[Fot] Final drive (differential) oil

Thu Aug 11 15:03:40 MDT 2022

i offer some comments based on decades of dealing with this issue in lots
of different race cars

to select the correct viscosity, you really need to know the operating
temperature

Adhesive temp indicating labels on the outside of the main diff case are
usually the easiest method. they will give you a good idea of
whats happening inside

typically, the outer case is a few degrees cooler that the circulating oil,
so be cautious here as it is most likely a lot "cooler" then the oil film
between the ring and the pinion at the point of their contact

if you are seeing temps much over 100C on the outer, then the old 90 weight
diff oils are highly unlikely to acceptable

once most 'off-the-shelf" oils get to about 100C, they are starting to
degrade ,  some irrevocably (ie they are stuffed!!)

once you have an idea of temps , start looking at kinematic viscosity of
the oil being suggested. simplistically, its this value that allow the oil
to function as a metal to metal separator and the hotter things get, the
lower the viscosity becomes, and the lower the chance of it keeping metals
apart. the various brands of "race oils" can differ widely in this regard

in most modern rear-drive race cars we are using 140 grade purpose-made
race gear oils, and these have all sorts of fancy additives

microfinishing the ring and pinion gears prior to a diff build, can drop
working temperatures considerably

hope this helps in some way

Terry
Australia

On Fri, Aug 12, 2022 at 12:35 AM Phil Gott via Fot <fot at autox.team.net>
wrote:

> Thank you, everyone!
>
> It would seem that lubes designed for the everyday street-driven car
> aren't up to the challenge of racing our hyping diffs.  I thought the folks
> at Mobil would have done better, but apparently not enough.  I've taken all
> your inputs into consideration and going with the Redline Shockproof
> (lightweight) oil.  I'm also thinking of bolting on the aluminum cover of
> the 4A IRS diff to get a little extra capacity and perhaps some better
> cooling, although the added thickness may offset the higher rate of heat
> transfer through the metal.  Will do the math.
>
> Your insights are much appreciated.
>
> Regards,
>
> Phil Gott
> Red '65 4A, #114
>
>
> -----Original Message-----
> From: Alexandre Camoletti via Fot <fot at autox.team.net>
> To: fot at autox.team.net
> Sent: Thu, Aug 11, 2022 4:38 am
> Subject: Re: [Fot] Final drive (differential) oil
>
> Gents, when heats becomes a problem then you should definitely try the
> Lucas oils. Measure temperatures before and after the change, the
> difference is usually quite big !
>
>
>
> *De :* Fot [mailto:fot-bounces at autox.team.net] *De la part de* fubog1 via
> Fot
> *Envoyé :* mercredi 10 août 2022 19:25
> *À :* fot at autox.team.net
> *Cc :* fot at autox.team.net
> *Objet :* Re: [Fot] Final drive (differential) oil
>
>
>
> Bob you bring up another good point as well, there's a big difference
> between a 20 minute sprint race & an enduro, the heat is a much bigger
> consideration...
>
>
>
> Glen Efinger
>
>
>
>
>
> -----Original Message-----
> From: Bob Kramer Gmail via Fot <fot at autox.team.net>
> To: fubog1 <fubog1 at aol.com>
> Cc: fot at autox.team.net
> Sent: Wed, Aug 10, 2022 11:51 am
> Subject: Re: [Fot] Final drive (differential) oil
>
> Good point Glen. Welding up the center section makes the soft yellow metal
> cone washers moot.
>
>
>
> I’ve found EP90 GL4 from Car Quest (available from Advance) as a good
> substitute for StaLube GL4, but it overheats and failed us in endurance
> racing.  It has always worked in the shorter vintage race, and is cheap
> enough the drain and refill often.
>
>
>
> Sent from my iPhone
>
>
>
> On Aug 10, 2022, at 10:03 AM, fubog1 via Fot <fot at autox.team.net> wrote:
>
> 
>
> Welded rear gears aren't that fussy about lube, any good hypoid gear oil
> should be OK;
>
> I usually use 80-90 Valvo in them.
>
> The metal in the sample is a different story, they normally don't "make"
> any metal in operation.
>
> You'll have to remove the cover & get a visual on things, check the lash,
> mesh pattern & preloads best possible in situ.
>
>
>
> Glen Efinger
>
>
>
>
>
> -----Original Message-----
> From: Philip Gott via Fot <fot at autox.team.net>
> To: Friends Of Triumph <fot at autox.team.net>
> Sent: Tue, Aug 9, 2022 9:53 pm
> Subject: [Fot] Final drive (differential) oil
>
> Amici:
>
> At the risk of opening Pandora’s box, May I ask what gear oil you would
> recommend for the rear end in my TR4A (solid axle)? I am running Mobil 1
> 75-140 and found some metal flakes on my magnetic filler plug after Pitt
> Race. Usually there are some whiskers, but the metal flakes are concerning.
> The rear end is a welded diff carrying a relatively new (3 seasons) 4.1
> gear set.  I have yet to pull the cover. Backlash seems “normal.” The rear
> end was set up by Quantum Mechanics whom I trust.
>
> What do you all run for oil (brand and viscosity) and what is your
> experience?
>
> Thanks and regards,
>
> Phil
>
>
>
> Sent from my iPhone
>
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