okay, now we're getting somewhere. if you can't reproduce your problem at a stand still, you really need to be using the term "load" instead of "rpm". and, if in fact this is a problem that goes away when you put a load on your drive train, you need to look harder at your rear drive line, the cv joints and even the rear pinion as something is clearly off.

 

tried to reproduce it in parking lot at a stand still, couldn't get it. the reason i used the term rpm is that even while cruising at a constant speed or (low load) but different rpm there is not a shake. the shake only occurs at a constant speed or (low load) at 1200-1400 rpm. so driving at low load on the drive line of around 40 mph.

 

well, that still makes sense as the more load you put on, the more things change. if you're sure this isn't a tire balancing issue (and honestly, it still could be based on the fact that this could be a speed related issue), i would give the things i pointed out a look.

 

I've had this same exact issue you are describing with mine for about 7 months, ever since moving from 2.5" lift to 4." Like the OP's sitution, as soon as I increase the rpm it goes away. I've taken out the rear ds and it still shakes. I've taken out the front ds and it still shakes. It's a feeling that is similar to driving a standard in too low (numerically) a gear. I'd love to figure this out because it's driving me crazy. BTW, after reading WOL response mine too seems to be a load issue (in other words I don't get the shake with vehicle in park and revving up engine.

 

Thanks. i appreciate the input.

 

did you balance your tires? i have not done that yet. a friend at the tire shop thought it was not a balancing issue. i did rotate the tire with no difference.

 

I have not had my tires balanced since the new lift. I did rotate my tires, however, and that did not have any affect on the shake. I might try having my tires balanced and see if that helps.

 

I would definitely balance the tires, however as said it sounds like a driveline issue to me as well

 

I'm thinking I might borrow my friends gopro video camera and mount it somewhere underneath the jeep to try and record what's happening with the suspension. Hopefully there will be some external sign of the vibration. If I have time this weekend, I'm going to try it. I'll post results.

 

I just got new tires and from 39-42 mph I get a little vibration but then it goes away. I feel that it's just a "sweet" speed for the tires that I can feel the tread hitting the road just right that it transfers to a "vibration". I don't have it anywhere else and it happens on every surface in any weather. No problem with alignment or driveshaft.