Change diff/gearbox washer without draining oil?

  1. My model of MX-5 is: NC2 2.0 Sport Tech
  2. I’m based near: Hertfordshire
  3. I’m looking for technical help or recommendations on: Changing washers


Long story short, mechanic didn’t properly tighten (or replace old washers) when changing gearbox AND diff oil, so slight weep from both gearbox and diff.

I’m going to take it to a different place - will they be able to change the washers on the plugs without having to replace all the gearbox and diff oils? It is fresh oil (less than 100 miles) so don’t exactly want to change them both again!


Are the plugs tight enough, did they actually use washers?
Afraid draining any oil will bring any crud out with it too. Depends how clean it comes out whether it can be reused.
And one wonders why many DIY these jobs.

I’d be inclined to treat it as a flush and put new oil in.

Leaving aside of course whether you want to take it up with whoever did it.

To answer the specific question, can you take out a drain plug without draining the oil.
Whip out the plug, and put your finger over the hole. With your other hand swap the crush washer on the plug. Then pop it back in.
You will lose a teaspoonful of oil. The level plugs are easy as the oil should not be above the seal anyway. But leave them inplace (slacken them a fraction just to be sure they will come out and are not seized). You want to leave them in place as you swap the drain plugs as this acts lke an air lock and reduces the flow at the drain.

Whether a garage will want to do this is obviously up to the garage…


Thanks for the replies everyone - managed to sort the diff with a mate - just needed tightening and looks to be all good. Going to just treat the gearbox oil as a flush as suggested - when it was replaced the old stuff was pretty manky, so is probably for the best. Thanks everyone :slight_smile:

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