Help me understand my drive line angles !!

[Canadian1968]

The car is almost all back together after replacing the rear floor and frame rails.  I just replaced both U joint and put the drive shaft back up in place.  I have been reading and reading about pinion angle and drive line alingment. I still dont' totally feel that I understand it.

I got an angle finder and crawled under the car. It is jacked up with stands under the rear axle, and then stands up front where the crossmember meets front rails.

I put the angle finder on yoke of the rear diff. I got a reading of 5* UP. Then i put it on the bottom of the case itself I get 9* UP.  I then moved to the drive shaft itself 4* UP . Then up to transmission yoke , i get 0*  I triend a few points on the engien tranny they all gave me 0*

From what i have read I want my rear differ to be pointing down about 3*  I am pretty far from that.  I dont' think I can leave it like this ?

I made a crude sketch of what I just tried to explain.

[six-tee-nine]

Really no expert on this subject, but my guess is that you want the pinion to face downwards as you say it should. when you put power on the rear axle the pinion moves upwards.
In your case the 9° will become even more when you accelerate. That will probably cause issues with the angle the U joint will make.
You'll need to look in to adding angle shims to get the pinion angle from 9° up to the desired downward angle.

The angle of trans and engine is what it is and stays that way. Unless you add shims to the transmission mount.
Dont know if that is something that is done because it could bring stress onto the engine mounts in the front.
I leave that to the more expierienst guys out here.

[Paul G]

Is the driveline that is in the car now original to that car?

[RallyeMike]

To accurately measure the angles you need to do things a little differently:

First, the car weight needs to be as typically loaded. Put the front tires up on ramps or blocks, and support the axle with jack stands on the axle tube or centered along the axle on the bottom of the shock plate. If you support the car anyhow else, the weight on the rear axle and vertical location of the axle will not be per driving conditions and the nose of the pinion will be slightly rotated due to the elliptical springs. Do not support the car by the control arms or frame.

For accurate measurements:

For the engine, measure off the engine block oil pan rail. The angle finder typically can be held slightly at an angle to get it on the rail instead of the pan or pan bolts. The rail is aligned with the crank and output shaft of the trans which is why you want to use it.

For the driveshaft, just measure off the tube.

For the axle, take off the pinion snubber and measure across the top flat surfaces where the snubber mounts.     

If the car is in stock configuration with motor and trans mounts in good shape, it should be easy to adjust the angles to perfection only by shimming the trans at the trans mount.

[Canadian1968]

Yes this is all the original drive line of the car . I just replace the floor frame and perches . The springs have all new bushing and shackles and I put in new shocks .  The car has been up on stands for the last 7 months. I have not put it back on the ground yet . Maybe I should do this and rock the car a bit let everything settle into place . The jack it up again and check my angles again??

[john108]

Look at this website and see if it helps.

http://www.moparts.org/Tech/Archive/axle/8.html

[Paul G]

Look at this website and see if it helps.
http://www.moparts.org/Tech/Archive/axle/8.html

That is a great write up. Easy to understand.

If you are putting the original drive line back in the car it should be correct and not need adjustment. Doesn't hurt to verify it though.

You should drive the front end on to stands and raise the rear axle with a jack, then support the axle on stands. That keeps all the load distributed on the suspension properly. Jacking the front up and setting it on stands, is not the same as when the weight of the car is naturally resting on the suspension.

[Canadian1968]

Ya I had already read the article before I posted . I will keep working on it . I do have the front on jack stands so I will see if I can get some ramps some where . Will keep everyone poste