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MG Midget and Sprite Technical - Limited slip diff advice

Hello everyone. I've fitted a 3J driveline plate type LSD. First drive wwas this evening. It's a bit different! More understeer, and more rear end grip. It will step out sideways instead of just smearing sideways a bit while spinning one wheel. That's all expected and OK, I can dial out the extra understeer later. The biggest difference is a fairly noticeable tightening of corner line when I let off the power. Is that normal? Going to take a bit of getting used to. Any advice on preloads, ramp angles etc much appreciated!

I did a big bore standing start and it chattered a bit from the back and then went off like a scalded rat. I was intending to count seconds but I was too busy laughing. LOL.

Overall a success, but I'd like to (in a perfect world) get it so it stayed on the same line when on or off the power.
Rob Armstrong

I think you'll find that the pre-load and ramp angles are set in the manufacture of the diff and if you want them changed you'll need to return it to the manufacturer to get them changed.

Also, your starting point should be to establish what the current pre-load and ramp angles are from the manufacturer.
Daniel Stapleton

Ah, OK, thanks Daniel! Would the handling behaviour above sound normal?
Rob Armstrong

"Would the handling behaviour above sound normal? " Sounds lovely, we rally drivers adore it! Just the thing to get the tail out going into a corner :-) and then fine tune your line on the throttle.

Seriously, it's a feature I really like, if you get the oops I've gone in too fast feeling, or misread the corner and find it has a late apex, all you do is lift off and the car tucks nicely into the corner. And if you are going too fast you'll disappear honourably backwards off the road ...

Similarly, a bit much oversteer and applying the throttle can balance it. To an extent. With 1900cc+blower Widget can snap through that phase and go drifting, intentionally or otherwise.

Yes, LSDs do have a different feel. I recall when I first fitted one to the B everything happened much more quickly (I like the smearing sideways description) but once you are used to it the predictability and controllability make it magic.
Paul Walbran

To me it has the symptoms of a lsd that is set up too tight for the weight of the car
This might be because it's new and it will settle in once it has flattened the plates off a bit-maybe
What breakaway tension has it got ???
For a road going Sprite/midget I would be looking at 30-40 ft lb MAX
As Paul mentions , for rallying you can have them set up a lot tighter and drive to suit but in my opinion for a road car ,it will be a lot nicer to drive set up softer
The advantage of the soft setting is a lot less (normal)
understeer and a smoother transition with on/off throttle movements

An extreme example of too tight that I had to sort was a mate's motorkana miniMoke - He bought a ls centre for it and it had 60lb breakaway and because of the light weight of the Moke--When the steering was on the lock and reverseing it would actually sledge the whole car accross the asphelt in the direction the wheels were pointing---We reset it to 40ft/lb then 30 and ended up at 25ft/lb and it was like it was glued to the ground at that-

I'd be interested to know what yours is set at

William Revit

whilst obviously there will be differences with the lsd do bear in mind that you're possibly driving (even!?) harder (than you usually do) on the same tyres on roads possibly colder and damper than pre-fitting.

I had a lsd (in a different car) and the first time I took a regular route and turned off on a sharp l/h, uphill, opposite camber, with a soon slight right I was surprised how the back end danced, the lsd made things different, usually better but sometimes just different.

Just imagine how things will be when the roads are fully dry and warm and the tyres are warm too - rubber bits everywhere I'd imagine :).

Nigel Atkins

Do you know the 3JDriveline Part number of the LSD you have fitted ? From that we should be able to deduce the ramp angles & preload you have. I have some info on that as am in the process of changing form a Quiafe lsd to a 3JD the same as you.
Also if you Google Trannex LSD is possible to find useful information on setups,as that is basically an identical type lsd.

I think your driving comments are fairly normal for a first drive , generally an lsd will make the car understeer more (but that can be amplified if you certain settings) so I believe you might need to change your driving style to be more aggressive with the back end of the car to overcome the understeer

Ian Webb 1973 GAN5


The 3J LSD looks very similar, or maybe even identical, to the Tran-X (now owned by Quaife) plate LSD.

We have one in our Minor, so the same ,or similar, unit to yours.

