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MG Midget and Sprite Technical - Crown wheel & Pinion

When clearing out the darkest corners of the garage, I came across an unused and matched CW&P, which I vaguely recollect buying at Beaulieu about 12 years ago. I hoped it would fit my MGA, but I think it is probably Frogeye (can I say that here?)or midget, Can anyone help me identify it. Part number is MOWOG ATC 7397 - 8/41. As the part number suggests it is an 8 tooth pinion and 41 tooth crownwheel The Crownwheel is about 8 1/4" (210 mm) in diameter.
I had intended to build up another axle for the MGA to do some sprinting and hill-climbing, but never quite got round to it!
Geoff McGladdery

The Frogeye never had a ratio that low, but Austin A30s did.

If it is A30 and you want to part with it, I would be interested.
Dave O'Neill 2

Dave, Thanks for that. I assume that A30s shared the same axle casings as Frogeyes and early Midgets. Someone suggested that it might be the so-called "Post Office Van" CWP from a Moggie Minor. Did tey have the same axle casings too?

I would consider selling the CWP - feel free to call me on 07588 559698
Geoff McGladdery

Hi Geoff

See:
http://www.mmoc.org.uk/index.php?page=341

Although this page, apparently, has some errors which have been mentioned in earlier threads. Not the most useful advice I realise!

Cheers
Mike
M Wood

Peter

On a bit more digging suggests it might - and I stress not sure and looking for others to confirm/reject - from another BMC vehicle, possibly Austin Gipsy rear axle, Morris J Type van, Austin 6/110 (or even common with an early Sherpa van? And some Austin FX4 taxis?)

Cheers
mike
M Wood

Mike,
Thanks for the link, unfortunately the CWP part numbers are not listed, only the axle casings. It doesn't seem to show the 8/41 ratio, although a 5.125:1 ratio would suggest an application like a commercial vehicle or a very low powered vehicle.
Any more information will be gratefully received.
Geoff
GM McGladdery

According to my parts book its from an Austin Gypsy!
Bob Beaumont

Bob,
Thanks for being so specific. at least I can accurately describe it. I presume that it will fit any axle case of the same type - A30, A40, Sprite/Midget, Moggie Minor and of course - the Austin Gypsy!
Thanks again
Geoff
GM McGladdery

Having looked more closely at your original post, I think the diameter of the crown-wheel is too large for Sprite/Midget/A30, etc.

It seems that BMC produced three sizes of banjo-type diff. The small one was for our cars and the part numbers tended to start with 'ATA'.

Next up were the Farina saloons, MGA and MGB, whose part numbers seem to start with 'ATB'.

A part number starting 'ATC' would tend to suggest that it was for the larger diff, as fitted to Big Healeys, the larger Wolseley saloons and J vans.

I'm not sure which diff the Austin Gypsy used, but I'm guessing it wasn't the small one.
Dave O'Neill 2

Thanks to all those who helped me to identify the CWP and to Bob and Dave in particular. The CWP is indeed from a "C" type car - Healey, Westminster, Gypsy etc. I have just physically matched it up to my mates hillclimb Healey. Now all I have to do is find a Gypsy owner or a sprint/hillclimber with an overdrive Healey box - they should be delighted to find such a rarity.
Aren't forums wonderful
Geoff
GM McGladdery

could offer it to Bill Rawles
http://www.rawlesclassiccars.co.uk/
David Smith

You could advertise it the Austin Healey club's mag 'Rev Counter'?? or flea bay of course!

Bob
Bob Beaumont

Bob Beaumont-
Would you please Email me at Bigface66163319@yahoo.com ? I have a question that your parts book might answer. I've been trying literally for years to find an answer, and you might just be the only person who can help!
Stephen Strange

Stephen

Don''t be shy - what's the question?

This forum thrives on seeking obscure answers to unusual questions and satisfying our curiousity about these old cars, how they were designed, manufactured, maintained, reappeared and modified, and the people who did and still do these things.

I enjoy learning more about all this stuff.

Cheers
Mike
M Wood

Mike- the possibilities get rather involved. These are questions concerning part numbers for 5.125:1 and 3.545:1 crownwheel and pinion gearsets and the differential cages that they mount to. If Bob Beaumont has a parts list for Hardy-Spicer differentials, then he may be my only hope after over ten years of fruitless searching.
Stephen Strange

Stephen

Why not try asking Austin A30 suppliers and web forums for the 5.125 part numbers, and an Austin A30 factory mechanical parts manual?

