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MG MGA - How many different A diff ratio's were there?

I have 6 different diff from an ole 60's race car and a MGA axle was used how many different diffs are there and i think one of mine has a Zed F with 11/41 gear set in it....are they rare?
Tony Giordano
Tony Giordano

I believe there were 3 diferent gears 4.3,4.1 and possibility 3.9 which is very common in the MGB. Come to think of it, it may be only 2 different ones.
JEFF BECKER

Hi,

I believe there was also a 4.55:1 diff for sprints

regards,

Grant
G Hudson

Just a quick question on Diffs. How do you determine the ratio? Is it stamped somewhere or ??
Thanks,
Jim Sutorus

Jim, I believe that the housing had a tag attached to one of the retaining studs which had the ratio stamped as two numbers such as 11/41. Most of these have been lost over the years though. The numbers may also be obtained by physically counting the teeth with the center section removed. This of course refers to the number of teeth on the pinion and the number of teeth on the ring or crown gear. Simply divide the smaller number into the larger to get the ratio. The 11/41 would work out to a 3.7. As for Tony's find, yes I beleive that a 3.7 for the banjo axle is indeed a rare find. A common ratio for late model 1500 midgets, but not offered in the A or B as far as I know.
Bill Young

Yes you can see the ratio stamped into the metal on the pumpkin. It is located on an area about 3/4 inch by 3/4 inch. If you remove the battery cover and look down at the pumpkin, there is a flat surface to the left of center. (This is on the passenger side). You will probably need to clean off the dirt and oil. If I recall correctly for a 4.3 ratio, it would be 4/3.
All bets are off though,if the internal ring and pinion have been changed.

Ray
Ray Ammeter

3.7 was the salsbury ratio for MGC's
I've never seen one for MGA/B's though.

I've used 4.8 for racing before now too.
I have all the ratio's except 4.55 and possibly 3.7

As far as I know 4.55 is the hardest to find.

I'd be interested in a 3.7 if someone can turn one up... great for driving across Australia.

Barney has a great table, but no mention of 3.7

http://www.mgaguru.com/mgtech/rearaxle/ra201.htm

Cheers <MARK>
Mark Hester

This page seems to indicate that 3.7 is available in Banjo...

http://www.mg-club.org/mgcc/sf/sf100104.htm

Moss UK list BTA535, for £171 but I'm not sure if that's for A series Banjo or B Series !!!

http://www.moss-europe.co.uk/MossUK/ProductList.aspx?SubSubCategoryID=SPML_SPMLS015A1

Anyone seen a part number for the 3.7 C/W & Pinion?
Mark Hester

Mark,

there;s 4.55 on ebay.co.uk (about a day or 2 left on bidding), and it's from a guy in North London. Was thinking of bidding, but I've got no need for it - good luck,

Grant :-)
G Hudson

I have just updated my web page to show some additional sources (original uses) of gears which will fit the banjo type axle in the MGA. http://mgaguru.com/mgtech/rearaxle/ra201.htm

In the article http://www.mg-club.org/mgcc/sf/sf100104.htm
I believe this line
"MGA 1600 Mk2 and mgb roadster to '65, as 3.9 and 3.7 to 1."
is incorrect. The MGA 1600 Mk2 standard ratio is 4.1, adn MGB standard ratio is 3.9.

The 3.7 ratio was used in the later Salsbury (tube type) axle for MGC and maybe one year with the MGB automatic gearbox, but will not fit the bango type axle. There was also a 3.7 gear available for the smaller banjo type axle in the late MG Midget (and some other cars), but this also will not fit the MGA banjo axle. As far as I know, there was no 3.7 gear set manufactured which would fit the mid size banjo axle used in the MGA.
Barney Gaylord


Good stuff Barney.
Could you add a column on your table though for the actual pinion and CW teeth. i.e 3.909 = 11/43

One question though.
I know you can mix and match Crown Wheels and Pinions although this is not advisable unless they are new or freshly reground.

The 3.7 ratio from Midget or MGC (Salisbury) is it 41/11 ?

Could you take a MGB/MGA 3.9 pinion (11 teeth) and match that with a 3.7 crown wheel (41 Teeth) MGC say

Just wondering if the Crown wheels are interchangeable from Banjo to Salisbury (Most likely not midget though as it's smaller from memory)

Do you see where I'm coming from ???

Found this like, but not sure if it's 100% correct.
http://www.difflap.com.au/ratios/j-m.htm

<MARK>
Still determined to cross Australia on one tank of fuel.. My mate did it, but he had a trailer with two huge gas bottles in it though...
Mark Hester

Mark, I don't believe that mixing gears as you propose is possible. I once spent some time working in the rear axle plant at Buick and if I remember correctly the complexity of how they figured out the angles to cut the gears for the hypoid type axle was mind boggling. Ever so small a change in any dimension of the pinion to the ring gear or their number of teeth resulted in a complete recalculation and setup of the the cutting machines and tools. If you could find a rear axle which had exactly the same dimensions as the
A carrier as far as axle center to pinion center and ring gear diameter then it might be possible to use that gear set if it could be properly mounted with the correct bearings and shims. You might consider the possibility of mounting a later MGB tube type axle. I've been investigating the possiblity of having the axle tubes removed from the cast center section and substituting the cast section from a GM 10 bolt to get the wide range of ratios available for that axle. It would also enable me to keep my wire wheels without resorting to axle adaptors.
Bill Young

The crown wheels for the banjo and tube type rears are not interchangable.
John H

Bill, John,

Didn't think it was possible.

I'd like to stick with Banjo as it's easy to change the centres and they are much lighter for racing.
Plus I can't be bothered fitting a 5 speed when just changing the diff will give you the same result, but with one less syncro ring to wear out.

If they remanufacture new Crown wheels and Pinions for £200 ish, would it be possible to have a new 3.7 41/11 made ?

Looks like the 3.7 Banjo debate is raging on the MGB Technical area... So it is possible...

http://www2.mgcars.org.uk/cgi-bin/gen5?runprog=mgbbs&access=&mode=thread&subject=71&thread=2006011711454425094

Cheers <MARK>
Mark Hester



3.7 Banjo Ratio is available from here for

£175 Plus VAT.

http://www.autogear.co.uk/product/detail.php?id=684

Cheaper that a 5 speed conversion.

Cheers <MARK>
Mark Hester

Hey, score one for Autogear. I have just added 3.727 to the list. I also added the column for rnumber of gear teeth.
http://mgaguru.com/mgtech/rearaxle/ra201.htm

To answer Mark's queation, no, you cannot mate an 11 tooth pinion to a 41 toot ring gear which was originally machined as part of a 41/10 gear set. It won't mesh. Different combimations of number of teeth all require different tooth shape.
Barney Gaylord

This thread was discussed between 17/01/2006 and 19/01/2006

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