Anybody know if the driveshaft has to be shortened when upgrading from a 7.25 to 8.25 rear axle?
Ok. Lived this one. Ended up having to have a whole new driveshaft made.
So that said learn from my misery and do this:
Put the slider into the trans. Leave it out about a 1/4 or so. Don't bottom it out on the trans. Then tie string from the u joint on the slider to the joint pad on the rear end. You would have removed the u joint to get the slider by itself. Make sure the car is on the ground or on ramps so there is weight on the chassis. Mark the flange location for the u joint on the trans side and on the rear end side. Remove the string.
Then measure the length of the string between the two marks you made. Add the width of 1 u joint cap.
This is the length you need.
Now find a place locally that makes semi truck drivshafts. Google is your friend. I found a place in Cincinnati called Republic driveshaft. Take them the shaft you have and the measurements. Tell them you want a new shaft with the old ends and you want it balanced. Do not have the old one cut...it's 30+ years old. Not worth it. They will use a new shaft. Replace the u joint and slap it in. Done.