I've been following the thread about the preferred lubricants for our
xmissions/diffs. My son is a Chemical Engineer (Virginia Tech '93) with
Equilon Lubricants so I asked him to weigh in on this topic. He doesn't
have a Triumph but he used to drive my '71 GT6 to school.
Bruce
-----Original Message-----
From: Jordan BA (Brad) [mailto:BAJordan@Equilon.com]
Sent: Wednesday, October 17, 2001 12:00 PM
To: 'Jordan, Bruce'
Subject: RE: Transmission/ Differential Oil (long)
At low pressure and temperatures, the viscosity of the fluid is what keeps
the gear teeth apart and prevents wear. As the load and temperature
increases, it becomes the job of the EP, or extreme pressure, additives to
minimize metal to metal contact. EP additives in lubricants chemically
react under pressure and elevated temperatures with the metal in gears to
form a protective film and prevent this metal to metal contact. EP
additives are mostly made up of Chlorine, Sulfur, Phosphorous, Zinc and Lead
compounds. Due to environmental concerns, Lead is for the most part gone
and Chlorine is also only used in limited applications. These compounds
become active at different temperatures and therefore if balanced properly
provide protection at all operating temperatures. The problem in the past
with some Sulfur EP additive packages in gear oils and yellow metals is not
how much is in the oil, or that the additive breaks down and forms an acid.
This acid, if formed, would eat up yellow metals and steel alike. The
problem is the difference between what is called active and inactive Sulfur
in the EP additive package. "Active" Sulfur compounds chemically react and
form these protective films at much lower temperatures than "inactive"
Sulfur EP additives. In some cases these "active" Sulfur additives may even
stain the yellow metals in the gear sets.
Whether a particular manufacturer uses active, or inactive Sulfur EP agents
is really only known by them. API, GL-4 and GL-5 are performance specs, not
a formulation specs. Texaco Havoline gear oil 80w-90 and Shell Spirax HD
80w-90 are the right products for this application and do not stain yellow
metals. We also have synthetic products in both brands, but the smallest
quantity is a 5-gallon bucket. Most major manufacturers have steered away
from formulations with active sulfur EP additives to avoid staining yellow
metals. In general, I would say the API GL-5 Multigear EP SAE 80w-90
lubricants marketed by ExxonMobil, Chevron, BPAmoco, Castrol, Valvoline and
Pennzoil would be safe for yellow metals. Also, well known companies such
as Redline, who specialize in motorcycle and sports car racing lubricants
would have products that don't stain yellow metals. I would stay away from
the smaller little known companies that may be at trade shows selling "the
greatest lubricants ever". The lubricants may perform extremely well in
their table top bearing test against traditional motor oils, but they
typically contain active Sulfur, Chlorine and other undesirable additives.
As far as the difference between GL-4 and GL-5, API GL-4 rated lubricants do
not have the EP level to withstand shock loading. Unlike API engine service
classifications, API gear lubricant classifications are not required to meet
the specs of lower classes and it all depends on the application. In the
case of the Triumph, it probably recommends a GL-5, but even if it only
recommends a GL-4, I would go with the GL-5 fluid. Sorry this was so long,
but I hope it helps.
Brad A. Jordan, CLS
608 Churchill Road
Knoxville, TN 37909
Phone (865) 692-1177
Fax (865) 692-1221
<mailto:bajordan@equilon.com>
-----Original Message-----
From: Randall Young [mailto:ryoung@NAVCOMTECH.COM]
Sent: Tuesday, October 16, 2001 2:23 PM
To: Triumphs; Lumia, John
Subject: RE: Transmission/ Differential Oil (long)
John :
This is always a troublesome topic, there doesn't seem to be a lot of
agreement or consistency about it. The issue is that some gear oils use a
sulfur-based additive that increases the "extreme pressure" properties of
the oil (basically the film strength). Under some circumstances, some of
the additive can break down, and the sulfur can oxidize and combine with
water from the air to form sulfuric acid (H2SO4), which can corrode brass
parts over time. Even most conventional GL4 gear oils have some of the
additive (it's what gives them that distinctive smell), but most
conventional GL5 gear oils have more.
Unfortunately, the GL4/GL5 standards do not (adequately) address the issue
of how much of this particular additive is in the oil, so a GL5 rating does
not necessarily mean the additive is present in harmful amounts, and a GL4
rating does not necessarily mean it's safe. From reading the standards, it
appears that any GL5 oil would most likely also pass the GL4 tests, I
believe the only reason that more oils don't bear the GL4/GL5 rating is
because the makers don't want to bother with two sets of tests. According
to Redline, they do not use this additive at all in their GL4 rated
synthetic "Manual Transmission Lube", and only small amounts, comparable to
a conventional GL4 oil, in their GL5 rated synthetic gear oils.
The other issue is those "certain circumstances". I haven't yet heard of
anyone that has actually had a significant amount of corrosion from using
GL5 oil in a TR tranny. The brass parts do turn somewhat dark, but that
doesn't seem to hurt anything. The story apparently originated in a
completely different car (Ford Model T ?) that has brass parts in it's
differential. It may also depend on your driving habits, it apparently
takes a good deal of heat and pressure to cause the additive to break down.
I rather suspect that most street-driven TRs never get into the required
conditions.
So, I'm not sure there's anything to worry about in a TR, but if there is,
it's only in the transmission. There are no brass parts in the
differential.
Even if you were having corrosion from the GL5, that would not cause visible
pieces in the oil. It would take a chemical analysis of the oil to detect
the problem without tearing the gearbox down for inspection.
Randall
>
> I have a later non-OD TR-6. Does anyone known if the tranny and/or diff
> have yellow metal parts that I need to be concerned about?
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