Diff ratios / high revving

[Davey]

Hiya, hope you're all well

So, I've got my little 1954 2 door saloon (the cheesegrater style one). It's got a 948cc instead of it's original 803cc.

I've noticed that the speedo is wildly out - I reckon from comparing to satnav that it reads about 45 on speedo at 30mph on satnav, 60 at 40mph etc. Also, 1st gear isn't necessary even on a hill, and the car revs higher than I expect - I'm not really comfortable pushing her beyond about 40mph.

I thought I might have the wrong diff in there, which might explain both problems. Wondered if I might have something from a car with a smaller wheel or similar. Got underneath tonight and cleaned off the top face of the diff casing but couldn't find either a mowog stamp or numbers. It's a 1 piece axle tube so that looks right, and there's a filler on the diff casing itself.

To try and ascertain what diff I have, I put some tape on the prop shaft, marked the wheel, and pushed the car for one wheel rotation, counting prop shaft turns. Came out at about 5.3 turns to one full wheel rotation.

I believe my car should be 5.28:1, so it looks like I've got the right diff.

Can't be wrong gearbox (it looks right - smooth casing, not remote), and anyways, top gear is 1:1 on all.

Wheels and tyres seem right - 14" tyres.

So I'm thinking the only answer is incorrect / faulty speedo or drive, and my perception of how hard she should be revving. I guess with the slightly larger engine 1st gear would be redundant, and the engine is tired and noisy which might explain why it feels like I'm torturing the poor thing at anything over 35mph!

Before I accept that explanation, does anyone out there have any other ideas of anything that could be amiss?

Thanks very much,

davey.

[greendefender123]

Hello welcome to the forum. A 5.3 diff is very low geared. Iv got 948 cc engine and running gear as spares the diff for that is a 4.55. A 5.3 is right for a 803 cc engine. I would be looking for a 4.55 or even a 4.2 diff for yours. Sorry im not much help. I'm sure someone else will advise more.

Steven

[palacebear]

Hi Davey. Welcome to the world of Series 2 ownership. My Series 2 is a 1956 (facelifted) model. Like yours, mine has a 948 engine driving the original 803 gearbox and 5.3 axle with 14 inch wheels. The Series 2 is often acknowledged as being the least pleasing Minor to drive. The gearing is VERY low so 1st gear isn't often needed! Bear in mnd that the larger engine won't affect top speed so 65mph is pretty much flat out. The extra torque in the engine is sometimes blamed for shortening the life of the 803 gearbox. My 'box has done over 85000 miles (56000 with the 948 engine) and the bearings rattle like hell. Mine has the later centrally placed speedo. Its not very accurate (but I don't think many were!). 45mph on the dial is approx 38mph on a gps. Its possible your speedo is faulty or maybe the wrong drive gear at the gearbox end. Like several Series 2 owners I've spoken to, I'm not very comfortable doing much over 40 or 45mph unless its essential but the progress sounds painful at anything above 45. Depending on your budget and views on originality it may be an idea to get a 948 box and axle fitted (as I intend to do when money permits). For a little extra outlay you can convert the box to keep the Series 2 gearlever and avoid the need to chop the floor around

[liammonty]

If a 948 gearbox has been fitted and adapted to replace the original one, but not had its internal speedo drive gear on the third motion shaft replaced, it would overread as much as you describe. I thought that it could also be due to a series MM speedo being fitted in place of a he original, but thinking about it, I think it would actually lead to it underreading, so probably not the problem. I think the MM speedo is 1600 rpm, vs. 1000 for the SII. So, I suspect you've got a 948 box in there.

[myoldjalopy]

You can check if someone did fit an 'adapted' (i.e. 803 long gearstick retained) 948 gearbox by chocking the front wheels, rear on axle stands, handbrake off and in first gear. See how many revolutions of the starting handle it takes to get the propshaft to make one complete revolution. If it is a 948 box it will take about 3.6 turns of the handle. If it is an 803, it will take roughly 4 turns of the handle...........

[IslipMinor]

The SII speedo is calibrated for 1000tpm (turns per miles) - it should be in small figures on the face of the speedo.

