we replaced the rearend with an 8 3/4. This spring we put in a 340/727 combo. We measured and the drive shaft has to be cut down almost 12 inches.
 
How should I measure the driveshaft in order for the them to either cut it down or make a new one? And what was your price? Thanks
 
You need to cut it down 1.6 inches the difference is the 81/4 pinion shaft is longer which means the driveshaft has to be shortened. The u-joints are also different, you will need one for an 81/4. I have a driveline that came out of a car with a 81/4 if you need measurements from the ujoints Was that measurement of 52 1/2 from center to center of the caps? Ask your driveline shop how they want you to measure just to be sure. I'm getting ready to do the same swap, and glad you had that measurement, saves me from having to crawl under the car.
Bruce
 
My friend just did the 7 1/4 to 8 3/4 swap he had a new driveshaft made up at a cost of 240.00...you measure it by inserting the trans yoke in the trans then pull it out 1" and measure center of u-joint cap to the center of the pinion yoke,make sure the car is on the ground or a drive-on lift...
 
The measurement was the from the front end of the end cap to the rear end of the end cap. My dad has a '74 Duster same trans, with an 8 1/4. I'm sure I can use the measuremets off the Duster to give to the driveshaft shop?? I also think I need to see if the u-joint will fit the pinion yoke, correct?
 
Heres a partial list of factory driveshaft specs, in case some needs it. I had a longer list in an excel spreadsheet, but had to shorten it, print it, scan it, and resize it before it could post it.

driveshaft.jpg
 
I had a drive shaft cut for a truck of mine. The tech at the shop just told me to measure from the rear of the transmission output shaft to the center of the center of the pinion. Then he took my shaft and done the rest. It was shortened about 3" cost me $60.00.
As far as yoke, in todays rodder market you may be able to take both u-joints to a good parts store and match the 2 into one. what i mean is they make u-joints with 2 different size caps on one joint.
 
speedyb-cc...you were right it had to be cut down 1.6 inches. Got cut at the driveshaft shop and it fit perfectly. Thanks fellas!
 
You must log in or register to reply here.
-

Back
Top