Tranny swap and pinion angle question

[rallye72]

I'm doing a complete drivtrain swap in a 73 duster, I have to weld on new spring perches on an 8 3/4 and was wondering if I use an angle finder can I use the same pinion angle measurements from the 7 1/4 rearend that I removing? I'm also installing a 727 in place of the 904, the 727 is longer so will that effect my pinion angle significantly? I dont have the engine and trans installed yet, and still need a drive shaft made for this car so mocking it up in the car won't really help me, Plus I need the rearend in the car along with the engine and trans for a drive shaft measurement. Kind of a catch 22.

[FASTDARTCHESTER]

Isn't there a pinion angle measurement for the 727/8 3/4" setup in a manual for the Duster? I think 5-7 degrees nose down is std.

TD

[rallye72]

I looked it up in the mopar chassis manual and it shows how to do it with the drivetrain installed, but I'm missing my driveshaft. I took measurements before I shipped it, but made a mistake. I put the rearend on jackstands and a floorjack on the pinion snubber, with the pinion yolk at 90 degrees the perches were at 5.5 degrees. Now my mistake is, is it 5.5 degrees with the pinion up (closer to the floor pan) or 5.5 degrees down (pinion closer to the ground)? Thanks

[dwc43]

5.5 down since the pinion rotates upward on acceleration.

[rallye72]

I will take better notes from now on. You're not messing with me because of that toothbrush joke are you?

[dwc43]

Nawwwwwwww!!!!

[madscientist]

You need to have the drive line in the car to set pinion angle. 5.5* either up or down doesn't mean anything. Pinion anglr is the relationship of the pinion to the driveline, not the ground. If you put it 5.5* down (relative to the ground) and the drive line comes in at 5.5* down (relative to the ground) you have an 11* pinion angle. If the drive line is parallel to the ground, you could set the pinion angle relative to the ground, if the pinion and the drive line are on the same plane. You need to install the drive line and measure the difference.



M.S.

[rallye72]

I'm talking the relationship between the pinion and perches, can I use the rear I just removed from the car as a reference?

[madscientist]

You can try it, but, if the trans is longer, it will affect pinion angle.



M.S.

[rallye72]

thanks for the help

[rallye72]

I pulled out the 7 1/4 from my duster and found it to have a nose up attitude, Nothing like the set perches that were on the 8 3/4 I want to install, with a pinion angle nose down, Looks like the driveline has to go in to get this crap right!

[madscientist]

Yup, you will. And the 727 is longer so that makes a difference. I also think that the 8 3/4 is slightly longer than what you had. This will make a difference as well. I could be wrong about the difference between the two rear ends, but that all changes everything too.

[ehostler]

AS stated above, if you want to do it right, you need to make the measurements with the drivetrain installed.

[ehostler]

Here is a good article that someone had posted in the past.

Driveshaft angle