V8 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 the
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 up.
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".