Gear Lube

[Sarge]

I get about 3 or 4 PM's a month asking about gear lube. So I thought I
would share here. My thoughts are representative of my own efforts. I
read, and discuss with many engineers, manufacturers and of course
gearheads. I prefer data from industry accepted testing methodologies
over internet post any day and give little to no credence to internet
babble. I highly recommend you do the same.

Allow us to open with a statement. GM engineers have a "gun to their
head" to produce cars that meet or exceed air and MPG parameters. So
often times they will utilize a fluid or part that really is not what
they would have used if they had no air/MPG requirements. Us gearheads?
We want performance and could give two shits about air/MPG. Why do I
open with this statement? Because fluids have parasitic value. Heavier
fluids, be they engine oil or gear lubes, rob power and lower MPG. This
will be discussed but I wanted to get it out there right up front.

Gear lube operates in the toughest environment found on our cars/trucks.
Often forgotten. Brutally abused. Rarely discussed outside of "I run
brand XXX and go fast"......
Heat and pressure is abundant in our pumpkins. We need a lube that
provides a film to absorb the shock we introduce to our gears. We need a
lube that controls heat. We need a lube that does not allow thermal
"runaway"....what this means is a lube that gets too hot and falls apart
on you. When your lube falls apart so does your rear end as it loses
it ability to lubricate and cushion.
We need a lube that will stay on our gear surface. Cold or hot.
So lets look at various aspects of gear lube in 2011.

Viscosity. We all know all there is to know about viscosity and
understand it totally and completely. Lower viscosity is for cold and
higher viscosity is for hot. That is all there is to know about
viscosity. Right?
Well sorta.No.Let's look at the viscosity index.
"The viscosity of liquids decreases as temperature increases. The
viscosity of a lubricant is closely related to its ability to reduce
friction. Generally, the least viscous lubricant which still forces the
two moving surfaces apart is desired. If the lubricant is too viscous,
it will require a large amount of energy to move (as in honey); if it is
too thin, the surfaces will rub and friction will increase.
As stated above, the Viscosity Index highlights how a lubricant's
viscosity changes with variations in temperature. Many lubricant
applications require the lubricant to perform across a wide range of
conditions: for example, in an engine. Automotive lubricants must reduce
friction between engine components when it is started from cold
(relative to engine operating temperatures) as well as when it is
running (up to 200 °C/392 °F). The best oils (with the highest VI) will
not vary much in viscosity over such a temperature range and therefore
will perform well throughout.
The VI scale was set up by the Society of Automotive Engineers (SAE).
The temperatures chosen arbitrarily for reference are 100 and 210 °F
(37.8 and 98.9 °C). The original scale only stretched between VI=0
(worst oil, naphthalene) and VI=100 (best oil, paraffin) but since the
conception of the scale better oils have also been produced, leading to
VIs greater than 100 "
Important thing said here. The oils ability to separate two surfaces at
variable temperatures. Lets look at some viscosity index numbers across a
range of common gear lube viscosities.We depend on the ASTM D2270 test
for this.
"The viscosity index is a widely used and accepted measure of the
variation in kinematic viscosity due to changes in the temperature of a
petroleum product between 40 and 100°C.
A higher viscosity index indicates a smaller decrease in kinematic
viscosity with increasing temperature of the lubricant."
Remember. The higher the number......the better an oil will provide
lubrication between two surfaces across a spectrum of temperatures.
75-90 ....VI of 161
75-110....VI of 161
75-140....VI of 180
Notice the 90 and the 110 both are 161. This is due the viscosity
enhancers and the base oil being the same viscosity to start with. 90
and 110 both are in the same range with 110 having a thicker film but
the same VI.
Now a few gear lube manufacturers will tell you they have a film
thickness like a 250 weight with a fluid friction of a 90 weight.
Red Line ShockProof line of products
( http://www.redlineoil.com/product.aspx?pid=44&pcid=8 ) comes to
mind.What this really is a 90w base oil with significant add packs to
allow the lube to form a thicker film on your gears that absorbs "shock"
and chatter. Sill a 90w but with a thicker film. PAO additives are
wonderful things. We can have our low fluid friction and higher film
strength.
Heat. Lets look at flash points.
90w=410f
110=428f
140=410f
We require something with a flash point with a minimum of 300f so we are covered across the normal viscosity ranges. I hear thermal breakdown question quite often. Guys we are covered here with todays gear lubes.
I will say something here about Torco RGO oils. This is the conventional base Torco oils and many GTO guys (unique rear end) have jumped on this bandwagon because a Australian gear manufacturer recommended it and that recommendation went viral. Yup it is good stuff....but the Used Oil Analysis show me that it is pretty much shot after 10K miles or less....depending on how many hard launches etc. you do. So the Torco RGO stuff needs changed every 5K miles IMHO. After that you are running around with jelly in your pumpkin.
I left out tons of "stuff" and probably did a shitty job here...but I am trying to share some understanding of basics so you can understand what I am about to say.
With our modified and hard driven GM LSX rides we need more than what the manual calls for guys and gals.
I used two GM rear ends. One my Silverado 8.5 10" and the other test was the GTO funky ass Australian thing. I shared some of the results with the GTO rear end and 85-140 Torco RGO findings above.
What my latest results show me is simple. I used Amsoil 75-110 in both
and had the best results of any lube and any viscosity. Lowest wear metals. Quietest rear ends. Replaced the 85-140 and the 75-90 with 75-110 Amsoil and got the best of both worlds.
I highly recommend it. If you need friction modifier for your Limited Slip get the lil 4oz bottle of Amsoil friction modifier. I did not need any in the GTO.
Hope this helps explain why I do not recommend "what the manual calls for"......

