Freelander 1 Freelander 1 IRD drive ratio

This fred relates to Freelander 1's.

For many years Freelanderer's have discussed values of drive ratio between front and rear wheels. It's said that Land Rover changed the drive ratio on the 2001 model year onwards (started late 2000) Freelander's. I ask the question:

Did they change the drive ratio?
If so, what did the drive ratio change from, and too?

The rave disk states:
Source location = Freelander \ workshop Manuals \ system Description and Operation, page 47-6.

"...The rear wheels are 0.8% under driven, so in most conditions the vehicle is effectively front wheel drive, with the rear wheels turning the rear propeller shaft slightly faster than the IRD drives the front propeller shaft..."

In layman's terms... it's said the front wheels are driven 0.8% faster than the rear wheels. The difference in ratio of drive to front and rear wheels is achieved from within the IRD, using different gears, driven from a single input into the IRD from the output of the gearbox. As the gearbox drive into the IRD is a common point, this can be used as a reference point to work out the ratio of drive to the front wheels, separate to the rear wheels. Comparing the gearing in different IRD's will tell us what the ratio of drive is, and if it changed.

The issue of the VCU (Viscous Coupling Unit) must be considered here. In normal use the rear prop shaft spins faster than the front prop shaft, due to the rear wheels being turned by the road and the gearing within the rear diff. The VCU is located in the middle of both prop shafts and takes out the difference by slipping slightly. For the calculations used to calculate the drive to the rear wheels to work, we will need to replace both prop shafts and the VCU with an imaginary solid drive to the rear diff. It should be noted that a Freelander 1 should never be driven with a solid drive to the rear diff. If it is then transmission wind up will damage the IRD and/or the rear diff.

The main components of the Freelander 1 transmission are: (rough physical layout)


fl1translayout 0jIjDGG

What is the IRD and what does it do?
IRD stands for Intermediate Reduction Drive. It's effectively a fixed ratio transfer box which takes the output power from the gearbox (driven by the engine) and passes it to the front and rear wheels. Drive to the front wheels is split via a differential within the IRD. The diff controls the proportion of drive delivered to each front wheel, allowing the wheels to turn at differing speeds when cornering. Drive to the rear wheels is via the pinion located at the rear of the IRD. The pinion drives the rear diff via the prop shafts and VCU.

The photo's below show the contents of a cut open IRD removed from a Td4. The view yer looking at is the view from the underside of the IRD, when fitted to a Freelander 1. I have marked the front and rear drive path from the single input from the gearbox (larger of the two splines).


DSCN4923frontdrive txsjc3M


DSCN4923reardrive iphqTfh

The larger of the 2 splines is the drive connection from the gearbox into the IRD. The shaft drives the gear mounted on it. The shaft is hollow, which allows the shaft containing the diff to pass through it, allowing the small spline to peep out (front left wheel connection) on the RHS of the photo. Photo's of the shafts below. The smaller shaft is the one which receives drive from the gearbox.


DSCN4855 yRqKIPP


DSCN4868 wG0LA8s

What is the rear diff and what does it do?
The rear diff is driven by the prop shafts via the VCU. The rear diff controls the proportion of drive delivered to each rear wheel, allowing the wheels to turn at differing speeds when cornering.


DSCN4893 8Wrg06O


DSCN4901 SoLgKCO

Are all IRD's the same?
No. The gearing inside the IRD used on the v6 (rover kv6 2.5L petrol engine) has a different number of teeth on certain gears, when compared to IRD's used with other engines (Td4, 1.8 k series petrol and L series diesel). That means the v6 version of the IRD uses a different drive ratio through the IRD. The v6 engine became available on the 2001 model year onwards (started late 2000).

It's said that the IRD's used on the Td4, 1.8 k series petrol and L series diesel are the same. The Td4 engine became available at the same time as the v6 engine. At this point in time the Freelander 1 received many electrical/mechanical changes/improvements. One of these is said to be a change in drive ratio. If this is the case then I raise the question:
Why are the IRD's used on the Td4, 1.8 k series petrol and L series diesel the same, if the drive ratio changed for the 2001 model year?

Surely if there was a ratio change and this altered the front to rear drive ratio, then the gearing in the IRD wouldn't be the same? There's lot of references on the web telling us there was a change, but I can't find details of the exact change. Unless the change happened long before this date, very close to launch date, or not at all.

