Diff Identification

Discuss mechanical problems here.
Forum rules
By using this site, you agree to our rules. Please see: Terms of Use
alawrence10360
Minor Fan
Posts: 403
Joined: Thu Jan 31, 2019 5:54 pm
MMOC Member: Yes

Diff Identification

Post by alawrence10360 »

My 67 Saloon has a 1275cc fitted from a Sprite
The gearbox and diff were left standard by the previous owner who had no issues and used it as a daily driver .
The drive train is very good. I drove loads of Minors before i bought this one and the gearbox is the best I have driven by far.
He gave me the Sprite gearbox and diff and I would like to identify them if I can.
I have read a few posts on here that suggest the diff from the Sprite may suit the bigger engine better
I have attached a couple of pics
Thanks
Attachments
20190210_132053.jpg
20190210_132053.jpg (3.69 MiB) Viewed 7707 times
20190210_131756.jpg
20190210_131756.jpg (3.9 MiB) Viewed 7707 times
20190210_132038.jpg
20190210_132038.jpg (3.45 MiB) Viewed 7707 times
les
Minor Maniac
Posts: 8737
Joined: Tue Feb 12, 2002 12:00 am
Location: kent
MMOC Member: Yes

Re: Diff Identification

Post by les »

Looks like a 3.9 diff. (10/39) The shaft protruding from the gearbox bell housing should have a number somewhere round its circumference, from memory 22g229 for 1275 gearbox.

alawrence10360
Minor Fan
Posts: 403
Joined: Thu Jan 31, 2019 5:54 pm
MMOC Member: Yes

Re: Diff Identification

Post by alawrence10360 »

Thanks les
is the 10/ 39 the number of teeth (ratio)
If not how can you tell
every days a school day at tbe moment
alawrence10360
Minor Fan
Posts: 403
Joined: Thu Jan 31, 2019 5:54 pm
MMOC Member: Yes

Re: Diff Identification

Post by alawrence10360 »

alawrence10360 wrote: Sun Feb 10, 2019 3:18 pm Thanks les
is the 10/ 39 the number of teeth (ratio)
If not how can you tell
every days a school day at tbe moment
and if it is a 3.9 diff does that mean it is a Sprite and will that suit the engine better ?
IslipMinor
Minor Legend
Posts: 2147
Joined: Mon May 10, 2004 9:10 pm
Location: Oxford, UK
MMOC Member: Yes

Re: Diff Identification

Post by IslipMinor »

The diff ratio definitely looks to be 3.9:1 from the numbers stamped on the casing (10-39), which is correct for a 1275-engined Spridget. The primary shaft part number for A-Series in-line gearboxes is unique to the version, i.e. 948/1098/1275 and Spridget (close ratio) or non-Spridget. A 1275 gearbox should have the 22G229 primary/first motion shaft, as said by Les, which is the one specifically for the Spridget 1275 gearbox. The later 948, and all 1098/1275 engined Spridgets had the 'close ratio' version of the 'box - see the ratios at the bottom of the table attached below.

The 1275 synchromesh is basically the same design as the 1098 Minor, baulk ring, so if it is in good condition it should feel very similar to what you have now.
A-Series Gearbox Component Part Numbers v6.jpg
A-Series Gearbox Component Part Numbers v6.jpg (260.22 KiB) Viewed 8028 times
The mainshaft gears in the 1098/1275 Spridget gearbox run on needle roller bearings, instead of the bronze bushes of the lower powered engines. In that way the Spriget gearbox is better suited to the Spridget engine.

Apart from replacing the Spridget clutch release arm with the 1098 Minor one, everything else is a simple swap over.

