Diff oil change tips plz!

Hi. Totally not mechanically minded, but want to give it a go!

My diff is making this irritating buzzing noise, so I want to change the oil. Never done anything like this before, but found this to follow: http://www.miata.net/garage/trans/everything.html

So, I’ve got sockets etc, WD40 incase things are rusted soild, (is there any better way of dealing with things that won’t undo?) 75/90 oil, an oil tub and some hose and a funnel. Missing anything? I wasn’t going to buy a pump incase I couldn’t get the bolts off and decided to give it up as a bad job and take it down the garage.

Silly question time…I have ramps, but take it I shouldn’t use them as the car needs to be level. Is that right? I’m hoping with some wriggling I’ll fit underneath it!

Any other tips/things likely to go wrong I should know about? Or reassurance that it’s as easy as it looks…!!

Car is a mk1 mx5 1.8. 1996.

Ty! Big Smile

Hi, I’d jack or ramp the back then you’ll have enough room to work and be facing the bungs. I’d also get an oil syringe/gun (£8 from Machine Mart or similar) worth it’s weight in gold but you might manage with a squeeze oil bottle and tube. Then drain it completely and fill with 1L new oil. That way you don’t need the hole to check quantity or the car to be level.

Any proper penetrating oil will be more effective than plain WD-40 which isn’t really designed to do that job.  PlusGas is good, but Halfords don’t seem to stock it any more.  I got some 3-in-1 branded penetrant there instead which also worked well.

It’s a compromise - if the rear’s raised not all of the old oil will drain out, but if it’s not raised for better access you may struggle to get the drain and filler plugs loose.  You might find you need to use the ramps to get the plugs cracked loose in the first place but then you could nip them back up and drive off the ramps to do the oil change.  I had to do that the first time.  (Actually, to be completely honest, I had to beg the use of a vehicle lift to get a good swing at 'em with a 2 foot breaker bar.  Goodness knows what gorilla tightened them up in the first place.)  Oh, and absolutely the most important bit of advice for diff or gearbox oil replacement is make sure you can remove the filler plug before you remove the drain plug. Big Smile

The thing that’s missing from your list of parts is replacement aluminium crush washers for the two plugs - they’re identical to the sump plug washer your engine uses: http://www.mx5parts.co.uk/sump-plug-washer-p-1087.html

Have fun.

In addition just be aware the two plugs are different sizes one is 23mm, the other is 24mm Thumbs up

Dr. EunosGeek


Oh, yes, good point.  They both have the same screw thread though, as far as I recall.  If you get them mixed up, the drain plug is the magnetic one.

Indeed or 15/16" AF will do them both or 1/2" Whit will do the 23mm as that will be the one missing from a typical socket set…



In the big Halfords Professional set they give you both a 21 and 23mm 6 point impact socketWink 15/16"AF? nooooo! 1/2" Whitform??? - go and wash your mouth out! Lol!


ha ha you can’t beat an 'alf wit King Dick Taff lol…

Don’t forget the most important tip:

Always undo the filler before undoing the drain. That way if you can’t get the filler undone, you still have oil in your diff.

King Diick! Have always found it very amusing that the sweary Mary preventer will not let you use the shortened bersion of Richard Lol! 


yes unfair on D1cks everywhere lol :slight_smile:




I’m in the process of trying to do this. The bolts are stuck fast and WD40 made no difference so i’m waiting for the penetrating spray to soak in.

You will need to put the car on ramps/stands to get a good go at the bolts (as was said aabove). You’ll also need an oil hand-pump (unless you already have an answer to the issue of trying to pour oil uphill!). Mine was £5 on ebay and is perfect. Have fun!

Hello again!

Thanks for all the advice, was planning to have a crack at it this morning, but no where seems to have the washers! Any ideas where I can get one from?

Is it just a generic 18mm washer? Or is it something specific?

I’m in heathrow if anyone knows somewhere local I could run to to pick one up. Halfords don’t seem to do them according to their website. :frowning:

Any remotely decent motor factor. That doesn’t include Halfrauds I’m afraid.

Lol! I’m discovering that fairly quickly. Just can’t find anybody open today! :frowning:

They do tend to be Mon-Fri types of places. 90% of their customers are mechanics, who currently have their feet up in front of the Corry omnibus.


Did it!!

And the two bolts both came off easily!

Bad news is there’s still a noise. :frowning: Possibly it was wheel bearings all along. But I’m going to pop it into a garage for that one if it is.