The 1.8 k series petrol and L series diesel (both rover engines) were available from first launch of the Freelander 1 in 1997. When the Td4 BMW engine became available for sale the L series diesel stopped. The 1.8 k series petrol was available from 1997 when the Freelander was first launched and continued on sale until 2006 when the Freelander 1 stopped production (Freelander 2 started 2006). If the drive ratio changed then it didn't change the gearing in the IRD as that didn't change on the 1.8 k series petrol, which was available before and after the time the change was said to have occurred.

That makes me wonder what the difference in IRD drive ratio really is, between front and rear wheels.

It was always thought that the change took place to help reduce the effects of transmission wind up due to the front and rear wheels being driven (or travelling) at different speeds. The change being done to reduce the stress in the transmission. This can't be the case if the IRD's used on the Td4, 1.8 k series petrol and L series diesel are the same. Counting the teeth on gears inside different IRD's will provide us with the exact difference in front and rear drive ratio within the IRD. It's the IRD drive ratio we assume the change refers to. The rear diff ratio's are said to be the same on all Freelander 1's.

I have a genuine v6 IRD, Td4 IRD and v6 rear diff. Sadly the Freelander's that donated these parts are no longer on the road.

The photo's below show the contents of a cut open Td4 IRD. It failed due to too much stress in the transmission (see ere:

http://www.landyzone.co.uk/lz/f9/cracked-freelander-1-ird-278571.html)

The view yer looking at is the underside of the IRD, when fitted to a Freelander 1. I have counted the teeth on all gears.

V6 teeth count:


DSCN4923v6ratio 8NpFTeC

Td4 teeth count:


DSCN4923td4klratio 7zjRtVO

V6 rear diff teeth count:


DSCN3151v6count 6Ro0d4o



The v6 IRD has different ratio's to all other IRD's used on the Td4, 1.8 k series petrol and L series diesel. The rear diff is said to be the same ratio on all Freelander 1's. Rear diff's were upgraded with a stronger bearing journal, but the ratio is said to have remained the same.

We don't really know what the front and rear drive ratio difference is. The rave disk mentions a value of 0.8% but we don't know for sure if this is the original or later ratio. We assume it's the later ratio. The only way to know for sure is to calculate the ratio's using the teeth counts within the IRD.

There's several IRD drive ratio's to calculate:

1. drive ratio's from the IRD input (output from gearbox) to the front and rear wheels.
2. drive ratio from front to rear wheels, which is representative of what happens when the gearbox is in neutral with freewheeling road wheels (assumes direct drive to rear wheels)
3. drive ratio between front and rear props with the VCU removed and the gearbox in neutral with freewheeling road wheels.

To make the calculations below fair the following assumptions will be made:

1. all 4 road tyres are of the exact same circumference
2. Freelander is on flat level ground
3. front wheels turn at the exact same speed due to assumption 1 and 2
4. rear wheels turn at the exact same speed due to assumption 1 and 2
5. both prop shafts turn at the exact same speed due to our imaginary direct drive to the rear diff (don't try this on a Freelander 1 or transmission wind up will break it)

Assumption 3 above is so we can ignore the possibility of the IRD diff inner carrier and planet gears turning, within the diff, as all drive will go to the ring gear and split equally to both front wheels.

Assumption 4 above is so we can ignore the possibility of the rear diff inner carrier and planet gears turning, within the rear diff, as all drive will go to the ring gear and split equally to both rear wheels.

The following calculations are based on the IRD input spline being turned one full rotation, which is 360 degrees. It's assumed only the ring gear in the diff will turn. Hence the front wheels turn at the same speed.

V6 IRD input (gearbox output) to front wheels:

((( 30 / 23 ) x 22 ) / 39) = 0.735785953


ratiov61 UvhiRqH

V6 IRD input (gearbox output) to rear wheels: (via imaginary direct drive)

((((( 30 / 23 ) x 38 ) / 21) x 14 ) / 45) = 0.734299517


ratiov62 BbncFyF

Therefore the v6 IRD drives the front wheels faster than the rears by:

( front ratio / rear ratio ) x 100 = ratio

( 0.735785953 / 0.734299517 ) x 100 = 100.2024291

This would suggest the v6 IRD drives the front wheels 0.2024291% faster than the rears.

