Blue Hammer

I just had put in new 4.56 gears in my 07 f150 4x4, front and rear. I also had a true trac limited slip in the rear. When I picked it up, I immediately heard a whining sound coming from the rear. You only hear it when your off the gas. As soon as you touch the gas it goes away.

Anyone have any thoughts? The tech at the 4x4 shop is not sure what it is. Thinks it might be the true track breaking in. It's not a grinding sound, more of a whining/whistling. What's weird is as soon as you touch the gas and torque is applied from the drive shaft it goes away.

My thoughts are it's not a break in issue; there shouldn't be any noise on the break in correct?
Wrong gear oil?
Bad u joint?
Bad pinion bearings? ( they installed with a master install kit, new bearings seals, shims, etc )

Any help is appreciated.

Chris@Stage3

I would take it back to the shop and have them recheck the gear lash for the preload. Sounds to me like it may be to tight. I have also heard in the past that some gears are just noisy I do not know if this would be the culprit or not but?!?! from what I am being told tho have the lash rechecked

Chris@Stage3

on a side note how do you like the feel of the 4.56s? I am on the fence as to if I want to do 4.56 or 4.10 in my truck?

Blue Hammer

I like he 4.56 on my 35's with a 6" lift. Gave me back the power without being over kill

Blue Hammer

No one?

BIGDAWG78

man I would take it right back to the shop that did the work and have them correct the issue. goodluck man

Chris@Stage3

did you read my first response on the lash etc...?

LUVmyDUX

I think Chris is right, my friend does gears at a shop and says if it howls the backlash is off. Also, I was told 4.56 may howl a bit at highway speeds but your issue should be addressed by that shop.

BIGDAWG2

I would go back and let the shop take a look. But if set up correctly it really doesn't matter about the ratio, but some gear manufacturers sets do make noise no matter what due to their lack of QC. Make sure they didn't install made in China in your truck. I run Yukon 5:13 in my Jeep with no whine at all. Good Luck.

firehart2

I recently installed a set of 4.56's in my truck and they whine as well. I have done numerous sets in various vehicles, with this one being the first that I have ever encountered noise with. I have the most experience with 8.8" rear ends, but the 9.75" is nothing more than the 8.8 on steroids. Everything was set up to the "T", and I an still experiencing the whine...... Although mine is at approx 52-55 mph. My gears were purchased from Wayne @ diffsonly.com, and after speaking with him, even he doesnt know what could be the reason for the whine. The same goes with the techs at yukon gears. Yukon only warranties against failure, not noise.

My neighbor, who is an installer for a very reputable local 4x4 shop, said that some gears are inclined to have a slight harmonic to them. He and I pulled the rear diff back down and rechecked everything.....of course, everything was still well within spec.