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IRD/Gearbox... we made it wrong...

Discussion in 'Land Rover Freelander' started by matko, Nov 22, 2019.

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  1. Avocet1

    Avocet1 Well-Known Member

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    Ah! No, I definitely didn't have one of those - nor the one under the IRD! Mind you, mine's a TD4 and the exhaust doesn't run above it either. (Plus, as Nodge says, it runs a lot colder than a petrol exhaust).
     
  2. Avocet1

    Avocet1 Well-Known Member

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    I've heard this mentioned before and would be curious to know the reasoning behind it?
     
  3. Hippo

    Hippo Lord Hippo

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    Nowadays they say to put deeper tread on the rear of all cars. Previously they said to put them on the front. Theory being if you go round a corner in the wet... the deeper tread front end will hold the road betterer.

    That theory changed. If you image drving round in a circle getting faster and faster... you will lose the front end first before the rear. You will feel the front being lost before you lose the rear. That will make you back oft the power when sensing losing the front. If you feel the front slide you will back oft the power. If the rear end slides you've lost it and too late. You will spin.

    If the deeper betterer tires are on the front then it will take more for you to lose the front end. There is a possibility you will loose the rear at the same time or before losing the front, if the front tires are on deeper tread than the rear tread.

    There was a video on youtube about it several years ago. Propper tire wet road testing and changing treads depths about to prove the theory and show what happens, when trying to see what the highest speed is that yer can do while driving round in circles.
     
  4. Avocet1

    Avocet1 Well-Known Member

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    Ah! OK, yes, that's fine, I just thought it was advice about preserving the VCU or lowering loads on the IRD. Again, going back to the X-Trail, the slightly different gear ratios in the front and rear half of the drivetrain meant that they were always "fighting" each other very slightly and you could reduce that by having the tyres with the bigger overall rolling radius on the back. I've got a set of "Event" tyres on at present and I have the least worn on the back, but they're noisy as hell, so I think I'll put the least worn ones on the front, so I can even out the wear on all 4, and then replace them with something more "road" orientated. Otherwise, I'll end up with too much tread on the back ones and then I'll feel obliged to replace the fronts with the same sort when they wear out, because otherwise I'd be wasting some life on the back ones!

    The thing about having the better tyres on the back (for any car, not just a Freelander or X-Trail) that you outline above, is still hotly debated. In a straight line (assuming the front and rear track are the same), it is still regarded as best practice to have the deeper tread on the front because you're less likely to aquaplane as the rear wheels will tend to run in the "shadow" of the fronts, in the area of tarmac already "squeegeed" dry by the front tyres. But there has been a realisation, over time, that this isn't where the most danger occurs.

    As you say, once the car is going round a bend, the rear tyres don't follow the path of the front ones and could then aquaplane anyway and once you're at the point where one or other end is going to let go, understeer is the preferred way to lose adhesion because it's easier for the driver to correct. Instinctively, people lift off when they realise the car isn't going where they point it and that, in itself, helps to tame understeer. With more and more cars having electronic stability control, it's easier to control understeer because the ESC system can take over control of the throttle as well as the brakes. Plus, of course, if it all goes very badly wrong, all the car's passive safety systems (seat belts, airbags, crumple zones) are set up to work best if you go forwards into something, rather than backwards or sideways. Pretty much all cars are set up to understeer at the limit for those reasons. The clincher, I think, is that as most cars these days are front wheel drive, they'll wear out the front tyres first, so having the most worn ones on the front, forces you to replace them sooner. You then put the new ones on the back and the back ones on the front, wearing out the front ones (which used to be rear rear ones) sooner, meaning that all 4 tyres are never as old as they would be if they're rotated to even out the wear all the time.
     
  5. Hippo

    Hippo Lord Hippo

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    On the Freelander 1 you put the deeper tread tires on the rear for the same reason. It is thought to reduce the stress on the vcu and transmission.
     
