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MG Midget and Sprite Technical - Wire wheels and half shafts

My MkIV sprite had a major rebuild by a previous owner. He fitted wire wheels and reused the standard rear axle rather than the "correct" narrower wire-wheel axle.

I am in the middle of replacing one (worn) hub-extension and have removed the original, complete with half shaft, pressed out the shaft and fitted a new hub extension.

So far so good.

In the unit that was removed, the half shaft had been pressed through the splined hub to a point where it was just short of the step which locates the welch plug. I assumed that this was correct and assemble the new hub extension the same way.

When I reassemble the shaft into the axle I am finding that it is only the last 1/2" of movement that actually locates in the dif. This seems very little considering that there is 2" of engagement at the outer end (in the hub) and that the dif end tends to be the end which fails.

Gut feeling suggests withdrawing the half-shaft from the hub by about, say, 1/2". This in theory would double the dif-end engagement.

What I don't know is how much engagement the pinion on the diff assembly provides. Would allowing the half shaft into the dif by another 1/2" actually increase engagement (it wouldn't if the spline in the pinion is only 1/2" anyway)? Is there a risk that the extra half-inch would foul something internally in the dif?

What would be very usefull would be if someone could tell me how long the spline section is in the pinion in the dif, but all comments/thoughts welcome!

BTW I don't know whether I have standard half shafts or the ones intended for wire wheels (I believe the legths are different. Mine are 24 3/4" long!

G Williams

The standard steel wheel halshaft is a one piece item so if you have a shaft which is splined at both ends, it is a W/W shaft.

From the marks on S/W halfshaft splines, I would guestimate that the engagement is at least 1&1/4" at the diff end.
Dave O'Neill2

I agree with Dave, the WW half shafts that you have are too short for your non-WW rear axle housing.
Norm Kerr

Would appreciate if someone could measure a half shaft for me. As long as you know which type it is (steel or wire) that would help.
Playing around with a steel rod it looks as though the max engagement at the did end is around 1 1/4" before it hits the internals. Now presumably some of that is free air so....
if I slipped the half shaft an extra 1/2" out of the hub, I would have 1 1/2" engaged at the outer end and about 1" at the inner end.
That means going back to the man with the press!
G Williams

the splined bit of the sun wheel is 1 1/8".
I don't understand 'As long as you know which type it is' as they are totally different at the hub end and even a blind man could not confuse them!
The steel wheel shaft is 22 3/4 measured to the back face of the mushroom. The w/w shaft is approx 22 1/4 (I measured it with wrapping still on it).
David Smith

Graeme,

I had the same problem with the sebring replica when i changed to wire wheels , i know people that have used the short wire wheel halfshaft in the steel wheel case but i am unsure of the longevity of it but i would certainly get it repressed so there is some more in the diff.

Other options are Peter May halfshafts for wire wheel cars but they are made the extra half inch longer so they can be used in the steel wheel axle case , they are 200 + vat each so 480 all in , lots of cash but a great product and this is what i went with.

Or try Richard Wooley mg spares and he will probably have a wire wheel axle / ebay and get it blasted and repaint , could probably do for £100 , lots more work but would save a lot of cash and be right from then on

Other option is put it back on steel wheel half shafts and use wire wheel adaptors , i have never used and know some people hate them but cannot comment on them

Andy
Andy Chaffey

I take your point about the mushrooms but I bet they are splined onto the end of the shaft and can be pressed off.

The interesting number is the length of the steel wheel shaft from the back face of the mushroom, at 22 3/4".
If, by back face, you mean the face which mates with the bearing hub then this is a fixed datum for both steel and wire wheel assemblies. My shaft protrudes 22 1/4" (Eureka!) indicating that it is indeed 1/2" too short ie 22 1/4" compared to your 22 3/4" (or more correctly said, has been pushed into the wire wheel extension by 1/2" too much).

I think I have standard steel wheel shafts which are 24 3/4" long (I would guess, David, that the mushroom has 2" of shaft buried in it, making the shaft itself 24 3/4" long ie same as mine.) The wire wheel extn hubs are made with 2" engagement (same as steel wheel mushroom ???) but the slightly bodged "wire wheel conversions" have no option but to compromise on engagement lengths using the longer of the two shaft sizes (steel wheels). After all, if you were doing the conversion, that's what you would have to hand.

