CerealKiller

My 2005 STX has a bad rear end vibration pulling out from a stop and I'm probably going to end up having to change the clutch pack however it also vibrates pretty bad between 55 and 65 mph around 70 it smooths out again. I have read a thousand different posts about people having a vibration pulling out from a stop but haven't heard anybody saying about this vibration at highway speeds could the clutch packs just be really bad or could I have another problem in the differential? Also will it get worse and could I damage something else driving with bad clutch pack?

PerryB

Assuming you are driving in a straight line, the condition of the clutches won't affect the operation of the rear end as there is no differential action occurring. I'm thinking you may have a U- joint going out.

snowborderus

Vibration at higher speeds could also be tire imbalance. Cheap and easy thing to check.

homank76

I would check the u-joints as well.

WestsydeGuy

Could be many things as mentioned a bad u joint or just out of balance tire.
Maybe a bent rim or a tire seperating?
Start at the simple things first.

CerealKiller

Well I'm pretty certain that the vibration has nothing to do with wheels or tires or brakes last year I put a 6 inch rough country lift on my truck and new moto metal wheels with Toyo open country 35 12.50 17s. I changed the differential cover with an aftermarket mag hytech cover with royal purple 75w140 gear oil with the friction modifier additive. less than a year later the vibration started I added extra friction modifier and after some time it seemed to help. So I changed the royal purple out with Motorcraft 75w140 gear oil with the Motorcraft xl-3 friction modifier which also helped a little bit first but the vibration didn't go away so I added more of the friction modifier but it still hasn't fixed it but yes it does it at highway speeds in a straight line up Hill or downhill under throttle or coasting

CerealKiller

And I forgot to mention the 35s have sandbag weights not the traditional rim mounted tire weight and the tires have less than 10k miled on them. It's got a very bad vibration accelerating from a stop that doesn't seem to be any worse turning or going straight and most recently I've heard squealing noise while driving under light acceleration. So to sum it up my truck vibration under acceleration up until about 30 mph then acceleration is smooth up until around 55 mph at which point the vibration startd again. the highway vibration could be something else maybe? I appreciate any input anybody can give me

Mod (Ret.)

The rotational mass of the 35's may be the vibration you are feeling. Try having them re-balanced.

You also mentioned a 6 inch lift. This places the drive shaft at a new angle, and that will add to premature wear/failure of the u-joints. I'd have them checked out, especially if they are the originals.

PerryB

Ditto on the driveshaft angle. The front and rear joints should be running at equal inverse angles. The usual problem is the pinion needs to be shimmed down. This seems counter-intuitive on a lifted truck but thats likely the problem. A high pinion (insufficient angle on the rear joint will typically manifest as a launch shudder accompanied by a highway speed vibration. Took a couple of installments by the OP to get all the facts. I've been there done that with the lifted truck/driveshaft vibe issue. I'd put money on this being the problem.

Toshbar

If the shudder only happens while starting out with the front wheels turned to the side pretty steep, put some friction modifier in the rear diff. I know all the new synthetic oils say it isn't required, but I added 6oz (bottle and a half) of FM to my syn gear oil in the back and it removed 97% of the turning shudders.

Does your 55-60 shake happen all the time, just under accel, just under decel, or what? The 50-60 bed shake of these trucks is well known. I get it at 56-68 even with a fiberglass camper and my bed loaded with ~500lbs of additional stuff. It also comes back at 70-72mph. I swapped tires with my dad and nothing changed.