Changed my diff!

Post by **bmcecosse** » Sun Nov 02, 2008 10:47 pm

As some of my loyal readers may know - after some considerable difficulty I recently purchased a 3.7 diff. Since today was nice and sunny - I set too to fit it into my Traveller. On blockinng up the car I noticed (for the first time in 8 years!) that I had two filling plugs - one in the diff casing, and one in the axle casing. How odd! And indeed - when I removed the diff it was as suspected a 4.55 ratio and not the expected 4.22 which a 1965 1098cc Traveller should have. So - this explains why the car has always been quite 'nippy' (even before engine mods took place) - but always poor on petrol consumption. So the 3.7 is now in place - a change of almost 20% in the ratios -so I guess my 3rd gear will now be equal to 4th gear with the old diff! Problem is going to be how to get a realistic mileage and speedo reading. The speedo in the car is 1508 tpm - and was reading almost perfectly correct mileage (1% high) on 155x14 tyres -but the speed was always a good 8% high. So - I guess I am looking for a speedo with tpm ~ 1235. Anyone know of such a speedo - probably from a Mini ??
Short test run (had to get cleared up in time for the GP!!) proved the new diff to be working well - and it appears the 1098 engine with 940 head etc will pull it just fine !

Post by **PSL184** » Sun Nov 02, 2008 10:59 pm

Good result then Roy! Can't help with the speedo (I'll sit and work it all out one day, I'm sure) but glad to know that the 3.7 pulls OK. My 3.9 never did come to anything but I have a promise on a 3.7 so I will probably be going the same way....

Post by **bmcecosse** » Sun Nov 02, 2008 11:02 pm

Heh - if I had known it was a 4.55 in there, I would have fitted the 4.22 spare I have in stock, and probably never bothered with the 3.7 in the first place ! One good thing - I inspected the half-shaft splines and they look ok with no 'twisting' or obvious wear on the splines - or, is that just tempting fate !!!!!

Post by **PSL184** » Sun Nov 02, 2008 11:16 pm

bmcecosse wrote:or, is that just tempting fate !!!!!

Yep

Post by **bmcecosse** » Sun Nov 02, 2008 11:22 pm

I can see I had better add a spare half-shaft to my on-board spares collection!

Post by **PSL184** » Sun Nov 02, 2008 11:23 pm

In which case that will guarantee that you will NEVER need it

Post by **bmcecosse** » Sun Nov 02, 2008 11:28 pm

Exactly - that's why I carry lots of spares!

Post by **mike.perry** » Mon Nov 03, 2008 12:09 am

Don't over do the spares or you will need to lower the axle ratio again to carry the extra weight!!!

Post by **bmcecosse** » Mon Nov 03, 2008 12:20 am

That's the snag!

Post by **moggyminor16** » Mon Nov 03, 2008 10:12 pm

not sounding silly but what type of diff can i put in for better speed ie not reving teh engine to much im running a 1275 1098 box stanard diff

Post by **rayofleamington** » Mon Nov 03, 2008 10:32 pm

not sounding silly but what type of diff can i put in for better speed ie not reving teh engine to much im running a 1275 1098 box stanard diff

A 3.9:1 would be the most common choice but very hard to find without paying through the nose. However a 3.7:1 would be fine (maybe better) for motorways etc...
If you're on big hills everyday, the high diff (low number) will get tiresome! My pickup with tired 1098 and 3.7 diff was fine everywhere apart fom hills where the gears were too high and too far apart so you'd end up in a very low gear going nowhere fast.

Post by **Kevin** » Mon Nov 03, 2008 11:39 pm

On blockinng up the car I noticed (for the first time in 8 years!) that I had two filling plugs - one in the diff casing, and one in the axle casing.

Hmm dont change the diff oil too often then.

Post by **downsey** » Tue Nov 04, 2008 3:01 am

You can fit a 3.90 mgb rear end extremely cheap.

Post by **rayofleamington** » Tue Nov 04, 2008 2:02 pm

You can fit a 3.90 mgb rear end extremely cheap.

IIRC it has 4.5" PCD so you can't fit Minor wheels and may end up with non matching front and rear, needing 2 spares etc...

Post by **downsey** » Tue Nov 04, 2008 4:00 pm

yeah they do 4.5 inch pattern, but the early morris' had the same pattern. I think you would have a hard time telling the difference between early morris and late morris wheels, especially with the hub caps on

Post by **bmcecosse** » Tue Nov 04, 2008 8:11 pm

Yes - but finding early Minor wheels is not easy!
As for the diff oil - I have changed it in the past, just not noticed (or if I did notice - didn't appreciate the significance!) there were two filling plugs! The oil that came out (just over a litre) seemed not too bad - but I decided to traet thye new diff with new EP90, and keep the old oil as 'lighting up' fuel for Morayshire!