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MG Midget and Sprite Technical - Gearbox Oil

For midget and Sprite (plus other BMC cars) 'Engine Oil' was specified for the gearbox. The Midget or Sprite particually in 1275 form could wear a gearbox out in a relitavly short time in the early days.
I rebuilt the gearbox in Anita's Midget some 6 years ago. In that time it has covered many many miles, some of those in a very 'spirited' fashion, even some very hard driving on MGOT Track Days. I've always run this (and other) gearbox on a 75/90 semi synthetic gear oil.
I had reason to remove the gearbox last weekend thinking that I could hear a bearing noise. Once stripped and inspected, the entire gearbox looks like it has never been run.. it's in perfect condition. Bearings are all superb, first and reverse show NO signs of wear, same goes for the selectors.
I've always advocated the use of the std gearbox in a Spridget in preferance to any 5 speed conversion. This just backs up my thoughts.
I'm convinced that using a modern gear oil has contributed totally to the longlivity of this gearbox... There are those out there who will vouch for how it has been driven.... :-)

Mark.
M T Boldry

Very interesting Mark, I've always been one for sticking to manufacturer's spec but this could persuade me. Maybe try one it in the next gearbox of our UK car, first is getting a bit ratty after a few years autotesting etc.
What brand of oil did you use?

Are you still heading this way over the summer?
Paul Walbran

I think it was Millers that I used, but that's not available over here....

Still undecided re trip to NZ. I don't think we'll have enough leave to do that and go to Midget 50 in June 2011

We will of course let you know.

Cheers
Mark.
M T Boldry

I use whatever good quality 20/50 I can lay my hands on in SCCR race boxes and they work well, don't wear out or break or fall apart. I think it was Mobil 1 for a few years until I gave in to all the bullsh** around how much damage synthetics do to old boxes, currently I'm using Duckhams. Unfortunately there is as far as I can tell absolutely no scientific evidence one way or the other, it's all anecdotal.
David Smith

EP90 in our two SCCR dog boxes.

Even after inverting one of them several times (car of Nev) and having the flywheel spin off the 2nd one and requiring it to be recased (that'll be down to me). Both boxes have had all their internals re-used without the need to swap anything over, excluding the damaged parts caused by hooliganism of course.

A.
Andrew McGee

interesting to hear.

I always followed the engine oil clan putting in duckhams 20w50.
It looked perfect last time I drained it without anny particles and nice and green so I reused it.

Though since then it has started to jump out of 1st (sh*tty in trafic) and getting noisy in 3rd (thank god for 1380 torque and use 4th more)
So a rebuild may be looming.

That would be the perfect time to switch oils I think.
Would switching now cause contamination issues?
Onno Könemann

I always understood that the reason for not using an 80 or 90 weight gear oil was that it didn't get through to the layshaft bearings very easily.

Also, I've never had any real problems with using 20/50 for road or track.
Dave O'Neill 2

Andy, who builds SCCR dog boxes on A series cases? The Groves ones are Triumph boat anchors and different oil applies.
David Smith

Interesting experiences.

I suppose the one type of oil that should be avoid is an 'EP', which 'eats' the yellow metal components? I use a 75W/90 semi-synthetic oil in our Toyota 5-spd, but it is not an EP.

Using the Castrol technical specs, the 75W/90 is roughly equivalent to a 10W/40 engine oil, i.e. it is less viscous when hot or cold than a 20W/50.
Richard Wale

Most of the Spridget racers I know use Castrol VMX 80 in the gearbox and LSX 90 in the diff. And because that's what is in the shed it goes in the road Midgets also. Very happy with its performance, and it can be bought from Supercheap when they have a 20% off everything sale.
http://tinyurl.com/3dm5ln
Mike Allen

Dave, as far as I can remember the 80 grade gear oils have a very similar viscosity to 20/50 engine oil. I chose 75/90 in the hope it would be similar to the 20/50 too. I'm told by our oil supplier here in Aus that 80/90 is the same viscosity as the old 90 grade.
It's Hypoid that used to eat 'yellow' metals, but I think that too is a thing of the past now. To be on the safe side, if using straight gear oils, use an EP (Extreme Pressure).

Mark.
M T Boldry

Dave

the two boxes I've got are "old" ones from the other Dave S.

The gearbox that you saw at Oulton after the flyhweel came adrift was the original one I got from him when we put my first 1380 unit into the car. It must have been over 6 years old if not more at that time. I was expecting it to need new bearing etc, but when it went up to a gearbox specialist near Nev (after the flyweel cut through the bellhousing), they were astounded at the servicability of the bearing etc so reused them.

We fitted the other unit also from the other Dave S and that behaved perfectly until the old car was rolled, and likewise that went back up for a replacement selector when we found that one of those had become slightly bent. Again all the bearings etc appeared fine so that was also a simple refresh.

Different folks have told me to use different oils at varying stages, most of them cost a fortune and need changing often along with the gearboxes needing overhauling regularly. I've stuck to what Dave S has told me to do and that's the results we've had so far.

Is it right, who knows, but it works for me.

A.

Andrew McGee

Jack Knight Dog boxes both...

JB
James B

Tough as old boots James.

How much running do you reckon they've had over the years?

A.
Andrew McGee

I would have thought in excess of 100 Class A Halfords and FISC races between them before you had them - multiple FISC Championships too...

I have always run ST/JK SCCR Synchro boxes (never having the wherewhithal to purchase aforementioned dog engagement boxes). I use 20/50 as I find that EP90 doesn't allow the baulk rings to grip the synchro ring properly...

Happy Christmas Andy

J
James Bilsland

This thread was discussed between 23/12/2010 and 24/12/2010

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.