  6. Avocet1

    Avocet1 Well-Known Member

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    OK, ta. Back where I was then! Do you know if anyone has ever posted anything on the reasons behind that? I never really fully understood the different ratios at both ends of the X-Trail. It's true, you can get the gear ratio figures and verify it, but I never fully understood WHY. I think it was to do with the small electromagnetic clutch on the nose of the rear diff. It's not a big hydraulic pump like the Haldex, and isn't powerful enough to hold the plates of the multi-plate clutch together, so the system relies on the natural wind-up in the transmission to do that, once the electromagnetic clutch starts the engagement of the plates off.

    I wonder, with the FL, whether it's just to try and "take the play out" as it were and reduce transmission "snatch" a bit? I could see how if (say) the rear wheels were always "pushing" a tiny bit, it would take up a lot of the backlash in the transmission?
     
  7. GrumpyGel

    GrumpyGel Well-Known Member

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    I think it was said on here that the slight gearing ratio difference in the axle was to give the car a 'front wheel drive feel' to the driver.
     
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  8. Hippo

    Hippo Lord Hippo

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    Originally the ratio difference on the FL1 was said to make the driving feel betterer. It feels more like a front wheel drive with the ratio off set applied. It off set the differing prop speeds but the vcu could take this out anyway. Lots discussed about it on this forum many years ago. Some correct. Some not correct.

    In the early days the FL1 had some complaints on how it felt a bit tight to drive. It was different and it reality most FL owners were new to driving heavier bulky vehicles as they came from the traditional saloon car market. It was also said there were lots of rear diff failures. As if this were a major problem. There were probably sone diff failures as all parts have problems but there was never a significant problem that was ever proven to have happened. The web has the ability to out grow facts sometimes. There would have been problems with the 4x4 setup being abused like tire problems.

    Later on when the 2001 model year came out the 1.2% difference in prop ratio's was reduced to 0.8%. It was believed this was done because LR wanted to reduce the stress on the transmission. I did some work on ere looking into this and it got trashed by others. It's my belief from what i did that the ratio change was only on the v6 because the ratio in the ird from gearbox input to front wheels changed on the v6. So the ird ratio between front and rear wheels had to change too.

    Regardless of what ratio you have... The front wheels take more weight so the tires are squashed more. When you compare the squashed rolling diameter of front and rear tires through the transmission ratio's, they tend to cancel out to near 1:1. The v6 wasn't popular in the uk but it was the second most popular engine built into the FL1 from production figures, because it was far more popular world wide where petrol is more popular and cheaper. It's heavier front end pushes the tires down more. The differing 0.8 ratio caters for this change on rolling diameter tire size to make it tend to 1:1 ratio anorl.

    When comparing a FL1 with and without the vcu and props fitted, fitted with vcu does make the drive feel different. In general some like the drive feeling with vcu. I do as it feels it has more stability. Some like the drive feeling without the vcu. In general peeps tend to like the feel they have driven first. If they first drive without vcu they like it betterer. If they first drive with vcu they like it betterer. Both tend to not like the drive option they didn't drive first.
     
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  9. Nodge68

    Nodge68 Well-Known Member

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    The Freelander needs identical tyres all round. The AWD system also has to have its tyres rotate in pretty tight synchronisation, to prevent unintentional VCU stiffening when not needed.
    When new tyres are being fitted, ideally all 4 should be replaced together, which guarantees correct rotational synchronisation. However it is allowable to replace just 2 tyres, providing the new tyres are identical to what is currently on the rear. The new tyres must be fitted to the rear, the half worn tyres from the rear, being moved to the front.
     
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  10. Nodge68

    Nodge68 Well-Known Member

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    The rear diff is slightly under geared compared to the front. This has the effect that the VCU is being turned faster on the rear output, compared to the front input. The difference is small with 4 new identical tyres. However as the front tyres wear faster than the rear, this slight speed difference between front and rear decreases as the ratio between difference between front and rear reduces There will come a point where the front and rear are actually the same ratio, due to the front tyres rotating at a higher rate, as they wear faster. I think the "sweet spot" is when the fronts are just about half worn, and the rears are new.

