There are some things that I know and some things that I do not know / unsure of. I have to replace the U joints on the drivers side rear...and while I am at it, I want to replace the fluid in the diff. I have read that there is no drain plug, only a fill plug.

1) Where is the fill plug exactly, and how do I drain / fill the diff?

2) While I'm there, I know there is a differential breather valve located somewhere. Can someone tell me where it is located and the best way to clean it?

3) Lastly, what diff fluid should I use that can be purchased at the local parts store? What weight? 75w90?

 

The fill plug is on the rear of the diff quite far down, you will easily see it.
You need to suck the old fluid out with a pump. A cheap hand pump will do just fine.
The breather is on the top near the rear of the diff. Just stick up your hand and you will feel a little cap that should be a bit loose.
The breather takes a 14mm spanner if i remember correctly.
I just replaced my breather as it's a cheap part. But you can probably clean it with some brake cleaner.
I used 75w90 GL-5 oil.

 

Back in `04, Jaguar released a new specification for older models like the X308, which stated it needed to be synthetic, and meet M2C 192A, which is limited slip additive specific, and then specified 75W-140. There seems is a lot of misunderstanding about fluids and weight. 75W-90 and 75W-140 both start as 75W oils. They have viscosity improvers added to give the lubricant high temp viscosities. The 75W-140 actually provides better high heat viscosity, and better protection. As far as getting the old stuff out, many take a small section of copper pipe and bend it into a J to get it to the bottom of the case. Works like a charm.

 

The only plug that I see looks like you stick a socket extension into it to remove it. Is this the correct one?

As for the diff fluid, I dont think I have seen 75w140. I will check the parts stores. I am sure the dealer would charge a pretty penny.

 

I can vouch for Valvoline Synthetic 75W-140. It meets the specs. Any AutoZone has it. And concerning your plug question, yes, you place a ratchet into it.

 

I will look for the Valvoline. What is the diff capacity? 3 quarts?

Also, is that breather valve readily available at the dealer, or is it a special order item? I may just replace it.

 

here is the plug on the differential :





XJ8 rear differentail plug


As you can see , mine was wet as a leak was coming from a dead gasket on the right axle shaft !

Now fixed by replacing bearing(differential sealing ring already fitted on the bearing) +bearing retaining collar+studs