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MG Midget and Sprite Technical - Changing Gearbox Oil

I gave the Sprite a good run out today to warm the gearbox oil up prior to changing it.

It's a 1275 car with ribcase box.

S*ds law, the gearbox plug is stuck and rounded off.

I started trawling the archive to see what I could find on gearbox drain plugs when I came across one thread where the general consensus seemed to be on high mileage gearboxes leave well alone and just top up if necessary. You can propably guess who provided one of the best pieces of advice!

The common view was that changing the oil in a high mileage gearbox would remove a lot of the residue that's helping to reduce play in the bearings and would result in a failed gearbox in a few hundred miles.

Does anyone have any (helpful) advice before I either attack it with a large pair of Stillsons or splash out on an oil suction kit?

Cheers

Colin
C Mee

Stilsons ought to do the job.

Personally, I think leaving knackered old oil in there is a bad idea.
Dave O'Neill 2

Colin,
Ogger's recent thread on diff plug stuck gives the usual advice on different methods of removal, IIRC Stiltons worked in the end. You've seen my advice on such dozens of times - patience, time, repeated application of PlusGas (nothing else for me) and perhaps the right tool for the job.

Spray liberally with PlusGas and leave at least overnight, you can't have done at least the second part yet, then try to tighten (yeah alright if only you could but you might with the right tool) then try to loosen. If it don't work first time then repeat, at least twice more, spray leave overnight, tighten, loosen.

Once you know you can loosen the drain plug then you must check you can get the refill/level plug out before removing the drain plug or you're worse off that before you started with a gearbox empty of oil.

If it's only crud and muck holding your gearbox together then you might, in the short term be better off leaving the old, depleted oil and muck and crud in the box but medium and long term if your box is that bad it can only get worse, surely?

MGB with engine oil in the gearbox is service replace at 2 years/24k-miles whichever is the sooner but that's for road not sports use.

But as you know I'm not an expert, or anywhere near, in anything.

ETA: Dave posted whilst I was typing - surely the crud/protective stuff would be suspended in even old depleted oil so offering no protective value.

Nigel Atkins

Should have also put - thoroughly clean the plug and the area around it before liberally spraying with PlusGas (not WD40 or not even perhaps the likes of ScrewFix No Nonsense(?) but Chris Madge might know more about that than I).

Crud will bind the plug if not perhaps the gearbox internal components. :)
Nigel Atkins

I would offer you a replacement plug, but currently everything is packed, pending house move.

I had to unpack a box today to find a jubilee clip for my water pump hose. It’s still leaking, so I’ll have to unpack another box tomorrow in the search for my spare hose.
Dave O'Neill 2

Dave,
I am resplendent with fine s/s clips of many sizes (but only water pump bypass hoses) so if you're stuck Royal Mail can be first class.
Nigel Atkins

Thanks for the advice.

Plus gas applied and an 11/16" impact hex socket added to tomorrow's shopping list. Not planning to resort to impact but I think there's enough left on the flats for it to grip better than a normal socket or spanner.

Thanks for the offer of your spare plug Dave but, as the drain and filler plugs are the same item, if I get it off this week I'll swap them temporarily until my next order for Sprite bits goes to MGOC.

Has anyone ever tried welding an extension onto the filler plug so that you can fit it by hand and be sure that it's not cross-threaded? I might try welding a suitably sized bolt to the filler plug so I can tighten it with a spanner or socket.
C Mee

"Has anyone ever tried welding an extension onto the filler plug so that you can fit it by hand and be sure that it's not cross-threaded? I might try welding a suitably sized bolt to the filler plug so I can tighten it with a spanner or socket."

That's an interesting idea.

It's not helped by the fact that you can't seem to get a straight run at it. It wants to start at an angle.
Dave O'Neill 2

You are likely to find that an agricultural engineering shop/tractor repair shop can supply a plug with the correct thread (which I think is BSP or BSPT) and a nice hex head. If it's a parallel thread it'll come with a dowty seal or copper ring.
Greybeard

If you really want to drain the gearbox oil you can always remove the propshaft and stand well clear or have a large container well positioned.
Jeremy MkIII

Thanks Nigel.

