Column for May 2007
Update on rear axle oil for
the RV8 Quaife torque bias differential
Stuart Middlemiss (Nightfire Red 1215) from Norfolk has obtained a
confirmation from Shell of an improved oil for the RV8 differential.
He also provides an important reminder regarding the Quaife differential.
This is RV8NOTE263.
As I am about to have the rear axle oil renewed and have seen many
references to the "Quaife limited slip differential" and
know that LSDs require special LSD oil, I thought I would check with
Quaife to clarify which oil they currently recommend for the RV8 differential.
Just as well I did. They enlightened me by highlighting the fact that
their Quaife diff is not an LSD but a torque bias diff. I have since
found RV8NOTE84 in Volume 3 where Roger Parker starts his note by
mentioning the differential is a Quaife torque bias type. He noted
"the original Rover press pack at the launch of the RV8 described
the operation of the differential as follows: 'Traction is transferred
from the slipping wheel to the wheel with grip automatically, without
the use of friction plates or pads common on some older designs. Using
a series of spiral gears reacting against the differential casing,
harshness and snatch is eliminated'."
Quaife emphasise that special LSD oil must not be used. They continue
to recommend the Shell Spirax HD80W/90 as per the manual, or a good
quality equivalent. I have since found that the Shell Spirax HD80W-90
oil specified in the RV8 Repair Manual AKM7153ENG for the rear axle
(0.9 litre) is no longer made.
The technical department at Shell now specifies their Spirax AX 80W-90
which is an improved version of the Spirax A. This meets the API GL5
requirement as set out in the repair manual. The replies from Shell
to my enquiries included: "We now recommend use of Shell Spirax
AX 80W-90 or Shell Spirax A 80W-90 for your vehicle. An 80W-90 is
a direct replacement for HD. AX
is an improved
performance product including improved oxidation, better frictional
properties and it is more environmentally friendly". Regarding
specification codes, Shell says "it is not strictly an approval
but rather a set of physical properties and tests that need to be
met or passed. Both A and AX claim API GL5 and as MIL-L-2105C is
based on this specification, also meet that too. API is the American
Petroleum Institute and MIL-L-2105C is a US Military specification
not really relevant in the consumer car industry any longer."
As transmission oils need to be changed less often than engine oil,
they are frequently forgotten and for this very reason, the correct
grade and specification should be used for refilling and topping
Stuart Middlemiss later made a further posting on the V8BB noting
"I found that the Spirax AX 80W-90 oil is only available in
quantities of 20 litres upwards - a bit over the top for the rear
axle!" He was surprised by how little oil the rear axle takes
- just under a litre according to the manual. So he contacted Quaife
again "who now tell me that they specify fully synthetic oil
for all their differentials, and recommend Silkolene's Silktran
Syn 5 75W-90 GL5. Note the GL5 specification because quite a few
gearbox oils are to GL4. If you cannot find a fully synthetic oil
in your local shops, try Opie Oils at www.opieoils.co.uk who stock
several including the Silkolene mentioned above".
Paul Wiley responded to Stuart's V8BB posting saying "Silktran
is dual rated GL4 and GL5. The EP package in GL4 is half to two
thirds the level of the GL5. Most quality gear oils now use a "non-reactive"
sulfur-phosphate package. The new add packages are esterified and
only react under pressure/heat of shearing and loads. There is a
discount available for members if you use Opie Oils.
Stuart Middlemiss later reported in a V8BB posting that "Guy
at Opie Oils gave me a healthy discount. Opie Oils are a good source
of quality and specialist oils not seen in the usual retailers and
they offer free delivery on purchases over £30".