Diff question. 3.54 24 spline into 4.7 10 spline

As per the title really... I've googled this and trawled the forums but am getting slightly baffled by over technical arguments and just want a simple answer before my head explodes...

Can I buy a pair of 3.54 24 spline diffs and put them into my current 4.7 10 spline set up?

Obviously I'd need to get new 24 spline half shafts but would there be any issues on the outer end, ie mating 24 spline halfshafts with the stub axles? ( if I've got my drive train geography right )

I'm aware of the potential filler hole issues and 3 or 4 bolt flanges. Is there anything else to be aware of?

Cheers,

Si.

Not sure what reason you'd have? What does it achieve? You'd also need to buy new drive flanges. I'm not sure if the differential ends are an available part. The drive flanges are cheap around £13 plus VAT. When you order these and the half shafts make sure you get the circlip and retaining stuff to secure the halfshafts. All this is dependent on getting the part's for the diff end. Someone in the past has dicked around with my diff and I've got 10 on one side and 24 on the other. The differential is a precision piece of kit. I'd leave it alone if it's running OK.

Simon Goodall said:

As per the title really... I've googled this and trawled the forums but am getting slightly baffled by over technical arguments and just want a simple answer before my head explodes...

Can I buy a pair of 3.54 24 spline diffs and put them into my current 4.7 10 spline set up?

Obviously I'd need to get new 24 spline half shafts but would there be any issues on the outer end, ie mating 24 spline halfshafts with the stub axles? ( if I've got my drive train geography right )

I'm aware of the potential filler hole issues and 3 or 4 bolt flanges. Is there anything else to be aware of?

Cheers,

Si.

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they will fit physically
but they arent any half shafts that will fit them and a series rover axle
24 spline was only fitted to salisbury axles or later disco,defender axles and there lengths differ to what you need

It would be easier to simply buy some 10 spline 3.54:1 diffs than faff about. It isn't impossible, but you won't be able to simply buy stuff off the shelf to do this in a Series axle (coil axle yes).

However I'd say don't do it at all. It'll knacker the low range crawl speed.

Thanks chaps.

The reason I asked was that I found some 24 spline diffs at a decent price so thought if just changing the half shafts was an easy option then I'd go for it to get better MPG ( got a V8 )... also I believe that 24 spline half shafts are stronger than 10 splines? On reflection I think that I'll hang out for 10 spline diffs to magically appear instead.

Thanks again.

Si

In theory 24 spline is stronger than 10 spline. In practice I think there is very little in it. But remember Series axles are narrower than coiler axles. So your choice is somewhat limited unless you want to look at custom made parts.

If you off road much, seriously consider the implications to your low range speeds if you change diffs. And tbh I really doubt you'd massively improve your mpg with 3.54 diffs anyhow.

Having got a 200tdi in a 109 2a with original rover front and rear axle. I'd say it's much easier finding 10 spline from an early disco, Range Rover or 90/110. Front and rears are interchangeable so you don't need to be a rear diff to specifically go in the rear.
The coil sprung axles had oil fillers for the diff in the casing whereas on series vehicles they are on the diff housing itself so you'll need to drill and tap a filler in there somewhere.

I wouldn't worry about half shafts. I've pulled 3 tons with my 109 up a 15% hill in just 2 wheel drive and nothing broke. With the higher geared diffs you are somewhat protecting the half shafts more than with the 4.7 however this puts more strain on the series box.
I don't find low range that high. I can put it in 1st low and get out the vehicle on flat ground and it moves at about walking pace.

You could consider higher ratio transfer gears instead. These won't affect low range.

If you've still got the series box Ashcroft do a kit. Or if you've put a defender gearbox in you can add a disco transfer box.

The drive train components really aren't that weak if you drive correctly. It's the snatching by accelerating to hard or letting the clutch up too quick that can cause damage. As well as losing traction in 2 wheel drive then gaining traction quickly.

4th is the kindest gear to be in to put all that power down. So if you want to accelerate hard do so in 4th.

