To quote from the Red Line brochure:
"...MTL may be used in transmissions which recommend 75W or 80W GL-4
gear oils, ATFs, or SAE 30 or 5W/10W/30 motor oils. If a 90W GL4 or
SAE 40 or 10W40 is required, MT-90 may be used. <snip> Seal
compatibility has been designed to be similar to petroleum lubricants,
and leakage should be no greater than any other oil of comparable
MTL is classed as a 75W/80W (but closer to almost-70W/almost-85W, they
claim), while MT-90 is 75W90. Neither has the EP (GL-5) additives
which eat syncros, and, as well, Red Line has taken into account the
fact that most synchros (and overdrives) require some friction between
mating surfaces to operate properly. They claim to maintain a much
better coefficient of friction, shear stability, and relatively
constant viscosity across a much wider range of temperatures than
Since the recommended lubricant for all MGB gearboxes, according to my
Haynes manual, is Castrol GTX 20W50, it sounds to me as though Red
Line MT-90 would be the preferred choice, of the two.
I have been using Castrol GTX 20W50 in the warmer months, then
switching to 10W40 for winter use, because otherwise the LH overdrive
on my B's gearbox works very poorly when the temperature drops below
freezing. This year, I'll still put GTX 10W40 in the engine, but I'm
going to try MT-90 in the gearbox. My local Britcar store, Autosport
(Seattle), sells and recommends the stuff, and they haven't given me
any bad advice on anything so far.
1967 MGB GT (with a '78/'79 drive train)
> How about in an OD unit? My first thought would be not a good idea.
> Anyone know for sure? Chris
> From: mgs-owner
> To: mgs%autox.team.net
> Subject: Red Line MTL in British trannies?
> Date: Friday,October 25,1996 7:47AM
> After putting Red Line MTL 75W-80 into my '79 Toyota truck gearbox,
> I was amazed at how well the thing shifted. Has anyone had
> experience using MTL or the slightly heavier MT-90 in MOWOG
> trannies, specifically an MGB 4-synchro with overdrive?
> I'm usually a stickler for Factory specs, but MTL didn't exist when
> our beasties were built. Any experience out there?
> Thanks, PK
> Paul D. Kile
> (916) 355-5162
> GenCorp Aerojet
> POB 13222
> Dept 5784 Building 20019
> Sacramento, California 95813-6000