HELP!! Why am i breaking pinion gears

[Kabooms]

I have gone through two differentials in 6 months, both times the differential began whining and it continually gets louder until the pinion gear ends up shedding teeth when doing a pull. Here's the setup:

First Diff-S13 R200 Differential with Nismo 2-way lsd, Motul 90PA fluid, changed twice in 4k miles. Broke at around 5500miles

Second Diff- S13 R200 rebuilt with new OEM bearings and crush sleeve at local shop, same Nismo 2-way differential (cleaned and checked for damage) KAAZ LSD diff fluid.

CAR- S14, 1JZ, R154 Trans, 435whp,370tq. The car has never seen the track but I do occasionally make a few 2nd through 4th gear pulls.

Has anyone had this issue before or know why this is happening? I have read that the R200 is good for 500hp in a track car, and i know others with close to the same hp that do not have any issues.

[zerodameaon]

Is your lashing and spacing correct? Have the pinion and ring gears been from the same diff in each case? If you change ring or pinion gears to a different tooth count you must change the other gear IIRC.

[Kabooms]

In both assemblies the ring and pinion and housing were from the same car(junk yard) After the original the original one broke the pinion teeth, i put the differential in a new(used) housing with the corresponding ring and pinion and had all of the bearings replaced and the spacing and back lash set at a local reputable performance shop. I assumed that improper installation was the culprit in the original one( purchased assembled, used from someone local). Is it possible that excessive heat generated by the differential itself is causing the fluid to break down prematurely and cause the gears to wear and possible loose their temper(hardness)? I am running a smooth s14 rear cover. The original unit began making noise before the first fluid change. There was no metal at all in the fluid upon draining.

[az_240]

You could always go with a z32 NA or J30 diff cover which holds more fluid and has cooling fins if you're skeptical but unless you are doing continuous laps at the track I do not see the diff generating enough heat.

My guess is the fluid got really low at some point (happened to me once...noticed it was low so filled it to bottom of fill hole and the thing whined and blew up anyway) or improper installation.

[brndck]

Sounds like the backlash/gear engagement is incorrect. If the teeth are not fully engaging they will eventually shear.

Also, kinda a side note, motoiq has a really interesting article on cryo treating gear sets. A few seasons ago walker Wilkerson was having similar issues and they ended up using cryo treated stock gears, with excellent results.