As has been said above your mpg won't really improve with a v8. Wrong engine of fuel bills are a concern. At a steady 60mph with Tdi in with 3.54 diffs I get around 35mpg. With the old diffs I was getting about 28mpg at the same speed. In a v8 you might get 1 more mpg?

109inches said:

I don't find low range that high. I can put it in 1st low and get out the vehicle on flat ground and it moves at about walking pace.

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If you do technical off roading or trials you'll really notice it.

A stock geared Tdi Series is quite a bit quicker at ticker over low 1st than a Tdi 90 is. 3.54 diffs would make a huge difference.

109inches said:

At a steady 60mph with Tdi in with 3.54 diffs I get around 35mpg. With the old diffs I was getting about 28mpg at the same speed. In a v8 you might get 1 more mpg?

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Not that I want to disbelieve you, but those figures seem rather too high to be accurate.

With 3.54:1 diffs your mph/1000rpm in top is not so different to that of a standard Defender. And there is no way in hell a Tdi Defender will do 35mpg, not even if you drive it off a cliff.

300bhp/ton said:

If you do technical off roading or trials you'll really notice it.

A stock geared Tdi Series is quite a bit quicker at ticker over low 1st than a Tdi 90 is. 3.54 diffs would make a huge difference.


Not that I want to disbelieve you, but those figures seem rather too high to be accurate.

With 3.54:1 diffs your mph/1000rpm in top is not so different to that of a standard Defender. And there is no way in hell a Tdi Defender will do 35mpg, not even if you drive it off a cliff.

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You notice low range doing really technical stuff off-road. But I find low range first too low in a stock series or defender for my off-road uses. Now I don't do stuff much more extreme than greenlaning so doesn't affect me much. Unless you're doing rock crawling or carrying heavy gear down a steep hill first low is to low. I find second low better most the time as for steep hills that are slightly sleepy first low is so low you end up losing traction so have to accelerate out of it anyway then you end up coming down the hill screaming at high revs to keep traction.
This is just based on my experience I have not done extreme off roading or really technical stuff that need the super low first low range gear. As the OP is worried about fuel economy I'm sure he doesn't do really technical off roading all the time that requires first low range.

There are many series owners who get 35mpg as an average on a run running a Tdi overdrive and 3.54 diffs. 60mph in 4th overdrive which is higher geared than 5th in a defender means the engine is only doing around 2000rpm. A series with the above and Tdi is good for 90 odd mph. Although your balls of steel would be the only thing weighing you down and keeping you from going faster.

But for trials you are absolutely right about the gearing I was just assuming that as the OP was looking for fuel economy that he does more on road than off-road stuff and so low range wouldn't be an issue.

109inches said:

There are many series owners who get 35mpg as an average on a run running a Tdi overdrive and 3.54 diffs.

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I suspect the reality is, there are a lot of people either making it up, or calculating it wrongly. I have seen this many many times and not just with Land Rovers...

109inches said:

60mph in 4th overdrive which is higher geared than 5th in a defender means the engine is only doing around 2000rpm. A series with the above and Tdi is good for 90 odd mph. Although your balls of steel would be the only thing weighing you down and keeping you from going faster.

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To be fair, you did not mention OD, you said Tdi and 3.54 diffs. That said, I still don't believe the figures.

On 7.50 or 235/85 tyres (31.73" tall)
Series with 3.54 diffs = 58mph @ 2500rpm
Defender 100% = 57mph @ 2500rpm

They have the same aero properties and weigh similar (Defender slightly more).

A Discovery is more aero efficient and has a higher mpg rating than a Defender. Land Rover claimed 27mpg for the Discovery. A Series will not be doing 35mpg under the same conditions unless you are running it on pixie dust. If you truly believe you are, don't you think Land Rover might have done better with their official figures.....


A Defender with the 1.22 transfer box = 66mph @ 2500rpm or 53mph @ 2000rpm
These will also not manage 35mpg either.

Series with 3.54 diffs and Overdrive = 73mph @ 2500rpm or 58mph @ 2000rpm and in all reality probably struggle to pull 5th gear and won't like hills.

I would think that last setup might be less economical as you'll have to run at a wider throttle input to maintain speed on anything other than level or down hill ground.

