I have been reading a number of past posts about pinion angle and I must say, I am very confused on the subject. I would like to determine what I need to do to my car, if anything, regarding pinion angle. So I would like to explain what I am doing and hopefully I can get the answer I need. I have pulled the slant six, 904 and 7 1/4 rearend out of my 68 Dart and I will be replacing them with a big block, 727 and a Dana. I also plan on moving the rear end back 1-1 1/2" for tire clearance. What will I need to do to be sure that when the perches are welded on the rear end housing that I have the correct pinion angle and what should that angle be? Will I have to wait until the engine and trans. are in the car to set the angle or can it be done with the entire drivetrain out of the car? Is there any chance the angle on the rearend will be O.K. as-is so all that would need to be done is weld the new perches on parallel to the old perches?

You'll have to have the drivetrain installed & the car level & the Dana moved laterally so the wheels are centered equally. On moving the Dana rearward be sure & mockup & check the rear shackles & you want the bottom end of the verticle shackles to point somewhat rearward & with that in mind you can only go so far more to the rear. Then you tack weld the perches to locate them then dissassemble & take out the springs & complete the welding. On the angle you could weld them at the std A body angle for a marketable commodity if you ever resell it & use shims if needed to get the angle right or if the trans is ie 3 deg "UP" then you'd want the Dana 3 deg DOWN plus an additional ~2 deg down as the pinion rises on accelleration so you end up with the trans & the Dana parallel but in different planes. I dont have the final word on the angle situation so wait for others with more knowledge to chime in

Personally I'd wait until you have the driveline where you want it, esp if doing a custom install, I'd install the springs,desired tires, ride height, etc, etc...I'd install the axle on the perches in the springs UNWELDED, so that I can rotate the housing/pinion angle to where it's required, then tack weld, remove, finish weld, re-install, keep in mind there are a lot of variables in setting your pinion angle, I'll assume this is street use only?, if so remember the pinion on average rotates upward 2-4 degrees upon acceleration, so you need to factor that in, based on what your final driveline angle is, you want to see at least 1, and 3 degrees max deflection of the u-joints

mike

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I'll assume this is street use only?

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Yes it is.

How are you going to move the rear back?

I found the first part of this in the yellow-orange area helps you understand it alot. Ron
http://www.moparts.org/Tech/Archive/axle/8.html

The easiest way for the novice to set pinion angle is to install all of the drivetrain...(unwelded perches)jack the car up until the drive line is level, be sure to use jackstands, Then simply rotate the rear end housing down to the desired angle. 5-10 degrees for leaf springs, 1-3 degrees for ladder bar or 4 link. Ideally you like to see 0 degrees in a full race car at speed, but the gains for this are very minimal. I use one of these inclimeters found at most hardware stores for setting angles, they are inexpensive and do the job quite well.

Pinion angle is the relationship between the transmission and the pinion, NOT to the driveshaft and NOT to the ground.

Ideally, you want the pinion to become parallel to the transmission as the pinion wraps up a couple degrees under power. This is how a 2-joint driveshaft is designed to operate.

1. Make the pinion parallel to the transmission as a base-line when the vehicle's weight is resting on it's suspension.

2. Roll the pinion downward 2 degrees from this base-line and weld the perches.

The result is a true 2 degree negative pinion angle.