Ryanc

I wonder since the exhaust piping is like 3 inches away from connection between the shaft and transfer case, this heat is fubaring the stock shaft, and if their is a double carden after market in that area heat expansion is causing increase in vibration resulting in kaboom.

ronjenx

The most likely cause of vibration at the double cardan is an angle greater than 0° at the single on the other end.
My research has indicated 3° max, and even that will cause some vibration.

racer83l

this thread right here, while only a small amount of members are reporting issues, is a scary one...

Im running 35's, stock 3.73's, lifted 4" and have Tom Woods front DS, I do a lot of highway driving. and I can tell you right now the angle at my pinion is much more than 3 degrees.. In order for me to adjust my castor the way I liked it, the pinion is at a fairly large angle.. its about parallel to the ground. I will say tho there is no vibration that I can tell...

Wonder If I have anything to worry about

ronjenx

Most people say that. The problem is when you get the right combination of factors. When you hit just the right combination, (resonant frequency), the amplitude of the vibrations goes up exponentially. The front of the t-case receives the energy of all that, and just explodes.

Your 3.73's and 35's may have prevented you from hitting the critical drive shaft rpm at the speeds you have driven so far.

I have seen vibration tests on electronic equipment for the military.
Every piece of equipment had its own critical frequency. As the frequency was turned up, I watched the fasteners back off to the point of falling out. If the frequency was adjusted rapidly through that point, so the fasteners remained in place, at a certain frequency, the piece of equipment would explode. The thing is, you can't see the piece vibrating, so it's not like it is being thrown around.

racer83l

What im thinking.... gears (5.13's) and high speeds.. the DS must be spinning VERY fast.. probably faster than I can even duplicate with my stock gears at 100 MPH

Im wondering, IF we all keep our speeds relatively low (65, the local speed limit here is only 55) the chances of this happening should be minimized, and Ill be adjusting my arms to line up the pinion a bit closer to 0.

To me, this pretty much seals the deal that I wont be doing a regear

ronjenx

Vibration can never be eliminated. You can, however, move the critical point up or down the scale.

A regear can be offset by larger tires.
I have noticed in the cases here, they were regeared and had bigger tires, but the combination still resuted in a higher drive shaft rpm for a given road speed.

Ryanc

IT appears that Transfer case explosions occured with gear ratios >4.1, am I correct? Did this occur with older TJs, other vehicles? Or is the RockTrac just another shotty piece from Chrysler.

ronjenx

It's not just the RocTrac, (look at the poll) and I don't think Chrysler made them.

mkjeep

Don't know how many of you have noticed that our tcase sits at about a 5 degree angle up towards the front. It doesn't sit level. Seems to me this may help contribute to the poor angle we have to run in front for castor, maybe even poor lube of the front bearing. On the auto tranny anyway.

ronjenx

Since all the t-cases are tipped back a little, it would seem to not be a factor regarding drive shaft angle.

It might be a factor regarding front bearing lube if you also consider lifted JKs have probably eliminated the stock forward rake, effectively tipping the t-case back a little more.