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MG Midget and Sprite Technical - Changing Diff and Halfshafts

As I've got a halfshaft to replace on the frogeye. I'm going to take the oportunity to replace both halfshafts and also at the same time, swap my my 4.22 diff for a 3.9 one.

I've got tools, axle stands, 2 x halfshafts, 2 x halfshaft gaskets (whatever they're called), 1 x 3.9 diff. I suppose I need something to flush out the diff housing and some diff oil.
What oil should I use and is there anything that I've forgotten?

Thanks in advance

Gary
G Lazarus

I know you haven't mentioned it but don't bother with a gasket between the diff and axle casing, use RTV instead. The gaskets never fit right and mine always end up tearing and being thrown away anyway.

You might need the O rings to go with the halfshafts gaskets.
Tarquin

New set of propshaft bolts, big hammer ????
Alex Sturgeon

Any Synthetic gear oil. I like Mobil SHC but when I've not been able to find it I've used a Castrol synthetic gear oil from Halfords (even though they are a cr ap shop).
Daniel Thirteen-Twelve

I use Castrol EP 80/90

have a washing up bowl handy and a few litres of paraffin to wash out with, gear oil is foul stuff wear latex such gloves (cos I know you like cooking and I doubt if Lois will like anything you cook if fingertainted with petrochemical cats-p*ss) and a 1 inch paint brush to clean the diff casing inside

Lots of rag, many copies of the Big Issue or the Grauniad to soak up the splashes

and it will take far less time than you thought

You will certainly find sharp particles of steel all around where the shaft broke then cut a spike on its way to failing to turn

you will definitely need a big 'ammer to get something a moving

you might want a new washing up bowl later...
Bill

and a big bunch of flowers for the other half after you walk oil though the house
Alex Sturgeon

Cheers for all of your replies.
G Lazarus

Wanna come and do mine after?
Toby Anscombe

yours wont need "severe metal fatigue" deep cleaning either

Go on Gary

you know you want to


:-)

Bill

Hi Gary , just a tip , when you jack the car up , support the body of the car with axle stands not the axle this allows the axle to droop lower and makes getting to diff ( and getting it square to go back in as well and reach top nuts easier ) probably just told you how to suck eggs :-) but hope it sort of made sense
Darren1800frogeye

Gary, you need to order enough space either side. In my garage I have to slew the car on the trolley jack when one side's done.

Worth thinking about beforehand if you're in a lock-up size of garage. Get the car central, and measure with one of your new shafts.
Nick

Thanks Nick,

I'd thought of that and with all the junk (and I don't include the car in that description) in the garage, I'm going to have to have the rear of the car sticking out to get the clearance that I need.
G Lazarus

square drain plug spanner?

Is your new diff in good condition, or are you refurbishing that too?. It may be worthwhile replacing the olive-shaped thrust washers on the 2 planet gears, and the thrust shims on the sun gears. It is very easy/ cheap to do without disturbing the crown wheel & pinion mesh, and will reduce lash at the wheel rim if it is excessive.

Guy
Guy Weller

Whats the oil capacity of the diff please?
G Lazarus

You fill it to the level plug on the casing. The manuals don't give a capacity AFAIK. But I think it is about 1 litre, from memory. Maybe someone else knows for sure?

Guy
Guy Weller

Cheers Guy.
G Lazarus

Gary

I have a book that knows (says it does anyway)

The 1989 Spridgebits catalogue (one of the finest small reference books I own) states:
Oil And Water Capacities
Rear axle (all models) EP90
1.75 imp pts
2.1 US pts
1.0 litres

I hope this helps
Bill

mu local car factors place only had semi synthetic SX75W-90 made by a company that I don'r recognise. Will this do or should I search out a Halfrauds for the EP80-90?
G Lazarus

I know the wieghtss will work, but not sure what the "SX" repersents....I think I would use the trusty norm of EP...Im using synthtic EP75w-90 fro lucas oil.

prop
Prop

I'd pop along to Halfords myself

(err whats fraud about them? They started by selling bikes and still devote more staff time to selling bikes)

EP 80/90 for me
Bill

Gary - I have just checked and a 1/2 socket will remove the rear plug but not the bottom one. Get a drain plug spanner while in halfords...

