ID on MOWOG diff - ATB

[dudford]

Pulled the diff on my pickup this afternoon and decided to look up the part numbers. I've hunted around and found a table posted previously on here but my diff doesn't appear to match any listed there or elsewhere... bit of a head scratcher. Any chance any knowledgable person could take a look at the below and tell me what I've got sitting in the shed?

[les]

Divide the 39 by the 8 will give you the ratio.

[philthehill]

39 divided by 8 = 4.875

Originally fitted to A35 Van.

The number ATB7057 is the part number.

The list(s) you have viewed does not state the part number of the crown wheel only the part number of the carrier and the crown wheel carrier.

[dudford]

Thats great thank you! That's a fairly high ratio, just trying to get my head around all this diff/ratio business. So with that hooked up to a 1600 lump I imagine it will be good for top end speed but not necessarily racey out the blocks?

[philthehill]

Think of the ratios the other way round - the bigger the number i.e. 4.875 the lower the ratio.

4.875 to 1 is a low ratio. So will be quick off the blocks but you will quickly run out of engine revs at about 70mph

3.7 to 1 is a high ratio. Will give a good cruising speed with low engine revs.

5.3 to 1 is a very low ratio - fitted to GPO van.

To get the best out of the 1600cc you need a diff of at least 3.9 to 1.

Phil

[dudford]

I really appreciate the help on this. It's clear i need a 3.9 or 3.7 then, I shall trawl eBay and hope for a deal as they don't seem cheap. In the meantime would this diff I have be beneficial to anyone?

[oliver90owner]

Dudders,

It is unfortunate that if you look back in the archives (doing a 'search') you may well come across some posts where one person in particular always insisted on the opposite to the convention of the whole of the motor industry from about a hundred years ago.

Think here of the car gearbox. Which is regarded as the higher ratio? Bottom (low) or top (high) gear? Think of the good old Landrover with high and low ratio gear boxes, where the low ratio gearbox always selected 4 wheel drive at the same time. So think faster output speed for the same input speed is the convention for automobile differentials. The fewer input turns of the propshaft for each turn of the wheels will mean potentially higher top speed (I say 'potentially' because if the ratio chosen is too high, the engine may not develop sufficient torque to drive the vehicle satisfactorily).

RAB

[dudford]

Have been shopping around for this elusive, and apparently expensive 3.7/3.9 diff, in the process I've been learning a few bits and pieces along the way. Was it normal for the a35 van to have 25 spline spider gears as mine evidently has?

A large proportion of the diffs I have looked at are 10 spline spider gears, did any mowog diffs come in 3.7 or 3.9 with 25 spline spider gears to accommodate my half shafts (the more splines being preferable) or would I be looking at blowing my diff apart to make one usable diff?

[philthehill]

The A35 normally has 10 spline (coarse) spiders and half-shafts. If you have fine splines the diff has been changed/uprated.
See the attached link for details of differentials especially the fine spline diff / halfshafts.
http://www.mgparts.co.nz/advice/technic ... ear-axles/

Here is a link to the MG Midget rear axle which shared some parts with the A35.
http://www.moss-europe.co.uk/shop-by-mo ... 500cc.html

[dudford]

The A35 normally has 10 spline (coarse) spiders and half-shafts. If you have fine splines the diff has been changed/uprated.
See the attached link for details of differentials especially the fine spline diff / halfshafts.
http://www.mgparts.co.nz/advice/technic ... ear-axles/

Here is a link to the MG Midget rear axle which shared some parts with the A35.
http://www.moss-europe.co.uk/shop-by-mo ... 500cc.html

Thanks for these links Phil. After reading the New Zealand MG link I'm of the opinion that's my half shaft have also been part wasted:



Either that or they are part wasted as standard? Happy to keep the 25 spline element, definitely the better option.

[philthehill]

See also the link below regarding upgraded halfshafts:-

http://www.frontlinedevelopments.com/pa ... alf-shaft/