Edited on 2008-03-15 14:24:23

Edited on 2008-03-15 14:23:58

My 1987 Jaguar XJ6 will soon have the two leaking upper seals on the differential replaced. The Jaguar book calls for 90 weight gear oil. The new products, especially the synthetics, offer 75-90 and 75-140 weights. I do have a "clunk" at various times that is apparent just before a stop. Two mechanics tell me the noise is from inside the differetial and may be the clutch. One 30-year mechanic suggests using the 75-140 with an additive. Anyone using 75-140 blend or synthetic gear oil?

Scott W. Moseley

Submitted by silver007@shaw.ca on Sat, 03/15/2008 - 16:18

Hi Scott,
if you do have a posi rear end the additive must be installed period or it will destroy itself. I have used the synthetic for many years now with no problem, my rear end is a posi so I have the posi additive in there , I think I used 75/90 in mine.
As John suggests your noise may simply be excess wear of the ring and pinion gears.
Good luck, Art

Submitted by SC20-30420CJ on Sat, 03/15/2008 - 14:51

The 75-90wt should be fine for your 87 Scott. You should be able to find straight 90 wt though. The additive your mechanic is referring to is likely for a power-loc, aka limited slip or posi-traction differential. You don't have that type of diff in your car unless it was originally delivered as a European spec Sovereign.

The noise might likely be just your ring/pinion getting sloppy.