Stub shaft angle questions

[boondockster]

I do not agree. Length has nothing to do with it. In my opinion, drive line vibrations can occur because of four reasons:

1. Out of balance (this could also include a bent shaft or sloppy splines)
2. The U-joints do not form a supplementary (180 degree) angle
3. The U-joints are running at too great an angle, causing binding
4. Other binding (this is the issue with this setup and I explain below)

If you map the path of the U-joint cups, they follow an elliptic path; i.e. they speed up and slow down twice per revolution. That is why you typically want the joints to be form an 180 angle. That way the two elliptical paths (90 degrees relative to each other) cancel each other out resulting in a net path close to a circle. The U-joints do not know the length of the shaft, they just know the angle they are running at. If you keep the U-joint angles within spec and there is no other significant imbalance or other sloppy components, there will not be any noticible vibration.

In this situation however, since there is no splined slip, there will be problems if the tranny and transfer case move relative to each other due to things like rubber mounts, frame flex, etc. When they move, the shaft wants to change length but it cannot because there is no splined slip which will result in excessive loads on the U-joints, the tranny's output bearing, and the transfer case's input bearing. This will be felt as a vibration.

You could run that short of a shaft if it had a splined slip and the U-joint angles were within spec. The reason that Bob and Bob have had good experiences running the very straight shaft is simple geometry. A straight shaft that has an end wanting to move up or down translates into almost no axial displacement. A non-slip shaft at a steep angle that tries to move up or down will result in a relatively large axial displacement but since there is no slip it binds against the bearings,

So, Bob and Bob are right that a straight shaft (almost no angle at the U-joints) will run good, just for the wrong reasons. It has nothing to do with the length.

[fng]

Outstanding Answer!

[saxon]

I got with the t-case with the factory slip stub shaft,(so there must have been a steeper angle on the dodge doner) because it was out I did'nt see the original mounting angles. But because of my limited length options,I can't use the slip yolk. I think I'll shorten up the stub shaft as much as possible, and raise the unit to be directly behind the trans.(like whats been suggested) I'll have to hog out and cap the through compartment. Keep all the knoledge coming and opinions too, I love it! Thanks

[BCOWANWHEELS]

gee i wonder why the stock m715 jack shaft is perfectly straight. i,ve said my piece.
bob

[rpgdeity]

Well obviously the stock 715 jackshaft was perfectly straight, as well as every Ford/Dodge/Chevy jackshaft I've seen was straight. The U-joints in your driveshafts would last much longer too if they were straight, but that is not an option, obviously. Saxon CAN'T raise his x-fer case up because he would have to cut heavily into the 715's "cross box" due to the extra length by the added Gear Vendor Overdrive. I am not agreeing that his setup will work well, I think he will have problems due to the fact that his jackshaft has no slip joint, I'm just stating why he is trying to do what he is trying to do. So if he puts a new jackshaft with a slip joint, and he is within acceptable working angle of the ujoints, then he should be fine, right?

[boondockster]

That is what believe rpgdeity. Less angle is obviously better but it can be done, if done properly.

BOBCOWANWHEELS, I already agreed that stright is better. You're not the only one here with experience.

[BigWheelBob]

Normally, max operating angle of a ujoint is 3 degrees, As the angles grow, so do the magnitude of the accelerations and decelerations, and the less effective the matched angle are at eliminating vibration.

[tacoma]

3* huh? No truck I've ever owned has had ANY Ujoint angle that small.

I don't mean to sound insolent. This topic has really got me curious. Unfortunately I have not been able to do any reading whatsoever, as I have been printing an enormous run of books at the shop.

Carry on, gents.

[Mikel]

All you ever wanted to know about driveshafts, but were afraid to ask:

http://www.pirate4x4.com/tech/billav...aft/index.html

[BigWheelBob]

3* huh? No truck I've ever owned has had ANY Ujoint angle that small.

I don't mean to sound insolent. This topic has really got me curious. Unfortunately I have not been able to do any reading whatsoever, as I have been printing an enormous run of books at the shop.

Carry on, gents.

Really the joint operating angle has some to do with the shaft speed. I think it is something like 5000 rpm of shaft speed, as in the 715 1 to 1 trans, is good for 3.25 degrees of continues operating angle, and if the shaft rpm were 1500, the angle would be good for 11.5 degrees. There is tons of reading out there on joint angles, so help yourself peoples.