pinion angle

[68400BIRD]

I thought I would try this again. I had a post in suspension but felt that it would be better in here. I'm working on setting the pinion angle in my 1968 Firebird. I'm installing a 12 bolt that was originally out of a 1968 Camaro. The perch pads had already been removed.

This is what I have right now. The car is not on a level surface but the car is on it's suspension and is sitting on the ground.

Front u-joint cap that is closest to the output shaft on the tranny 2 degrees angling down.

Drive shaft closest point to tranny is at about 0 degrees.

Driveshaft closest to rear pinion has a angle of about 1-2 degrees angling down.

U-joint cap closest to pinion has a angle of 4 degrees angling down.

I put the driveshaft at 0 degrees closest to the pinion and the lower u-joint cap on the pinion had a angle of about 2 degrees angling down. I added in two more degrees angling down to get to 4 degrees and that put the drive shaft at 2 degrees angling down. If needed I could shim my tranny mount up a few degrees or shim the rear a few degrees one way or the other.

Does this sound close enough to weld it solid???

[another69]

Maybe I don't follow you, but it sounds like you have 2 different angles on your driveshaft?

Re- measure at 3 spots: 1) trans output or seal 2) drivshaft angle 3) rearend yoke. Make sure the areas are clear and retry several times until you are sure they are correct.

You're kidding about welding solid, right?

[John Wright]

Rob, I think when you put the angle finder on the driveshaft itself, it confuses the numbers.
Use the pinion angle(placing the angle finder on the pinion across the flats of the yoke) and use the tailshaft angle(measured by placing the angle finder on the end of the tailshaft) and work out the numbers from there....but be sure to zero your angle finder on the flat of the rocker panel or top of the sub-frame...something to keep the angles relative to the car and not the floor the car is sitting on.

Hope this makes sense.


another69, I think he's talking about welding the spring perches...not the drive shaft.

[John Wright]

Copied off a website online.... http://www.buickperformance.com/Pinion.htm

"measure across the surface
of the rear transmission seal vertically(see illustration 1). This
surface is perpendicular to the output shaft of the trans, so
subtract the measurement from 90 to get the drivetrain angle. Let's
say that the measurement is -2 degrees(pointed down). That is our
reference point. Look at illustration #3. The pinion angle is the
difference in the angle of the rearend to the angle of the
drivetrain. So, in order to have zero pinion angle, the rearend
would have to be tipped upward (pinion yoke pointing upward) 2
degrees. If our drivetrain angle measured -5 degrees, we'd have to
tip the rearend upward 5 degrees to have zero pinion angle. Get it?
Now turn the pinion yoke so that the u-joint cups are sideways, and
measure across one side of the pinion yoke vertically(see
illustration 1) where the u-joint strap connects. Again, this
surface is perpendicular to the pinion, so subtract the measurement
from 90 to get the rearend angle. compare this number to the
drivetrain angle to get the pinion angle. If the drivetrain angle
was -2 degrees(pointed down), and the rearend angle measured +1
degrees(pointed up), then the pinion angle would be -1 degree. If
the drivetrain angle had measured -2 degrees (pointed down) and the
rearend angle had measured -3 degrees (pointed down) then the pinion
angle would be -5 degrees."-end quote

[another69]

Oh- the perches- duh!

Try to have your pinion point down to whatever your "level" reference point is on a leaf spring car.

[68400BIRD]

Thanks guys. I think the biggest blunder on my part was that I was confused on postive pinion angle. I thought anything past 90 or 0 would be postive. What they mean is that you want the pinion and tail shaft parallel to each other. So with that being said you don't want the pinion angling up any more degrees that the tail shaft is pointing down. from what I have read you might want it down just a few degrees for pinion wrap. I'm still running leafs and they have the most deflection out of all the different style suspensions.

[MonzaRacer]

Very simply, get a digital level at Sears, put one ujoint cap down on the diff. zero the level on the drive shaft, then put a socket on the ujoint cap, and set the level on the socket. figure for drag racing in the 3 to 4 degree down, for ujoint longevity keep it in the 2 to 2.5 degree down.
Most drag cars I set in the 3.5 to 5.5 range, pinion angle is the tuning point for bite at the track. figure more down makes it bite harder, less loosens up the bite.

[Skip Fix]

I just went though doing pinion angle. The digital is SO much easier to read than the normal swinging pendulum ones! Wixey from Amazon. I couldn't find one at my local Sears.

The guy that welded the perches on my 12 bolt had it with 14 degrees negative! I had to get some of the higher angle in steel to get it right. Many of the 4x4 places have them. Blue Torch had the nicest finish. Most bolt on the spring using the bolt or you can drop them over the bolt head and add a centering locator for the perch or weld to the perch.