R

RRMaximus

Member
I have a 2002 4.4 Petrol L322 with front and rear diffs at the ratio 3.73, with the 5 speed ZF5HP gearbox.

My front and rear diffs are badly rusted on the outside but I do not believe that they need to be changed.

I plan to make a trip from England to Portugal and I was thinking to get two second hand diff that are in better condition, with the 2.76 ratio.

From looking at pictures of both types of diffs it seems that they have the exact same mounting points.

My reason for doing this would be to have a lower RPM when driving at 60 mph / 100 km/h on the trip.

Given that I could buy replacement diffs for around £100 each, I would most likely save the cost in reduced fuel consumption on the trip.

But my major concern is running the engine for a long time on a highway at a higher RPM than necessary.

I am not someone who needs or uses powerful acceleration, but I do prefer to run at a lower RPM on the highway.

If my current diffs were perfect then I would not consider this but as they are in bad shape on the outside it is something that I am considering.

I know that this would change the speedometer but I am not worried about that as I would use the GPS speedometer on my phone to mark the speed limits on my speedometer.

Please do not suggest that I sell my L322 and buy a supercharged version with the six speed gearbox because I have spent the past year fixing many issues on this car and I would not buy another car with unknown issues.

Is this a crazy idea or a good one?
 
This info is a little confusing kiddo.
If your dropping the revs on the motorway, how are you running at higher revs as well?
One thing that will happen is an amount of extra strain on the rest of the transmission dealing with the extra pull needed to get upto speed.
Also, if you had a six speed box you'd probably find that the engine speed would be similar in the 6th gear at motorway speed anyway🤷
 
I'm not dropping revs or running at higher revs. With my current differentials at 70mph on the motorway it runs at about 1,300 RPM. With the 2.76 diffs it will run at maybe 1,100 RPM. So a lower RPM for long trips.

I would not put more stress on the rest of my system by it taking longer to accelerate because I would not be putting my foot to the floor. I don't drive like that so I don't need the acceleration.

Some people want a lot of acceleration so they want to have the higher diff ratio. I just don't drive like that. I also never tow anything. So my system is never stressed.
 
RRMaximus said:
I have a 2002 4.4 Petrol L322 with front and rear diffs at the ratio 3.73, with the 5 speed ZF5HP gearbox.

My front and rear diffs are badly rusted on the outside but I do not believe that they need to be changed.

I plan to make a trip from England to Portugal and I was thinking to get two second hand diff that are in better condition, with the 2.76 ratio.

From looking at pictures of both types of diffs it seems that they have the exact same mounting points.

My reason for doing this would be to have a lower RPM when driving at 60 mph / 100 km/h on the trip.

Given that I could buy replacement diffs for around £100 each, I would most likely save the cost in reduced fuel consumption on the trip.

But my major concern is running the engine for a long time on a highway at a higher RPM than necessary.

I am not someone who needs or uses powerful acceleration, but I do prefer to run at a lower RPM on the highway.

If my current diffs were perfect then I would not consider this but as they are in bad shape on the outside it is something that I am considering.

I know that this would change the speedometer but I am not worried about that as I would use the GPS speedometer on my phone to mark the speed limits on my speedometer.

Please do not suggest that I sell my L322 and buy a supercharged version with the six speed gearbox because I have spent the past year fixing many issues on this car and I would not buy another car with unknown issues.

Is this a crazy idea or a good one?
Click to expand...

So the diffs look bad on the outside? What does the oil look like from the inside or do you have any other reason to suspect they are not good?

I take from what you are saying the SC runs that diff ratio?
Thats quite a change in ratios and i am sure JLR worked out the best they could at the time.

So you would get a drop of 200rpm@70mph over a long run. how often do you do this long run? You would probably get better MPG on said long run than you do driving around daily.

Have you looked at how much work it is to change the diffs, front and back?

J
 
300bhp/ton said:
Clearly you are the first person in history to use a Range Rover for a long journey. You should share your idea so that other people can now use such vehicles without worry too.....
Click to expand...
I am not the first person to modify a Range Rover to better suit their specific needs.

In fact Range Rover changed from a five speed gearbox to a six speed gearbox to an eight speed gearbox.

I don't see any problem with improving something beyond its initial design while other people might fear change or improvement.
 
marjon said:
So the diffs look bad on the outside? What does the oil look like from the inside or do you have any other reason to suspect they are not good?

I take from what you are saying the SC runs that diff ratio?
Thats quite a change in ratios and i am sure JLR worked out the best they could at the time.

So you would get a drop of 200rpm@70mph over a long run. how often do you do this long run? You would probably get better MPG on said long run than you do driving around daily.

Have you looked at how much work it is to change the diffs, front and back?

J
Click to expand...
The SC has an 8 speed gearbox.

I think the 2.76 diffs are from a diesel L322.

The oil was dark when I changed it but I have no reason to suspect that the internal diffs are not OK.

But on my latest MOT they noted the rust on the diffs as a potential future issue.

It's not just about the petrol saving, it's also about not running the engine at a higher RPM for such a long time.

It's just that the petrol saving would pay for it.

Changing the diff is a reasonably simple job.

I was really looking for someone who understood more about it from a technical point of view who might have some input.
 
So I will try my best.

RRMaximus said:
The SC has an 8 speed gearbox
Click to expand...
What year did the 8 speed box come in? what year did the SC come in?

RRMaximus said:
I think the 2.76 diffs are from a diesel L322.
Click to expand...
I can find no info for that can you link?

