Ok Guys I'm getting ready to take my 8-1/4 out of my 73 Roadrunner and installing a 9-1/4. Can somebody walk me through this ?
The 9-1/4 had the perches cut off of it before I got it. I have new perches but I don't think they will work with the ISO mounts that I have and plan to keep. I might need to cut the perches off the 8-1/4 and re-use them. Welding them on is not a problem ( I'm a good welder)
The things I need help with are :

1. Setting up the car ( should the chassis be level ?)

2. When I set the rear end should the weight of the car be on the rearend with jack stands under the axle?

3. When I set the pinion angle what should it be ?

4. Where should I measure the pinion angle from ?

I have done this before but never paid attention to the pinion angle I just centered it side to side and eyeballed the pinion so it lined up with the trans and it's worked fine. After reading some of the posts here it seams that pinion angle is more important than I thought 20 years ago.

Nobody ??? WOW !!!

Give it some time, folks are just getting out of work. I know there are folks here that can help.

The output shaft of the transmission and the pinion should be parallel to each other when the car is supported by the wheels or by four jackstands (two under the rear axle) that put the car in a level position.
Others may have a better idea, they'll post.
R.

I remember reading about setting it with an angle finder I hope I didn't waste a whole $10 on my Harbor Freight angle finder

Why can't you set it up the same as the 8-1/4" housing?

I understand the pinion pokes out farther but that shouldn't make a huge difference.

Aren't the 8 1/4 and 9 1/4 the same length from centerline of axle to u-joint?

R.

If that's the case, measure the 8-1/4 rear and stick the perches on the 9-1/4 in the same place and angle.

I was thinking about doing that. Measuring the distance from the floor to the yoke on the 8-1/4 then set the yoke on the 9-1/4 in the same place. This should get me in a good spot right? Will the pinion snubber from the 8-1/4 fit the 9-1/4 ?