Diff identifying

Post by **listerjones** » Thu Oct 08, 2009 2:56 am

Hi is there any serial numbers etc that identifies the moggy diffs as to what they are. We got two diffs with our purchase but don't know what they are. the engines were 948 and a 1098.

Any ideas or advice please cheers.

Post by **PSL184** » Thu Oct 08, 2009 8:11 am

The ratio's should be stamped on the case or diff carrier - Something like 9/41 - This will give you the ratio and hence which car they were fitted to. 1098's had a 4.22:1 diff and 948's had a 4.55:1

Post by **RobThomas** » Thu Oct 08, 2009 8:33 am

If you have the nose of the diff facing you, the stamped number is at 1/2 past 12 position, about 1 inch forwards of the flange that has the bolt holes. Large digits about 1/4 tall.

Alternatively, count the number of teeth and divide the big gear by the small gear. (ie: 9 teeth and 41 teeth)

Post by **mike.perry** » Thu Oct 08, 2009 9:12 am

The ratio should also be stamped on the crown wheel, at least it is on my diff (10/39)

Post by **listerjones** » Thu Oct 08, 2009 11:33 am

cheers for that, will look at them on week end. I've been reading that a 3.7 diff from a riley 1500 fits, would like to look at that in more detail.

Any difference between the original diffs besides the ratios

Post by **bmcecosse** » Thu Oct 08, 2009 12:02 pm

Later ones are stronger - and don't have filler plugs! Tricky if the axle casing doesn't have a filler plug either!

Post by **listerjones** » Thu Oct 08, 2009 3:41 pm

No filler plug?

Post by **mike.perry** » Thu Oct 08, 2009 3:57 pm

Some diffs have the filler plug on the diff, some have it on the axle casing behind the diff. If you have the wrong combination of diffs and axle cases you either have two filler plugs or none at all.
I expect some expert on diffs will be able to tell you where all the filler plugs are.

Post by **PSL184** » Thu Oct 08, 2009 3:57 pm

listerjones wrote:No filler plug?

4.55:1 diffs had a filler plug. Later 4.22:1 diffs do not because it is on the axle casing.

Post by **mike.perry** » Thu Oct 08, 2009 3:59 pm

Out of interest how about 5.375, 3.9 and 3.7?

Post by **PSL184** » Thu Oct 08, 2009 4:17 pm

mike.perry wrote:Out of interest how about 5.375 3.9 and 3.7?

5.3 on diff. 3.9 & 3.7 on axle casing.....

Post by **listerjones** » Thu Oct 08, 2009 4:28 pm

Right got it, thanks everyone. any one got a 3.7 for sale by any chance....

Post by **PSL184** » Thu Oct 08, 2009 6:20 pm

listerjones wrote:any one got a 3.7 for sale by any chance....

Noooooo

But keep an eye on ebay - they do come up fairly often

3.9's are cheaper and just as acceptable IMHO.....

Post by **bmcecosse** » Thu Oct 08, 2009 10:47 pm

Not sure if there is an 'exact' Mini speedo to suit the 3.9 diff. It would need to be ~ 1345 tpm.

Post by **MColes** » Thu Oct 08, 2009 10:59 pm

mike.perry wrote:Some diffs have the filler plug on the diff, some have it on the axle casing behind the diff. If you have the wrong combination of diffs and axle cases you either have two filler plugs or none at all.

I have the problem of no filler plug

Post by **mike.perry** » Thu Oct 08, 2009 11:22 pm

Shouldn't you have the Morris axle in the early Series II? Or have you had an engine transpant?

Post by **PSL184** » Fri Oct 09, 2009 11:29 am

bmcecosse wrote:Not sure if there is an 'exact' Mini speedo to suit the 3.9 diff. It would need to be ~ 1345 tpm.

I think mine is 1350 but I'd have to check that....

Post by **mike.perry** » Fri Oct 09, 2009 12:47 pm

I haven't done enough research on Mini speedos yet. Only got the 1248 and 1376. There were a lot of different ratio diffs on the Coopers etc.
There are 3.444, 3.647, 3.765, 3.938, 4.133, 4.267 & 4.35 to choose from, all with different speedo TPM

Post by **bmcecosse** » Fri Oct 09, 2009 4:08 pm

The ratios beginning with '4' (and the 3.9) were never fitted to Minis as standard - these are competition ratios only. There is also a 3.1 and a 2.9 - fitted to late model cars - but not with centre 'Minor' type speedos.

Post by **mike.perry** » Fri Oct 09, 2009 4:15 pm

That reduces the options then.