Gear oil vs. motor oil viscosities

We were discussing this subject a while back. Just found this link:
http://www.vintagetriumphregister.org/maintain/oil-overview.shtml

 

More info from here:
http://www.vintagetriumphregister.org/maintain/lubricants-
redline.shtml#basic

(all on one line)

Excerpt from above:
"Gear oil viscosity is measured at 150 F vs. 210 F for motor oil.
Therefore, 40 W motor oil is the same as 95 W gear oil.

"Gear oil is acidic, motor oil is alkaline. Gear oil needs very high wear
protection - Extreme Pressure (marked as EP). Therefore, it has a very high
sulfur and phosphor content. Sulfur and Phosphate reactions start at a
lower temperature, and Gear Oil has much more additive than motor oil. This
additive is corrosive to copper bearings and bronze synchro rings."

 

Gear oil is for gears, hypoid oil is for differentials. The last thing
you would want in a sychromesh is a sulfonated hypoid oil.

Herewith a war story from my misspent youth circa early 1960s:

A friend of mine bought a brand new Volvo of which he was very proud.
Only one problem with it he said, and that was he could smell
something burning sometimes. "Probably a plastic label on a tailpipe
of something like that," I suggested. "Let's have a look."

Crawling underneath, we discovered the differential was smoking hot.
Not right for any car, let alone a showroom new one. We waited until
it cooled off, then I pulled the filler plug and stuck a finger in.
Sniff-sniff! No stinkie! The pinion of the differential was low down
on the casing, it was obviously a hypoid differential. Should have
stinky sulfonated oil in it...

Off to the local Chrysler dealer for a can of his best EP oil.
Differential now running nice and cool. My friend wrote an irate
letter to Volvo Canada. A few months later a service bulletin was
issued to dealers. "Put hypoid oil, not gear oil in the differentials
you idiots!" Or words to that effect.

 

What's a good transmission fluid for a 92 Honda Civic? I'm not asking for
the best, just for a decent fluid at a decent price.

Thanks!

John

 

older manual trannys specify motor oil- 10w40, i think. if its an
automatic, id ONLY use honda fluid from a dealer. it should all be in
the owners manual.

 

The older manuals specified 10W-30 (at least as far back as 1991). But that
was before they drastically reduced the oil's zinc (ZDDP) content, which
those gears and synchros need.

The only known-safe fluid is Honda's own Manual Transmission Lubricant,
which appears to be the same viscosity as 10W-30, but smells like it's
heavy in sulfur anti-wear additives. There are other safe fluids out there,
I'm sure, but their additives and compatibility with Honda's tranny innards
is uncertain.

I do not know who makes the MTL for Honda.

 

The lube used in a gear box or final drive depends on the tooth contour,
metallurgy of the parts and desired wear characteristics, including
bearings of course. The helical cut gears in a modern synchromesh box are
subject to sliding forces similar to that in a final drive and their
lubrication requirements are similar. The syncromesh design and metallurgy
has to be part of the entire "equation" of course.

There have been many mfrs who have specified API GL5 for a combined manual
transmission & differential - VW may still do it AFAIK but they certainly
spec'd it for both RWD and FWD transaxles. API GL4 & GL5 are both EP gear
oils: the GL5, which can handle higher pressures, can have sulfur and/or
phosphorous in it and generally has sulfur (often this is added as what is
known as "flowers of sulfur" - a fine colloidal form of sulfur... IOW they
just throw some sulfur in the tank and stir) IME -- the smell is
distinctive -- and may have phosphorous in some form; the GL4 is suited to
somewhat lower pressure applications and generally has some organo-metallic
EP additive more akin to the ZDDP used in engine oils until recently, but
in a much higher proportion.

On the other end of the scale, the BMC Minis used the same oil for engine
and transaxle lubrication - they just had to choose the metalllurgy
required and throw in a little British car design attitude... err,
aptitude?.

BTW the Honda Australia site started to push Honda lubricants fairly
recently and now recommend Honda MTF for manual gearboxes; prior to that
they used to recommend a SAE 75W-80 API GL4 lubricant.

 

Yeah, but then how do you make your sychromesh work? It depends on
friction and a sliding force lube would be counterproductive.

 

I forgot to say, it's a manual transmission. So should I get the genuine
honda MTF or are others compatible for my specific car?

Thanks!

John

 

Does it really matter if you buy the Honda MTL? What if you save 2$ off the
other brands? You don't change fluids every month!

Same goes with Coolant. I mean, a gallon bottle of coolant already diluted
from Honda is 10-12$CAN. Prestone might be 6-7$? undiluted. Add another 2$
for distilled water. Are you really saving any money? It's a service that
you do every 2 years or more depending if it's the long lasting coolant.

Why is it so difficult to use Honda fluids? They are not like 100$ per
bottle and needed changing every 3000kms!

 

Nothing really, but there are better out there.
Honda MTL is dino oil, and I regularly experience winter temps
below -20C.MTL is a _bitch_ to get into 1st gear when cold at those temps.
I've recently tried some Royal Purple Sycromax, and so far am very pleased
with the easier shifting.

The MTL was less that a year old.

 

I don't know precisely how it's done but would guess metallurgy is
important here - a steel which does not allow for strong Fe-S bonding. At
any rate, VW and I believe Porsche does it... with balk-ring synchros?

 

By what measure?

Huh? You won't know whether to be "pleased with it" as a substitute for a
long while yet... until the box fails or doesn't at high mileage. Extreme
cold shifting is just one part of the entire performance spectrum and the
record is not good, even in this NG, on extended use of some of the
synthetic gear oils... notably plastic bearing cages which umm, disappear.

 

Nope.

I'm pleased with it now.
Thanks!

 

Notice how at least some synchros have grooves cut into one face? I think
that's to concentrate the frictional forces so the bronze can burn through
the oil film and drag against the other side.

 

borg-warner synchros are bronze cones which act a bit like a morse taper
- when they bite, they really bite. fwiu, there remains a boundry
layer, but the overal friction area is sufficient to slow the moving
parts to a point where metal-to-metal contact can be made.

porsche synchros are baulk rings that jam against the inside of the
sliding pinion. they have a rough sand-cast exterior that offers very
low contact area and consequently very high local force per that area -
just cuts through the lube for metal-to-metal contact and sufficient
friction to work.

the really interesting stuff is in automatics - a whole bunch of
lubricated clutches??? a lube that's not a lube??? and a fluid that
can be used for hydraulics, but still provides extreme pressure
protection for the gear tooth faces? that's a tough job!