I think I would rather get 100% standard engagement at the dif and reduce it at the hub since the hub is a press fit on the shaft and so there is no relative movement to wear or fret the staft end.

G Williams

Andy: I think I have it clear in my mind now. The critical dimensions Dave supplied have all tied up with my measurements and explain the problems I have.
I only have a standard engine and don't hammer it so I'll make sure I get full engagement at the dif end and let the hub fall a bit short.
I have just removed and fitted "standard" wire wheel hub extensions which provide 2" of engagement. I bet that if I bought a "conversion" set, the spline would be 1/2" shorter so that when the half shaft is pushed in "flush", it has the 22 3/4" correct overhang.
I'd never get the budget for new half shafts or replacement axle passed the Management!
G Williams

Steel wheel shafts are cast with the mushroom as part of the casting. The mushroom is not a separate unit.
Growler

Graeme?

As I said earlier, the steelwheel halfshaft is made in one piece. It does not have the flange pressed onto a spline. If it did have a 2" spline at the outer end, it would protrude 1.5" beyond the mushroom.

The W/W conversion hubs just bolt onto the outside of the brake drum, in place of the wheel. They are not splined at all.
Dave O'Neill2

Here's a picture I prepared earlier. Years earlier.


Growler

So now totally confused! I don't understand where my half shafts would have been sourced from but they are def longer than the dimensions Dave quoted for wire-wheel half shafts. 24 3/4" - just been out and checked them again!
If one breaks I could be up that creek without a paddle!

G Williams

longer steel wheel shafts come from Morris Minor (1000s and earlier), and even longer still from Riley 1.5 and Wolseley 1500.
David Smith

But they would need splines both ends David, which presumably they don't as they would have the same sort of steel wheel hub flange.

I don't really want to start throwing away expensive components which have been on the road without problems since the rebuild in 2008. I had to replace the hub extension due to wear (I know from the bills that only one of the pair was new at rebuild time, together with a complete set of wires). This seems to have opened a complete can of works, I guess typical of most jobs tackled on a 40 year old car where others have "had a go" at it. The hub I bought is identical to the original and the two parts assembled the same. It must have been running with just 1/2" engaged! In fact even as the hub slides onto the studs in the hub the dif hasn't yet engaged with the half shaft.

At the moment I am quite happy with the plan to pull the shaft out by about 1/2", giving 1" in the dif.

Unless of course someone tells me different. Picked up a wealth of information through this post. Thanks everyone.
G Williams

Your suggestion to pull the shaft out of the hub by 1/2" sounds like the best solution short of replacing the housing with a correct wire wheel car housing (or buying custom longer axles). Of course, with the incorrect housing the track width is wider than stock, and so clearance to the outer guards will be reduced, but if you aren't planning to fit wider wheels/tyres and you haven't had an issue with rubbing in the past then it should not be a problem. The ideal solution is still to fit the correct rear housing, but to pull the shaft out as suggested is probably the best option that doesn't involve purchasing replacement parts.
Andrew F

I'm guessing you can see the 1/2" of diff engagement by looking at the wear marks on the splines? Adding another 1/2 inch does sound like the best plan.

Just make sure the splines aren't too worn, and clean up any sharp edges that may have been created through wear, as the splines will now be engaging on a different part of the differential. These halfshafts *love* to break at the differential, and don't really need any extra stress raisers.

Good luck!

Growler

If it helps, I have converted a 1932 Morris Minor to take a Morris 8 rear axle (Stick with it....there is a point!)
Morris/Wolseley/MG etc were all a bit tight and robbed bits from a collective 'parts bin' so many items are interchangeable, or seemingly so. The Morris 8 axle is 3 inches wider than the pre-war Minor so the shafts are 1.5 inches longer on each side although the hubs and bearing carriers are interchangeable (Morris 8 studs are shouldered and there are 6 against 3, you get the idea? Not QUITE interchangeable.)
The MGPB shafts are 1 inch shorter than Morris 8 ones but are wire wheel hubs, not bolt-on. The MG axle is about 2 inches narrower than the '8' but the shafts plunge deeper into the hub than bolt-ons.

