I started asking this question awhile back after I first got the truck, and I'm posting it in the 1st gen and 3rd gen engine & driveline forums now as well, because it not generation-specific. I believe it actually involves a universal principle applying to all vehicles which employ a driveshaft and u-joint type driveline.

More searching revealed a thread with this link to a Dodge TSB about driveline shudder. In it you will find a diagram which clearly shows what I am talking about.

http://dodgeram.info/tsb/2004/03-003-04.htm

Note 1 in the diagram towards the bottom says the rear's pinion angle should be set up with the output shaft and pinion yokes in what they refer to as a "parallel plane." This was always my understanding building chassis/rear combos for Mopar drag cars (taking into account negative angle compensation for torque-induced axle wrap and suspension travel relative to the particular setup/combo).

Now mine is not like that and it is bugging the chr@p out of me. I want to make it right when I get around to the Gear Vendors OD upgrade here pretty soon. According to everything I knew before and now this TSB I just stumbled across, the pinion angle should be equal and OPPOSITE the output angle for proper setup (in the same plane). Mine is equal but exactly NOT opposite. i.e. it basically has the driveline wrapping from the output up front around and down into the rear through the same arc, if you can imagine that. I'll post a pic if anyone needs it to really understand this.

BTW, there are no ill symptoms, vibration, shudder, etc. at my current power level, but I am afraid I'll see a catastrophic failure at some point, if I don't make it right.

So. How do you guys with the high lifts and traction bars for sled pulling and whatnot do the pinion angle on these 4x4 trucks? TIA for any advice.

 

I will be interested to hear more about this as well. I am no expert, but it has been my experience, in dealing with my tractor implements' PTO shafts, that having one of the joints as close to straight with the shaft as possible, even if the other joint is at even more of an anlge, makes the driveline quieter. When I hook up my tiller I angle the tiller, using the 3 point hitch, so that the PTO shaft is as close to direct alignment with the input shaft of the tiller as I can, and on the other end, going into the tractor, I have a heck of an angle, but this is quiet and relatively vibration free. If I do not angle the tiller correctly, and the u-joint on the tiller end has too much angle in it the driveline gets noisier and more vibration is felt.
Hance why I am interested in the theory here. I can actually test it with my tiller driveline.

Thanks,
Chris

 

I'm pretty sure it's just to cancel out vibrations because the u joints will be binding at opposite times, which cancels any vibration out. If they weren't in the same plane you could get some resonance which would be a vibration. The front is a whole different ball game because it has a CV in it. In this case you want the pinion to be exactly parallel with the front output shaft of the T case. At least this is what I've always read...

If yours isn't perfect and you have no vibrations then I wouldn't worry about it.

 

OK, here's what we're looking at:

http://66.17.171.114/PhotoAlbum/Cars/Pics/CTD_68.jpg
http://66.17.171.114/PhotoAlbum/Cars/Pics/CTD_69.jpg

Is that some seriously whacked positive pinion angle, or what?

 

I found this, which may answer some questions.

http://www.4wdonline.com/A.hints/Universal.html

Chris

 

That rear diff does look weird. Id swear the rear diff on mine (which is a 4wd so no carrier bearing) is pointing straight back and not up. You might have gotten some wrap from loose axle clamps? Maybe ljack the frame and loosen the four nuts on both sides and try to twist the diff back so its level with respect to the transfer case. I cant remember if theres a slider on the rear shaft to accomodate slight changes in length, or if that was only the front. I dont think theres anything solid above the diff you could use a bottle jack on, so twisting it down wont be easy.

 

No, the axle housing is snug down on the 3 degree shims that the PO who installed skyjacker springs under it last year put in - BACKWARDS! At least that is the theory I'm going on now.

The rear pinion is definitely riding about 2-3 degrees nose up, approximately equal to the TC output, anglewise. But obviously the same "wrong" angle. It should be about that matching amount nose down. It's not causing any problems or vibration because the angles aren't too extreme, and there are no blocks between the springs and perches anymore, so axle wrap is going to be minimal anyway.

But it is at a disadvantage, torque control-wise, according to all the conventional wisdom I can dig up. So I will reverse the shims soon as I get a chance and see what it looks and drives like then.