Is the engine a standard 1275 Spridget one? Whether it is or not, I think I would do the changes in 2 stages:

Change the gearbox first and see how the closer ratios feel in a Minor, as 1st, 2nd and 3rd are all 'higher geared' than the Minor. Does it get away as you would like? If that is fine, then swap the final drive unit over as well. I would expect that the combination of the two will make the car seem noticeably slower off the mark. The gearing in 4th, of course, is a function of the rear axle ratio and not the gearbox.
Richard


alawrence10360
Minor Fan
Posts: 403
Joined: Thu Jan 31, 2019 5:54 pm
MMOC Member: Yes

Re: Diff Identification

Post by alawrence10360 »

At the moment I suspect I wouldnt need 1st gear at all . It would pull away in 2nd happily.
On an A road Im in 4th very quicky , probably before I hit 40 mph.
Once there I can get up to 70 mph ( only done this once )
I was hoping I could first go for changing the diff if it was a higher ratio. It seems like an easier thing to do. Is 3.9:1 higher than standard for a Minor ?
oliver90owner
Minor Legend
Posts: 1653
Joined: Thu May 12, 2016 6:33 am
MMOC Member: No

Re: Diff Identification

Post by oliver90owner »

On top of all that, your wheel and tyre size will make a difference, too. 13” to 14” rims is just one factor, aspect ratio is another.
alawrence10360
Minor Fan
Posts: 403
Joined: Thu Jan 31, 2019 5:54 pm
MMOC Member: Yes

Re: Diff Identification

Post by alawrence10360 »

alawrence10360 wrote: Sun Feb 10, 2019 4:28 pm At the moment I suspect I wouldnt need 1st gear at all . It would pull away in 2nd happily.
On an A road Im in 4th very quicky , probably before I hit 40 mph.
Once there I can get up to 70 mph ( only done this once )
I was hoping I could first go for changing the diff if it was a higher ratio. It seems like an easier thing to do. Is 3.9:1 higher than standard for a Minor ?
Will it be noticeably lower revs at say 60 mph ?
oliver90owner
Minor Legend
Posts: 1653
Joined: Thu May 12, 2016 6:33 am
MMOC Member: No

Re: Diff Identification

Post by oliver90owner »

That depends entirely on what is in there at present? Any higher ratio differential will lower the engine revs from the previous lower ratio unit. Check what is in there and you can easily calculate the change in rpm at any speed for the change.
philthehill
Minor Maniac
Posts: 10767
Joined: Thu Jul 19, 2012 12:05 pm
Location: Hampshire
MMOC Member: Yes

Re: Diff Identification

Post by philthehill »

The diff ratio numbers can be usually found stamped on the top part of the rim of the diff carrier where it bolts to the axle casing - so no dismantling should be required to find out what the current ratio is.

paul 300358
Minor Fan
Posts: 467
Joined: Thu May 11, 2017 8:23 pm
Location: South Cheshire
MMOC Member: Yes

Re: Diff Identification

Post by paul 300358 »

Park on flat, level solid ground. Handbrake off and out of gear, jack up a rear wheel and place on axle stands, rotate the wheel once and count the number of turns the prop shaft makes. If it turns just over 4 times you have a 4:2 diff, if it turns just less than 4 times you have either a 3:7 or a 3:9.
liammonty
Minor Legend
Posts: 1185
Joined: Mon Apr 23, 2007 2:32 pm
Location: Dartmoor
MMOC Member: No

Re: Diff Identification

Post by liammonty »

A '67 Minor would have had a 4.22:1 diff fitted as standard. I fitted a 3.9:1 in place of my 4.22:1 diff in my '68 Traveller with its standard (but good) 1098cc engine, and it was a worthwhile improvement, and the car did not 'struggle' despite the noticeably longer gearing. A 3.9:1 diff with your Midget 1275 engine (65 bhp vs. 48 bhp for the 1098?) will be a big improvement - higher speeds will be a bit more relaxed and the engine (assuming it's in good order) will have plenty of power to cope.

As IslipMinor has pointed out, the Midget gearbox has a taller first gear, but, even with the slightly heavier Minor (compared to the Midget) I think it will be just fine, should you choose to fit it. As has been pointed out, though, it won't change cruising RPM in (direct drive) 4th gear. If it was my car, I would change the diff (easy) and keep the gearbox as a spare, unless you fancy changing it too, as it's a more involved job than a diff change, and won't bring such appreciable benefits.

