Front driveshaft-induced lurching in diff
 

I installed my lift a few months ago but finally received the correct U-bolts from the manufacturer for my 1350 front driveshaft. Excited to finally return my Jeep to 4wd, I installed the driveshaft last night. I previously had no problems in 2wd but with the front driveshaft in, oddly, there was a major clacking (more severe than a clicking...:what?:) or catching with what sounded like it was coming from the front differential. Even barely moving, it was bad going forward and even worse in reverse. When in 4wd, this did not happen, only in 2wd. And it happened even in neutral when rolling forward or back.

Needless to say, I spent the couple hours in the cold and dark removing the driveshaft as it's my daily-driver but I need to figure out what could possibly be catching. It's a JE Reel driveshaft but I know the driveshaft is functioning correctly. I was working on nothing else on the Jeep at the same time so I know it is a result of putting the driveshaft in.

Did the pinion slide too far into the diff or too far out during installation of the front yoke? Is there some way to fix that? I'm really hoping to not have to undo the laboriously-installed control arms, coils, shocks, etc, to take apart the axle. I can not for the life of me figure out why the catching/clacking/jolting/whatever would happen in 2wd with the driveshaft in but not at all when in 4wd. Any thoughts or suggestions are most appreciated. :bowdown:

I'd look closely at the flange and front u-joint. First, is the u-joint seated properly in the flange? If so then I'd have to suspect that u-joint, then that the flange was improperly machined. How too long does the shaft on the flange have to be to screw things up inside the diff when torqued to 160 or so ft/lbs?

Thanks for the response - the flange and u-joints both look good and were seated into each other properly (the u-bolts were able to easily be tightened all of the way). The flange itself also seated all of the way and looked good. I'm not sure whether I can control how far in or out of the diff the pinion is seated - it seems to all fit properly and snug when putting that nut on though to tighten the flange itself (before putting on the driveshaft/u-joint and u-bolts).

Again, the driveshaft must be fine since it drives, feels, and sounds properly when in 4wd but not in 2wd (when that front driveshaft is in). I would understand if the catching/jolting was happening in both 4wd and 2wd but it was only happening in 2wd. :thinking:

What angle are you running the u-joints at? 1350's have a pretty poor operating angle. They are stronger than 1310's, but 1310's have a better operating range. So it may be the u-joints themselves binding.

I haven't measured the pinion angle exactly but the angle is already pretty big. My coils are already almost touching my sway bar - and they frequently do touch/rub. If I were to increase the pinion angle any more, the coils would be jammed onto the sway bar. I'm rocking a 6" LA so it's pretty big and my pinion angle needs to be and is pretty big.

Again, I don't think it's driveshaft (or u-joint) related since it drove fine in 4wd with the driveshaft in, but just not in 2wd. And it's not a vibration/rubbing, it's a catching/jolting. I'm suspecting it may have something to do with the pinion bearing but I don't know how to fix or change this. :dontknow2:

aha. Here is the problem you may be having. When you rotate the pinion up like that, you cause it to get less oil. You may be starving that most outer pinion bearing for oil.

BTW: By moving the pinion up, you are making the operating angle smaller. Straight would be zero angle. As the angle is measured between the pinions plane, and the drive shafts plane.

But, i think you need to pull the dif cover and look for pieces of metal in there. And pulling the pinion to check the bearings would be a good idea.

I know this thread is old(er), but I have a question. I too am running at or very near 6" lift on my 07 4 Door Rubicon, and am running the stock driveshaft in front (soon to be replaced, due to issues with fat stock shaft contacting exhaust crossover at full left front droop). I have about 4.5 degrees of caster in my front axle, and it is a little bit "darty", or wanders as it is. I understand to correct that, I need upwards of 6-9 degrees of caster. In order to get that kind of caster, you actually lengthen the lower front arms, and rotate the pinion DOWN. As you do this, you make the driveshaft angle worse. Now, my question is, if you've rotated your pinion up, in order to run a CV style front shaft, you have got to have negative caster numbers. How do you hold it in the road?

There is two ways around this. The more expensive (and correct way) is to have the knuckles on the axle turned. This allows you to get a good caster angle, but also have your pinion pointed up for a better drive shaft angle.

The cheaper way is to run a high angle drive shaft. When you say CV I assume you mean a double carden joint, as opposed to a ball and socket CV. A double carden is not contant velocity. A high angle shaft uses double carden joints on both sides. This allows you to have some pretty steep drive shaft angles, and does not require one side to be in line like it does when you have a double carden on just one side.

Old thread but this is the exact same problem I am having after swaping out my front dana 30 for a rubi 44... anyone know what the soulution was from this old thread

Could be two things.

Do both axles for sure have 5.13's in them?

And, I have never run a tru-trac in a front axle without locking hubs. Do you get the lurching when going straight, or only when turning perhaps? Also, is it fine in 2wd?