It's this rather annoying hose (24) between the pump and the elbow on Mk1 MGB.

30 years ago, I did away with the elbow and two short hoses, replacing them with the later one-piece hose (26). When the smaller heater take-off hose detached itself from the large hose, I reverted to standard.

Apologies for thread drift/hijack!


Dave O'Neill 2

Colin,
there was a recent tread on fitting the filler/level plug, David Smith's suggestion in particular was a good un, (I won't try to remember it and get it wrong). As I put then I can't remember having much difficulty with the ordinary plug and I'm pretty inept, perhaps different style plugs could be used too(?).

ETA: Dave surely you could ransack the recycling for a suitable tin can, I might have enough clips to run its length. :)
Nigel Atkins

Update (on my previous post).

Colin,
easy ways to refit the filler plug info is in the thread in the 2018 Technical Archive called ‘Gearbox oil level' last updated 25 March 2018.

Nigel Atkins

For some reason I can't find the thread in the archive to which Nigel refers. No doubt due to my ineptitude.

But I did find this post in another thread, which looks intriguing:

tthew
Monroe
NY
moment88@aol.com
Posted 11 June 2006 at 21:19:47 UK time
1974 MG midget 1275cc. I always dread changing my gearbox oil because I know at some point, I’m going to have to fight with getting that damn filler hole plug back in. I found a solution today. A 2” long piece of 5/8” (ID) rubber hose fits perfectly over the raised “hex” portion of the plug. Two inches is short enough to allow you to get it into that damn (too small) access hole in the transmission tunnel and still hold the plug square to it’s transmission hole without cross threading the bastard. Wish I had thought of this years ago. Hope this helps someone else.
Greybeard

Similar to the technique I use for removing/replacing the spark plugs on my Honda. It’s only a V-twin, but has 4 very hard to reach plugs. I still have to remove the petrol tank, though.

Damn, more thread drift - sorry!
Dave O'Neill 2

Colin,

Are you sure that the advice you read about leaving the old oil in the gearbox was talking about a standard transmission? I've heard that said for automatics, but never heard anyone say that for a standard.

Charley
C R Huff

Greybeard,

. click-on ‘Archive’ at the top of this page
. (on the page it takes you to) click-on ‘2018’
. (then on the page it takes you to) scroll down to ‘Gearbox oil level’.

Nigel Atkins

I would't worry, modern oil is fantastic stuff. The gearbox oil on my VW (I know different car etc) did 280K miles and then only got changed because the clutch slave sprang a leak. I've also been doing the engine oil every 20K with a suction thing since 40K miles, never had to remove the sump plug.
AdrianR

Unfortunately, we don't know how modern it is.
Dave O'Neill 2

And the gearbox and engines are very old and ancient design, plus engine oil is usual put in the gearbox not gearbox oil.

But I'm 100% with you that better quality modern oils are much better.
Nigel Atkins

Success at last.

It took me ages to track down an 11/16" impact socket. BML Hayley/Bearing Man finally came up trumps after I'd tried all the local motor factors, but even they had to order it in specially. I could have gone on line but I prefer to buy local if I can. Disappointed to find that Cromwell Tools have pulled out of Telford.

Due to the rounding off of the plug I had to hammer the socket on but then it gave up the struggle when I applied my long socket handle.

I'm embarrassed when I realise that this is the first time I've changed the gearbox oil since I bought the car six years ago, mind you, that's only about 4000 miles.

Although the oil was pretty dark, I was pleasantly surprised at how little swarf came out. Given the number of missed gear changes we've had on the hill I was amazed that there were no shiny bits, the hollow in the plug was only about half full of fine fiings and a magnet trawled through the old oil in the tray came up almost clean.

I've fitted a brand new plug - this one came with a 3/4" AF head - and I Araldited a small magnet into the hollow - and vowed to change the oil a bit more regularly!

I'd read the gearbox filler thread but in the end I didn't have any problems fitting it with a socket on an extension bar.

Thanks for all the advice.

On to the next job - swapping the diff for a 4.55 that I've had re-built and installing longer wheel studs for the Minilites.

Many Thanks
Colin
C Mee

This thread was discussed between 24/06/2018 and 05/07/2018

MG Midget and Sprite Technical index

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