I started asking this question awhile back after I first got the truck, and I'm posting it in the 2nd 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 hear ya on the increased down-angle pinion and axle wrap. Especially on the mopars which like to rise when axle wrap occurs (love them SS springs )

The only thing I can think after reading that is they are considering a load on the back of the truck either in the bed or as tongue wait. The truck is not going to rise and the axle 'shouldn't' wrap due to the thickness of the spring and the length of the front segment. I would guess the front segment is quite longer than a A or B body spring. ( Remember B-bodies use a modified front spring hanger to make the front segment of the spring shorter. Amplifying the rotation/rise. )

Picture the pinion angle from the side of the truck without cargo weight and then picture weight added. The rear axle would rise rotating the opposite way on the front segment giving you negative rise on the front segment and increase the pinion angle. Opposite of a mopar car launching under hard acceleration.

My guess is:
-For the car you need the increased down angle to counteract the rotation decreasing the pinion angle.
-For the truck you need the decreased down angle to counter the opposite rotation increasing the angle.

Edit: Also the SS springs have a heavy front segment and a thinner rear segment which helds the axle roll/lift. Allows the spring to bend the rear segment. The scary "remove the rear clamps on stockers" comes to mind



Den

 

I have a fairly sophisticated SS setup on my 340 Duster right now (Caltracs, truck shocks, beefed up 8 3/4, the whole 9 yards), which I basically built myself, so I understand what you're saying - except the part about the difference with weight on the truck doesn't quite do it here.

Pinion angle should go more negative with more weight right? This suspension won't go down more than about 4 -5 inches MAX no matter how much I put on it due to the Timbrens, but that is beside the point. The way it is now, the pinion couldn't do more than coming down to zero degrees relative to the driveshaft, which still makes it positive relative to the output - actual positive pinion angle to start with under ANY load. So unless the Cummins is rotating the opposite direction or the D70 pinion somehow pulls down rather than climbs the ring gear under torque, it seems to me I'm looking a weak link that gets worse under increasing power.

Did that make sense?

Paul

 

So at the present time you have neutral (close to zero degress) or up angle while resting static?

The TSB is increasing the downward angle. The 91 manual says 1 degree. They've changed it to 3.

What condition are the springs in?
Do the front segment still have an any arc to them? If they are flat or bowing the opposite way that'll add negative pinion angle.

As for the weight rotation theory... Hold your index fingers 24" apart (front segment length). Right hand is axle. Now raise your right hand 4-5" and look at the angle between your to fingers. That was what I was thinking about.

All this aside..I say go for a slight down angle. Not the 8 degree car thing..but between 1 and 3.

I just went and looked at mine and it's a slightly downward. I have a magnetic 'angle thing-a-ma-jig' at work. I'll check my axle tomorrow if you want.

Got a digital camera? Let's see a pic

Den

 

If you have 1 or less degrees, the u-joint will fail early do to the rollers not moveing far enuff in the u-joint cap causing pit in the surfice and if the u-joint angle is grater then 4 or 5 degrees you can get a vibration that the T.S.B. depicts........ a .......allthow the theary is good on that T.S.B...A what thay found out was that the u-joint were not getting vibrating form bad angle but that the u-joint were'nt loose when thay are wearing out, but thay were seizing!!!

This T.S.B SHOULD BE THROWN IN THE TRASH!! ..........exsept for some vary remote situations!!!!!

the u-joint were seizing in there caps due too.....I don't now but have my thieryssss ......... any ways, these u-joint would get so lock up that when you would undo the bolts to the rear of the rear end and get the prybar out to brake it from the rear yok it would eather drop the rear end down or would sling out and try to knock you out!!!(mostly when it was the mid u-joint that when bad).. or at least off you feet!!!
luckoly the first time that i had expierenced this, the drive line swung a way form me instead of at me!

vary rarely dus a 03 and up u-joint get loose and vibrate... it lock up and shakes......on the rear that is

Even with are vary stiff spring you would be amazed how much that pinion will pich under a load!

 

Yes, it's got positive pinion angle at rest, no load. That was what I meant describing the u-joint angles going through the same arc front-to-back. Springs are like new, no probs there.

As for the load changing angle, I haven't checked it precisely yet, but it I am absolutely certain it could not be enough the get out of positive pinion angle territory under any circumstances.

I am really starting to think what happened was the PO put the perch shims in backwards when he installed the Skyjackers, and for some odd reason it has just not done anything weird running positive pinion angle. I think I'm gonna take it apart next weekend and do some real checking.

Too little angle is probably the reason for the u-joint problem. They need at least a couple degrees in order for the bearings to move.

 

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?

 

the front look fine to me but the rear dus look nose up

Have you put a angle finder on the drive shaft of the u-joint and the compered to the yok side of the u-joint (nose up or down.

I know that the rear end is point nose up but is it actualy nose up compaird to the drive line?

It shore look like it.....just curious if it real is!

 

If you read the TSB it states. I think this is what they are refering to.

NOTE: This bulletin applies to vehicles equipped with a two piece rear driveshaft.

Meaning ones with carrier barrings. The angle from the transfer case is almost flat to the carrier barring. There is quite an angle to the rear end from there. To fix this you shim the carrier barring with a piece of 1" steel thus making the angle to the rear end not so drastic thus making the shutter should go away or decrease.
If I'm wrong let me know.

Greg

 

The reason I referred to that TSB was because it had a diagram that describes the plane of the front and rear yokes which basically describes pinion angle. Pinion angle is relevant to proper driveline setup in any u-joint/driveshaft application, two piece or single shaft. I thought I would need that to get anyone to understand what I was talking about.

The TSB calls for zero degrees pinion angle in these 2-piece shafts with carrier bearings. Single shafts should have a negative pinion angle to some degree. Probably anywhere from 1 to 3 degrees in the case of these trucks. More for ones with blocks, maybe less for setups like mine, but certainly not positive!

Flash, no fancy measuring tools required to see this one is definitely a few degrees on the positive side. That basically means the way it sits now, if I ever get it into a high-traction, high-torque situation it will probably twist that u-joint to bits. Probably only reason it is still there is the truck hasn't been really slammed much back there yet and these 1410s are STRONG.

OBTW, Gear Vendors claims a yoke with the spline to fit their output shaft and a 1410 joint does not exist. Could be, but I doubt it.

 

ACE.
In a sever situation the slip spling could slide out
probably not but it is some thing to consider.