[Wesman]

Interesting topic.

I recently did a pinion seal on my friends GTO, and we used Redline Shockproof 75W-250. So far its been great, nice and quiet and it really sticks to the bearings and gears very well.

I'm going to put some in my car once the new gears are broken in.

[pajeff02]

Good info. Any idea why Moser recommends a non-synthetic gear oil for its 12 bolts equipped with the True Trac posi unit?

[35th-ANV-SS]

Subscribed for later reading.

[Sarge]

Good info. Any idea why Moser recommends a non-synthetic gear oil for its 12 bolts equipped with the True Trac posi unit?

This pains me to say this......but it is what it is.

Over a decade ago Eaton tested some "mystery" synthetic oil.....it didn't work very well......so the "myth" of using a synthetic in various manufacturers lockers spread from there. I have spoken with techs at almost all rear gear manufacturers and not a single one can tell you why....outside of they heard years ago blah blah blah.... I have been told by one tech synthetic is too "slippery".....OMG! Clueless...totally clueless.

So in the fuel altered we have been running synthetic for many seasons.
Have not touched the gears...we crack the pumpkin every once in awhile and it is pristine. You will find tons of other gearheads who have done the same thing with not one single issue. OF course not. Conventional and Synthetic gear lubes are all conventional base oils. DUH!!!!!

If you set to close to the TV you will go blind.

I have first hand knowledge of Moser and Eaton being offered a full test of a synthetic, at the total cost to Royal Purple and Amsoil. They declined both. I bet Compsyn can confirm this.

[SteveC]

Good info. Any idea why Moser recommends a non-synthetic gear oil for its 12 bolts equipped with the True Trac posi unit?

At a guess, ALOT of the synthetic gear oil does not mix well with the posi additive, this was told to me by the rearend shop that changed my gears in my 01 Z28. I currently use 85W-140 dino oil with the additive.

SteveC

[5150]

Good info! Learning alot about motor oil's and lubrication. Thanks Sarge!

[pajeff02]

Thanks, Sarge.

I do run synthetic in our Corvette rear and have had no problems. The info I was given at that time is that a friction modifier would probably not be necessary and this has proven true. The posi works fine, no chatter or anything, with straight synthetic gear oil.

[tatertot91]

Subscribed for later reading.

Same

[CompSyn]

This pains me to say this......but it is what it is.

Over a decade ago Eaton tested some "mystery" synthetic oil.....it didn't work very well......so the "myth" of using a synthetic in various manufacturers lockers spread from there. I have spoken with techs at almost all rear gear manufacturers and not a single one can tell you why....outside of they heard years ago blah blah blah.... I have been told by one tech synthetic is too "slippery".....OMG! Clueless...totally clueless.

So in the fuel altered we have been running synthetic for many seasons.
Have not touched the gears...we crack the pumpkin every once in awhile and it is pristine. You will find tons of other gearheads who have done the same thing with not one single issue. OF course not. Conventional and Synthetic gear lubes are all conventional base oils. DUH!!!!!

