Diff whine

[tech10002]

Is it normal for the super duty rear differential to get louder as the miles accumulate? My 06 just rolled over 42k, and the diff seems to be making more noise. I can hear a whine from it at lower speeds. It's really noticeable on the country roads near my house at 25-35 MPH. I've always been able to hear it every once in a while when it was cold, but it just seems to be getting worse.

Would changing the fluid to something like Royal Purple synthetic help? My 95 F-150 has 180k on it, and the diff is completely silent. I just hope my diff isn't going out at only 42k.

[regor]

Sounds to me it could be low on gear oil or maybe it is starting to wear the ring and pinion funny

[tech10002]

Man, I hope it's just the fluid. Is there anything special about a fluid change on the super duty? I'll try dropping the cover and throwing some synthetic in it I guess.

Does anyone know what type and viscosity of oil I should use? I read the fill plug was on the top. Is there some kind of dip gauge I need to buy to fill it to the right level?

[regor]

I know on most of the rear ends i have messed with you can check the gear oil level by unscrewing the plug and stick your finger in and see if it is low if you can't touch the oil then you can add it until you see alittle come out the hole and it should be fine as for what kind you can ask the local parts store they should know if not it will be in your manual for the truck maintinance.. There should be some other guys on here with more detailed info , i hope this helps

[jacksd3]

Unless your diff seal is leaking it's easier to just stick a hose into the hole where the plug was and pump the old fluid out then refill with the fresh fluid of your choice. Buy a cheap hand pump from Walmart for about $7. You'll find a million uses for it. I put Amsoil 75W-90 Severe Duty in mine a few weeks ago but everyone has their preferences. It did quiet my rear diff down. I bought the Ford Friction Modifier but I haven't put it in yet. Some guys say you must use it but I'm unsure.

[Lonno]

I would pull the whole cover just to give it a check. The fill plug is probably on the front of the diff, not the cover. I'm doin mine today and i'm puttin lucas 85-140.

[jacksd3]

Hi Dlonno, with high mileage trucks you would be right but he only has 42k miles on the truck. If I were him I'd take 5 mins and take off the plug and inspect the magnet. If it's got a lot of shavings stuck to it then definitely pull the cover, inspect, and then replace the fluid and the seal.

But most likely he's low on fluid. If the problem is a low fluid level and no serious amount of shavings on the magnet then just top off with the gear oil of choice.

[Lonno]

Originally Posted by jacksd3

Hi Dlonno, with high mileage trucks you would be right but he only has 42k miles on the truck. If I were him I'd take 5 mins and take off the plug and inspect the magnet. If it's got a lot of shavings stuck to it then definitely pull the cover, inspect, and then replace the fluid and the seal.

But most likely he's low on fluid. If the problem is a low fluid level and no serious amount of shavings on the magnet then just top off with the gear oil of choice.

Yeah, makes sense, I didn't notice his mileage.

[tech10002]

Thanks for the replies. I think I will try checking the magnet and the fluid level tomorrow before I drop the cover. I've never messed with one with the plug on top. All the ones in the past had the plug on the top of the diff cover, and I just filled them to right below the threads.

How high from the top should the fluid be in the super duty? I hope the owner's manual has the gear oil weight. If it's low, I'd like to just try topping it off with the original stuff to start with.

[jacksd3]

Hi tech10002, you got it right. Look for the fluid to be level with the bottom of the fill plug hole. Chances are with only 42k miles you are just a bit low. But before you fill it up check and clean the magnet. Poke your finger in there to see the level. Take a look at the oil on your finger. It shouldn't be dirty or smell burnt. Drop a bit on a clean paper towel if that helps. Then fill it up until it starts flowing back out of the hole.

If you have any doubts about the condition of the gear oil then completely flush and refill it. If you have an LSD then make sure the gear oil you use has the LSD additives. It will say so on the bottle. Buying those cheap pumps really make filling easier.

Best of luck!