Differential level plug

[Old Dave]

Hi All,

Some of you will have seen my Post recently dealing with a sender unit for my new A7 RN rear tank. Not comletely resolved, but decisions made and hopefully another Job jobbed soon.

While there is no tank in "Alice" obviously the vacated area needs prepping for the new installation. BIt of paint, maybe a film of Waxoyl.

Last year, a little before the July Jamboree, I did an overall service, had a dummy MOT done and I decided to check the level of oil in the differential. As you will all know the plug on the back of the diff is very close to the front of the petrol tank. So close in Alice's case that the plug fouled the tank before it could fully clear the diff. I decided that it must be OK!!!  

Anyway with the tank on holiday I decided to do the job properly and I checked the level (don't ask)   The plug appears to have a fibre washer? I was expecting a copper one? From the mating face of the head the plug is 3/8 inch long (without the washer) which looks plenty. I assume that these plugs are standard length?

If I want to check the level in the future I either need a shorter plug, or I could mount the tank, say 1/4 inch further back in the car (I will need to drill the mounting holes anyway)

Do you have any advice? And should the oil level be a bit below the bottom of the hole on the diff, or do I fill until a little oil runs out? Is a complete diff oil change recommended while I am at it?

[AustinWood]

Jack up the car on the chassis and let the axle hang free. It should then be low enough to access the filler plug.
Only fill it up to the level of the plug. That is plenty.

[Old Dave]

Thanks Jim - I guess I am not going to do it very often am I.

[Reckless Rat]

If you don't check the level with the axle hanging on the rear springs, you'll end up with too much oil in the diff, which will eventually escape via the rear brakes. The level plug will be below the tank if you check it this way. Put the jack/axle stands under the rear cross member. After filling, let it drip overnight before replacing the plug.

For the 'D' type axle, no more than 250ml from empty. 140 grade oil.

[Peter Clayton]

Just a note of warning , my RP (with the rear tank) started seeping fuel from the tank which I assumed was from the sender unit. On inspection though I found that the tank had been scored by the diff filler plug and had a hairline crack. The problem was that the body had sagged to such an extent that on bumps it would allow the diff and tank to collide. I had to remove and repair the tank. The bodywork I discovered was not so easy and not a fix I could economically undertake  , but that's another story.

[Old Dave]

Thanks RR. Sounds like an easier way of getting the right level. I remember reading a couple of years back that the level should be about half inch below the filler hole and I guess that would be achieved by hanging the axle/diff in this way.

Since the tank has been out I had tried a bent bit of copper wire to see how far the oil level was below the hole and, well it is a long way down. So I think I will drain and refill with the 250ml max in mind, especially as I have 2.5 litres of 140 on the shelf.

---

A useful warning Peter thanks. The tank is tight on the diff at the best of times.

[David Stepney]

On my RP, there is sufficient clearance between the diff and the fuel tank to remove the plug, but not to be able to check the axle oil level. I have always checked mine as Bruce has suggested, with no weight on the axle. I fill the axle until the oil is level with the filler with the axle hanging down. No issues so far.

[Old Dave]

Thanks All - very useful as always.

I will drain off the diff oil and then jack-up as suggested filling to the bottom of the hole in the tilted position.

Might as well get it done while the tank is out.

Thanks again

[Reckless Rat]

Dave, three things you can do to make this easier. Firstly, buy yourself a 100ml plastic syringe with a filler tube on the Bay of E from Mr Woo's emporium.
Secondly sit your 140 grade oil in a pan of boiling water before adding - it will become much easier to pour/inject when it's hot.
Lastly, rotate the diff internals so you can get the tube for the syringe past the crown wheel.

After use, give the syringe a good clean so the oil doesn't rot the rubber seal.

[Old Dave]

Thanks Bruce. Thanks for the advice. Just got the syringe ordered from Amazon. so drain today (and maybe tomorrow) and fill soon.

Thanks again