Nowwwwwwwwwww, all of these shafts are 6 spline on the outer end (same as midget/Sprite) but the inner ends are either 10 spline (IIRC) for the Morris diff and 6 spline for the MG diff.

Ultimately there must be a dozen different splined shafts that you can stuff into your Spridget splined hub and they are all slightly different in length.

Are you sure you've got "POST WAR Midget" shafts and not "PRE WAR Midget/Morris" ones?

Incidentally, all of the above mentioned cars use 4 inch PCD but are 3 or 6 bolt fitting on the pre war stuff.


r thomas

Gentlemen, thank you!
Off to the press shop!

(probably again for the other half shaft next week)
G Williams

I can't get my head around why w/wheel half shafts are shorter than steel ones. I know the axle is narrower but the half shft protrudes much further out beyond the brake drum compared to the mushroom head on steel half shafts.

(This is the problem with experience based on wires and no corresponding "let's take it apart" knowledge of the steel sheel alternative).
G Williams

nomenclature and terminology !
when we say w/wheel shafts are shorter than steel wheel ones, we are only measuring to the same datum (the hub face) so we are ignoring the bit of the w/wheel shaft that pokes up the centre of the splined hub. Any better?
David Smith

David, thank you, thank you!

I thought my maths was getting decidedly unreliable.
Not realising that custom and practice has caused me great confusion.
So I suspect my half shafts are probably just standard wire wheel half shafts.
If the axle casing is 1" narrower that explains why I have to pull the shaft out of the hub by 1/2" inorder to get the correct position relative to the dif.

Man with press has done the work and I have tried it in position. Not ideal but I think I will get away with the short fit in the hub -preferable to the dif end anyway. About to check the other side.
G Williams

So, that idea doesn't work!!!

THe half shaft diameter increases where it fits into the hub extension. Whereas in the correct solution the increase in diameter is well-recessed behind the flange face on the hub extn, when I pull the shaft out by 1/2" the diameter change is much nearer the face of the flange.

As the hub extension is pulled up to the main hub, the axle casing body tube now fouls the point where the diameter changes!

I can only see two options short of new, narrower axle casing. Either work with a reduced fit in the dif (probably back to 1/2" again), or turn back the shaft so the diameter change is moved nearer the end. This would reduce the length of the spline by about 1/2" by maintaining the reduced diameter for a greater length.

Hind sight is a wonderful thing!

G Williams

Either option doesn't sound too good! I had a look at my spare steel wheel shafts and they appear to go into the diff by approx 1". The half shafts are not fantastically strong. The later shafts fitted to 1275 cars used higher grade steel. The steel shafts were stamped with the later part number but there is nothing on the wire wheel ones I believe. The risk of turning down the shaft or only having 1/2" in the diff could mean shaft failure. particularly as the shafts may have come from a 1098cc car.

I would suggest running it with the existing set up for now and look out for a wire wheel axle case. it also would mean the rear wheels were in the right place!
Bob Beaumont

Hello Bob.

THe shafts have a "circlip" style groove at one end. Did I see an article which suggested this means a later version with a higher grade steel?

If I get the shoulder cut back "properly" ie no stress raisers, I can achieve 2" in the hub end (interference fit) and 1" in the dif.

There don't seem to be many narrow axles about. Peter Mat alos makes longer shafts for just this dilemma - not cheap though.

THere is a current post about how a simple job just gets worse and worse. Think this is another one of those.
G Williams

Hi Graham Not sure if the circlip groove means anything. I have the later 1275 shafts with and without the groove. It may of course be different for the W/W shaft. The machining you suggest may indeed work especially if you don't let the clutch in too sharply in 1st! Bob
Bob Beaumont

Hi Bob,

This is the groove reference
http://www.mgexperience.net/article/midget-rear-axle-knowledge.html
Def suggest that the groove means better quality steel.

The inner end of the hub-end splines are pretty simple. A turning tool with a suitable radius ought to be able to take them back leaving a good transition and I would need about 1/2" removed.

Don't know what that would cost (in addition to the "here's that bloke with his half shaft again!" at the workshop).

Steep learning curve on this lot!
G Williams

This thread was discussed between 13/09/2012 and 14/09/2012

MG Midget and Sprite Technical index

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