There are 2 settings in the diff - the 'ramp angle' and the 'pre-load' on the clutch pack.

A typical 'road' ramp angle would be in the range of 40° - 60°, and the standard options from Tran-x were either 45/90° or 55/90° (On throttle° / Off throttle°). The angle can only be set with the diff is completely disassembled - so not a 'road or track side' option!

I see that Quaife now offer a 35/90° option with the 45/90°, but that was not available when we fitted it almost 15 years ago, and we selected the shallower option of 45° ramp angle, in combination with a clutch pack pre-load of 30 lb. ft. Not sure if 35° is road use?

What combination of ramp angle and pre-load did you specify?

All great for the first 200m, until at the end of our road, where there is a climbing LH turn at a T-junction. A slightly enthusiastic start and a 'click' a second or two later from the rear indicated a problem! The torque transfer from the almost unloaded LH wheel to the RH, had snapped the RH 'toughened' halfshaft.

A few £100's later and Peter May's EN24 'Competition' halfshafts were fitted and no problems in the 40,000+ miles and multiple track days since then.

What oil do 3J recommend? Plate LSD's are notorious for 'clicking' when the oil is hot and you are manoeuvring at slow speeds - to overcome this Castrol suggest using their SAF-XJ 75W-140 fully synthetic oil (now Syntax Limited Slip 75W-140).

For our first fill I went to our local BMW dealer and bought the LSD oil from them, and all fine. A few years later I decided to change the oil and used the 'normal' LSD oil from Castrol and immediately had the 'click' on turning. A call to their Tech Dept identified the solution - use the 75W-140 oil developed for BMW!

Problem solved and used it ever since.

Richard Wale

" ... you might need to change your driving style to be more aggressive with the back end of the car to overcome the understeer"

You've not seen Rob's videos then(?) (particularly the Rover P6) if he puts in much more aggression the tyres 'll be ragged and back end probably dislocated to the verge or hedge :).
Nigel Atkins


Loads of great info in here. Ramps are 40/90 and preload I think is 35, just waiting for confirmation from Kim at Magic Midget.

I reckon I can learn to drive round it. More welly needed! But not when it's cold and damp or all of me will be in a hedge, probably rear end first!

It's the first thing I've driven with an lsd so getting used to it will be required.

I've got adjustable almost everything so I should be able to dial the understeer out.

An example of what Nigel is on about can be seen below. Very smeary on road tyres and one wheel drive!

Hence the move to lsd, and bigger brakes, and track tyres.....
Rob Armstrong


40° ramp angle might be a bit sharp, but the 35 lb. ft. pre-load is definitely the right setting.

On a trailing throttle, it is only the pre-load that is having any effect - the 90° ramp angle means there is no clutch pack loading at all.

Exiting enthusiastically from damp roundabouts does need a bit of care and/or lightning reactions!

Richard Wale

You've got what you've got and as you say you'll learn to drive around it but for a road/ sealed road car as light as a Midget I'm still thinking it's a bit aggressive
A setup with a less aggressive angle like 50-55 and lighter preload like 20-25lb would be the go------------- -----------------in my opinion but it's not my car

William Revit

There's good info for the 3JD LSD's here at Burton Engineering :

It confirms what others are saying.

You have the same 40/90 as I do , I'm not sure but I think your diff may well have 25lb pre-load which is probably just right to start with, 35lbs might be bit high, it all depends on the individual and what you use the car for.

Your diff also already incorporates a 30/90 ramp set up which is slightly more aggressive, but to try that you would need to strip out the LSD and change around the ramps to the alternative position, as you've already rebuilt your diff that's a straightforward job. There are available three alternative pre-load spacers thin / med /thick, at £20 each. These fine tuning adjustments are one of the reasons I am changing from the Quaife ATB that I had before......I want to have a play with all that over the next couple of years.

I did speak to 3JD about which oil they recommended and they said any LSD oil will work.... but and its big BUT the best performance and reliability is fully synthetic 75W-140 LS, he said you get what you pay for basically.

