I've not really considered the GL-4/ GL-5 issue until reading this reply,
so I though I'd check out a few things online.
Mobil.com states that Mobil One Gear Lube (75W90, I think) is GL-5 and can
be used in rear axles rated for GL-4 but not transmissions rated
GL-4. Redlineoil.com states their MT-90 (75W90) GL-4 is good for GL-4
rated transmission as it does not corrode the brass/bronze syncos. The
GL-5 additive package helps that oil handle extreme pressures, but causes
the accelerated brass/bronze syncro wear (shortens life by half). GL-5 is
required in many axles, as it can withstand the stressed unique to that
environment. Transmissions do not stress their lubricants as much as rear
drive axles, hence GL-4 is fine most manual transmissions. Both Mobil One
and Redline MT-90 are synthetic oils.
All of the above was gleaned from those two websites...Redline MT-90 for
the tranny and Mobil One for the rear differential?
---------------------------------cut-----------------------------
Date: Fri, 4 Jan 2002 12:13:05 -0500 (EST)
From: "Robert M. Lang" <lang@isis.mit.edu>
Subject: Re: 1973 transmission/reply
On Thu, 3 Jan 2002, Valerie Stabenow wrote:
> I buy Valvoline 85-90 GL3 or 4. As I understand it (or maybe it's urban
> legend stuff,) there are additives in the GL 5-6 that are not good for the
> parts. Perhaps another lister can illuminate/verify, etc.
This is not urban legend. The GL5 oils have high sulphur content and they
to eat the brasss/bronze synchros and bushings. If you've used the wrong
oil, when you drain your tranny after 10k miles it looks like liquid gold
with all the brass metal flakes in suspension.
The main problem with this is that if your tranny sits for a while, the
metal falls out of suspension in nice clumps, and these sometimes block
the drain hole from the tail back to the main gearcase. This has
predicable effect on the tailshaft bearing.
> Valerie
regards,
rml
William Whitmoyer
69 TR6
90 BMW iX
91 CRX Si
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