I have a slide hammer, correct size socket and some spares if you get stuck on the weekend.
Toby Anscombe

A 1/2 inch drive will fit the bottom drain plug if you grind a slight taper on it. Not recommended for your top quality Snap-On, but if you have a spare cheap one.....

Guy
Guy Weller

Out of interest whats do you need a slide hammer for ?

From my distant memory of numerous broken shafts in an old tuned minor (old low grade shafts)the only trickey bit was if any of the broken shaft sticks out of the diff a bit - makes it difficult to get out of the casing.

Not broken any 1275 shafts (yet famous last words).

Richard.
richard boobier

Taking the good one out, if it is stuck.

Are you replacing the bearings at the same time?
Toby Anscombe

Well I've ordered a set of bearings so let's see if they arrive in time.
G Lazarus

slide hammer

as redundant as a slow AA man

undo the screws and the half shaft almost falls out
Bill

Bill,

Thats what i was thinking (not the AA Man bit !), also not sure what you can fix it to on a standard midget halfshaft.

Rich.
richard boobier

Take care when removing the bottom plug if you are really lucky (not) the damn thing is stuck in with paint and surface rust. Apply a seemingly reasonable amount of force and the stupid plug cracks, guess how I know!!!!
Graham.
Graham P 1330 Frogeye

Like Graham, I wrecked the plug in my old axle casing getting it out. The replacements sold by MGBHive have a hex in place of the stupid square that nothing fits properly. Much, much better 'cos you can give it a decent pull without the socket spanner falling out and the part only cost a few pence.

First time I put it back, there was a tiny drip-drip - I've put it back in with plumber's PTFE tape as well, seems to stop the slow leak from the plug very effectively.
MarkH1

Boys boys, you safe yourself so much troubles and pain by just getting the proper tools.
They dont have to be Snap-on because most of us dont use the tools on daily base.

On image is the perfect tool to open the plugs on your rear axle.
If you do proper maintanance youll freshen up your diff/axle oil every year/2year (depending on miles).
Therefore it makes sence to buy this tool as it will be your friend for the rest of your life(because a spridget is for life!!!!!).

Image:


Arie de Best

Got the right tool, still broke the stupid plug! PO had probably never removed it since rebuild in 1998.
Gary, even if you break it you can use the fill plug in your old diff anyway, it's just a real pain getting out the remnants of the old plug.
Graham P 1330 Frogeye

Hi Graham,
I'm not changing the housing, just the diff.
The "O" rings, extra gaskets and bearings arrived today.
Ordered from Moss yesterday lunchtime. They're not the cheapest but I find their delivery times very good.
G Lazarus

Gary, if you want to do the bearings at same time, do you have a hub nut socket? I think Toby has a socket if you can tie up with him.

Have the bearings come with oil seals? you'll need those too.

Having said all that, you can still change the diff just to get her going and then do the bearings on another day. The diff won't need to come out again for that, just the shafts.
Bob T

Hi Gary, you still gotta take out the drain plug to drain the oil :)
Graham
Graham P 1330 Frogeye

I use a short (about 3 inches) 1/2-inch socket extension for my diff plugs. I bought an inexpensive one and took it over to my grindstone and worked it down to a perfect fit (or close to perfect anyway). It still works as an extension if necessary, but it also fits my hammered impact driver as well as my pneumatic impact wrench. One of them will shift it!
David "a little impacted" Lieb
David Lieb

True (rolls eyes in recognition of my own stupidity).
G Lazarus

Gary, if the bearings ar not causing troubles and you dont wanna go double-bearings i would leave the originals in and save the new ones for when nessecary.