IMO 3JD have a very good product at the right price but they could publish more setup information guidelines on their website......I know you can call them (I did) to discuss your application, but its much more helpful to have something written down IMO

Nigel : I didn't suggest that Rob wasn't aggressive already. What I am saying is that he might need to adjust his driving style a little to get the car to rotate more with back end, this is necessary to rebalance the grip, so that you balance out the understeer so hopefully not ending up off the road you seem worried about! IIRC every one I have spoken to about LSDs told me that they had to change their driving technique to get the BEST out of the diff. That is exactly my own experience.

I want to echo what Paul said on your other thread ; that once you have tried the LSD you won't want be without it, much more fun....... better fun-value per pound than spending £800 on your engine.

By the way Rob what do you use the car for ?

Ian Webb 1973 GAN5

'the best performance and reliability is fully synthetic 75W-140 LS'

Yes definitely, as above, I use Castrol Syntax Limited Slip 75W-140 full synthetic in our Tran-X LSD, and it works very well, no clicks!

I had to strip the diff a few months ago, for an unrelated reason, and all the clutch plates were near perfect, and that is after 40,000+ miles.

Richard Wale

I have limited experience of both the ATB type LSD and the plate type having one of each in my midgets. I fitted the ATB last year to make the standard 1275 a little faster and better controlled on the loose (forest roads in classic rallies). I guess that when you fit a LSD and the wheels don't spin some additional force is transmitted back up the driveline; on our second autotest I broke a first gear tooth and had to fit a recon gearbox, we then took it to the Berwick classic and completed 3/4 of the tests etc and it broke a half shaft. So fitted the uprated Peter May ones and all has been well since. As someone mentioned earlier I would plan/budget to get uprated half shafts- if you have not done so already. THe LSD does make the car handle better on the loose and it feels much steadier on the road. The only problem I have is trying to get the back end to break loose on dry tarmac autotests. Either the car does not have enough umph or I am not rough enough with it (mechanical sympathy sometimes overrides the right foot)---probably a bit of both. Having said that on a wet/icy tarmac autotest it drifted wonderfully.
The other 'go faster' 1293/weber car came fitted with a plate type diff but I don't have any details. Again it keeps it on the straight and narrow on the loose stuff with a slight tendency to understeer. I was also advised by one who knows to use the expensive specialist gear oil.
I think that we met once on the MG Cumbria Xmas cracker run at Reghed. The run is this weekend and we will be taking the 1275 midget as the other is awaiting new universals to be fitted (perhaps another consequence of fitting a LSD!?).
You will really enjoy the benefits once you have got a feel for it.....find a damp car park or forest track and have a hoon!
John S
J Sloan

Hi Ian,
my previous comments were tongue-in-cheek, I'm with you that the lsd will make things different, and most usually better. I'm not too worried about Rob keeping off the green stuff as he's used to trying out stuff on his car. Plus it's better (with suitable caution) to learn this time of the year - and there'll still be possibly even more fun in 9 months or so time.
Nigel Atkins

Thanks again all. I think I recall chatting on the Christmas Cracker Run! Car is used mainly on the road but used pretty hard. I've now got a taste for track days which has exposed lots of (mostly rear end) issues. Front is well sorted so pretty straightforward to tweak damper settings and the arb to suit. I reckon the biggest improvement will be gained from me getting used to it!

I now have the stronger coarse spline shafts, lsd, and double bearing hubs after massive half shaft flex and oil leaks at Croft. Hopefully this back end will be fairly unburstable, I've got 98lbft max torque from my 1400, so hopefully won't stress things too much. I've also got anti tramp and rear discs which I'll pop up in a different thread.

Rob Armstrong

The stronger half shafts with the nut on are substantially heavier than the standard ones. Hopefully the type 9 should withstand the abuse too. I've put that special lsd oil in the lsd.

I'm looking at autotests now as well as a way to hone driving skills in a low speed environment where the biggest thing I can hit is a cone....

