Diff Identification

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alawrence10360
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Diff Identification

Postby alawrence10360 » Sun Feb 10, 2019 1:49 pm

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
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les
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Re: Diff Identification

Postby les » Sun Feb 10, 2019 2:04 pm

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
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Re: Diff Identification

Postby alawrence10360 » 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

alawrence10360
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Re: Diff Identification

Postby alawrence10360 » Sun Feb 10, 2019 3:23 pm

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
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Re: Diff Identification

Postby IslipMinor » Sun Feb 10, 2019 3:27 pm

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 902 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
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Re: Diff Identification

Postby alawrence10360 » 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 ?

oliver90owner
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Re: Diff Identification

Postby oliver90owner » Sun Feb 10, 2019 5:38 pm

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
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Re: Diff Identification

Postby alawrence10360 » Sun Feb 10, 2019 9:51 pm

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
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Re: Diff Identification

Postby oliver90owner » Sun Feb 10, 2019 11:07 pm

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
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Re: Diff Identification

Postby philthehill » Mon Feb 11, 2019 8:52 am

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
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Re: Diff Identification

Postby paul 300358 » Mon Feb 11, 2019 9:11 am

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
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Re: Diff Identification

Postby liammonty » Mon Feb 11, 2019 11:40 am

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
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Re: Diff Identification

Postby alawrence10360 » Mon Feb 11, 2019 2:57 pm

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
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Re: Diff Identification

Postby liammonty » Mon Feb 11, 2019 3:11 pm

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
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Re: Diff Identification

Postby oliver90owner » 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?

alawrence10360
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Re: Diff Identification

Postby alawrence10360 » Mon Feb 11, 2019 5:55 pm

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
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Re: Diff Identification

Postby philthehill » Mon Feb 11, 2019 6:38 pm

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
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Re: Diff Identification

Postby alawrence10360 » Thu Feb 21, 2019 10:37 pm

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
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Re: Diff Identification

Postby Declan_Burns » Fri Feb 22, 2019 9:11 am

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
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Re: Diff Identification

Postby paul 300358 » Fri Feb 22, 2019 9:49 am

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


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