Diff advice please

[welshrat]

Hi all,
I realise that the diff subject has been discussed many times but I am srtuggling to get my head around it all.
Currently driving a 61 minor with original diff, midget 1275 engine and box and 185 x 13 wheels, the problem I have is that it appears to be very low geared, 1st is pull off only (2nd feels more like 1st), soon as get moving need to go to 2nd then 3rd. 4th is great for travelling beteen 25-60 but faster than this seems to be pushing it (hope that makes sense). Thinking that I should be looking at a diff change, what would you recommend, have a spare in the shed but not sure what the markings mean. The markings look like 9 41 and 7a/091c.
The other question is can I use my halfshafts or do these need to be changed aswell.
Would welcome any advice.
Thanx.
John

[chrisryder]

fit whatever diff you like, your halfshafts will fit, but may not lost depending on how you drive it!

what engine was in there before? its a 61 minor so it would have had a 948 engine originally, and that comes with a 4.5 diff. it sounds like you may still have that diff in there. a 3.9 diff was original fitment in a midget, so that, or a 3.7 would be a good place to look.

you can determine what ratio diff you have (if it's out of the axle casing) by finding the markings on the outside edge of the large 'crown wheel' gear in the diff. you should see a fraction, 9/38 for a 4.22 dif. 10/39 for a 3.9 etc. if it's something else, take the second number and divide by the first number and it gives you your ratio. some diff casings have that ratio stamped on the outside too, so you can see it if its still in an axle casing, but they're not always there, and if they are, covered in paint or underseal or roadmuck.

[bmcecosse]

So your spare is a 41/9 = 4.55. Not much good. Look for a 3.7 or at a pinch, 3.9

[welshrat]

Thank you, if the ratio is stamped on the outer casing, is there a particular place to look for it or was it a random place. I ask because I have another complete rear axle and would rather not dismantle it. Have checked on the prices of a 3.7 or 3.9 diff, they are a tad expensive, guessing because they are now becomming rather rare.

[welshrat]

Hi, found where the ratio is stamped on outer casing, not actually stamped but raised as part of the moulding process. On the top, on one side of the ridge you will find mowog, the ratio number is on the opposite side. See pic, this was not the diff I was looking for either, another 4.5.[frame][/frame]

[faversham999]

This diff is on Ebay dont know if its any good but its a 3.7
http://cgi.ebay.co.uk/MG-MIDGET-DIFF-70 ... 45fa619a68

[bmcecosse]

Bet it's got about 100 'watchers' now!

[MarkyB]

[welshrat]

Found a good 4.2 diff, do you think it's worth the effort, current one is 4.5.

[bmcecosse]

Not really..... but better than the 4.55 I suppose. Each time you swap the diff - you also need a different speedo.......... Your 13" wheels aren't helping either.......

[daveyl]

I did that same conversion. Didn't make a huge difference. You may find that if you do fit the 4.2 diff, you will be missing an 'oil filler' plug (axles slightly different). I ended up using the 'breather outlet' to top up with oil.
Sorry to say but it may be a case of saving your pennies and buying a '3.7' diff.
Eventually, you may get lucky and get a good second hand one.
In the end I bought a new crown wheel and pinnion, bearings (at huge cost) and fitted that according to the manual. Strangely it didn't come with 'shims' for packing the pinnion shaft. I had to use second hand ones
I think I got lucky, as it worked fine. Not for the faint hearted though. In hindsight, should have waited for a 2nd hand one!
An easy job to fit a whole (2nd hand) unit over. If you do a lot of motorway driving, then it will be worth it.

[welshrat]

Is there a reason for changing your axle, I thought all of the diff's were the same and would drop straight in. Just put a 4.55 into the axle that I have taken the 4.2 from, again have I missed something regarding the swap of diffs.

[daveyl]

From what I remember, the oil filler plug on the 4.5 axle is actually on the diff housing. Whereas the 4.2 axle has it's filler plug on the axle casing. Hence, if you fit a 4.2 diff to a 4.5 axle, you will be missing an oil filler plug.
If you get underneath the car, you can see one way or another.

[bmcecosse]

The oil filler is the only significant difference. I ended up with two - with my 3.7 final drive.

[welshrat]

Just watched a 3.7 diff sell for £262 on ebay, world gone mad!!!
http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... K:MEWAX:IT

[bmcecosse]

I was watching that one too - well worth the money I think........ Just about doubles the value of my Traveller!

[welshrat]

RESULT - took a while but managed to pick up a good 3.7 diff off ebay for £50. Would like to give it a good clean out and remove old oil before fitting, any advice on what product to use.

[bmcecosse]

Paraffin. £50 ?? You sure it is an A series diff????

[welshrat]

Hi BMC,
Thank you for that, yes sure its the right diff. Will send you a PM.

[bmcecosse]

Well done - sounds like a bargain!