I have been out and timed a 0 to 60 with an app. It's less than 6 seconds.
Rob Armstrong

Dito on the oil
Ford recomends it for all their heavy duty and lsd rear ends here
It was SAF XA 80/140 here but now changed to Syntrax80/140

On the turbo and v8 Falcon diffs they have heavy duty hob cut crownwheels which aren't the smoothest machined gears you've ever seen-- If they get filled with 90lsd oil by mistake (which we've had one or two---or three) on a longish run when they get nice and toasty after 250-300 klm they get a minor howl in there at about 90-110 kph and the limited slip gets clunky, especially round slow speed corners with light load
Change the oil to this Castrol 80/140 synthetic which has all the additives in it for limited slips already and you never hear a sound out of them
William Revit

about the oil - "... but and its big BUT the best performance and reliability is fully synthetic 75W-140 LS, he said you get what you pay for basically."

There are various types of "fully synthetics" and you might find an even better suitable oil than the Castrol for a couple of quid more.

A good oil is a good oil regardless of its particular make up or formula but possibly you could consider an ester oil to cover the full range of your use of your car. You want the high temp protection for track and "fast road" use and if you're using your car on the road in weather like we have now, or colder, you also want the cold temp protection.

As you've found track use really puts wear and tear on road going cars, track use is about high performance and temperatures, more limited use with more maintenance and reduced margins of use, whereas road use is more about a wider use with more variables requiring wider margins. It's a not-so-easy balancing act to have a car for both track and general road use for all components including the oils.

More than once the extra, sometimes only a couple of quid more, I've invested in a good oil has paid me back in multiplies by providing the extra margin and protection that has saved me time, hassle and money - and my car isn't used on tracks (other than once a year offering passenger rides at road speeds).
Nigel Atkins


I'm intrigued to know what you have in mind when you say 'you might find an even better suitable oil than the Castrol for a couple of quid more'?

The Castrol Syntax Limited Slip 75W-140 is, as the name suggests, specifically formulated for LSD, has been proven on a number of years to work very well indeed. In our case 40,000+ miles of road and track, with in effect no wear on the clutch pack at all - what might be even better than that?

No, I have no connection whatsoever with Castrol, but I don't understand your comment.

Richard Wale

Neither did I; was hoping for a specific example...
David Smith

Me too !!

I bought this Gulf oil .......probably a "couple of quid cheaper" than Castrol no good then ! (now that's tonque in cheek , Nigel)

Ian Webb 1973 GAN5

I bought that Gulf stuff too.
Rob Armstrong

I use the Castrol as recommended by Richard. Still working fine after about 8 years of abuse. I change it every couple of years which is probably less than a thousand miles in my car.
john payne

Myyyyyyyyy you racing guys are prickly.

I was just following on from the theme of "but and its big BUT the best performance and reliability is fully synthetic 75W-140 LS, he said you get what you pay for basically." So the possibility is that if you get a better fully synthetic 75W-140 LS then that would (could?) be better.

I'm not saying that Castrol isn't a good oil, and note previously I put "A good oil is a good oil regardless of its particular make up or formula" I should also have added regardless of it's selling price. Obviously from your experience the Castrol is a very good oil (I often recommend a Castrol (and other makes) and I too have no connection with them) but it could be possible that another oil could offer even more protection for even longer but I wasn't thinking of a particular oil. If you (and Rob) use your cars in cold winter weather as well the hard track driving then Rob might want to consider the Castrol (but I see he's bought Gulf competition oil). John put that he changes the oil every couple of years (similar to me), do you change the oil or is it the one fill for 40k? (which would be even more impressive and cost effective).

(you naughty boy) sorry but you've either mis-typed or shot yourself in the foot, the Gulf you linked to costs more than the Castrol not less.

better to have been in hope than distress - oh, dear I hope this comment doesn't distress you ;)

Dear All,
please try to remember I'm not a ruffy-tuffy racer, I am of a more delicate nature, fragile, possibly not as manly, my arms are skinny and forearms feeble, mentally I'm not strong either I lack sufficient competitiveness - and . . . I'm going to come out and say it ... I don't like any sports!

(I did follow professional boxing for a while but that's much more of a business than sport)

So please make allowance when I transgress.

If you can, with this post please try to ignore the humour or the factual reply(ies) but not both, if you can, or want to.

