Originally Posted by mmain
I have a persistent problem with vibration on my 2005 GC 5.7 Limited, which occurs in the 40 – 55 mph range, albeit intermittently, although it does seem more likely to occur when you push down the gas pedal and / or climbing upwards. So far I have rebalanced all the wheels, replaced the torque converter and even replaced the ECM on the possibility that it might be a problem with the torque converter clutch modulated signal, which clearly is not the case. I am now looking for some further advice and wondering whether the front differential, prop shaft, transfer case and associated mounting components are likely causes, particularly when the problem is intermittent and worst over a specific range of speeds. I should point out that I have never had any EVIC error codes. Any advice welcome.
Depending on where you had your wheels balanced, this may still be the issue. Apparently there are good machines, and ones that don't do as good a job. I have had a set of wheels balanced at one shop, they still had a bit of a vibration at highway speeds, took them to another (that had a hunter something or other balancing machine that they were quite proud of) that was able to get things taken care of.
Other than that, I would likely start with the u-joints on the prop shafts. They could certainly cause a vibration within a certain speed range and are relatively easy to check. If you crawl under you can visually inspect, and check for excessive play in the joints by applying some force to it. You could also detach the joint, and move the end around feeling for stiff spots. The rear is a little more common to go than the front, but checking both wouldn't hurt.
I wouldn't suspect it is the diff itself, as they will usually howl/whine/growl etc., before they would cause a vibration. The diff mounts, on the other hand, are certainly a known area that wears out. I don't know if it would cause a vibration like you describe, typically it causes the vehicle to clunk into drive from park and reverse.
Wheel bearings also usually give an audible warning before they would cause significant vibration, but you can check for excessive play by lifting up the vehicle one side at a time, grabbing the wheel at 6 and 12 and giving it a good shake. Repeat with your hands at 3 and 9. If you feel play in the wheel, the bearings are a likely source.
As for the transfer case, there isn't too much that you can do other than check fluid quantity and quality. I wouldn't list this high in probability with your symptoms, but anything is possible!
I am by no means an expert, and there are many, many possible causes for a vibration like you describe (as anyone who has experienced the death wobble in an older jeep can attest to!), but that is where I would start with things.
Though I like to handle most things with my Jeep myself, sometimes it is easier just to take it to a good shop to at least diagnose what the problem can be...sometimes being able to get all 4 off the floor can help immensely!