For the record, I used to run a Disco 200Tdi on 33" tyres, it ran strong and was tuned by Allisport, but it didn't really have enough puff to pull fifth until about 50mph. And the overall gearing on that isn't as tall as you are suggesting.

I also have a 200Tdi Series III and not way in hell does it get close to 35mpg. I've also had a 300Tdi D90, by brother has a 200Tdi 90, my Uncle a 300Tdi 90.

Remember though that although a discovery is slightly more aerodynamic it weighs a lot more with an all steel body.

The defender will weigh a bit more when you add in all the little bits added drag for permanent four wheel drive, longer wheel base, wider axles, heavier gearbox, heavier doors, larger windscreen, more sound proofing and head linings.

I have spoken to a few members on the series 2 club who get mid 30's fairly easily in their 200tdi powered series vehicles.

I have a genuine 200tdi defender with returns around 30mpg.

It's not unachievable and with a steady right foot can be achieved. The Tdi pulls fourth overdrive rather nicely from 30mph up to whatever it's top speed is but by then you are on motorways or dual carriageways which for the most part are quite flat.

A discovery has roughly the same gearing as a Tdi in a series with 3.54 diffs. The discovery is only just slightly more aerodynamic but weighs an awful lot more. Fourth overdrive and 5th in an lt77 are relatively similar and discoveries are not that laboured in 5th gear so a lighter series vehicle geared roughly similar should not be assumed to struggle in 4th overdrive.

I can't explain why you don't believe the figures when numerous people including myself reach these figures.
On glencoynes website for converting a series Land Rover to 200tdi he claims an average of 33mpg this is without the turbo. Although without the turbo you are putting less fuel in the engine, due to the lack of power in DI form you will have to be at higher revs.

This has strayed somewhat from the original post.
To sum up yes 3.54 diffs will be good if you do road miles and the odd bit of off-roading as the differences in low range will be negligible for on road use. You won't see a huge increase in fuel economy as the v8's are thirsty lumps. However if you off-road a lot and need a super low gear then stick with the original gearing.

Crikey....

Yes, my main use is on the road with a bit of off roading now and again. I have a smallholding and use it if I want to nip up the hill quickly rather than digging the RRC (which I use a tractor / mobile workshop / fencing unit / ladder) out of the barn, rather than any serious mud & rock crawling. It's also needed to take the stepsons to motocross which involves muddy fields. So, in short, the very low range crawling capabilities aren't too much of a factor.

I figured that if I put 3.54 diffs on instead of the standard 4.7s then I'd get around a 25% increase in fuel economy which sounds impressive but when you put it in MPG terms ( an extra ~3mpg! Woo! ) if I lay out £100 or so on a pair of diffs it's going to take a few thousand miles to break even again....

I think I'll do what I do best and dither for a year or three and see what happens.... of course if anyone reading this is in the Hampshire / West Dorset / Devon / Somerset area and wants to dispose of a pair of 3.54 10 spline diffs for not very much dosh then that would alter the economics of the whole thing!

Many thanks to everyone for all your input.

Simon Goodall said:

Crikey....

Yes, my main use is on the road with a bit of off roading now and again. I have a smallholding and use it if I want to nip up the hill quickly rather than digging the RRC (which I use a tractor / mobile workshop / fencing unit / ladder) out of the barn, rather than any serious mud & rock crawling. It's also needed to take the stepsons to motocross which involves muddy fields. So, in short, the very low range crawling capabilities aren't too much of a factor.

I figured that if I put 3.54 diffs on instead of the standard 4.7s then I'd get around a 25% increase in fuel economy which sounds impressive but when you put it in MPG terms ( an extra ~3mpg! Woo! ) if I lay out £100 or so on a pair of diffs it's going to take a few thousand miles to break even again....

I think I'll do what I do best and dither for a year or three and see what happens.... of course if anyone reading this is in the Hampshire / West Dorset / Devon / Somerset area and wants to dispose of a pair of 3.54 10 spline diffs for not very much dosh then that would alter the economics of the whole thing!

