Model S rear small drive unit oil drain/refill procedure

[soarhead25]

Good evening everyone,

Question here regarding the MS small drive unit.

So in reviewing the service manual for the MS(2016), it specifies a very specific fill procedure for the rear, small motor DU that instructs to NOT fill the rear DU thru the upper fill plug, but to instead go thru all the trouble of removing the axle shaft and filling the DU thru the axle shaft hole, being careful to only refill with the proper amount of oil.

So my assumption was that the fill plug was not at the correct height for a proper fill, and removing the axle was the only way to overcome this engineering oversight. However, I did just perform a service on the rear DU and made a few observations.

First, the upper fill plug bore does open up into the DU housing, as I put some oil into the diff with it coming out of the bottom drain plug. However, there is an internal part of the DU(unidentifiable/maybe oil pump?) that prevents inserting a fill hose anymore than a 1/2“ or so, but this part does not prevent oil from filling the DU.
Second, I performed a measured fill-(2,250ml) thru the upper fill plug despite what the Tesla service procedure states. I ran out of oil from my container just as the oil level came up to the bottom of the fill plug bore.

It appears that the upper fill plug IS in the proper location despite what the Tesla service procedure would have you believe. So my question is does anyone know why Tesla would instruct to remove the axle to fill when it looks like it’s completely unnecessary?

 

[N4HHE]

I'm holding my breath waiting for an answer. Must start planning now, mine is due December 2025.

 

[Lukez]

I can only think of one thing, if you were to use something less manual, like a pump, you'd need to use the lower plug so that a) the oil doesn't leak out the bottom while filling and b) when you are pumping the air has somewhere to escape

 

[philip295]

This may be helpful : there used to be a similar instruction on the old Jaguar x type when refilling the transfer box, remove the shaft to fill. They change the procedure to jacking the left side of the car to an extreme angle, so that oil could be filled via the drain plug.