As for 3.545 - is that a Big Healey ratio?

Info:

http://www.mg-tabc.org/library/diff.htm

http://www.historic-cars.net/historic-cars-net/eshop/28-1-AUSTIN-HEALEY/780-4-Differential-BN1-221536-BJ8

http://forum.austina30a35ownersclub.co.uk/

http://www.austina30a35parts.com/shopcatall.php?cat=6-Rear%20Axle---Propshaft


Also transmission specialist such as Hardy Engineering and Midget raceparts supplier Peter May Engineering?

Best wishes
Mike




M Wood

Mike-
I've spent over ten years trying that method of research- No Luck Yet!

Yes, 3.545 is a Big Healey/Austin Westminster ratio.

My problem is that in some cases Hardy-Spicer made the same ratio crownwheel & pinion for different size rear axles. For example, both the Spridget and the MGA/MGB rear axles were made in a 3.909:1 ratio, but used different crownwheel & pinion parts which, naturally had different part numbers in order to distinguish them from each other. They are not interchangeable.

Perhaps the simplest way to put my question is: Did Hardy-Spicer ever produce 5.125:1 or 3.545:1 crownwheel & pinion gearsets that would install onto the differential carrier of the Hardy-Spicer differential that was used in the MGA/MGB? If so, what were the BMC part numbers?
Stephen Strange

I have just stripped my diff, and it is marked 10/39, does this mean its a 3:9 ratio?.

Dave
Dave Barrow

Yup. Divide the number of crown wheel teeth by the number of pinion gear teeth. 3.9.

Here's a link to a useful pdf file for you.

http://tinyurl.com/pz27j4r

The file is called V2I757070.pdf in case the link doesn't work. Just google it.

Lawrence Slater

Steve

The Spridget diff was exactly 3.9:1 as it had 10 pinion teeth and 39 crown-wheel teeth.

The MGB was 3.909:1 as it was 11/43.

Similar, but not the same.
Dave O'Neill 2

Here's some info from the Special Tuning section of the MGB parts book. It covers banjo and Salisbury axles.

Dave O'Neill 2

...and this is from the section on the banjo axle.

Surprisingly, they don't mention the 4.1 ratio, which was available for the MGA.

Dave O'Neill 2

Stephen

No part numbers, but if you look at the table in
http://www.wolseleyforum.com/index.php?showtopic=10289 it looks like the 5.125 ratio in the medium width banjo axle (same width as MGA) was in a Morris J2 van and Austin 10 cwt and 15 cwt vans.

But no 3.545 in medium width axle.

Finding a Morris J2 van with the correct axle would be a challenge.

Best wishes
Mike

M Wood

I was going to suggest the Cambridge & Oxford Owners Club, as the half-ton van may have had a short ratio.

http://www.co-oc.org/vehicles/half-ton-van-pickup

I think the J2 van used the 'C' type diff.

Dave O'Neill 2

Dave-
thanks for the info. Very Useful!

Mike-
Thank you for the link to the table. It seems to confirm that the 5.125:1 ratio was available in the Hardy-Spicer Medium axle. It also seems to imply that the 3.545:1 was not available in the medium axle. Now all that I need is the BMC Part Number for the 5.125:1 ratio!
Stephen Strange

Stephen

More info on medium axles in
http://www.fastmarinamagazine.com/index.php?option=com_jfusion&Itemid=12&lang=en&jfile=viewtopic.php&f=1&t=2740

Still no part numbers for Morris J2 van or Austin A55 van diffs.

Thanks
Mike

M Wood

I can confirm that the 5.125 CWP was available for the BMC banjo axle for MGB / MGA and others, as I had a brand new one a few years ago. I sold it to Colin Parkinson.

It had a strange thread on the pinion for the drive flange, as I had to recover this later and send to him separately.

I have no idea what the original vehicle was.

dominic clancy

Hi Geoff,
Is it possible the CW&P is from a TC? They had a 5.125 (8/41) ratio as standard. They were not "hypoid" type but "spiral Bevel" which means the centreline of the pinion ran at the same level as the centre line of the crownwheel. I have a vague memory of some J van part fitting a TC. A TC CW is a bit bigger than Spridget. An image of the CW&P might help identify it.
Bob Schapel
R L Schapel

This thread was discussed between 09/12/2014 and 17/12/2014

MG Midget and Sprite Technical index

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