Swap from 7.25 to 8.75 advice

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Penstarpurist

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So my son picked up a '71 dart parts car. It has the 8.75 in it with 2.76 gears, 741 case. He bought it to swap the rearend into his '71 valiant to upgrade from the 7.25. His question was, "do I have to swap to the springs that came with the 8.75 or can I reuse the current springs from the 7.25." I told him I thought that he would need to swap the springs out as he has to use the 8.75 shock plates with the 8.75. And it seems to me that the 8.75 would have thicker stiffer springs and his 7.25 springs are sagging anyway. I think his reason for not swapping them out is the extra work to completely remove the ones in his valiant.
 
while it's true that you don't have to swap the springs, I would suggest that this is the prime time to put in some fresh springs and restore the stance and handling of the Valiant. I would suggest ESPO Springs and Things as a vendor. A set of springs with a fresh front bushing pressed in is downright CHEAP. You can order 5 leafs per side like performance a bodies had from the factory and even have the springs custom arced for up to 2 inches of raised ride height (in .5 inch increments). No shackles, no air shocks, no sagging back end...
 
If the donor car was a 340 car it should have heavier springs in it. You can keep your existing springs if you like, they will work but you need to use the larger shock plates to match the bigger axle tube.
New springs would be idea but its not hard to change them later. Just do one side at a time and its an easy job. I believe your going to need the driveshaft as well.
 
It was a 318 car, his valiant is a 318 car. Both are 2 door cars, 904 transmissions. But we did get the driveline as well. It came as a complete full drivetrain from radiator to rearend. It was a coastal range car, so it is completely rotted from the middle of the car to the bottom of the quarters. Lots of good parts on it. Pulled the numbers matching engine and transmission already. As well as the driveline and rearend today. Pulling k frame and front suspension next. Then glass, dash, seatbelts, etc. Is the dart a longer wheelbase? I know dart and dusters differ.
 
Check wheel base between the Valiant and the Dart - the dodges are often a bit longer and that shows at the driveshaft length. Somebody got a chart that has the answer???
 
Here ya go for driveline lengths.
(I didn't put the red box on it so disregard that)


driveshafts.jpg
 
Looks like there is a difference between them in length. Hopefully between the two driveline one of them will work. Cause the $ the driveline shop charges is no joke. Our big block duster was $350 for a driveline.
 
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