Td4, 1.8 k series petrol and L series diesel IRD input (gearbox output) to front wheels:

((( 29 / 24 ) x 21 ) / 37 ) = 0.685810811


ratiotd41 mPzSlKh

Td4, 1.8 k series petrol and L series diesel IRD input (gearbox output) to rear wheels: (via imaginary direct drive)

((((( 29 / 24 ) x 38 ) / 21) x 14 ) / 45 ) = 0.680246914


ratiotd42 TfhPse4

Therefore the Td4, 1.8 k series petrol and L series diesel IRD drives the front wheels faster than the rears by:

( front ratio / rear ratio ) x 100 = ratio

(0.685810811 / 0.680246914 ) x 100 = 100.8179232

This would suggest the Td4, 1.8 k series petrol and L series diesel IRD drives the front wheels 0.8179232% faster than the rears.



Another interesting calculation is to calculate the difference between the front and rear wheels when freewheeling. This is the freewheeling difference when the front wheels drive the rear wheels via the IRD an our imaginary direct drive to the rear diff. All tyres are the exact same circumference for these calculations. The gearbox is in neutral so there's no drive to the IRD from the gearbox. When doing these calculation the results confirm the above results.

The following calculations are based on both front wheels being turned once, which is 360 degrees, at the same speed so only the ring gear turns in the diff. It's assumed only the ring gear will turn in the rear diff too. Hence both rear wheels will turn at the same speed.

V6 front wheel to rear wheel ratio: (assumes imaginary direct drive to rear diff)

((((( 39 / 22 ) x 38 ) / 21 ) x 14 ) / 45 ) = 0.997979798

Therefore the v6 rear wheels turn slower than the fronts when driven directly by the front wheels (via the IRD):

( 1 - (0.997979798 / 1 ) ) x 100 = 0.202020202%


ratiov63 Yis4Fgx

Td4, 1.8 k series petrol and L series diesel front wheel to rear wheel ratio: (assumes imaginary direct drive to rear diff)

((((( 37 / 21 ) x 38 ) / 21 ) x 14 ) / 45 ) = 0.991887125

Therefore the Td4, 1.8 k series petrol and L series diesel rear wheels turn slower than the fronts when driven directly by the front wheels (via the IRD):

( 1 - ( 0.811287478 / 1 ) ) * 100 = 0.811287478%


ratiotd43 y4UGh59



Another interesting calculation is to calculate the difference between the front and rear prop shaft speed with the VCU removed and the Freelander 1 freewheeling. This is the freewheeling difference when front and rear wheels turn naturally when turned by the road. All tyres are the exact same circumference for these calculations. The gearbox is in neutral so there's no drive to the IRD from the gearbox. When doing these calculation the results confirm the above results.

The following calculations are based on both front wheels being turned once, which is 360 degrees, at the same speed so only the ring gear turns in the diff. It's assumed only the ring gear will turn in the rear diff too. Hence both rear wheels will turn at the same speed.

Rear diff ratio:

Drive / driven = 14 / 45 = 0.311111111...
Driven / drive = 45 / 14 = 3.214285714

Which matches the ratio of 3.214:1 mentioned in the rave disk.

V6 front wheel to IRD pinion:

((( 39 / 22 ) x 38 ) / 21 ) = 3.207792208

Therefore the v6 front prop turns slower than the rear prop when freewheeling with no VCU by:

(( 3.214285714 / 3.207792208 ) x 100 ) -100 ) = 0.20242915%


ratiov64 Mr3Q8t9

Td4, 1.8 k series petrol and L series front wheel to IRD pinion:

((( 37 / 21 ) x 38 ) / 21 ) = 3.207792208

Therefore the Td4, 1.8 k series petrol and L series diesel front prop turns slower than the rear prop when freewheeling with no VCU by:

(( 3.214285714 / 3.188208617 ) x 100 ) -100 ) = 0.817923186%


ratiotd44 v0fxx5A



My conclusion.
Assuming I can count gears correctly, and the above calculations and theory are correct... this provides us with evidence that any changes that may have happened regarding drive ratio's on the Freelander 1, didn't alter the drive ratio within the IRD to the front and rear wheels.

All Td4, 1.8 k series petrol and L series diesels have the same IRD drive ratio difference between front and rear wheels, which is 0.8179232% (rounded oft to 0.8%).

The v6 IRD drive ratio difference between front and rear wheels is 0.2024291% (rounded to 0.2%).

