[railing68]

Had my 12 rebuilt a couple of years ago maybe 1500 miles on it since. 12 bolt, Tru-trac, new moser axles 33 spline, new ring and pinion. The rearend should be damn tuff, but it has been making noise when not underload decerlerating (churning thump/repetitive bumping, the noise is a reciprocating) at ~35-15mph, more noticeable on a smooth surface. It also doesn't do it all the time or when, driveline is cold.

Anyway, called the builder and he is basically shining me on at this point. Another dif guy in town stated that the ring and pinion (Yukon) is junk and is likely the culprit.

He also stated that if the fluid is silverish (fleck) in it that is going bad due to irregular wear! Yukon gears are supposedly inferior and imported?

And of course the fluid has quite a bit of fleck, but looked normal coming out of the drain plug, in the pan it can definitely been seen and sheen and fleck.

Now anytime I have ever drained diff fluid, or even sequential moto trans fluid, it always has substantial fleck.

I recently replaced both axle bearing thinking they were going, and had been wash out by dif fluid due to a leak, no change!

I don't expect anyone to diagnose the noise, just input on the shaving(metal) in the fluid, no chunks, mag plug had a 1/4 of fine sludge on it.

The noise is hard to describe and isn't always present; Could it be the True-trac or?

Input please, SS.

[big gear head]

Yukon gears are as good as any other. They are imported, but many gears are now. The metal in the oil could be coming from a bearing. Check the pinion and see if you have any in and out movement or any side to side movement. I wouild suspect a pinion bearing first.

[bkerns925]

Are there clutch packs in the Tru Track that could be causing the fleck?

[big gear head]

The Truetrac does not have clutch plates in it. This differential uses gears to provide resistance so that the wheels turn together. The gears can wear and cause some mteal in the oil. This wouldn't cause the noise.

[Luwi67]

Can you notice a wear pattern in the gears yet?

[railing68]

checked the pinion, doesn't seem to move but definitely has an engagement knock to it when the axles are moved forward and backward or vice versa. originally I thought that this was drivetrain slack but there is knock in the vicinity of the pinion when rear tires are moved back and forth.

Is this backlash?

. Hard to explain but seems abnormal?

SS

[big gear head]

There are several places where there will be backlash in the rear end assemlby. The splines on the axles will have a little backlash where they fit into the axle gears, the differential gears will have some backlash in them and the ring & pinion will have some backlash. When you add all of them together there could be quite a bit of total backlash in the assembly.