The SII gearbox has a 4.5:1 speedo drive ratio and the 948 onwards has 2.6:1, so if a SII speedo is fitted it will overread by ~70%, or ~50mph for a true 30mph!

With a 948 engine you really need to have at least its original 4.55 diff ratio, or maybe even the 1098 4.22 ratio. That then leaves the speedo reading - the 'cheesegrater' cars had the oblong speedo I think? Not the later round one?

If it is the earlier speedo, there are no alternatives that will solve the problem, I don't believe? That means taking the rear of the gearbox off and swapping the SII speedo drive gear for the later one - at least the speedo will be a bit nearer right!

[liammonty]

The SII speedo is calibrated for 1000tpm (turns per miles) - it should be in small figures on the face of the speedo.

The SII gearbox has a 4.5:1 speedo drive ratio and the 948 onwards has 2.6:1, so if a SII speedo is fitted it will overread by ~70%, or ~50mph for a true 30mph!

With a 948 engine you really need to have at least its original 4.55 diff ratio, or maybe even the 1098 4.22 ratio. That then leaves the speedo reading - the 'cheesegrater' cars had the oblong speedo I think? Not the later round one?

If it is the earlier speedo, there are no alternatives that will solve the problem, I don't believe? That means taking the rear of the gearbox off and swapping the SII speedo drive gear for the later one - at least the speedo will be a bit nearer right!

So I think we are both saying the same thing then Richard - i.e. it's unlikely to be an issue with the speedo itself, as an MM speedo (which is also round, as is the early SII version, just smaller than the later centrally-mounted speedo from late '54 on – no oblong speedos were ever fitted) would lead to an under-reading speedo. Therefore, , in all likelihood, the car has been fitted with a 948 gearbox without having the 2.6:1 drive ratio changed to a 4.5:1 gear from the SII.

Davey – if that's the case, you'll need to strip the box as suggested by IslipMinor to resolve it .

[Declan_Burns]

...
If it is the earlier speedo, there are no alternatives that will solve the problem, I don't believe? That means taking the rear of the gearbox off and swapping the SII speedo drive gear for the later one - at least the speedo will be a bit nearer right!

Richard,
There is an alternative-fitting a corrector gearbox on the back of the speedo like the ones that I build.
Regards
Declan

[IslipMinor]

Always helps to check - I was thinking of the oblong instruments either side of the speedo and had extended that into the speedo head itself - wrong!

BUT, looking at the various images on Google for Morris Minor speedos, there looks to be an SII looking head with 1600 tpm - is that from the MM?

A 948 gearbox and 4.55 ratio axle needs a speedo with 1504 tpm, so 1600 should be about spot on, allowing for the original optimistic readings. Going to a 4.22 axle would under read by ~9%.

Saw the posting from Declan after I had pressed submit - depending on cost that could be a very good way to go. Decide on the diff ratio and then calculate the 'correction' required - nice one!

[liammonty]

BUT, looking at the various images on Google for Morris Minor speedos, there looks to be an SII looking head with 1600 tpm - is that from the MM?

Yes - someone's listed that incorrectly I think!

[ampwhu]

...
If it is the earlier speedo, there are no alternatives that will solve the problem, I don't believe? That means taking the rear of the gearbox off and swapping the SII speedo drive gear for the later one - at least the speedo will be a bit nearer right!

Richard,
There is an alternative-fitting a corrector gearbox on the back of the speedo like the ones that I build.
Regards
Declan

I admire the engineering!

I have an 803 speedo, 948 engine, 948 internals in 803 box and a 4.5 diff. (soon trying a 4.2 diff).

[Davey]

Wow, thanks for all the suggestions, very much appreciated!

I'll check the little digits on the face of my (small, round and in front of the driving seat) speedo over the weekend, and will do that check with a starting handle to count revolutions on the prop shaft at first opportunity too.

I'll not worry about the speedo until I've worked out what's going on with diffs and gears, and if I change the diff I'll do that first too. I like the idea of the adaptor, but the odometer doesn't work so I'd be tempted to send it off to be fixed... at which point I could get the unit calibrated to whatever setup I have. Good to have options.