I've thought about why the IRD drive ratio may be lower in the v6 IRD than other Freelander 1's with different engines. I'm guessing this could be because:

- LR wanted to reduce the stress in the transmission by making the drive ratio closer to 1:1, but still maintain the front wheels turning faster than the rears.
- Reducing the IRD drive ratio to compensate for the heavier front end on the v6 Freelander 1 when compared to other FL1's with different engines, as the heavier front end would put more pressure on the front tyres, reducing their radius to the road, and therefore alter the difference in ratio of front to rear wheels turning.

reserved post

Hippo said:

reserved post

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superb post my friend

hope we can have that as a sticky , so it's in a dominant position , must have taken u ages to write and investigate that

thks mate for sharing such an informative post

Are you certain about differences for models stated, your 0.8 and 0.2 figures are very indicative of the different ratios pre and post 2001 models when changes allegedly took place, why was the v6 ird not the same one used in the td4and 2001 on k series?

freelance said:

Are you certain about differences for models stated, your 0.8 and 0.2 figures are very indicative of the different ratios pre and post 2001 models when changes allegedly took place, why was the v6 ird not the same one used in the td4and 2001 on k series?

Click to expand...

I don't know. That's something I was wondering too. Hence why I assumed front tyres taking a heavier weight on the v6.

The v6 rear diff came from a v6 Freelander as I also have it's gearbox. The owner said it was a v6. He run it for a while until it started playing up. The v6 ird came from a v6 Freelander. I have it's gearbox too and had a look round the engine at the same time when collecting. You never really know but I trust both people and don't have any reason to think they made a mistake.

The Td4 ird came from a garage. He said it came from a Td4. Can't remember if auto or manual. It was advertised as spares or repair as the bearings have started to go inside.

If what peeps say on the web is true... that all Td4, 1.8 k series petrol and L series diesels all have the same IRD (I read that as all having the same number of teeth on the gears inside) then what I put above is correct. If they're wrong then I'm wrong too. That would mean all those selling recon ird's are wrong too, or have all made a mistake that the Td4, 1.8 k series petrol and L series diesel share the same ird.

I will look out for another ird to count the teeth on, from a 1.8 k series or L series diesel.

If anyone wants to offer up their teeth count then please do.

I marked the teeth with a yellow paint pen so I know how many I counted. I also counted them 3 times on each gear just to be safe, when I realised they had different teeth counts. I still have all of them.

hippo

I just took a pic out of the jatco books I bought to see if it may be of any use to u

hope im not being rude in case you've already got it

sorry this is the other bit to it

gstuart said:

hippo

I just took a pic out of the jatco books I bought to see if it may be of any use to u

hope im not being rude in case you've already got it

Click to expand...

No problem. Thanks. The diff it refers to will be the diff in the auto. The auto contains a diff on the engine side. They will be listing the ratio for that diff I think.

Hippo said:

No problem. Thanks. The diff it refers to will be the diff in the auto. The auto contains a diff on the engine side. They will be listing the ratio for that diff I think.

Click to expand...

Nice work Hippo.
The Jatco book Gary posted is referring to the internal diff (when fitted to a VW car). There isn't a diff in the gearbox when it's fitted to the Freelander. There's a link tube that takes the drive through the box to the nearside drive shaft. Don't forget, the Freelander's front diff is inside the IRD.
The front/ rear ratio difference you are seeing is likely due to the 1.8 /L IRD is an earlier version. The ratio was changed after late 2000. All V6's got the later front/ rear ratio but also the overall ratio of the V6 was higher than that of the 1.8/L/TD4 IRD. I can't really decide why LR made the V6 higher geared. It was likely to create a more economical car with a more relaxed, upmarket drive. The V6 has more than enough grunt to drive with the higher gear ratio.

Nodge68 said:

Nice work Hippo.
The Jatco book Gary posted is referring to the internal diff (when fitted to a VW car). There isn't a diff in the gearbox when it's fitted to the Freelander. There's a link tube that takes the drive through the box to the nearside drive shaft. Don't forget, the Freelander's front diff is inside the IRD.
The front/ rear ratio difference you are seeing is likely due to the 1.8 /L IRD is an earlier version. The ratio was changed after late 2000. All V6's got the later front/ rear ratio but also the overall ratio of the V6 was higher than that of the 1.8/L/TD4 IRD. I can't really decide why LR made the V6 higher geared. It was likely to create a more economical car with a more relaxed, upmarket drive. The V6 has more than enough grunt to drive with the higher gear ratio.

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Well remembered. I always forget the diff bit.

The problem we're seeing with the ird is the T4d ird I have, is said to be the same as the 1.8 k series and L series. The L was made before the change. The Td4 was after the change. The 1.8 was on both sides of the change. So we can't work out why the 3 of them share the same ird. That would mean the change only happened to the v6, or it didn't happen.

