I climbed under my car to change the diff fluid today and ran into a problem...

Is there a black plastic cap on my fill plug or did someone use some sort of plastic plug in place of the original fill plug?

I can't get this thing off/out. It just keeps spinning. I don't want to use too much force lest I break it off and part of it falls into the differential.

Can anyone offer any help here?

 

That black plug isn't the fill plug. I'm not exactly sure what it is but I think it's the breather plug. The fill plug is about 2 inches under that and you'll need a quarter inch extension ratchet to remove it

 

I'm no expert here, but that looks more like a breather than a fill plug

It looks much like the breather on the bevel-box(similar to a diff) on my Moto Guzzi?

 

Well that's great news.

I guess looking at it, it looks similar to a Miata diff so that's what I thought it was(fill plug on top, drain plug below it)

This is probably dumb but where is the drain plug that I'm missing?

Thanks!

 

It is in fact a breather, and will not come off without taking rear-end apart. Luckily just cleaning around it with a toothbrush is all thats needed. Often times the breather gets plugged forcing the fluid to come out of other areas thus making you think you have a bad rear-end. I'd give it a good cleaning then top up the fluid and also use some limited-slip additive if called for.

 

The drain plug is going to be directly under the rear end. There's a hole in the subframe. It's a square so you'll need a socket that fits it just right.

 

Yeah, that was a dumb question. Been working on a Miata for so long. Both of the plugs are on the back of a Miata Diff.

Anyway.

Got it all done!

Filled it until it was pouring out of the fill hole. Then I let it reduce down to a very slow drip and put the plug back.

Thanks!