Morris Minor Owners Club

Fitted the 3.7 diff today, cannot get over the difference, it's like driving a completly different motor. 2nd is now like 4th was and can drive along at 65 (I think) with the engine puring rather than screaming. As a bonus my very violent clutch is now cured, before removing the 4.5 diff pulling off in 1st was scary stuff as the clutch felt like it was going to bite your leg off. I now do not have a filler/level plug, no problem with getting the oil in though as it went in easily through the breather, no more top ups for me as will need to empty and re-fill with the correct quantity (0.994 litres). The only other thing to try and sort now is the speedo, speed check is saying 30 when my clock says 25. Any advice on what speedo to look out for, car now has midget 1275 engine and box with 3.7 dif and 13 inch wheels.

1248 tpm is the one to go for -from a Mini.

what tyres size have you got as they will make a difference as well I believe..

Tyres are 185/70.

Took the car to work for the first time today, I live in a fairly flat part of south wales, work is 20 miles away up the valleys where it is definately not flat. Ratio is great in my area and for fast roads, if i lived in an area with lots of hills it would have to be a 3.9 diff I think as a bit of a struggle on some of the steep ones. Saying that its pretty quick comming back down again.

Your tyres have pretty much same rolling radius - so 1248 tpm will be fine. Mine is deadly accurate on speed and miles with 155X14 tyres. Your's won't be far away if you get that speedo.

bmcecosse wrote:Your tyres have pretty much same rolling radius - so 1248 tpm will be fine. Mine is deadly accurate on speed and miles with 155X14 tyres. Your's won't be far away if you get that speedo.

http://www.alloywheels.com/tyrecalc.asp begs to differ.
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That's near enough - you won't get a more accurate speedo......

I think Welshrat is using 185/70 13, rather than 175/70 13 as you have on the calculator, which gives a slightly closer match:

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Useful calculator!!

ah my mistake. worrying how short my memory is from one website to another.

serves me right for being half asleep!

glad someone's on the ball!

silloyd wrote:I think Welshrat is using 185/70 13, rather than 175/70 13 as you have on the calculator, which gives a slightly closer match:

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Useful calculator!!

It is 185/70 13, and the match is pretty good, however this calculation only considers wheel/tyre changes (I think), what about the change of diff. I ask because speedo is 24/25 when speed check is flashing 30/31. Also does this mean that my mileometer is now recording less miles than I actually travel?

welshrat wrote:It is 185/70 13, and the match is pretty good, however this calculation only considers wheel/tyre changes (I think), what about the change of diff. I ask because speedo is 24/25 when speed check is flashing 30/31. Also does this mean that my mileometer is now recording less miles than I actually travel?

it takes into account the change of diff, based on bmc saying that with that speedo, and the tyres 155/80 R14 tyres his speedo is 'spot on'.

so if you've got the same setup as bmc, same box and diff, and if you had the same speedo, the only difference would be the tyres. hence the calculator.

the mileage will be the same percentage innaccuracy as the speed. so if you're reading 25 when actually doing 30. your mileometer will say you've done 25 miles when you've actually done 30.

The price is right at the moment.... http://www.ebay.co.uk/itm/SMITHS-SPEEDO ... 3f0b6d9b48

Already watching that one and driving another 5 or 6 sellers mad who have not included the TPM no. on their listing. Thank you all for the valuable information, the majority of my questions are about trying to gain a better understanding rather than challenging the response.

Hello,
Just bought a '65 1098 Traveller which seems quite standard apart from a servo. Rear axle is whining, probably due to a previously long standing leakage. Not ready to uprate to 1275 or 5 speed box yet but finding it currently feels under geared with its standard 4.2 diff. I am no racer and prefer better economy and the chance to keep up with the wagons if I occasionally resort to motorways, i.e. to do 60 mph without ear plugs.
Question is, if I've got to change the diff, do I go for a 3.9? I imagine 7 or 8% isn't going to kill the acceleration?
Thanks in advance,
John

I've fitted a 3.9 and I'm very happy with it.
The most noticeable thing around town is that it makes 1st gear one that you use rather than get out of ASAP.
There is a slight performance hit when going up hills, a bit of light tuning should sort that out if it's a problem.

It will affect the acceleration - by that 7 to 8% - just as it will reduce the revs (and the hill climbing ability) by that same 7%... It won't make any worthwhile improvement to fuel economy. Up to you if you can find a 3.9 final drive for a 'good' price. As above - it's easy enough to squeeze a bit more power out of a 1098 if you find it flagging with the lower ratio fitted.

Many thanks. I know you will disapprove, BMC, but I have just bought a used Sierra box and kit and will replace the noisy diff with another 4.22. That should just give me the 'overdrive' option for quieter cruising at 50+. After a variety of classics over the years I am conscious of 'getting under the feet' of HGV's.
Regards
John

Hahahahaha - I do approve! I just don't think it is value for money. But please let us know how you get on fitting the box (pictures please!) - and then how it performs in service.

Will do, but it may take a while. I intend keeping my Traveller for some time and have just started work: one step forward and two steps back! Swapped to negative earth and fuel pump stopped. I had no idea that there were such things as positive earth electronic SU pumps - things have moved on since the 60's. I have a lot to catch up on, but looking forward to it.
Thanks again,
John Naylor

Oh dear - the electronic pumps don't have a great reputation....... You should also clean and regap the points in the dizzy.