So I can destress and fit a v6ird to my 1.8

Diesel Do said:

So I can destress and fit a v6ird to my 1.8

Click to expand...

Not sure if the physical shape of the v6 ird is the same as others. I would need to compare what I have.

Current situation is we need to know from others what their teeth count is. If they took photo's when taking theirs apart, they may be good enough to count teeth. Same for peeps taking the pinion oft... allows us to see the gears on the right of the pinion hole.

From what Bell said to me ages ago your conclusions seem to agree. He said they were all the same except the v6 which seemed odd with the my2001 supposed changes

I enquired about this some months ago. From what you said Hippo the difference between the L series, TD4 & the K 1.8 series front and rear wheels is 0.8% compared to 0.2% for the V6. In principle then could there be an advantage in fitting a V6 IRD, which I know can't be done, to the L series, TD4 & the K 1.8 series? If it were possible it would reduce the difference between from & rear wheels by 0.6% and reduce stress to the VCU - IRD - diff. Theoretically could the 'key' V6 IRD internals be fitted to a L series, TD4 & the K 1.8 series IRD to give that reduction?

htr said:

I enquired about this some months ago. From what you said Hippo the difference between the L series, TD4 & the K 1.8 series front and rear wheels is 0.8% compared to 0.2% for the V6. In principle then could there be an advantage in fitting a V6 IRD, which I know can't be done, to the L series, TD4 & the K 1.8 series? If it were possible it would reduce the difference between from & rear wheels by 0.6% and reduce stress to the VCU - IRD - diff. Theoretically could the 'key' V6 IRD internals be fitted to a L series, TD4 & the K 1.8 series IRD to give that reduction?

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The V6 IRD is physically a different shape to the 1.8/L/TD4 IRD. It's casing is different as are 90% of the internals. From memory, the V6 bearings are larger, presumably to take more torque. The only parts that are interchangeable are the rear pinion/housing and crown wheel. I'm reasonably sure that the actual IRD as a complete unit will fit non V6 gearboxes, but I don't think one of the bolts lines up. The cooler pipe work is a different shape too, but that's not really a problem.

Nodge68 said:

The V6 IRD is physically a different shape to the 1.8/L/TD4 IRD. It's casing is different as are 90% of the internals. From memory, the V6 bearings are larger, presumably to take more torque. The only parts that are interchangeable are the rear pinion/housing and crown wheel. I'm reasonably sure that the actual IRD as a complete unit will fit non V6 gearboxes, but I don't think one of the bolts lines up. The cooler pipe work is a different shape too, but that's not really a problem.

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Thanks Nodge, you can see I was wondering about swapping some internals over. If it were possible would it reduce stress on the VCU - IRD ...?

Ideally it would be great to have both IRDs open to make careful comparative measurements. Are the differences so obvious to make it not worthwhile, or is that a possibility Hippo?

htr said:

Thanks Nodge, you can see I was wondering about swapping some internals over. If it were possible would it reduce stress on the VCU - IRD ...?

Ideally it would be great to have both IRDs open to make careful comparative measurements. Are the differences so obvious to make it not worthwhile, or is that a possibility Hippo?

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I could swop over the internals at the weekend to see if it works. Natuarlly one of them has been cut open but I did wonder myself when messing with them if it's possible to change over the gears.

The v6 IRD would presumably need to be stronger due to the v6 giving more power in the standard form, as well as the Callaway v6 option in the US market which was super charged to 250bhp. LR were involved with this. I assume the IRD is the same on that as the standard v6 setup.

just seen this thread ..
cheers for posting the info Hippo
excellent

hd3 said:

just seen this thread ..
Cheers for posting the info hippo
excellent

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+1!

Hippo said:

I could swop over the internals at the weekend to see if it works. Natuarlly one of them has been cut open but I did wonder myself when messing with them if it's possible to change over the gears.

The v6 IRD would presumably need to be stronger due to the v6 giving more power in the standard form, as well as the Callaway v6 option in the US market which was super charged to 250bhp. LR were involved with this. I assume the IRD is the same on that as the standard v6 setup.

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The V6 IRD isn't a weak unit. Both the standard IRDs are well up to the task of a standard or modified power unit. It's only damaged when the VCU begins to stiffen up. When this happens, it's under constant heavy loads which will eventually destroy it. Driving the Freelander along the road doesn't do anything like as much damage to the bearings and gears.