.. at speeds above 70 km/h, the steering doesn't vibrate but the whole car vibrates.. it feels like its originating from rear of the transmission but can't figure out exactly what it could be.. tranny mount is good, engine mounts are good.. steering doesn't vibrate so I suppose tire's balance is good as well. Could it be because of bad ball joints? Anything else? I know because ball joints and other related things need to be changed What could be the cause of this vibration?

 

do you have a lift kit? if so, it can be your rear driveshaft angle is too steep and causing alot of vibration.. I have that problem with 4.5" of lift and still dont have SYE or cv driveshaft( feels like it might come off one day)

 

I would start with checking tires ,tire belt separating at higher speed on the rear I have had that happen - check balance on machine at higher speeds for start.

 

if the steering doesn't vibrate it doesn't mean that the rear tires are not out of balance or ovalized.

 

I would start with balancing the tires then if the problem persists then i would throw a steering stabilizer at it cause when i start getting the death shake i just throw one at it and it seems to fix it for a while

 

No, don't have a lift kit but it is actually slightly lifted from the back I will get the leafsprings done then see.. (it was on CNG when we bought it and had two Cylinders weighing 60 KG each) now they are removed and the Jeep is lifted from the rear.. will get that done, get the tyres and the driveshaft angle checked..

 

Steering stabilizer is good..and don't want to band-aid the problem..