Like you tea drinkers say: if its not broken, dont fix it!
Arie de Best

One of my halfshafts has arrived. It looks unused although bought as 2nd hand (99p on ebay).
Are the halshafts marked anywhere stating what type, as I can't see any markings on it?
G Lazarus

I'll go and look at my spare one (ex-offside)
Bill

Ah, I've found it under the dirt on the face of the hub. BTA 806, I think it's a standard earlier halfshaft. But I can't complain for 99p
G Lazarus


BTA806 doesnt seem to be year specific Gary

Moss's Restoration parts catalogue does quote another for uprated as BTA806X

The BTA806 is quoted for all models in all of my catalogues, does it have any particular wear marks along its splines which may help you to see which side it was fitted?

(if it was)
Bill

No there is no wear as far as I can see.
the full numbers and letters are
BTA806 OMES KD
G Lazarus

do you need another one?

You can have my spare offside one

Sunday do you?
Bill

No thanks (and many thanks too)Bill.
I now have two spares plus the one undamaged (hopefully) one already installed.

I intend to drive the Frog up on Sunday.
G Lazarus

So Gary.... did you get it done?

Mark.
Mark T. Boldry

Yes we got it done. It was the nearside shaft which snapped halfway along the splines very cleanly and the advantage was that the broken end acted like quite an efficient plug and kept most of the debris out of the diff.
The broken halfshaft needed a bit of extra force to pull it out.
Both the existing shafts look to be the original weaker ones and they've both been replaced with later ones, so hopefully a little bit stronger. Which is good as it's not a job I'd like to have to do on a regular basis.
There were only some tiny bits of swarf left in the diff casing.
Interestingly the new 3.9 diff, really didn't want to go straight into the casing without a lot more than gentle persasion. It's almost as if the lip around the inside of the carrier assembly was a bit larger than the one that came out. We had to use the nuts to pull it up really close to the diff carrier. I'll see if there is a puddle of oil under the diff tomorrow morning.

I've found a way (although far from fullproof) of determining whether your car is fitted with an early or later differential as the carrier on the early cars has an additional drain plug on the offside, whereas the later ones don't.

A massive thanks to Bob T who braved torrential weather to watch over me (and even do some of the messier jobs).
At one point I was lying under the car with water cascading down the rear of the Frogeye and settling in a pool in my crutch. That's my story and I'm sticking to it.

Thanks once again for everybody's help and input.
Hopefully I'll see some of you tomorrow at the meeting.
G Lazarus

On our way Gary, see you shortly at the AGM.

Mark & Anita.
Mark T. Boldry

Gary,
Your comment about rain reminded me ... ...
My son has no garage and often works on his car in the street up in Edinburgh. He bought himself a small nylon garden Gazebo from Aldi or some such. It has shock-corded fold out legs and is self-supporting (no guy-lines to fix) he just pitches it over his car when he needs to work on it. It was cheap at about £20 it seems like a good idea.

Guy
Guy Weller

Reminds me of when I was 18, almost 40 years ago!!!!!

I had a Morris Oxford, pre Farina, and it broke a diff, same symptoms as a half shaft breakage. A few of my friends got together and we pushed the car back to my parents house and parked it in the yard. That night it snowed and the following week or so was terrible weather. So in snow and ice I had to go to the scrap yard to get a diff then fit it to the Morris. I swore at that time never again so you have all my sympathy.
Bob (Robert) Midget Turbo


I think the internal hex diff plug supplied as a replacement (under the original part no as the square one) takes a 3/8" allen key or socket.
Daniel Thirteen-Twelve

Just an update for those of you who didn't read it on another thread.
The diff is working great and I did about 220 miles in the car yesterday.
One great additional bonus and a complete coincidence is that with my 5.5 wheels, 175/13 tyres and Datsun five speed box. My speedo is reading as accurately as could ever be expected on a Spridget.

With the Speedo reading 40mph, the sat-nav read 41mph.
with the Speedo reading 60mph, the sat nave read 61/62mph.
And at a theoretical (obviously) speedo reading of 80mph, the sat-nav would have read exactly 82mph, which is accurate enough for me as long as I remember that the speedo is reading 1-2% too low.

It was very noticable on Sunday that high speed motorway driving was greatly improved.

Thanks again to everybody especially Bob T.
G Lazarus

This thread was discussed between 03/11/2008 and 10/11/2008

MG Midget and Sprite Technical index

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