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MG Midget and Sprite Technical - Rear axle oil

Just finished overhauling my 1275 differential, thought I would pop out and get some EP 90 oil to fill it up. Found I now have a choice of EP 80-90 GL4 or GL5, I looked up GL5 on the net and it seems it has additives that can be detrimental to white metals, especially gearbox syncros. I don't, believe there is any white metal in the rear axle, so I have two questions?

A) Is EP90 GL5 OK for a midget rear axle.

B) Why has life got so complicated?

Dave
Dave Barrow

B) because we are maintaining components designed 60+ years ago.
David Smith

Dave,
go with GL4. As you say, GL5 is detrimental to white metal and copper I believe.
I'm not sure what the midget diff thrust washers are made of but why risk it.

Q2, Progress ;) lol

Best of....
MGmike
M McAndrew

I haven't seen GL5 as being detrimental to white metal rather yellow metal, basically metals containing copper as the sulphur EP compounds can react with it, so that would be the sun wheel thrusts, if bronze, and the planet wheel thrusts. I have seen information that this reaction only occurs to any significant degree at elevated temperatures so for normal use they'll likely be fine but why risk it when you can get a suitable oil.
David Billington

Thanks everyone, having gone to the time and expense of overhauling the diff. (very satisfying job),I would hate to cause damage by using the wrong oil, so will stick with GL4. David,thanks I had forgotten about the thrust cup washers.
Great site to get 3 answers in under an hour.

Dave
Dave Barrow

Bit late in the day but I just read on a Triumph site (looking for info for a mate who has a GT6 in kit form) that only GL4 spec oil should be used. I had read something of the kind before, but the author of this page was VERY emphatic that GL5 spec would attack the copper in diffs of our vintage.
Also spotted something else - apparently the Spitfire 1500, for Switzerland only, had a 3.27:1 diff ratio. Presumably the Swiss don't like having too much fun! Been idly wondering if that diff gearset would go in a late 1500 midget axle - after all the two cars are second cousins at least!
RS Hughes

No, the Spitfire axle is completely different. The r/b Midget, even though 'Triumph-ised' retained the BMC axle which dates back at least to the A30 of the early/mid 1950s.
David Smith

Thanks for that, I had already decided to ditch the GL5, and found some Castrol GL4 at Halfords.

Dave
Dave Barrow

I thought as much Dave S. Was only idle speculation at best. My diff's the late high ratio one (3.7:1?) but still the revs are shaking the fillings out of my teeth! I suppose a type 9 eventually..........
Why mess about with it when Ford spent millions getting it right :-)
RS Hughes

Why are you getting vibrations, a high RPM should not equate to vibrations, my 1275 with 3.9 ratio will cruise all day at 70, the only vibrations come from some of the rotten road surfaces around UK these days.

Dave
Dave Barrow

In fairness it's not so bad. Just a bit unnerving as I've been accustomed so long to big lazy diesels. My Merc estate, which I sold to buy the Midget, cruised at 70 with about 2300 revs on the clock! I'll get used to it eventually I'm sure.
RS Hughes

Morris Lubricants still do a mineral GL4:
http://www.morrislubricantsonline.co.uk/lodexol-80w-90-api-gl4-gear-oil.html

As well as Comma:

http://www.commaoil.com/passenger-vehicles/products/view/183

Cheers
Mike
M Wood

2300rpm is almost idle!
Just did a nice 4000+rpm drive home.
Engine is nice an quiet then, just the wind noise!
But got a "new" 3,9 in the boot ready to fit.
Though I don't think it will drop my average RPM alot...... Just increase the speed ;)
Onno K

Why not go for an overdrive conversion?



Cheaper than a type 9 and less aggro.
SR Smith 1

I've thought a bit about overdrives SR. The box in the 1500 is a modified Marina box I believe so I wondered if there is an O/D around that would fit it. Don't remember Marinas having O/D.
On the other hand am I right in thinking the late Marinas/Itals had a 5 speed box, or did I imagine it?
Nothing against the Ford box - I had 3 Cortinas and a Sierra and never a problem with the gearboxes - but I wonder if there's an alternative that would be easier to fit.
What about the O/D box from a late Spitfire? The engine's essentially the same after all.
Just idle speculation, but I'd be interested in picking the brains of people who know more than me!
RS Hughes

Spitfire OD fits 1500 GB but easier to swap for Spitfire OD & gearbox complete. You still have to butcher your cross member to get it to fit.

The thing about the type 9 is it's physically quite small being a little longer than a 1500 + OD.

More modern gearboxes like MX5 or Lexus IS200 are quite a bit bigger.

There was an article in MASCOT magazine a few years back about BMW E30 ZF gearbox (manual NOT automatic and NOT GETRAG) that fits without cutting cross member but they are as rare as hens teeth in UK. More easily obtained in Germany.

