Drive shaft alignment

Shaun · #1 (**permalink**) 07-29-2002, 11:15 AM

Cannot seem to get a straight answer on this question. What is/are the proper alignment "angles" of the rear pinion to the engine that will limit U joint wear?? I have heard things like, the pumpkin needs to be about 3-4 degrees down angle and the engine needs to be about the same. Also heard they should be "parrallel" to each other. Can anyone give me the "right " answer backed with some facts?? MUCH APPRECIATED!!

Bob Putnam · #2 (**permalink**) 07-29-2002, 12:10 PM

Ideally, the driveshaft and transmission axis should be parallel at ride height. Depending on how flexible your rear suspension bushings are, you might angle it down 1-2 degrees so that on accelleration it becomes parallel, but it's not that critical unless you've got very soft bushings.

It doesn't hurt to check for driveshaft u-joint bind at full jounce and droop...

Roscoe · #3 (**permalink**) 07-29-2002, 02:02 PM

I put in adjustable upper control arms in order to get my pinion angle correct.

Check out:

http://www.drivetrain.com/driveline_angle_problem.html
http://www.go-fast.org/z28/pinionangle.html

Roscoe

Shaun · #4 (**permalink**) 07-30-2002, 11:22 AM

Thanks! I found a few websites that explained proper alignment. Seems that for no vibration, the rear pinion and the xmission slip shaft have to be parrallel but in two plains.

Shaun

Campy · #5 (**permalink**) 08-01-2002, 08:53 PM

Shaun,
That is exactly as I understand it. The reason for the two planes is that it causes a "stir" in the drive shaft. There needs to be sufficient stir to help reduce vibration and help lubricate the u-joint bearings. Just how much stir is left to the experts

Cobra20646 · #6 (**permalink**) 08-02-2002, 07:14 AM

Shaun,

To add to Campy's post.....

The center lines of the transmission yoke and the pinion yoke should be parrallel non intersecting lines. When rotating, the U joint does not rotate in a circular mannor, but rather in an elliptical pattern (each joint rotates this way). When properly installed, (parallel non intersecting) the elliptical motions are canceled out, and smooth, rotation occures.

Another important thing to consider is the angle between the two U joints. Too much angle can cause binding and eventual failure of the joint. If my memory is good (?), angles of 12 to 14 degrees can be safely handled. I understand that vehicle manufactures strive for angles not to exceed 7 degrees.

The amount of distance between the two parallel lines becomes important when considering the length of the drive shaft. A longer drive shaft can tolerate more "offset" than a shorter one to maintain the same drive shaft angle.

Also, there can be two offsets. One in the vertical plane and another in the horizontal plane to further confuse the builder. I believe simply adding these two angles together will provide you with the total angle that must be in the 12 to 14 degree range to be satisfactory.

An IRS is easier to design for as there is no change in the drive shaft angle during suspension travel. With a live axle, you must consider this travel in your calculations so as not to put the U joint into a binding situation when the axle is at pushed to its limites.

Im drawing this from memory....... somewhere in my files at home I have the reference material and web sites from which they came. I'll post them later if you would like them.

I hope I didn't add to your confusion ;-)

- Jim -

justa6 · #7 (**permalink**) 08-02-2002, 07:43 AM

Maybe someone can help me with a problem I'm having.

My car tends to "eat" the rear universal joint in 1000 miles or so. BUT it only damages the two cups that are bolted (u bolts) to the pinion yoke. The other two bearings (pressed into the drive shaft) are perfect. If it were a misalignment wouldn't all four bearings show wear?

The car has NO vibrationg in the driveline either under acceleration of deceleration.

Any ideas?

Regards,

Junket · #8 (**permalink**) 08-02-2002, 08:26 AM

Justa6
Somthing you might look at some of the C clips on the joints don't make a 3/4 circle make sure they sit completely in the yoke and not in the bolt side as it would cause a movement. Also if not make sure the studs on Y joint if equipped are in good shape.
Good Luck Ken

justa6 · #9 (**permalink**) 08-02-2002, 09:02 AM

Thanks for the reply. The universals that are on my car don't have C-clips. There is a "tang" on the pinion yoke that holds the universal in the yoke and then U bolts hold it in place. I've got an idea that because of the short 8 1/2" driveshaft the pinion angle may be off a little. (Down) I just can't figure out why only the two cups that are in the pinion yoke wear but the other two show no wear at all...

Regards,

Cobra20646 · #10 (**permalink**) 08-02-2002, 01:09 PM

Bob,

Any chance of the cups becomming distorted following installation due to too much torque applied to the wrench?? Also, are the 'U' bolts you're using the correct part to use with the pinion yoke?

Just throwing a few things out there....... like you, I can't understand why just these two bearings are failing.

- Jim -

justa6 · #11 (**permalink**) 08-02-2002, 01:53 PM

Thanks for the reply. When I was at Run & Gun last year we "ate" the rear universal. I was very lucky that the driveshaft stayed in place as I felt the vibration during the Road Race time trials. Thanks to some fine people there we got it fixed within a couple of hours. We thought at the time that I had overtorqued the U Bolts as only the caps in the U bolts failed. The other two were perfect.

When we put the driveshaft back up we did not overtighten them for sure. Everything worked fine for about 1000 miles with maybe 20 1/4 mile runs. When I was driving this spring I again noticed a VERY mild vibration on acceleration. I could even see it in my rear view mirror. Kind of like on a motorcycle when the mirrors "buzz".

Took the car home, put it on the lift, and pulled the driveshaft. Removed the bearing caps and again there were some of the needle bearings broken. Removed the universal and looked at the two bearings that are pressed into the drive shaft and they were perfect, again.

Its really hard to figure out why all four bearings don't suffer the same fate...

In closing, as I think I mentioned before, for the first 1000 miles there is no vibration. My rear view mirror is nice and smooth both accelerating and decelerating.

Thanks again,