Jeep Wrangler 2-door, 3.8 automatic from 2010.
Installed bigger than the standard tyres, now 31.5" , no vibrations. Needed to switch overdrive off many times, engine revs only 1700 rpm at 60mph. Installed 4.58 gears front and back. Have a vibration starting at 50, stops at 65 mph. Very noticable in steering wheel, and more present on the left side of car. Changed wheels front to back, no change. left to right, no change. Checked the diff front and back, clean oil, backlash within spec. pinion preload 2Nm also in spec. At highway speed put trans in neutral, engine revs and load a lot less, vibration is still present. Imho this means this phenomena is really speed related. Balance of wheels is OK. Why is this more noticeable on the left si de of the Jeep, and why after regearing. Engine is OK, gets regular maintenance, only 56000 miles. It puzzles me. It feels like something is unhappy, and if gears of diff are in conflict, but they look perfect, contact area is spot on, oil stays clean.
Any good suggestions are very appreciated. Here in Holland there is only a small Jeep community, so very little good and/or useful info available.

 

Hello to Holland! Suggest removing the front drive shaft, then take a drive and see if the symptoms change. If no change, you could do the opposite in 4HI (front drive only) and see what it sounds like.

Are you sure the tires are 31.5" (800.1 mm) in diameter? 4.10 gears would have been my choice for 31.5" tyres. Is there a lift on the Jeep that might be changing the drive shaft angles? 2-door or 4-door Jeep?

 

@ Mr.T: Thanx for your reply, Tyres are 255/70 R18. Jeep runs great with 4.58 gears. Today I torqued all bolts and nuts of trailing arms shocks and related stuff to count that out. Did not make a big difference. Next step will be the removal of front driveshaft. I will keep you informed.

 

BTW, Jeep has no lift, and is a 2 door.

 

A couple more thoughts: I re-read your initial post, and feeling vibes in the steering wheel tends to point to wheel related rather than drive shaft related - especially using the stock drive shafts without a lift. Check that the bolts that hold the unit bearing attached are torqued tight. Also, maybe jack each front tire off the ground and check for play in all directions -- and use some muscle on it. A friend of mine had some work done and those unit bearing bolts were left loose, it had similar symptoms.

 

Mr.T, I will check these bolts

 

Sounds like an axle joint is seizing up.

 

@ MrT: Checked these bolts today, they are tight.
@ D-Dub: Axle joints are renewed, during re-gear operation, the old ones were bad, so changed them for new ones (Spicer)

Vibration occurs between 85 and 104 km/h independent of load, headwind etc. above 104 vibration almost gone. Frequency of vibes feels like rotation of driveshaft. To fast for rotation of wheels, to slow for engaging gears.

Any suggestions highly appreciated.

Next job is to remove the front driveshaft

 

Before removing the front driveshaft, suggest a quick check of both driveshafts for play at each end, and that all the fasteners are installed tight. Then with tires jacked up, rotate each driveshaft and verify they run straight and true. Afterward, remove the front driveshaft next. If vibes are still there, install front driveshaft, remove the rear driveshaft, and drive it in 4HI for a test.

From the sequence of events, odds are it's related to the work performed during the gear install. Sometimes the CV joints don't separate easily from the flanges and mechanics resort to methods that can damage the joints or flanges. Keep an eye out for that sort of damage, it may be a CV joint isn't centered or seated properly in the flange. Side note, there are holes in the rear of the CV flange for the rear driveshaft to use a long steel punch for removal.

Best of luck, hope it's something easy to fix and obvious when you get underneath.