Solving manual trans whining sound.

We're about to get nerdy... This may be a little tough to understand for those not familiar with lubricants. Any questions, ask away and I'll try to respond. I've been in the lubricants industry for 9 years now so I'll do my best

Reference this chart: https://www.kewengineering.co.uk/Auto_oils/images/Table_5_viscosity_comparison_chart.jpg

What you need to know
-Viscosity is the measure of thickness of the oil. It is usually measured in centistokes (cSt) but also may be measured in other units
-Viscosity changes with temperature (non-linear). Cold makes it thick, hot makes it THIN
-Viscosity is measured at standard temperatures

So let's take a look at the 75W-90 gear oils
-The chart is not going to show it well, but the standard for the "75W" part of this specification is a maximum thickness at a very low temperature. For the 75W spec, it has to be less than 150,000 cSt at -40 degrees (Basically, it needs to flow under it's own weight at -40)
-for the "90" part of the specification, it is measured at 100C / 212F - the range as you can see from the height of the box is very wide. Compare it to the SAE 40, 50, 60 for the motor oils, or to the ISO 150, 220, 320 for the ISO gear oils. This means that manufacturers can formulate anywhere in that range and still be compliant

Next, what spec governs the gear oils? It is called API GL-5 (American Petroleum Institute, Gear Lube, Rev #5)
-The specification is primarily intended to solve lubrication issues in hypoid-style gears, like in your differential.
-These type of gears have primarily "sliding friction" due to the design style, and also deal with very high spot loads.
-For this reason, the GL-5 gear oils are LOADED with sulfur-phosphorus additives, which are excellent in STEEL-ON-STEEL sliding applications. The very high temperatures (800+C spot temps) chemically bond the sulfur to the iron and then act as a sacrificial wear layer. BUT, these additives do not activate very well at lower temperatures, or lower loads.
-However, sulfur is very corrosive to bronze. This can attack the synchro's which are normally made with some kind of yellow metal

Engine Oils on the other hand, are formulated to handle a lot different type of challenges including
-Preventing wear in various types of lubrication regimes (sliding, rolling /// low, medium, and high loading)
-handling very high combustion temperatures
-keeping the engine clean from sludge due to combustion byproducts and degradation of the lubricant itself
-and on and on... more here http://www.asharrison.com.au/wp-content/uploads/2016/12/CK-4-Spider-Web-chart.png

So, the engine oils are formulated with a more "balanced" anti-wear package. Some of these additives are designed to activate at lower temperatures and pressures than the sulfur-phosphorus in the gear oils. It just so happens that your transmission spends most of it's time in a lubrication regime much closer to that experienced in the engine, than that experienced in the rear differential at hard acceleration

 

What you're saying then, Castrol Vecton 15W-40 CK-4 meets or exceeds the specifications you've become aware of over the past 9 years.
You seem quite convincing; I am willing to try it.

Please excuse my shitpost - I'm sitting in a coffee shop and a bunch of people just sat down all around me and I'm nervous now.

 

Yesterday it wasn’t as warm as usual, 79F as opposed to last weeks 88F. Yesterday there was no whining while accelerating with this recent switch to the Castrol GTX. This coming week, temps will get back to the 90’s again. We’ll see if the whine returns which it very well might. I live in So. Calif. where it doesn’t get cold. I wish there was an additive which would raise the weight of the fluid. BTW, it WAS my trucks first trans and diff fluid change when I put in some unknown 75/90 brand a few months ago. The whining started after that first ever fluid change (106k) and hot summer temps. As we get into fall and winter here, with cooler temps, I suspect I won’t hear any whine.

 

@HierAnarchy - I would say I know Vection 15W-40 CK-4 better than I know the other available products, but based on my experience, I would feel comfortable with other "major brands" 15W-40 CK-4 diesel engine oil in this application.

In a few more thousand miles, I'll post the results I have including used oil analysis

 

I do not advocate for running engine oil in the transmission at all outside of emergency use scenarios. I'm curious to see what your results are, though. CJ4/CJ4 engine oils are indeed engineered for diesel engines used for towing and hauling so I'd expect more protection than provided by other transmission "hacks" like running ATF...Rotella HD oils are quality and I have been running them in my diesel trucks for years.

All that to say... if they are in good health, these transmissions run fine with a proper GL4 75W90.

 

As far as my situation goes, I’m not going to lose sleep over this. Never was my fluid ever low. I doubt irreparable damage was done. I consider it a minor sound annoyance now. Still smooth shifting, no drop in MPG, no alarm from trans techs that the bearings are going. High quality fluid in both trans and differential at the moment. It’s been an interesting read tho. Never did I realize trans fluids were that important, unlike engine oils.

P.S. I was surprised how many Google hits about transmission whine.

 

Run redline in the transmission!
It’s the best stuff and Amsoil in the diffs.

 

+1 on the MT-90. I ordered a

$95 Red Line (57105) 75W140 Non-Limited Slip Synthetic Gear Oil - 1 Gallon

gallon jug from Amazon.
I read either you or someone else used the 75W90 flex bags to fill the transmission.

I walked into AutoZone, with your image in mind for the AmsOil, but I walked out with Valvoline FlexFill thinking I got the right product.
I got as far as this very moment before realizing I didn't buy the same product and I already replaced my rear differential fluid.

I also stripped the hex front differential drain plug (a $5.00+ mistake).

 

You can replace those hexagon nuts with the Lexus bolt instead.
Yes I love the flex bags,
Here are the Lexus bolts to replace the top and bottom hexagon ones for the front diff. The bottom one usually gets stripped out because of the higher torque spec
for that drain plug