LX 450 - REAR DIFFERENTIAL FRONT OIL SEAL

[Beast of Berlin]

Hi everybody,.. leaking oil seal - rear diff.
I'm looking at the manual - Source SA−72/1996 FZJ80 FSM - and wondering why the taper roller bearings and the crush sleeve have to be replaced when changing the oil seal. I don't see any reason for this, since the taper roller bearing preload shouldn't change. The bearing seat is adjusted exactly as it was before. The crush sleeve is nothing more than an ajustable spacer/shim. Any ideas...?

 

[Malleus]

You can just replace the seal. Mark the nut and try to get it back where it was.

 

[Kernal]

If you're just replacing the Pinion Seal, after you've removed the old seal and installed the new, when you reinstall (or replace) the pinion nut IME can go a tad past the original spot (depth of the pinion nut), idea being to take up any slack in the used high mileage pinion bearing.

Short story: I did this when I replaced my rear diff pinion seal and and pinion flange a couple of years ago and went past the original nut position without major drama. I did something similar with a front diff pinion seal replacement over 10 years ago, no issues.

Long story: Some might be uncomfortable with this part but I tightened up a new rear pinion nut a bit past it's original position/depth, not just stopped at a specific depth where the original nut was before. As I already had the axle shafts out (for brake/wheel bearing service) I checked the running (rotational) torque of the pinion gear/diff using a dial indicator torque wrench on the tightened pinion nut. The numbers I got were IMO what you might see with one caveat, the diff was complete ie: ring gear/bearings were installed but the diff was not full of gear oil, only light penetrating/lube oil on the gears so they weren't dragging through thick gear oil when I checked the running/rotational torque.

Point is IMHO that the process above did not appear to change things dramatically by tightening down the pinion nut (snug) a bit past it's original position.

Once the rear axle was all together and the truck was back on the road there was a (new) slight whine from the gears, best guess is by taking the slack out of the pinion bearing the pinion and ring gear teeth were not meshing exactly the same as before ie: the pinion gear may have been slightly more stable but the carrier bearings were still slightly loose from 240,000 miles of wear possibly causing the pinion gear and ring gear teeth to not mesh exactly as they had been running together before (one explanation at least).

Either way that slight whine has quieted down over the last ~20,000 miles.

Disclaimer: I'm not a mechanic and none of this is exactly "by the book" but IME it worked, so far at least (20,000+ miles).

 

[Irish Reiver]

I swapped in a new seal on my '96 a couple of years back. My seal was completely destroyed by rust. I pretty much did what @Malleus suggested and it has been fine since. I do have a whine/drone which is likely due to the bearing being contaminated. I did buy the new bearing and crush sleeve but haven't got round to replacing it yet. I have never worked with a crush sleeve before so I am uncertain as what effort is required to properly set the pre-load. That said I am pretty sure unless you have a lift getting the nut up to 181 ft/lbs might be difficult with limited space.

 

[Malleus]

Naw, you just use the weight of the truck, same as you do getting the crank nut off.

Seriously, if you have access to a surface grinder (or have a friend who does) solid shims are much better...they take far less effort to install. Lots of differentials are still built from the factory with solid spacer stacks. The assembly lines are built using a measuring station which tells the operator which stack to use. It's not rocket surgery.

The reason the crush sleeves are used is that they're cheaper than a stack of precision ground shims, and assembly lines have presses so the force required to shorten them is not a problem – for them.

 

[Beast of Berlin]

IME you can go a bit past the original spot (depth of the pinion nut) if you don't go crazy ie: to take up any slack in the pinion bearing from wear assuming you have some miles on the original gears/bearings/diff set-up.

Short story: I did this when I replaced my rear diff pinion seal and and pinion flange a couple of years ago and went past the original nut position without major drama. I did something similar with a front diff pinion seal replacement over 10 years ago, no issues.

Long story: The thinking is that the original crush sleeve takes a lot of torque (ft lbs) to crush it further so if you're using a torque wrench and don't go anywhere near the original spec needed to crush the sleeve further it shouldn't cause a major issue. IIRC I went to more than 50 ft lbs when I tightened up a new pinion nut (the diff already had ~240,000 miles on it), some people go much higher without problems. As I already had the axle shafts out (for brake/wheel bearing service) I checked the starting rotational torque of the pinion gear/diff using a dial indicator torque wrench on the tightened pinion nut and the numbers I got were within spec for used bearings by the FSM method.

Point is IMHO that the process above did not appear to change preload dramatically by tightening down the pinion nut to less than (ft lbs) where the orignal crush sleeve was set (crushed) when the diff was built at the factory.

Once the rear axle was all together and the truck was back on the road there was a (new) slight whine from the gears, best guess is by taking the slack out of the pinion bearing (preload) the pinion and ring gear teeth were not meshing exactly where they were before due to wear. But also I did not tighten up the carrier bearings ie: so the pinion is a tad tighter than before, carrier bearings slightly loose from normal wear, causing the pinion gear and ring gear teeth to not mesh exactly as they had been running together.

That slight whine has quieted down over the last ~20,000 miles, likely due to the gears settling in to a new pattern IMO. I considered also tightening up the carrier bearings slighty but didn't have a fixture to hold the diff so went with what I had. I ran that idea by ZUK who said you can wing it by tightening both sides slightly but equally (carrier bearings) with an open LC Diff to take up for wear. I didn't have a holding fixture for the differential carrier so went with what I had and buttoned it back up without touching the carrier bearing preload.

Disclaimer: I'm not a mechanic and none of this is exactly "by the book" but IME it worked, so far at least.

The whining noise when bevel gears mesh should not occur. Thats another topic, since the alignment of the pinion teeth with the ring gear is already adjusted on the shaft by shims which should not be changed. However, if too little preload is applied, the rolling elements in the bearing will not make contact and will no longer roll. Brinelling occurs in the bearing race. With too much preload, the bearing race/rollers are pressed too hard and tent to overheat.

I will try it this way ....measure the drag torque by attaching a spring balance. The wheels are disassembled. I must later achieve this previously measured value again. The balance will hang on a bolt of the flange through-hole connection.

 

[Kernal]

"The whining noise when bevel gears mesh should not occur"

Right, maybe with new gears, new set up.

But I'm working with used gears with ~240,000 miles, so IMHO changes in pinion preload may alter pinion stability and running position enough to slightly change the established contact pattern on the worn gears, which may contribute to gear whine which is what this sounded like.

One way to look at it IMHO is that when replacing just the pinion seal in this set-up you have two choices:

Option 1: try to get the pinion nut exactly where it was before but the risk is if you don't get the pinion nut to the exact same depth (not deep enough) now the bearings have less (or zero) preload than before. And that can cause whine/roar and accelerated wear by itself.

Option 2: you can tighten the pinion nut past where it was which will take up any slack in the bearings which has developed over thousands of miles.

The reduction in the slight whine over time seems to indicate IMO that the bearings and gear contact surfaces have settled into a new operating condition.