Thanks again, I'll give some feedback on what I find!

All the best, and have a great weekend, davey.

[Davey]

Evening all!

Sun shone today, so I could get Ruby Morris out from under her cover and check as above.

Speedo is marked 1000, as expected.

Checked the gearbox ratio in first and it was indeed 3.6 turns of the engine to one of the prop. Double checked by doing the same test in reverse and it came up with the expected ratio listed for a 948. 948 box it is then. You guys are proven right Thank you.

This is good, as I'd rather planned on doing the whole adapted 948 box thing, and the cost and effort are now saved. I think I need to get shopping for a diff to drop in.

Having shopped around, it appears 4.55 diffs have a filler on the diff case, as my axle tube doesn't have a filler, it looks like this is the sensible way to go.

It's years since I've changed a diff, am I right they are a straight swap? I recall it's a case of removing the prop and drive shafts, unbolt, and then fit. Is there anything I've forgotten?

Thanks very much, and have a nice evening,

davey.

[firedrake1942]

I had this issue years ago when I put a modern diff on a 948 axle. I would fill it through the breather hole . The oil bottle had a plastic 'straw' which fitted into the breather to fill . I also adapted a paper clip to use as a dipstick so I could check the level through the breather.

[Davey]

Ah, thanks, that makes sense! I edited my post and removed my question about filling an axle without a filler (must have been while you were writing yours), as I think I've sussed the 4.55 diff has a filler in the diff casing, so I'll probably get one of those rather than a 4.22. But, your info on how to fill a fillerless diff will be useful if I do end up with a 4.22, thanks!

[liammonty]

You're right about the filler plug on the diff. With a standard 948 engine, I would go for the 4.55:1 - it's hugely better than the 5.375:1 803 diff you've got, and the ratio suits the engine well. That is exactly what I did with my early SII and it transformed the car. With a 4.22:1 diff from a 1098, you'll find it's a little overgeared on hills. My current Minor, with a modified 948 (around 55 bhp) pulls a 4.22:1 diff well, but I wouldn't want much less power with it. On that car, I got around the issue of a lack of filler by drilling a hole at the appropriate level on the axle casing and welding on a nut - a shortened bolt serves as the filler plug. A bit of a faff, but IMHO better than having to fill it through the breather, and not being able to check the level.

Edit- just seen Firedrake1942's cunning idea re using a dipstick - good idea!

[ampwhu]

if you go for a 4.2 you can fill quite easily. before putting back 1 x halfshaft, fill through the axle casing with the car jacked up that side.

simples.

[Davey]

Thanks very much for all the help. Weighing up that I don't drive quick and live in very hilly North Devon, I reckon it's a 1:4.55 for little Ruby Morris. I'll get one ordered up, along with all the gaskets!

All the best,

davey.

[Dean]

If you can get hold of an MM rear axle from the side valve engine, they are pretty much the same. MMOC spares do have one in Derby I believe.

This is a note I got from Mike Perry if you wish to keep the original set up on the rear drums.

Hi Dean,
The standard diff ratio on a Series MM is 4.55:1 the same as the 948 = 9/41. The ratio is stamped on the front of the left axle tube, near to the diff.
The standard for a Series 2 is 5.375 = 8/43. Any other ratios are specials?
The TPM for a Series MM speedo is 1600 but if the drive gearing is different in the 948 box then it still may need recalibrating nearer to the 1508 tpm of the 948 speedo, it is always worth checking with a sat nav.
Hope this helps
Regards
Michael

I have generally got used to the high revving, I put a tiny amount of oil down the speedo cable to stop the bounce and I can get it to 50mph, but I don't trust it any faster as I start to overheat. The acceleration actually helps me nip into traffic at islands. I just start and hold it in second a bit longer than normal lol.

[IslipMinor]

The 4.22 diff comes in both versions - oil filler in the diff casing and no filler in the diff casing. For a hilly environment, I think the 4.55 would probably be the best with a standard engine.