Title pretty much says it all. A few years ago, I ordered some differential oil for my 2001 XKR coupe with stock differential, and was given Valvoline 75w90 sythetic gear oil instead of the 75w140 that I'd requested. I didn't notice until after changing it, and it began to make a moaning noise when turning from a stop after driving for a bit. Eventually I bit the bullet and changed it for NAPA-branded 75w140 synthetic fluid, and the noise is gone. I don't think I did any lasting damage, as the fluid that came out looked pretty clean without any metal particles, but the noise was always annoying. Just a heads-up for anyone planning on doing a differential fluid change.

 

There are very few references out there, apart from those written by me, which specify that higher viscosity differential oil should be used because neither Jaguar nor Shell themselves ever specified the viscosity of the specially produced Shell oil which is now obsolete.

Richard

 

I have posted several times about the positive benefits of using a quality synthetic 75w-140 rear end gear lube. Especially if one uses their car for trips that last long enough to get the gears good and hot.

I’ve been using the Mobil 1 75w-140 in numerous classic cars, all daily drivers, for at least 20 years, probably longer. It is a superior product that is instrumental in ensuring long life for all of the rear end moving parts.

the only drawback is the price. As it costs double what the 75w-90 products cost. But that price differential (pun) does fade away as the miles accumulate.

Z

 

When I changed it, I used a 75/90, and since then, especially when the engine is warm, I’ve been hearing a clunk when the transmission shifts into gear at very low speeds. The viscosity is probably too low, so I’ll have to try a 75/140 too.

 

We also use NAPA Synth dif, lube 80W-140 and does great at161K dif. is quiet. Changed it at purchase112K with Castrol 90w and some whine could be detected. Went to NAPA 85w-140and whine at 155K is gone.