Transfer case whine after Royal Purple Synchromax fluid replacement (2 Viewers)

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I changed the transfer case fluid in my '07 GX470 in December using Royal Purple Synchromax, as it was the only aftermarket fluid I could find that claimed to be compatible with the Toyota OEM spec (that costs $50+ per quart). Since then, i sometimes get a relatively quiet gear whine from the transfer case that goes away if I apply light pressure to the transfer case lever. The transfer case was filled until fluid came out the fill plug, so it is full.

I'm thinking this has to be due to the Synchromax. Has anyone else had this problem with this fluid? I'm about to drain it out and pour in some 75W90 gear oil and see if the noise goes away. Any other fluid recommendations that are NOT the $50/quart OEM fluid? I put Lucas 75W90 full synthetic gear oil in the differentials and it seems to work great.
 
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I'm not sure where you found that Royal Purple Synchromax is compatible, this is not true.

If you go on to Royal Purple's website, it calls for gear oil application chart

So change ASAP!!!

Synchromax is generally used in manual transmissions that are designed for lightweight ATF style fluids.
A transfer case is a highly loaded gear set, similar to a differential, so it needs a heavier weight oil.
 
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I just use any old 75w 90 GL-5, why over think it. Plus synthetic seams to make the transfer case louder in my experience.
 
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It is recommend for use in Toyota LF gear oil applications per Royal Purple's website (http://www.royalpurple.com/wp-content/uploads/2019/01/Royal_Purple_Transmission_Reference.pdf), but that being said it is coming out since it appears to be making an annoying noise. I'll just dump some Lucas 75w90 in it this weekend (perhaps non-synthetic) unless anyone has another good option. I plan to change it ever 20-30k miles so whatever goes in won't stay in for long.
 
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It is recommend for use in Toyota LF gear oil applications per Royal Purple's website (http://www.royalpurple.com/wp-content/uploads/2019/01/Royal_Purple_Transmission_Reference.pdf), but that being said it is coming out since it appears to be making an annoying noise. I'll just dump some Lucas 75w90 in it this weekend (perhaps non-synthetic) unless anyone has another good option. I plan to change it ever 20-30k miles so whatever goes in won't stay in for long.
The file linked above is for transmissions.
 
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Redline MT-LV and Ravenol 75w MTF-3 are applicable to Toyota Transfer Gear Oil
Thanks, I found the Ravenol on Amazon and ordered two liters. I'll report back if it quiets things down or not. The Redline is very hard to find; from my former days as a Subaru guy I heard that the Redline is one of the few non-OEM lubricants that works well in a Subaru manual transmission. I could never find it anywhere and ended up just driving 80 miles to the nearest Subaru dealer to get OEM gear oil (which was cheaper anyway).
 
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Ah, I remember mixing up the infamous cocktail from NASIOC and doing the change in my '08 WRX.

Per the owners manual all you need is a Hypoid API GL-5 gear oil with a weight of 75W90. I was going to do a basic 75W90 this spring when I give my GX an overdue re-baseline.
 
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Allot of guys/gals in the 80 section run synthetic in their transfer case, but at the same time complain about the whine noise while on the highway.

"There are no solutions in life, only alternatives"
 
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I returned the Ravenol, drained the Royal Purple, and filled it up with $16 of Valvoline non-synthetic 75w90 (conventional gear oil is hard to find - only Autozone carried it here).

The noise completely went away. And it's quieter in 4-low too.

Lesson learned, sometimes the cheap stuff works best.
 

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