If you set to close to the TV you will go blind.

I have first hand knowledge of Moser and Eaton being offered a full test of a synthetic, at the total cost to Royal Purple and Amsoil. They declined both. I bet Compsyn can confirm this.

Yes, I’ve talked with the Vice President, Technical Development at Amsoil about this matter and he described what Sarge is talking about here.

The Eaton test was done over a decade ago and I want to say more like 15 years plus. Anyway they used some non-specified synthetic gear lube that according to Eaton didn’t work out so well.

So a few years back Amsoil caught up to an Eaton representative at a SEMA show and offered to support more up to date testing with Amsoil gear lube. Initially it was a go, but over time the new testing got pushed back by Eaton and has not happened. Amsoil still stands behind their offer today.

And that’s just it. Whatever synthetic gear lube product Eaton used many years ago; products change, formulations change. Anyone who pays attention to the lubricants market knows it’s a constantly evolving beast. Yet in some cases people hear things, they repeat things, and without knowing it, there’re holding on to myths that are in some cases 30+ years old.

CompSyn

[Sarge]

At a guess, ALOT of the synthetic gear oil does not mix well with the posi additive, this was told to me by the rearend shop that changed my gears in my 01 Z28. I currently use 85W-140 dino oil with the additive.

SteveC

Steve I have no doubt they told you that.
They are probably damn good gearheads and clueless in the art of tribology. Like a butcher not being a chef. A carpenter not being a good painter....a great mechanic does not mean they know jack shit about tribology. So they (like many) just regurgitate what they "heard". I would ask how they know that? What lab did they use to determine the add was not "mixing"?


Run a $25 UOA on that lube. You will be changing it out about like motor oil when the data comes back. It will be wore ass out. Depleted. Shot after about 5K miles. I am aware people run it a lot longer than that. And their gear wear is 20 times what it would be on a solid modern synthetic gear lube. Spend the $25 bucks and see for yourself.

[Sarge]

Yes, I’ve talked with the Vice President, Technical Development at Amsoil about this matter and he described what Sarge is talking about here.

The Eaton test was done over a decade ago and I want to say more like 15 years plus. Anyway they used some non-specified synthetic gear lube that according to Eaton didn’t work out so well.

So a few years back Amsoil caught up to an Eaton representative at a SEMA show and offered to support more up to date testing with Amsoil gear lube. Initially it was a go, but over time the new testing got pushed back by Eaton and has not happened. Amsoil still stands behind their offer today.

And that’s just it. Whatever synthetic gear lube product Eaton used many years ago; products change, formulations change. Anyone who pays attention to the lubricants market knows it’s a constantly evolving beast. Yet in some cases people hear things, they repeat things, and without knowing it, there’re holding on to myths that are in some cases 30+ years old.

CompSyn

Thanks man.....sad....but thanks. I mean I have spoken with Eaton myself. To have an offer like that and ignore it is just irresponsible and ignorant.

[Eganslp]

Sarge, sry I must be mildly dense, but I'm getting from this right. That it would be ok to put synthetic in a Moser/Eaton rear. B/c if so then am I able to put synthetic in my detriot locker that is in my moser housing, or no? they told me to use 80w-90 non-syn..... but you guys are saying otherwise. So plz forgive, for I only ask bc I don't know. I'm not tryna be smart-ass.

[TLS_Addict]

Good info Sarge!

Having 2 different 10-bolt 8.5s rebuilt (one was late 70s and one was early 70s) each worked fine with conventional oil and additive. I am going to use just the Mobil 1 synthetic in the rear and if it chatters I will add the posi additive. I will report my finding back after I drive the car for a while.

How long does it usually take to get chatter?

[INMY01TA]

I ran some synthetic Redline gear oil in my stock 10 bolt about 8 years ago and started getting one wheel peels. My rear end guy says to use any dino 80/90 in my Eaton/12 bolt so that's what I've been doing. Seems to be working fine.

[02transamce]

ok Sarge,I have a year old Moser 12 bolt with a eaton posi (friction disc type,not true traci) running Valvoline 80w90 conventional with 4oz of GM friction modifier, about 12k miles on the rear end.what rear gear lube you advise me to use.thanks.
Posted via Mobile Device