dvs4.6

read about a TSB on the rear axel whine that my '04 f150 is doing these days. has anyone done this replacement and if so what was the investment?

it is the whine that only shows its self when on the gas, coasting no whine.

NashBulldawg

It's probably the pinion gears. I had the same problem on my 07 and they fixed it under the powertrain warranty. Thank got because it would have been around $1000 with parts and labor. Good luck!

munoz2105

I had that problem to and also vibration making a right or left turn. I changed the differential fluid with Royal Purple 75W-140 and added two bottles of XL3 friction modifier from the dealer. Drove it for one day and problem solved, didn't have to replace any parts in the differential. There are many posts about this. If your truck its not under warranty its worth the money to change the fluid first before giving the dealer $1000.00.

dvs4.6

that is what i wanted to hear! Is the xl3 modifier only available at the stealership?

munoz2105

Yes is the Motorcraft xl3 friction modifier. They might sell a different brand at an autopart store but its only about $6 a bottle so I would just get it from the stealership.

dvs4.6

Yeah just bought some xl3. Will try the 75/140 and xl3. Head mech. Said that they r well versed in this problem. But thought that changing the fluid was worth a shot, before making a huge investment. Will try tomorrow and post update. Thanks for the heads up!

dvs4.6

did the fluid change, but whine is still there. what damage, if any, if i continue to drive like this?

Mod (Ret.)

"rear whine"....that's usually what I hear when kids are in the back seat.

driver444

A whining noise in the rear is usually from bearings going bad, or an improperly set up rear end. It could be from worn gears, but that's not nearly as common. My guess would be pinion bearings. The pinion shaft thrusts forward on acceleration, and gets "sucked" into the differential on decelleration. Those bearings take alot of abuse, and do wear or fail occasionally.

As the previous post said, other noises can be fixed with the friction modifier. The "chattering" noise you may hear when cornering is due to the clutches in a limited slip differential slipping. They are supposed to slip, but the fluid keeps them moving smoothly, so you don't feel it when driving.

First, see if you have a limited slip differential. If you don't, the friction additive will do nothing for you, and is not required or necessary. The problem is something else.

As far as driving it... If its gear wear, the wear will EVER SO SLOWLY get worse, until you can't take the noise, (could be years) and you'll get it fixed before it fails altogether. If it's bearings, you could save a little money by fixing them now before you need a new gear set too, if its not too late already.

This is easy to check. First, grab the pinion drive shaft yoke, and see if there is any play in it (in and out, or side to side. Use a prybar if you need to. Pull the cover, inspect the gear teeth. Then gently pry on the differential carrier, and see if there is any left to right movement. There shouldn't be ANY AT ALL.
The problem might make itself evident right away.

dvs4.6

thanks for the advice that is what i was looking for as an answer.