Corrosive? Active vs Inactive sulfides in gear oil

[antiqueshell]

Can someone in the know chime in and explain how to tell WHICH type of sulfides used in a gear oil ARE corrosive to yellow metals versus the ones that ARE NOT? Looking for chemical names of these sulfide products.

I have heard that INACTIVE SULFIDES are NOT corrosive, while
ACTIVE SULFIDES ARE CORROSIVE...

Chemical engineers please comment. Thanks.

 

[camelCase]

They are both corrosive. Active sulfides are just more likely to corrode faster since they "bond" to the surface and basically turn into a sacrificial soap.

Copper + Sulfur + Heat = Copper Sulfide = Bad

 

[antiqueshell]

Thanks for replying camelCase!

Now regarding heat in this equation....

In my typical passenger car (1996 VW Golf 2L engine 5 sp manual, weighs about 2300 lbs. Is that gear box going to generate the necessary heat to create that corrosion process. I have done some surfing on the net and found that gear temps must surpass 250 F to start this process. Most of those articles claim that typical passenger car gear box temps will not come close to that. What is your view?

 

[Tempest]

To the best of my understanding, modern gear oils have "buffer" or scavenger chemistry to help absorb "loose" sulfur that is floating around. These buffers eventually do "wear out" over time.

What is the recommended lube for your trans?

 

[antiqueshell]

75w-90 GL-4 Transaxle/Gear Lube.

Must be yellow metal SAFE, not just yellow metal friendly.

Also must have compatibility with synchronized gears.

I can tell you there are plenty of these transmissions out there even in the USA, however there are very few choices and some are very expensive for what is needed.

Head over to Europe and there are literally scads of such spec oils available from all the big oil companies, many have the
VW 501.50 (G50) endorsement as well. Shell "Spirax S4 G" is a good example, and it is reasonably priced as well.

I have found that Valvoline makes something calleds
"Valvoline Synchromesh Manual Transmission Fluid" which
appears to meet my needs with a cst of 14.5 and it states that is it yellow metal safe.

 

[MolaKule]

Yep, Amsoil MTG and Redline MT-90 meets the specs but antiqueshell doesn't want to buy it, thinks they're too expensive, and has two threads going:

Other Thread

 

[MolaKule]

Again, fixating on a particular base oil or additive component tells us nothing about the performance of the totality of the finished product.