Date: Tue, 28 Aug 2012 08:21:08 -0400
Reply-To: Mike S <mikes@FLATSURFACE.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Mike S <mikes@FLATSURFACE.COM>
Subject: Re: Fwd: Gear box oil - Redline MT90 or Swepco ?
In-Reply-To: <503C6ED7.3030706@gmail.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
On 8/28/2012 3:10 AM, Gene P wrote:
> 1) The German mechanic that installed a rebuilt transaxle for me 9
> years ago said "use GL-4 oil only, NOT GL-4/GL-5, GL-4 ONLY. Wrote
> it that way on the invoice. 5) A clip from a dandy 2-page technical
> article on Redline's website: "GL-5 gears oils which are required in
> hypoid differentials are not used in most synchromesh transmissions
> because the chemicals used to provide the extreme pressure
> protection can be corrosive to synchronizers, which are commonly made
> of brass or bronze. Typically, the use of a GL-5 lubricant in a
> synchromesh transmission will shorten the synchronizer life by one
> half."
This thread started with someone saying "don't use Redline MT-90..."
based on a forwarded message where a friend of some person was talking
to some other, unnamed person at Redline. Redline themselves says, in
writing, about MT-90 "Popular in ... VW/Audi ... Safe for brass synchros
... Recommended for GL-1, GL-3, and GL-4 applications." That's us. Where
it is not suitable, and they don't claim it is, is for a GL-5
application. Redline recommends their 75W90NS gear oil for that, in the
MTL/MT-90 spec sheet. It's odd that the forwarded "friend of a friend
told me" post was saying "use the GL-5, not the GL-4," the exact
opposite of what you usually see.
Again, the GL-5 comments above don't apply to Redline MT-90, at all.
But, regarding those comments, I believe this is where a lot of
confusion comes from. GL-5 has greater extreme pressure lubricant
requirements. Early formulations achieved that by using sulfur compounds
which corrode yellow metals (synchros). They tend to smell really nasty.
So, you will find people making blanket statements like "never use
GL-5," because they're ignorant of the reasoning behind it. It's not a
problem with GL-5, per se, but with _some_ GL-5 formulations. Many newer
GL-5 formulas use additive packages which are no more corrosive than GL-4.
GL-4 corrosion requirements are measured using a ASTM D-130 copper strip
corrosion test. GL-5 does not have to meet this test. ASTM D-130 is
designed to assess the relative degree of corrosivity of the sulfur
compounds contained in a petroleum product. The test is carried out by
immersing a polished copper strip in a given quantity of sample, heating
at a temperature and for a time characteristic of the material and
comparing the copper strip after it has been washed and dried with the
ASTM Copper Strip Corrosion Standards. This produces a rating, where
1a=best, 4c=worst.
Although GL-5 doesn't have to meet the test, the MT-1 spec (and
MIL-PRF-2105E & SAE J2360) does require a D-130 test. The MT-1
requirement is actually more stringent than the one for GL-4. The GL-4
requirement is 3b after 1 hour, the MT-1 requirement is 2a after 3 hours.
So, if you're going to use a GL-5, it should _also_ carry one of these
ratings. Such oils are not difficult to find.
The other reason you may not want a particular GL-5 is shifting. There's
a range of properties, etc. which fall into the 80W(-90) weight rating.
Some oils are affected by temperature more than others. Some
transmissions have a different shift feel than others. Various
combinations produce different results. But, the same applies for GL-4
oils, some just work better than others. I have MT-90 in mine, and it
works for me. I know there are lots people who use it in newer VW/Audis,
because it works for them.
If you Google "MT-1 ASTM D130", you'll find lots of info (and some
mis-info).
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