04' 2500 4x4 Hemi. Running 35" rubber with 3:73's. Took it in and had 4:56's installed.

So what i do love is the new power and torque that the gears give in relation to the tire size. Its a perfect fit. Happy I made the decision.

What is pissing me off....After a week I was getting two issues....

(also i drove it nice and easy for the 250 mile break in period) not horsing on it no burnouts ect...no nothing. im up to 500 miles now and i still havnt beat on it)

1) vibration at 63-66mph. Nothing audible but I could feel it in the gas pedal and the floor. Nothing major just a high frequency vibration almost that of an oversized cell phone if that makes sense. Since it was only at this speed area I mentioned already... my first thought was tires...maybe they knocked a weight or two off ect ect...Drove 75-80 miles yesterday with the cruise on at 75mph....it was beautiful....no vibration at all just the speed i mentioned does it.

This next one is really making me F**King NUTS!!!!

2) this one is hard to describe.... Not always...but sometimes after a couple minutes of driving...When I stop and start again i feel a sort of vibration thing in the rear....but it feels like tires.....The best way i can describe it is this...I need a 2.5" level lift in the front because my tires rub a little at full lock out. So imaging turning the tires(lugged tires) and hearing and feeling them rub a little.....OK....now forget the noise...but remember the feeling im describing.....now transfer that feeling to the rear.....thats how it feels....
Im like WTF!!! nothing can be rubbing?? Its making me batty!!! I DO have a factory limited slip and the only thing i can think of is it feels like maybe the limited slip is wanting to engage because theres more gear there now?? I dunno...I know **** about this part of things....
Just does it as I take off then it stops after a second or two. AND>...it doesnt always do it. I can stop at a stop sign and start and it'll do it....then the next stop light a mile away it wont do it again...then it will ect ect....
Doesnt "feel" like anything metal....arghh i dunno...


So fast fwd a another week I take it back....hey dude this thing isnt right...he has it 24 hrs and says come get it. He had to replace a U joint in the rear....ok..... So now it still does everything it did before. AND now...i get this what feels like tire vibration at 45mph ....only 45....not 50 not 40. ...
He says due to there being "so much more gear"....there might be a little vibration here and there.....I dont buy that. A brand new F350 with 4:56 from the factory isnt going to have any issues like this.
So I'm taking it to my friend soon to re balance all the tires. if that doesnt do it then im taking it to have my rear drive shaft spin balanced.
if that doesnt do it then im going to drive straight into a wall....

its not problem 1 above that gets me any where near as much as issue # 2....its really pissing me off. Problem 1 is likely tire... 2 sounds like tire when it happens but it cant be. WTF could be rubbing the tire only on take off...nothing...

It happens more frequently on turns it seems. I stop, turn the wheel a little pull out to make a left and through accelleration it does it til im straight then it stops. I even nailed the gas a few times when i felt it and it doesnt get better or worse...

 

Sounds to me like the backlash is off a tad...

 

Contributing to problem 1, 2 or both?

 

Hmmmm...have they used the right amount of LSD additive? Sounds also like the lsd clutches grabbing in #2 ??
Al.

 

2500's don't use the additive. Try rotating the tires and see if the vibration changes. I had some really weird vibrations start on mine, many similar to what you describe. Did a tire rotation during some normal P/M and the whole scenario changed. Basically, the tires are getting worn out, they're near impossible to balance anymore---they've been rebalanced several times. Last time 2 of them had to have the beads broken, tires rotated on the rim, then add the weights.

Also, if your gear guy changed the u-joint on one end of the drive line, he also should have changed the other. Ask him if he made sure that he re-installed the yoke in exactly the same location as it was before he pulled the u-joint-----if not, it can caused some drive line balance issues----like what you describe at 45mph.

 

If I ask him if he put the yolk exactly back where it was, hes going to say yes regardless. I assume there is no way to know where it was now if this did happen?
The tires on my truck are brand new. They have probably 1000 miles on them. Before the gear change I could go slow or fast from 0-90mph and had zero vibration coming from anything or anywhere.

and I forgot to mention....The 40-45mph thing it now does i can feel in the steering wheel too.
damn im pissed!!!

So tuesday im taking it to my close friends garage. Hes going to re spin balance all the tires and rotate them. Rear ends are the only thing he doesnt get into but im going to have him drive it before and after anyways to get his take.

Also******* The 2500's do NOT take LSD additive???!!! I remember specifically the guy saying something about making sure it was in there because of the LSD.
If this is the case then do i need to take it out and just use straight gear oil???
What happens with the additive when its not needed?

I was actually thinking...hey i wonder if he DIDNT use any would be why i feel what im feeling.

 

What brand gears did you get put in? I'd give that company a call and describe the symptoms and see what they say. LSD additive lowers the HP properties of gear oil and could be part of the problem.

 

Sorry about the additive thing. I miss read/overlooked the 2500 model info and automatically thought, you were a 1500 like myself.
So...Expletive away my friend !!!***???:
Al.

 

Yep, 2500 LSD is a worm gear and does not use clutches, therefore no friction modifier should ever be used.
I still say he's off on shimming the gears a tad. What's the break-in wear pattern look like?

 

I'd check tires first.
Modifier won't harm worm gears and isn't beneficial. ALl oils have a degree of modifer to them already. Modifier would not chatter or create a "rubbing" or "vibration" sound you describe in worm gears. They are pretty much feel-less type of gears. I think you may be paying more attention now than just before so it's always possible these issue's could have been there before especially if you have to pay close attention to when and how they happen!!! The only way you would be able to feel anything is when moisture is prevelant inside your diff, the oil itself is no good and/or broken down, or you have the incorrect oil weight in there.
I'd check your carrier bearings for your driveshaft. The 2500's use a center carrier bearing and the typical symptoms are howling at specific speeds on highway and clunk or vibration on take-off. Could also be u-joint issue as well. You need to take the driveshaft off to change gears, so it's possible someone bumped the driveshaft too hard and dinged or tweaked a ujoint cap. Also make sure your e-brake is adjusted properly. If it's dragging, it could cause some vibrating or noise isue's at slow take off speeds. The e-brake does get disconnected when changing gears.
Just some things to think about.