Differential crown wheel scars? (1 Viewer)

[sodafeld1]

1986 hj75 troopy wreck. Beginning to approach differential study. What would cause these sorts of scars on the crown wheel please? The scars run most way round.
I think it needs at least a new crown and bearings, seal? I imagine pinions are replaced the same time as crowns, they seem to come together in kits?

The backlash measures ok, within spec. No idea how she ran. It is the front diff , it had very dirty oil with lots of fine metal so the oil was like grease. Neglected, the seal leaks too of course..Funnily enough it kind of feels ok as in snuggly turns, spiders don't wobble around too much, compared to other diffs I am looking at from layman's eyes.

 

[mudgudgeon]

Debris in the oil. Dirty 30 year old oil.

It's toast.

 

[sodafeld1]

Yes but, as far as adjustment went, why in that particular spot? It looks cactus for sure.

If it was adjusted correctly, one would expect wear grooves on the lower outer edge, kind of figuring with gravity and metal fines.
Unless it was too tight , so forcing and grinding the pinion upon the inner crown teeth..

Anyway getting my head around all the ins and outs of diffs.

Also , wonder why there is not complete diff kits with spiders, pin, crown and pinion , bearings all one hit?
Spiders and pins seem to be sold separately for some reason.

Looks more straight forward than a transfer case, but geez expensive parts! The crown and pinion are beautiful things though.

 

[Malleus]

That's cavitation damage.

 

[sodafeld1]

Well I had to google that cryptic explanation. Looks like cavitation damage. I wonder if the breather was blocked, gas vapours built and swirled around blasting the crown in that particular spot...Must have been noisy when being driven at speed.

Still a bit of a mystery to me though.

 

[peesalot]

loks like evidence from a hard/heavy load pulled

 

[sodafeld1]

loks like evidence from a hard/heavy load pulled

strange thing though is it is not all the way around and does have the same appearance as cavitation. Bit like forensic mechanics , assessing stuff from a wreck, how the hell did this happen?! Most of it is sheer neglect and abuse.

 

[peesalot]

FWIW might run a pattern on the teeth with the yellow stuff to see if it matches that worn spot, my guess is it will be a bit different cause under heavy loads the ring/pinion deflect and the contact changes, check pattern if its good, polish those up and run it.

 

[sodafeld1]

FWIW might run a pattern on the teeth with the yellow stuff to see if it matches that worn spot, my guess is it will be a bit different cause under heavy loads the ring/pinion deflect and the contact changes, check pattern if its good, polish those up and run it.

wow! that is optimistic. First time for me to tackle a diff. Pulled it apart since. I had just ordered new crown, pinion and bearing kit. It is expensive stuff, but I feel it is worth learning.
thanks peesalot

 

[Malleus]

Well I had to google that cryptic explanation. Looks like cavitation damage. I wonder if the breather was blocked, gas vapours built and swirled around blasting the crown in that particular spot...Must have been noisy when being driven at speed.

Still a bit of a mystery to me though.

Cavitation is when small bubbles form in a fluid and explode under pressure. The result appears to be really deep shot peening.

It's generally the result of fluid breakdown, not air entrainment.

 

[Malleus]

I seriously doubt you can develop a good enough pattern to miss the chewed up areas. If they were half as long...maybe. But they're not.

Go ahead and play with it, though. It'd be interesting to see what you come up with.

 

[sodafeld1]

well when I googled I got this for example ;What is Pump Cavitation and How Do I Avoid It? - https://www.csidesigns.com/blog/articles/what-is-pump-cavitation-and-how-to-prevent-it.

But I kind of assume it is cactus. The kit I got has crown, pinion and bearings , flange. antoni masiero brand made in italy, bearings are koyo and nsk. $650 aud including ship. Seemed to be the best deal around. Sold as 'drive tech.

Be nice to feel what a new crown and pinion feels like. Not sure about the spiders yet, but they didn't wiggle like the worst spare diff I have.

 

[peesalot]

Check the washers behind the spider gears & side gears if you took carrier apart

 

[sodafeld1]

yes, shall do, those spider gear parts too are exy..
I think it is the spiders and bearings which are most often changed out?

 

[sodafeld1]

Actually in different light the scars do go right way around.

Measuring side gear backlash, to my ignorant judgement it actually feels pretty good. But then the side gears do kind of move a bit traveling in the axle direction??