What diffs do I need

[JohnnyP]

Hi
I want to increase the speed/fuel consumption of my S3 2.25 petrol 1982. I've been told I should replace the current diffs with 3.5's. I'm new to 4WD and have no idea what type/year of diffs I should be looking for. Can anyone help please

 

[crashbox]

No idea but I reckon if you increase the top speed of a normally set up S3 then you will end upside down in a ditch.

 

[jamesmartin]

Hi
I want to increase the speed/fuel consumption of my S3 2.25 petrol 1982. I've been told I should replace the current diffs with 3.5's. I'm new to 4WD and have no idea what type/year of diffs I should be looking for. Can anyone help please

yes fit 3.54 10 spline diffs from either defender disco or rrc ,fit just rear first see what you think,most ive done people were impressed but you do get odd truck that wont pull it,ensure oil filler hole in rear case other wise you may have to make one

 

[lynall]

Early 3.53 diffs already have the filler plug in the diff itself, well mine did!


Lynall

 

[V8jon]

Hi
I want to increase the speed/fuel consumption of my S3 2.25 petrol 1982. I've been told I should replace the current diffs with 3.5's. I'm new to 4WD and have no idea what type/year of diffs I should be looking for. Can anyone help please

Where do you live? I've got two 3.54 rangie diffs that came out of my series,they're a bit heavy to post so would need to be reasonably close if you want them.

 

[jai_landrover]

Its a trade off Low range is awful but its cheaper than an overdrive and if you do mainly road miles and not much towing then it'd be ok

 

[ebbadger]

LWB or SWB?? If it has a Salisbury axle its not quite as straight forward as you will need a spreader tool to get the rear diff in/out.
Cheers Steve

 

[300bhp/ton]

Hi
I want to increase the speed/fuel consumption of my S3 2.25 petrol 1982. I've been told I should replace the current diffs with 3.5's. I'm new to 4WD and have no idea what type/year of diffs I should be looking for. Can anyone help please

Before you get any further, you need to understand what you really want, and what affect people are proposing.

Standard Series diffs are 4.7:1, you can swap in a diff from an RR/early Disco and 10 spline 90/110's. These have a ratio of 3.54:1, so a taller geared diff.

What this will do is offer a higher terminal speed in gear, i.e. more mph per 1000rpm. So you'll get lower cruising rpms.

However, as the final drive gears are taller, it will affect performance, so acceleration is likely to be slightly blunted as will your low speed off road crawl speed.

So while in theory it will allow you to either cruise at the same speed with lower rpms, or at a higher mph at the same rpms, you need to consider you might have to drive it harder to make it go.

Some really like this change to the Series, but I think you'd be better off making sure you are unhappy with the current final drive ratio before changing it. It won't double your mpg and if you live in hilly area's or don't do much high speed work in it, then you may find it's worse.

Changing tyre size might have a more suitable affect, or maybe make such a swap less appealing.

 

[JohnnyP]

OK, now very confused. I use the old girl as a daily drive to and from work mainly which is a 20 mile round trip. I can trundle along at 50 mpg but it sounds like the gearbox is working too hard & screaming! and I didn't want to put so much pressure on the gearbox.

 

[jamesmartin]

put in 3.54 diffs wont strain your box ive fitted quite a few including in my own 21/4 petrol made driving the truck alot better it felt more right,just fit rear one first as is easiest see what you think,speak to most that have done it they wouldnt go back

 

[jamesmartin]

LWB or SWB?? If it has a Salisbury axle its not quite as straight forward as you will need a spreader tool to get the rear diff in/out.
Cheers Steve

no you dont have to use spreader,it is more difficult in that crown wheel and pinion need setting with bearing preloads but still worth it especially with tdi conversion

 

[300bhp/ton]

OK, now very confused. I use the old girl as a daily drive to and from work mainly which is a 20 mile round trip. I can trundle along at 50 mpg but it sounds like the gearbox is working too hard & screaming! and I didn't want to put so much pressure on the gearbox.

If it's mainly road miles, then yes, at 50mph it'll lower your rpms, which in theory might make your mpg better. But it will depend how you drive it though.

What size tyres are you running at the moment? Taller tyres will offer a similar gearing affect.

 

[jai_landrover]

wouldn't fancy a salisbury that I could get out without a spreader sloppy diff. In fact if I had one I could get out it'd be re shimmed correctly before it went in.

 

[jamesmartin]

maybe you havent built as many as i have,if diff carrier wont come out without spreader its too tight how much preload do you think theres supposed to be,i do know how to shim and set the diff ,apart from recons and diff changes ive also built them for lr as new parts and the mod for snatch vehicles when lr couldnt supply replacements they all seemed happy

 

[jai_landrover]

well done!

All my point is there is a correct way of doing it and there are many many other ways. I know if your careful you may well be able to do it and all credit to you for that.

I've seen plenty of knacared military re con/rebuilds Salisbuys supposidly rebuilt and gearboxes that I wouldn't give a tenner for either of em after seeing the quality of their work. This was most likley military
bodge inhouse it and run and not somone like yourself.

Getting some monkey to use pry bars isn't the correct procedure. I also read manuals and set up procedures to correctly shim drive gears and electro mechanical clutches daily albeit on smaller machines. I will not post my resume but if one of my guys in the workshop dared to use a screw driver to pry gears off they would get a slapped and sweeping duty until they learn to use a puller.

 

[jai_landrover]

i'm not getting into a slaging match I'm too old for my bollox are bigger than yours.

Back to help the OP,

its a big step 4.75 to 3.54 if you use your land rover for any offroad driving then it will be horrendusly high geared. Especially if you try trialling/competitive driving. As 300bhp says quite rightly is that know what your getting into before hand. To answer: fit 3.54 diffs is an incomplete answer yes it may suit but there is downsides. Swings and roundabouts as always in life. If it was that great why don't every series owner fit them?

So OP read up or ask because you may well be better off getting some bigger tyres to raise the speed lower the revs slightly say 205 tyres to 5all 750's opposed to swapping diffs and IMHO wrecking the offroad performance of your mota. I assume you use it offroad in some sort of capability maybe wrongly but this is because its the usual reason for owning a series but not always.

 

[jamesmartin]

the real thing is whether you fully understand engineering principles of what your trying to achieve or slavishly follow manual but not knowing exactly why,many units we did for lr didnt follow manual but where excepted by them as they had to sign off on the work ie setting pinion hieght using machined bar across bearing locations and measuring pinion height from that rather than using dti to measure height of bearing locations and arriving at average of the two

 

[jai_landrover]

using'a'machines cylinder and pinion height block is far faster than dti each one. but it still takes some time to do a pinion

i'm currently in the pub but isn't some rover diffs somthing like 36.3mm or sumthin like that I was once told being an engineer means you understand fully what you can get away with without causing damage harm or shortening lifespan. i underatand where your coming from using pry bars carefully and with mechanical sympathy which is very much lacking these days. Tbh the average Joe struggles to undo and do up bolts correctly let alone keeping it all clean enough and reinstalling a salisbury without a spreader. There are some exceptions but alot of people just seem to be oblivious

 

[JohnnyP]

People Calm down!! I'm going to get a LR specialist to fit them if I decide that's the route I wish to take. All I wanted to know is that if by changing the diffs it would improve the road performance of my landy an drop the revs so I'm not putting so much strain on the gearbox.

 

[jamesmartin]

yes