Thread: rattling diff / axle when coasting

Originally Posted by PhilipA

Rick I hear what you say but I found that on a hot day say 32C or more , towing my camper at say 900Kg I started to get noise from the front diff when I exceeded say 120Kmh to run up to a long climb. This to me suggested lubrication failure. I run 80/90 full synthetic in my transfer with an extended sump.

I plan to go to Queensland "shortly" ie when the lockdown ends. I doubt whether the fuel consumption will change much.

It was interesting that the wonka wonka sound only came from the front diff and at high load accelerating with 900kg on the back at 32C plus.

Seeing I plan a Kimberley trip next year I feel the 50/50 mix is justified and cannot do any harm. After all the CVs run grease and in RRCs the hubs went from ep90 to grease.

Regards PhilipA

A higher visc won't hurt on that trip, but when you're loaded up like that, and particularly going up a hill, there's far more load on the rear diff, and it's copping all the heat from the engine, exhaust and the rest of the driveline, the front diff gets all the lovely cool air.

I like the extra oil capacity with the bigger sump on the t/case, they run hot.
The poor thing cops all the heat from the engine, exhaust, and gearbox.

I started a recent thread on a similar noise on no load deceleration. I included a sound clip. Look it up.
None of the answers were right.
I ended up having a loose cross pin in the rover type diff (IIRC different to the P38 style).
Anyway, it let go offroad and grenaded the rear diff in a quite spectacular way.

To isolate (attempt to make noise disappear), one would need to:
1) Remove rear drive shaft
2) Remove rear axle shafts (or drive flanges)- not sure how P38 is set up in this regard, so ymmv
3) Drive to attempt to replicate fault with Centre diff lock engaged (so you at least get drive!).
...and if noise is gone, rear diffferential centre is the culprit> investigate further.

Thanks for the tip!

We've been in a bit of a pickle here due to all the high water stuff so did not yet get a chance to work on the rangie. It's not that difficult to remove the driveshaft, removing the half shafts though requires me to remove the hub carriers. I'll give it a go since I can check the bearing on the right rear side which is making a suspiciously loud noise.

On a final thought; how would one know if the backlash (which I believe is play from front back?) is too high and what I am hearing is actually gears "clunking" because they are misaligned?

Sorry guys, a complete diff noob when it comes to (re)building them

Cheers,
-P

Well,

After a wild goose chase around the car a mate of mine finally laid down flat on the rear lid and stuck his head underneath the car whilst driving and he pinpointed the sound coming from the rear right! Odd how sound sources can sometimes be so hard to find on a rolling car...

Anyway, turns out the rear right bearing was shot. It had very little to no play in it when checking but the outer bearing and race were rusting. The inside was just fine. I have had this happen to me several times now. In fact, the bearings are the only thing that are going on me on this vehicle. I replaced them using a mates 60 tonne press and all should be fine, for now. I have already replaced this bearing once it my ownership of the car so... Perhaps it's not the last time.

Thanks for all the tips!

-P

Originally Posted by prelude

....

Anyway, turns out the rear right bearing was shot. ....

I would have thought that if it was this RHS bearing, when you turned left, it'd have made the usual grinding/moaning bearing noises.

Though my car is not on the crab when driving ie it does not pull on the wheel, the sound only came to light when I let the vehicle coast and let go of the wheel making the car roll ever so slightly to the left over time and unloading all drivetrain parts. The car had to be on temp and the gearbox oil warm enough to lock up the torque converter and only then when coasting (slowly) would the sound present itself. It's an odd thing right? In any case I am happy I found it

Cheers!
-P