Many thanks to everyone for all your input.

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Very doubtful you will see that much improvement in fuel economy from fitting diffs. You might get a few % extra if you do a lot of high speed work, that sort of usage difference will be minimal.

I've a 2.3 l petrol with Weber dtml have 3.54 diff's and have recently done some economy testing worst was 15 liter,100 km best was 12 per 100 that was 88 series 3 towing 1 ton boat over mountainous terrain .the worst ever economy was running 4.7 s getting up to 20 l 100 km while towing , my engine is in good shape and running leccy ignition testing done with GPS

300bhp/ton said:

Not that I want to disbelieve you, but those figures seem rather too high to be accurate.

With 3.54:1 diffs your mph/1000rpm in top is not so different to that of a standard Defender. And there is no way in hell a Tdi Defender will do 35mpg, not even if you drive it off a cliff.

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Rmember a 90 is 300kg heavier than an 88", that makes the difference. Its why a 2.5NA can propel a series motor quite nicely but feel ridiculously slow in a 90

Plus i think diffs would make a difference to mpg as you wouldnt need to rev the bollox off the engine as much to get it up to speed. It'll just be like having an overdrive engaged all of the time. This is the reason why i dont want to swap diffs in mine, i like the versatility the overdrive offers you especially when going up hills and towing etc

Simon Goodall said:

Crikey....

Yes, my main use is on the road with a bit of off roading now and again. I have a smallholding and use it if I want to nip up the hill quickly rather than digging the RRC (which I use a tractor / mobile workshop / fencing unit / ladder) out of the barn, rather than any serious mud & rock crawling. It's also needed to take the stepsons to motocross which involves muddy fields. So, in short, the very low range crawling capabilities aren't too much of a factor.

I figured that if I put 3.54 diffs on instead of the standard 4.7s then I'd get around a 25% increase in fuel economy which sounds impressive but when you put it in MPG terms ( an extra ~3mpg! Woo! ) if I lay out £100 or so on a pair of diffs it's going to take a few thousand miles to break even again....

I think I'll do what I do best and dither for a year or three and see what happens.... of course if anyone reading this is in the Hampshire / West Dorset / Devon / Somerset area and wants to dispose of a pair of 3.54 10 spline diffs for not very much dosh then that would alter the economics of the whole thing!

Many thanks to everyone for all your input.

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On one of the local scuffle pages here in Devon a bloke is selling 10 spline complete axles for £60 each, £120 for both use the diffs then sell the other bits might end up getting some bits cheap?

samc88 said:

Plus i think diffs would make a difference to mpg as you wouldnt need to rev the bollox off the engine as much to get it up to speed. It'll just be like having an overdrive engaged all of the time. This is the reason why i dont want to swap diffs in mine, i like the versatility the overdrive offers you especially when going up hills and towing etc

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3.54 diffs really match Tdi torque and v8 torque well. First gear isn't needed with original 4.7 diffs and the ease to break a half shaft or driveline component is very high.

As I said with 3.54 diffs I was able to pull 3 tonnes up a 15% gradient in 1st high range which would pull up and that was doing 10mph now second gear high range with 4.7 diffs would also probably be about 10mph.

With the Tdi the noise was unbearable because the engine had to be revved to make top speed. 55mph in 4th overdrive doing a bit over 3000 revs was horrific. Increasing engine wear, deafening people inside poor fuel economy.
Now 60mph is very relaxed relatively quiet very efficient and in the perfect torque curve of the Tdi.

I would highly recommend switching diffs. Or at least just switch the rear and try it, it takes less than an hour see if you like it and then either switch it back or change the front just don't engage four wheel drive.

109inches said:

On one of the local scuffle pages here in Devon a bloke is selling 10 spline complete axles for £60 each

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Have you got a link for this please? We're heading down to Cornwall next week so could do a bit of a detour if necessary, or just nip down if it's North / East Devon...

https://m.facebook.com/groups/144895325564512?tsid=0.5603544146288186&source=typeahead

Have a browse through you have to join the group to comment or you can try messaging directly.

Brilliant, thanks!