Just to add, this is all based on your assertion that the current diff is unchanged, i.e. 'standard' 4.22:1 ratio currently.
alawrence10360
Minor Fan
Posts: 403
Joined: Thu Jan 31, 2019 5:54 pm
MMOC Member: Yes

Re: Diff Identification

Post by alawrence10360 »

Thanks all
Great response
Im going to swap it to the 3.9:1
Ive had a look at the unit and there is nothing that jumps out at me with regard to the diff (no broken teeth etc)
Although the manual doesnt say as much Im guessing you need to withdraw the drive shafts before taking the old diff out.
Also I will change the oil seal before I fit the 3.9 1. This looks a bit of a challenge getting the large not off when it not on the axle...
liammonty
Minor Legend
Posts: 1185
Joined: Mon Apr 23, 2007 2:32 pm
Location: Dartmoor
MMOC Member: No

Re: Diff Identification

Post by liammonty »

Correct re the half shafts. Remember ti keep them on the sides they’re currently on, as they become ‘handed’ over time and break quickly if put back on the other side :D
oliver90owner
Minor Legend
Posts: 1653
Joined: Thu May 12, 2016 6:33 am
MMOC Member: No

Re: Diff Identification

Post by oliver90owner »

If you look up the torque required on the pinion nut you might wish to modify your plan. I’v never changed one unless it needed changing. Does yours?
alawrence10360
Minor Fan
Posts: 403
Joined: Thu Jan 31, 2019 5:54 pm
MMOC Member: Yes

Re: Diff Identification

Post by alawrence10360 »

oliver90owner wrote: Mon Feb 11, 2019 3:32 pm If you look up the torque required on the pinion nut you might wish to modify your plan. I’v never changed one unless it needed changing. Does yours?
I dont know if it was leaking however I cant justify puting it on only to find it is leaking...
I willhave to think of a way to lock the system while I swing on the nut with large breaker bar
philthehill
Minor Maniac
Posts: 10767
Joined: Thu Jul 19, 2012 12:05 pm
Location: Hampshire
MMOC Member: Yes

Re: Diff Identification

Post by philthehill »

The spacer between the two pinion bearings is collapsible and if care is not taken can be reduced in length so putting excess loading on the bearings which can lead to bearing failure.
You need to hold the pinion flange to undo and tighten the pinion nut with a spanner similar to that in the link below

https://www.ebay.co.uk/itm/Morris-Minno ... :rk:2:pf:0

If you have not changed the pinion seal before it may be better to get someone who has previously undertaken the job and has a suitable torque wrench. 140lbf ft required to tighten the nut.

alawrence10360
Minor Fan
Posts: 403
Joined: Thu Jan 31, 2019 5:54 pm
MMOC Member: Yes

Re: Diff Identification

Post by alawrence10360 »

Well the nut came off relatively easily in tbe end
I made up something to hold/ fix the flang
Removing and replacing the seal also has gone smoothly
I do have a torque wrench that will go up to 140lbf and I suspect it was alot less than this prior to removal
So busy weekend ahead putting the diff back together and returning the rear hieght back to standard
What could possibly go wrong...
Declan_Burns
Minor Legend
Posts: 1956
Joined: Wed Apr 18, 2007 7:32 am
Location: Düsseldorf, Germany
MMOC Member: No

Re: Diff Identification

Post by Declan_Burns »

You would be surprised what could go wrong! As Phil has mentioned the diff usually has a crush spacer which has a lot of disadvantages as opposed to a solid spacer. The problem is that you do not know to how tight the nut was actually torqued. A crush spacer can only be used once. Assuming it was 140ft lbs may or may not be correct. I would have marked the position of the nut relative to the pinion flange before loosening it and torqued the nut to exactly the same position after replacing the seal. Normally the pre-load on the pinion bearings is measured with an in-lb gauge. You could tighten the nut until you have a reading of 11 ...13in-lbs which is the factory spec.
You can make such a gauge very easily with flat aluminium bolted to the flange and a 1lb weight located 11 … 13 inches from the centre of the nut.
Regards
Declan


Regards
Declan
paul 300358
Minor Fan
Posts: 467
Joined: Thu May 11, 2017 8:23 pm
Location: South Cheshire
MMOC Member: Yes

Re: Diff Identification

Post by paul 300358 »

I would suggest that you watch this https://www.youtube.com/watch?v=H9yKWKV8poc before starting.
Post Reply