Diff Ratios

[dawpooldad]

Hi fellow Morristers,

I have a 1954 Series II with the original 803cc engine which is in good nick and currently running like a Swiss watch, having been completely overhauled about 5000 miles ago. The gearbox is the original unit and so far, working OK. Total mileage mileage of the car is 67,000 miles.

Recently, the diff started making a rumbling noise and after draining the oil and filtering it I found some ominous brass bits. Then after removing the diff, I found that the brass cage on the left side bearing had started to break up. My original intention was to simply replace all the bearings, but now I'm in a dilemna as I now have the opportunity to improve the cruising speed by fitting a 4.55:1 (9/41) diff.

Has anyone done this and if so, is the 4.55 diff a straight swap, will the original half shafts fit and are there any other factors involved in doing this.

I realise that there will be issues with the speedo, but will eventually deal with that in time.

Any info would be gratefully received.

Best rgds
Dawpooldad

[philthehill]

Swopping the diff ratio depends upon what axle is fitted.
The early axle has the split casing and the later 2nd type the banjo axle casing.
The diffs cannot be swopped between the two.
A photo of the axle diff casing would be appreciated.

[dawpooldad]

Hi,
It's got the later banjo type casing, not the earlier split axle.
Rgds
Dawpooldad

[philthehill]

If that is the case the 4.5 diff ratio will fit without any trouble and the half-shafts can be reused.
Do you know what diff is already fitted?
Look on the top half of the diff casing and there should be some number stamped there for example: 9/41.
There may already be a 4.5 diff ratio fitted and fitting a replacement 4.5 diff you will not have gained anything other than perhaps a more reliable diff.

[dawpooldad]

Hi Phil,
Thanks for the prompt replies.
The actual ratio is 8/43 which equates to 5.375:1.
So, 4.55 should make a good difference!
Thanks again
Mike R

[philthehill]

For a few days I tried a 5.3 in the rear axle of my 948cc Minor - it would go most places in top so I can confirm from experience that you will have a much better and under stressed ride/drive with the 4.55.
I personally do not think the higher ratio will be detrimental to the running of the 803cc but you may find that you have to change down a gear slightly earlier but overall a great improvement.

[liammonty]

I'd be inclined to disagree with Phil on this one - the 803 is so lacking in torque that I think hills would become very frustrating with a 4.55:1. The series MM coped with it but has a much more robust engine. I added a 4.55:1 diff to my SII when I changed the engine to a 948 and that was super though. I think the massive gap between 3rd and 4th gear will be even more irritating with a higher final drive. But you could always give it a go - it wouldn't be hard to change again the the future if it didn't work out!

[pde2000]

I ran my sII with a 4.22 diff for a few years, and with the engine working in top condition it was fine, but a 4.55 would have been better. The diff was a straight swap. I have put the 5.375 back in, with it's worn teeth which whine, but my main bearings have worn out completely and are waiting to be replaced. However the brief time that the engine was performing well with the lower gearing it seemed much nippier, and made me realise the engine had been struggling with the 4.22.

I wouldn't fancy repairing a diff myself, but a reconditioned one can be bought.

[dawpooldad]

Thanks guys for all the info,

I think that I'll go for it, as the car could do with a little more top speed.

I've always been worried that on the Motorways and Dual carriageways, we can only cruise at about 45 mph, sometimes 50 mph. It gets a bit scary when people zoom up your backside and then pull out at the last minute, not realising that we can't really go any faster.

It's the lorries that are the worst, followed by teenage ladies!!!!

I've had some worrying sights in my rear view mirror on the way to rallies and such.

Anyhoo, thanks again for the info.

Now I'll have to post in the wanted section

Best Rgds

Dawpooldad

[ampwhu]

I am replacing a diff on mine at the moment and have a 4.5 diff in excellent order no longer required.