Amsoil Severe Gear 75w90 - 50,000 mile drain

[PT1]

Originally Posted By: mvw2
It's not that simple. The oil did fine. I can't even tell you what gear(s) the whining is coming from. I want to say it's not even from the rear diff. Visually, the diff gears look good.

The whine, whatever it's from,


The whine is probably from heat induced wear/distortion on the face of the gears where they contact each other. It is most likely off a few microns out of tolerance so you cannot see it visually. You would have to disassemble the gearset and use gear lab metrology measuring equipment to tell. But after reading this post if you subjected a VC to that loading it may be toast. If you melted the bushings on the rear diff then that would be a testament to the amsoil that you still have an operational gearset. I would try a heavier oil like an 85w140 and see if the whine is abated. You may also want to keep an eye on any of the rubber seals on the diff that overheated.

 

[mvw2]

I just looked through the hole. You can see the teeth. It looked fine. As well, you have the magnet which will show shavings which also was minimal. Everything was in rather good shape.

I think the only problem with overheating is you have a center diff constantly putting load on the rear gears. At the same time, you have under a quart of oil to absorb and manage the heat. It took a good amount of time at highway speeds to build up enough heat to do this. It's not like I drove 100 feet and it was instantly boiling. It was a simple matter of heat generation and dissipation. Doing 55mph down the highway, generation won, but it did take a while.

 

[mvw2]

Oil analysis is in:

The only part of concern was the silicon level, but that can simply be contamination from the draining/filling through the dipstick hole. It's very possible, some external dirt could have gotten mixed with the sample. Then again, it could have been in there ealier.

Talking to my local lube guy, he said 50k seemed like a good time to change oil simply from the amount of iron and the general desire to remove said iron. He said oxidation and nitration would have be known(at some extra cost) to check on the longevity of the oil itself. Otherwise, there's no concerns over excess wear from bearings, gear faces, and such, so that's good.

 

[Tempest]

I like it. Looks very good. Glad I have the 75W110 in mine.

 

[JohnBrowning]

WOW I never gotten a diff. that hot that was full of fluid and not leaking!!! 300°-400° it is a good possability that the heat treatment of the gears and bearing might have been comprimised since the internal temp had to far greater then the outside temp. I understand that 400° is a far cry from 1200°+++ that you normaly associate with heat treatment but I have to claim to be partial ignorant of how much or what type of heat treatment process is used on modern gear sets! I know when I install a ring gear I always heat it to 200°F in oil bath before installing while hot on the carrier thisis how I was taught as a young aprentice in Germany to do ring gears.

 

[JohnBrowning]

Actualy I wounder if the Silicone is not part of the alloy for the gears. High amounts of silicone would make the part machine finish much better and would add some durability and surface hardness to the finish product it would also help with abrasion resistance. I would imagine the alloy used is high in silicone and graphite with just a touch of nickle to improve heat resitance but not so much that it causes abrasion wear issues! I am just guessing though because gear sets are not my specialty at all. I used to make my own steel in H.S. for my knifes and routinely manufactured my own parts for my project car's in tool and die class for use in Shop Class! In fact I thought about makeing a metal shaper or buying one so I can cut my own gears as a fun winter project and maybe learn more!

 

[JohnBrowning]

In fact Molakule and one of the Austrailian guys on here taught me a lot years ago when Bob was still a regular poster about gear sets. These two have done a lot of field testing wich always beats book learning in my experince!