I just installed two axles which I had bought with 4.10 gears installed to accompany the 33's. According to the previous owner, the 4.10's were installed around 30,000 miles ago by a reputable drivetrain shop. (whether bearings were replaced I have no clue).

At any rate, the rear diff is whining/humming upon deceleration (manual transmission). This is only noticeable at speeds above approximately 50mph. It is noticeable over tire/wind noise at that speed, but isn't overly loud (low to moderate radio levels drown it out). My research has indicated this may be the pinion bearing. Question 1:

Is my rear differential about to explode, or is it likely safe to drive for a while?

Question 2:

How difficult is a pinion bearing/seal replacement on an 8.25"?

 

Not terribly difficult but that does sound like bearings to me, I remember having to swap fluids in mine about every 500 miles for 3000 miles so that any wear off was removed from the differential and I had humming to but after 5000 miles she is pretty quiet now. I did a complete axle rebuild in mine so it was fairly normal for this procedure. Well around my area that is. We have alot of hilly areas. Honestly sounds like the previous owner didn't do any break in period on the gears. So to answer your question, I would say drain the fluid, Inspect the gears, fill it up with the correct fluid needed and take it for a spin.

 

Gears look 100%, diff oil is brand new. Can't hurt to do another change I guess. I used heavier weight oil (75w 140) because I tow a bit, could that make a difference in noise? I know it didnt in the original D35.

 

Does it have any pinion movement (in & out)? This is a pretty common cause for noise on decel after a gear install. Also were the gears set up correctly? Do you know what brand gears they are? Some aftermarket gears are known to have some gear noise especially in the dodge 8.25 & 9.25 diffs. Setting up used gears is harder than new because you must get the settings back to the same as when the gears were installed the first time, otherwise you can get noises.

Miles

 

Id take your jeep into a shop that has a good reputation and have them take it for a test drive. Someone that's an axle expert should know right away whats going on.

 

Maybe

Pinion has to be shimmed like any other axle. Doing it properly requires dial indicators and the fancy torque wrenches.

I'd drain the diff and check the gear pattern inmediately. Whining after 30k miles raises alarm bells for me. Either it was set up wrong or bad parts were used. Gears are a huge investment so don't **** around. What was the warranty from the shop that put the gears in?

Your choice or oil is fine, by the way.

 

I just bought the axle with the gears already installed, and they supposedly had around 30k miles on them. There is definitely preload when turning the yoke. Ill check for shaft play and I will check the pattern hopefully tonight. The fact that there is only noise on decel is what is getting me. It could have made the noise since the day they were installed for all I know.

 

Check the shafts where they ride the bearings in the tube too.

 

Shafts are fine as best I can see, no scoring or signs of wear. Bearings seemed fine as well, I figured that if the issue were wheel bearings I would notice a difference when turning, no change in noise is noticeable.

 

My 8.25 with stock gears started making noise on decel a few thousand miles ago, recently its gotten a lot louder and more constant...I need to pull the cover and inspect. That will probably wait until I weld the spiders, then refill and run until it breaks or spits the carrier out

 

Just an update on this- Pulled the diff cover, this is with about 1000 miles of my driving on it (Apparently the gears had around 30k on install before I bought the axle) Gear oil looked good, no metal or any other signs of illness.

Somebody mentioned about gear brands- the only markings I could find were on the ring gear and said "C8.25-410 41x10 9224 05/03" Google wasn't helpful with this.

The gear pattern was good and centered, and the gears look to be in good shape.

I wasn't able to create any play in the pinion, both in and out of the housing as well as up/down or side/side.

The only thing I found concerning was that the vertical spider gears (ones attached to the cross shaft pin) seemed to have a bit of play on the shaft. The shaft looked fine when I pulled it, and the gear faces themselves on the spiders look good. I have a feeling this is unrelated to my issue, which is:

Whining noise upon deceleration, which is only noticeable at higher speeds. (manual trans)

The Jeep is my 70 mile/day DD so I can't afford having it down for a week. I am looking at getting some shop quotes and seeing if mechanic buddies have experience with gear set-up etc.

At any rate, is imminent death a good probability, or should I be able to fill'er up with some good oil and go until I am able to take a full weekend to get the bearings replaced?

 

Gear whine on deceleration is acceptable. I wouldn't worry about it as long as everything looked ok.

 

Is it slinging gear oil out through the pinion seal?

 

Nope, pinion seal isn't leaking at all.

 

Are you sure the noise is coming from the diff & not the transmission, i.e. a counter-shaft bearing going south?