Driveline angles changes in a drop

[gkesseru]

From another thread I was directed to read the importance of minimizing U-Joint angles changes in a driveline system.
see http://www.drivetrain.com/parts_cata..._problems.html

Using this info, it infers that when you drop the rearend you should also raise the transmission mount and the front pivot point of the trailing arm in a coil spring suspension to keep the u-joint angle back at 0 degrees. (for leafs they recommend shims)

In my 68 shortbed, the trannie mount is 38" from the engine mount and the rear axle is 112". The front trailing is 49 1/2 in front of the rear axle centerline. Doing some quick calculations, for every inch of actual drop in the rear I should raise the trannie mount point .34 inches and raise the trailing arm front pivot by .44 inches.

For a 4" drop therefore I should raise the trannie by 1.36 inches and the training arm front by 1.77 inches.
Are there any frustrated engineers out there that agree?

[Rollie396]

I can't find the link I had but there are shims available for coil spring rearends.Unless I'm missing the point.

[fixit-p]

You never want your u joints to have 0* operating angle, the needle bearings in the caps cant rotate. Always maintain a minimum 1* use speed chart for maximum operating angle, what you want to shoot for 0* is the pinion angle.
Lots of good info here>> http://www2.dana.com/pdf/J3311-1-DSSP.pdf

[gkesseru]

Thanks for the reply. I'll shoot for "almost" 0 degrees. I do doubt that I can measure to within .1 degree accuracy. The main point here is to keep the geometry close to factory specs for a shortbed, you should raise the transmission mount about 1/3 inch and the front trailing arm about .4 inch for each inch of spring shortening. The reason I brought this up is that none of the discussions I have read at this site cover the need to raise the transmission mount point as well as the trailing arm pivot point. Several have mentioned the need to move or replace the trailing arm mounts. If a lowered rear end messes up the rear yoke geometry, then it would also mess up the front yoke geometry.

Here's the plan: Once I'm ready, I'll put the engine and transmission in, remove rear springs and use a jack to raise the rear axle to proper height and do some measurements. I can them shim the transmission and move the trailing arm fronts until everything measures well. Then I'll cut the trailing arm mount rivets, flip them upside down if necessary and remount at the proper height.

[gkesseru]

Just read the Spicer Dana write-up. Great read. It pretty much explains what needs to be done:
1. Keep angle from transmission to drive shaft between 1 and 3 degrees.
2. Keep angle from driveshaft to differential front yoke between 1 and 3 degrees.
3. Make the previous two angles as close to equal as possible.

[fixit-p]

Originally Posted by gkesseru

Just read the Spicer Dana write-up. Great read. It pretty much explains what needs to be done:
1. Keep angle from transmission to drive shaft between 1 and 3 degrees.
2. Keep angle from driveshaft to differential front yoke between 1 and 3 degrees.
3. Make the previous two angles as close to equal as possible.

On a two piece drive line it's a little different, the first drive line should be installed so that the universal joint at the transmission has an operating angle of 1-1.5* and the axle's centerline needs to be parallel with the first drive lines centerline and not the transmission like with the one piece.
Most of the time I see pinion angle corrections the axle is cut from the saddles and rotated up or down then the saddles re-welded or using wedge type shims between saddle and trailing arm. Your idea of shimming the trans and raising trailing arm mounts makes sense especially if one doesn't have the means to cut and re-weld saddles.

[gkesseru]

It's the simplest way I can come up with pointing the transmission to the rear yoke (within 1-3 degrees). Thanks for the feedback. It encourages me to hear the voice of experience.

[fixit-p]

Originally Posted by fixit-p

You never want your u joints to have 0* operating angle, the needle bearings in the caps cant rotate. Always maintain a minimum .1* use speed chart for maximum operating angle, what you want to shoot for 0* is the pinion angle.

Oops where did that decimal come from I meant 1*