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MG Midget and Sprite Technical - Gear box oil query

Hi all,
Its a 1275 midget mk III
Sorry to be a git but plan to check / topup gearbox oil tomorrow. Once i get the oil filler on the box open should I drop the old gear oil or simply top up?
If I should drop the old oil , where is the oil drain for the gearbox as I can't find it described anywhere.
Cheers
colin
colin frowen

Colin,
you're asking about two different things

one is topping up the gear oil which is a regular servicing item in which case you just top up slowly as it's easy to overfill and have it running out, no big deal but even more messy than it need be

second is draining and refilling in other words an oil change for the gearbox, an irregular service item

if you don't know when the gearbox oil was last changed then this is a good idea and will do no harm but only good

to do a thorough oil change it's best to get the oil as warm as possible and leave to drain for as long as possible

the gearbox will hold up to 2¼ pints (depending on how much is left in) of good quality engine oil

the drain plug will be similar to the fill plug and obvious from under the car, a parts catalogue should show you its location

BTW if you fill in your car’s profile you wont need to remember to put the details with each post

my notes, I hope they make sense and help:-
Gearbox oil change notes:

· for all jobs allow loads more time that you think it will take, never be in a rush
· check for the correct oil to buy
· get the right tools to fit drain/fill plugs
· you may want to clean around both plugs and spray with a penetrating/releasing fluid such as Plus Gas (WD 40 is not as good) and let it soak in then slightly tighten to break muck/rust seal before undoing
· have the gearbox oil as warm as possible before draining (protect yourself from hot oil)
· taking the filler plug out will help to drain faster
· leave to drain as long as possible
· if gearbox has an overdrive unit now is the time to clean the filter too
· clean plugs and threads
· refill with less than ¾ of stated quantity of oil then top up very slowly until at bottom of threads, leave excess to run out (can take ages if you overfill)
· plugs can go back in 'dry' hand tool tight

unless the oil was very bad or there's a fault with the gearbox you'll not notice much, if any, major difference with this oil change but it will help maintain and ease the gearbox by having new oil of the correct type at the correct level

also if you do it you know for sure it has been done and when, the old oil will give you a clue to former maintenance by comparing it with the new oil and a clue to the condition of the gearbox if the old oil has metal bits in it

this job is often missed but is so cheap and easy I think it's worth doing every 3-5 years (check and topping up if required every 6 months)
Nigel Atkins

Colin, in a nutshell - do you know the history of the car? If yes then top up will be fine although it probably won't take much if any. If history not known then maybe a good idea to drain and refill with new. Drain plug is on bottom of gearbox, big hex plug just like the filler plug, obvious once you're under there.
David Smith

er, yeah, what David repeated only the drain plug and/or fill plug may have been changed by a prevoius owner so may not necessarily be a hex or both the same

if you do a drain you will get more muck out with a warm long empty

always take the fill plug out first that way you know you can refill and use the best of the two pugs in the fill hole as that's the plug that will be removed by far the most often
Nigel Atkins

And,
Topping up takes less time than it does to read Nigel's message!

Nigel, you know I like to disagree with you, but you recommend to "use the best of the two pugs in the fill hole". In that circumstance I would use the better plug in the drain hole because a) I would prefer to know that it was done up properly, and b)being removed so infrequently it is more likely to be difficult to slacken off, so needs to be in good condition.

Guy
Guy

Colin,

Drain is the large plug on the bottom of the box.

I think the fill plug is accessed from inside the car. Pull up the carpet around the gear lever. see the oval rubber gromet on the passenger side of trans tunnel (forward of gear lever). Pri that out and you will see the fill plug?

Also use a good quality 20:50 engine oil, not a gear oil. These boxes are designed with thin oil ways and thicker oil will not get through.

Lee
L Juby

Guy said,

"And,
Topping up takes less time than it does to read Nigel's message!"

Truly, that really did make me LOL.
Lawrence Slater

FWIW I've handled somewhere between 50 and 100 of these boxes in the last few years and never seen a non-standard drain plug.
David Smith

Guy,
I must admit I was thinking of the head condition, if you've got a duff one then in the filler hole and replace ASAP

and Colin might not just be topping up :p

I think Colin appreciates a lot of info, if he doesn't then he can ignore what bores him - as others can - I added the bit in about condition of plugs based on my experience

David,
what about filler plugs and matching of both plugs :)
Nigel Atkins

"use the best of the two pugs in the fill hole"

"if you've got a duff one then (use it?)in the filler hole and replace ASAP"

I didn't assume he was just topping up. If he were, then he wouldn't be removing the drain plug anyway would he?

Do try and be consistent with your advice!
Guy

yes always the same. As these are male hex cast iron plugs I cannot imagine how they could get buggered up. Especially as due to the access you have to use a socket on the filler plug.
David Smith

Guy,
I was ammending to agree with you, sorry to agree but it doesn't happen often does it

how about - use the best of the two plugs in the drain hole and if required renew the other plug as soon as possible before you forget

the not just topping up bit was to justify my long post on draining

David,
thinking about it it was the r/axle plug with square socket that was split on mine

I can't remember what the replacement g/box plug was that I got so I'll assume it was the correct type but haven't we had threads where it'd been suggested to use gas fittings or was that for the r/axle too - as you know my memory isn't the best

the male head plugs seem easier to use than the socket type too to me

no one commented on the O/D remark I forgot to remove, 5 mins is just too short for my edits
Nigel Atkins

Nigel, 5 minutes should be ample for you to edit, if you've not done it by then you'll have forgotten anyway.

And yes we all know the axle plugs are the ones that get buggered... I didn't bother mentioning that because they are so very different.
David Smith

yeap 5 mins should be but it aint for me and as if I'd forget, I remembered those gas fittings being used and they aint not standard no

plus my computer or the web link goes even slower than me somtimes
Nigel Atkins

This thread was discussed between 07/06/2012 and 08/06/2012

MG Midget and Sprite Technical index

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