Amsoil Transmission Oil (Gear Lube) - 75w90 GL2-GL5, MT-1 vs. 80w90 GL4 MT-1

[Eric_R_Kissell at whirlpool.com]

I called the AMSOIL Tech Line.  I discussed the rating of their 75w90 GL2
through GL5 MT-1 rated transmission oil and whether this oil was
appropriate for VW/Audi manual transmissions.

The short answer according to the man I spoke with is YES.

According to the AMSOIL tech rep, AMSOIL 75w90 does have additives to
achieve the GL5 rating, but it also contains buffers to prevent these
additives from attacking soft metals such as brass synchro rings, which is
part of what the MT-1 rating tells you. The technical representative from
AMSOIL said that their 75w90 transmission oil with a GL2 through GL5 &
MT-1 rating was suitable for the Audi/VW transmissions because of the MT-1
rating and the GL4 rating.

He cautioned that other manufacturers might not use buffers in GL5 rated
synthetic oil and that he could not speculate about the suitability of
other GL5 rated synthetics with soft metals.

He also said that if anyone was really concerned about the additive
associated with the GL2 through GL5 rating of their 75w90 in spite of the
protecting buffers, they could choose to use their GL4 MT-1 rated 80w90,
which would also work fine.

I was curious about the MT-1 rating, so I dug a bit deeper on the
internet.  I found a site that talked about driveline lubricants:
http://www.lubrizol.com/ReadyReference/DrivelineLubricants/15-gears/default.htm

A link in this writing summarized GL5 testing versus MT-1:
http://www.lubrizol.com/ReadyReference/DrivelineLubricants/15-gears/default.htm

This shows that MT-1 and GL5 have little overlap in test requirements, so
if an oil has both ratings it has satisfied the requirements of more test,
which should be a good thing.  One of the MT-1 test that is not required
under GL5 is ASTM D-130, which is stability of copper and copper alloys.
This may be the "soft metal test" that the AMSOIL tech rep mentioned. I
did not look at ASTM D-130 to understand if it means that brass synchros
will be OK, but my guess is that brass counts as a copper alloy, so a MT-1
means OK with brass.

In summary, according to AMSOIL the buffers in the AMSOIL 75w90 GL2
through GL5 MT-1 transmission oil should protect the brass in the VW/Audi
gearbox. AMSOIL also has a 80w90 that is rated GL4 MT-1 which will work in
the VW/Audi gearbox without any GL5 additives requiring buffers if this
concerns you.

I cannot comment about how AMSOIL gear oil compares to Redline MTL or
MT-90 in terms of the Redline claims about having enough friction for
proper synchro engagement. I am planning to try AMSOIL 75w90, 80w90 and
maybe Redline MTL to see for myself when I have time.

HTH,
Eric