RRMaximus said:
The oil was dark when I changed it but I have no reason to suspect that the internal diffs are not OK.

But on my latest MOT they noted the rust on the diffs as a potential future issue.
Click to expand...
So change it and check, noting rust on a casing as a potential issue is BS.

RRMaximus said:
It's not just about the petrol saving, it's also about not running the engine at a higher RPM for such a long time.

It's just that the petrol saving would pay for it.
Click to expand...

When we drive long distance our overall milage goes from 10-11L/100klm to 9.5ish its better on a run than around town.

RRMaximus said:
Changing the diff is a reasonably simple job.
Click to expand...

Go for it then.
RRMaximus said:
I was really looking for someone who understood more about it from a technical point of view who might have some input.
Click to expand...

So you gonna go there again? Cos you dont like what I suggest?
You do what you want.
I will attach docs for the 2011 Range rover when they introduced the 8speed box, not before when the SC was already out with the 6 speed box.
So do you have docs to show this diff ratio you state that you could share?

You think I dont have a technical point of view/input, fine.

J
 

Attachments

  • Diff ratio.pdf
    133.9 KB · Views: 4
  • Diff rear.pdf
    232.7 KB · Views: 1
marjon said:
So I will try my best.


What year did the 8 speed box come in? what year did the SC come in?


I can find no info for that can you link?


So change it and check, noting rust on a casing as a potential issue is BS.



When we drive long distance our overall milage goes from 10-11L/100klm to 9.5ish its better on a run than around town.



Go for it then.


So you gonna go there again? Cos you dont like what I suggest?
You do what you want.
I will attach docs for the 2011 Range rover when they introduced the 8speed box, not before when the SC was already out with the 6 speed box.
So do you have docs to show this diff ratio you state that you could share?

You think I dont have a technical point of view/input, fine.

J
Click to expand...
I'm not going to waste time answering your questions when you can look it up yourself if it actually matters to you.

You can just Google L322 diff ratios or look for a second hand L322 diff with the ratios that I have mentioned and see that they exist in the ratio that I have and other ratios.

I'm not going to just do it and see how it turns out, when I could just wait for someone with experience or knowledge to comment here.
 
RRMaximus said:
Given that I could buy replacement diffs for around £100 each, I would most likely save the cost in reduced fuel consumption on the trip.
Click to expand...

At that price you don't know if the diffs are for sale because they are old & noisy, or how they have been treated.
 
RRMaximus said:
I am not the first person to modify a Range Rover to better suit their specific needs.

In fact Range Rover changed from a five speed gearbox to a six speed gearbox to an eight speed gearbox.

I don't see any problem with improving something beyond its initial design while other people might fear change or improvement.
Click to expand...
Have you got any mechanical knowledge at all? An MoT tester saying a diff is rusty just sounds like a poor dodgy MoT tester tbh.

The ratio change you are proposing is HUGE, have you bothered to use a gearing calculator to see what the actual impact would be?

Why on Earth do you think running at higher revs in its current state would be bad anyway? It already has pretty long tall gearing, just go and look at how most high revving 4 cylinder cars are geared.

Are you 100% sure the diffs didn't change in any other way during production? Are they 100% a direct swap over? Not saying they aren't, I don't know. But the L322 was built for many years and changed a lot in that time.
 
Also at 70mph, surely lowering the revs from 1300 to 1100 is not gonna save much petrol ? Rememer you need a certain amount of energy or fuel to keep a brick shaped car rolling !!
 
pwood999 said:
Also at 70mph, surely lowering the revs from 1300 to 1100 is not gonna save much petrol ? Rememer you need a certain amount of energy or fuel to keep a brick shaped car rolling !!
Click to expand...
Might actually increase fuel consumption because even though the revs are lower, the engine may be working harder to maintain speed.
 
pwood999 said:
At that price you don't know if the diffs are for sale because they are old & noisy, or how they have been treated.
Click to expand...
Just the many diffs that are available on eBay and from wreckers of L322s in the UK.

As RRPhil mentioned elsewhere the 2.76 diff is from the 8 speed diesel L322 so they will all be relatively new diffs compared to mine from 2002 with 153k miles.

I have no reason to expect them to be better or worse than mine but probably better due to the difference in age.
 
pwood999 said:
Also at 70mph, surely lowering the revs from 1300 to 1100 is not gonna save much petrol ? Rememer you need a certain amount of energy or fuel to keep a brick shaped car rolling !!
Click to expand...
I am sorry that I mentioned the fuel aspect, only to stop people saying that it was a waste of money. My main reason is to run the engine at a lower RPM on a long trip. Just to put a little bit less stress on a 23-year-old engine.
 
300bhp/ton said:
Clearly you are the first person in history to use a Range Rover for a long journey. You should share your idea so that other people can now use such vehicles without worry too.....
Click to expand...
I go everywhere in mine lad. 6hrs to the off-road event every year, to blighty and even taken the old girl as far as italy and back👌😎
No range rover fear here girls🫵😜
 
Datatek said:
Might actually increase fuel consumption because even though the revs are lower, the engine may be working harder to maintain speed.
Click to expand...
I am not sure on the physics of this but I think the engine in my 2002 L322 will do ok given that it is built to tow, and I will have myself, my dogs and not much else in the car.

My main motivation is that there are long periods of steady driving at one speed and I would prefer a lower RPM to put less wear stress on a 23 year old engine.

Alternatively I could drive slower but I think that can create a danger on some roads forcing people to overtake you.
 
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