Nigel Atkins


In my first post I said that the oil had been changed and that is when I found the 'clicking' problem with a straight race spec Castrol B373 EP90 LSD oil. What I had used for the first fill was actually Castrol 75W/140 full synthetic LSD oil, but I did not know that - it was just the LSD oil that BMW use, and had been in my cars with LSD's for a number of years with no problems.

I don't have a regular change period in the Minor, but it has been around 12,000 miles and 4 years on average, as I think an LSD, especially a plate type, will degrade the oil faster than a non-LSD.

Richard Wale

On the oil question, years (decades) ago I found BP lockstop completely eliminated the clicking from my plate diff. So I boutght 20 litres, which lasted well at about a litre per fill. And I recently finished the last of it. So this thread is very helpful!
Paul Walbran

I am not wishing to get into 'mine is better than yours' competition - grand waste of time!

Looking at the Gulf Oils website and the technical spec for their 'Competition Oils', there is one statement that does concern me when they refer to their competition oils generally:

'They are not, however, recommended for long-term/everyday use in most road cars, unless the vehicle has been performance-modified and/or is used extensively for track days.'

I would guess that most of our cars are more road based than track for their usage? So what is to be made of that?

Richard Wale

Hi Richard,
I'm with you I'm not into willy-waving, I've not got the equipment to do so - by that I mean I don't have LSD.

I was just curious to see if you had a regular "service interval" for changing the diff oil and if so how long, just curious no more than that.

You've highlighted one issue that always comes to my mind when oils/greases are for competition use, as I tried to put in a previous post about track use and oil, they're design for specific use and probably temperature range. I wonder if a rally car oil might (underlined) be more suitable(?).

It states for the following oil "This oil has fantastic low oil temperature flow that ensures adequate bearing lubrication at temperatures as low as -40F ...", "Suitable for racing and street use" and it's a couple of quid more too!

It's the alternative oil on the filter I used on Opie Oil, (as we started out with Opie Oil) there may be other oils more suitable and even possibly at lower selling prices and this oil may be ruled out for some reason I've missed or don't know about.
Nigel Atkins

I don't know what LSD I have - supplied an set up by Frontline a few years ago. Interested to hear about the clicking - mine does that when hot, especially in reverse at low speeds when turning. Also does a rubbery groany thing at low speeds with minimal steering input - silent straight ahead.

Not sure what oil I've got in it and can't be ar*ed to go out to the shed to look, but it's a gold bottle - presumably castrol.

Maybe I'll try something else.
L McInally

The Frontline diff is a plate-type, and what you describer certainly sounds like an oil issue.
Paul Walbran

Sounds like you need to change the oil for a full synthetic 75W/140 - I know from first hand experience that the Castrol Syntax Limited Slip 75W-140 virtually eliminates the slow speed 'clicking'.

I get it from Opie Oils:

Worth a try?

Richard Wale

No clicks from mine yet. It seems to have bedded in a bit, lots of the things I mentioned in the first post have ironed out (or I've got more used to them).

Put another 150 miles on the car today, loads of traction, loads of speed, great stuff.

I've got the gulf version of that castrol oil in it. Should I be swapping it out now it's been in a bit?
Rob Armstrong

that Redline oil any good for ya(?) they seem to do oil for street cars too rather than just competition concentrated, I'm sure there are other makes too but I've not searched.

Redline are also good because they agree with me about draining to get metal bits out - or is it I agree with them - or that neither of us have that idea as original!
Nigel Atkins

'draining to get metal bits out'

With that in mind when I fitted the Tran_X diff, I attached a neodymium magnet to the drain plug. It has a hole in the centre, so it is fixed to the plug with a 5mm csk screw and Araldite, just to make sure.

When I dismantled the axle earlier this year, there was a very very fine paste on the magnet, and that is after ~10,000 miles. Much the same when I changed the oil previously at a similar mileages. I had expected more 'metal bits', but there is no visible wear to the clutch plates at all after 40,000+ miles.

Richard Wale

... perhaps it depends on the oil you use - dun, dun, tish
Nigel Atkins

This thread was discussed between 27/11/2016 and 11/12/2016

MG Midget and Sprite Technical index

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