Anything is do-able but as I found fitting a type 9 to a Frog it can be both time consuming and frustrating if you do it yourself, or expensive if you can find anyone else to do it.

Rob



Rob aka MG Moneypit

The Marina/Ital boxea are all the same apart from the bellhousings, none of which fit the 1500 triumph box'


And you are right no overdrive or 5 peed was ever offered by the factory on these models.


It is a reasonably straightforward conversion tho as someone has said. The gearbox can be sourced from a 1500 Spitfire, triumph 1500TC (RWD) or dolomite 1500HL. Use the matching clutch plate and the MG cover. The prop bolts straight on and you'll need a longer speedo cable, plus it'll need re-calibrating.


Cut away the square section in the tunnel and plate the holes. Fabricate a new crossmember and weld or bolt thro the floor.


The electrics are reasonably simple, either a dash switch a la MGB or the oe switch on top on the lever, which is what I did.



Works really well, mines been done over 25 years.


Any questions, just ask.



SR Smith 1

each to their own of course

I've had a couple of classics with o/d and a couple with 5 gears and I don't think overdrive is as good as a 5th gear

with o/d you should keep the load on as you engage and disengage o/d which feels strange when slowing down or using engine braking

though if o/d is on the car it is nice to use it for accelerating especially o/d 3rd
Nigel Atkins

Really?
IIRC my last O/D equipped car, an ex-police Triumph 2.5 PI with the troublesome Lucas injection system removed and replaced with a GT6 head, manifold and carbs, would neither engage or disengage the O/D under load.
You had to flick the switch, then ease off the loud pedal until you felt the O/D clutch in or out.
The 2000 Mk2 and the P6 Rover 2000 (my Dad's) were the same to my best recollection.
I always assumed this was to preserve the O/D epicyclic gear and clutch from damage from shock loading.
I admit it's a long time since I drove a car with O/D, basically since 5 speed boxes became near ubiquitous, but that's my memory of the technique. Ready to be corrected if I'm wrong, of course!
RS Hughes

Well I've never done anything to the throttle, just flicked the o/d in and out, been ok for 25 years!


Think yr memory is playing tricks RS, the P6's never had an overdrive option?


I had a 3500S in the 80's which really need a higher top gear and ended up fitting an SD1 5 speed which mad it a fabulous car. Still couldn't pass a petrol pump tho.



For 1500 owners the o/drive surely is a much more cost effective option than a type 9.


By coincidence I had a drive in a 1500 which had just been fitted with a 3.5 diff yesterday. Did take the edge off the acceleration I felt, compared to mine.But the top edge felt more relaxed.
SR Smith 1

Fair enough SR - I concede I may be wrong on the Rover. Dad didn't have it more than a few monthe before it was stolen from Heathrow car park. Both the Triumphs were mine tho'. I always liked them.

Interested in the 3.5:1 diff. Didn't know there was one. Where'd it come from?
RS Hughes

Rod,
you should keep load on for o/d engage and disengagement and you don't need to dip the clutch, just flick the switch

just flicking a switch is what makes o/d fun on acceleration and the fact you don't lift off the accelerator

regular changes of the g/box o/d oil (and keeping topped up if required) will help maintain them and to operate properly

a mate used to have a TVR with the Triumph 2500 engine and o/d, column switch, it's a ride in that car that got me into TVRs

about 10 years ago I had a Rover P6 3500S, the S is the manual with 4 gears but no o/d, (26-28 mpg on a good run but only 17 around town)

Nigel Atkins

All copied on that Nigel - cheers.
Neither of my O/D Triumphs would engage or disengage under load. Both of them needed me to ease off the juice before anything happened. Was something wrong?
The clutch I referred to was the electromagnetic clutch in the O/D that pulls the epicyclic into mesh, not the car's pedal clutch.
I really liked overdrive and I'd be really happy to have it on the Midget. Where I live is a very small town and if I go anywhere it's fast A roads all the way.
RS Hughes

Hi guys,


Like you RS I've never knowingly done anything when flicking in or out of overdrive on my current 1500 or on the MGBGT I owned in the 90's.


In fact the Midget is fitted with a "kick down" switch in the throttle linkage that disengages the overdrive relay if you floor the throttle!


And Nigel I well know the 3500S was fitted with what was basically an uprated 2000 box, the main difference was the Rover engineers added an oil pump in an attempt to increase longevity. The box was marginal in the V8 due to the terrific torque the engine developed.



Mine got rebuilt twice after partially stripping first gear on the laygear on two ocassions. The second time using a supposedly "uprated" police spec one,which broke again. Once the SD1 box got slipped in in was a far nicer car, tho the gearchange was far notchier.
SR Smith 1

This thread was discussed between 10/01/2015 and 31/01/2015

MG Midget and Sprite Technical index

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