    However if new tyres are fitted to the front, with half worn tyres on the rear, then the ratio difference between front and rear is increased, which can cause the VCU to transfer more torque than is should, increasing IRD and diff wear, and killing the VCU too.
     
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  11. matko

    matko Member

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    Wouhou what a debate on the tires. :D still don t know if I will do all this one time.

    They propose me one gearbox but it s a freelander with a rover motor... is it the same gearbox? maybe on somes models it differs.. i wait for your consil... :D
    Hope we suceed to do something with this car...
    Have a nice day!! :)
    Mateo
     
  12. Nodge68

    Nodge68 Well-Known Member

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    The gearbox is different, and won't fit the TD4 engine
     
  13. Avocet1

    Avocet1 Well-Known Member

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    Interesting points, all. Thanks! I have to say I'm struggling slightly with the "tyre compression" thing. It's common on most cars, for manufacturers to specify different tyre pressures front-to-rear, so if they were worried about different amounts of tyre compression at each end, they could have simply specified different pressures. Nodge's point about putting the less worn tyres on the back in order to reduce transmission wind-up, is how I originally understood the advice to be - rather than Hippo's point about aquaplaning. (Although, I do, of course, accept that current accepted wisdom IS to put the newer tyres on the back to make the rear wheels less likely to do so).

    I've never driven mine with the prop disconnected and it's interesting that Hippo mentions the ratio change in 2001, because mine is a 2001 car, so I'm not sure what rations it has. Can I tell from the VIN?

    Also, just to help get my head round this, are you both agreed on which end has the higher ratio? Am I right in thinking that (say, in round numbers) 100 crankshaft revolutions would give (say) 1 revolution of the front wheels and (say) 0.9 revolutions of the rear wheels, or is it the other way round?
     
  14. Nodge68

    Nodge68 Well-Known Member

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    It's generally accepted that the rear ratios changed on the 2001 onwards model (chassis prefix 1A), but some information suggests it was earlier,maybe early in 2000.

    The IRD rear output ratio was changed, rather than the rear diff itself. This was in response to large numbers of IRDs failing early on in the Freelander's life.
    Yes that's correct, although it's closer for the rear to be 0.98 to 1 rotation at the front.
     
  15. Hippo

    Hippo Lord Hippo

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    I thought we were talking more about wet driving although vcu's were involved as well. In general all cars should have newer tires on the rear. LR state this in the owners manual. It does help the theory of the vcu too which is also why LR say this.

    On a factory built standard FL1 the rear wheels are under driven which makes them turn the rear prop shaft faster than the front.

    If you put a brand new set of tires on a v6 FL with a working vcu, and mark the props with chalk, then drive 100meters, then look at the chalk marks, they will still be in line. Its an interesting test that not many have done. It sparked off a number of freds I created where I tried to get to the facts of it all.

    One if them includs tire pressure and rolling diameter when under pressure from the FL1 they're fitted too. LR want tire pressures to be the same all round, unless heavily loaded. Or when towing when it can be a problem.

    Not sure about yer comment about rolling diameter under pressure. If you set yer tires to the same pressure, then step back and compare the front and rear wheels, the centre of the front wheel will be closer to the ground. Therefore it's diameter has reduced when rolling. Take the engine out and the weight will reduce. The centre of the wheel will rise.

    On a FL1 the front tires will wear faster than the rear. Same as any car.

    We have talked vcu's to death on this forum. Most of which is opinion, not fact. You don't need to care or worry what yer ratio is. As long as the deeper tread goes on the rear, and they're the same make/model/size, then you will be ok. Test yer vcu regular with the One Wheel Up Test OWUT and get to know its
    timings. If the time increases investigate. It could be the hand brake catching or the vcu starting to stiffen up.
     
  16. Hippo

    Hippo Lord Hippo

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    There wasn't a large number of ird failures. Its internet myth. The ratio change was on the v6 only for 2001 model year starting late 2000, which matches part numbers. Unless enough peeps count the teeth in the ird's to prove otherwise. The part number would have changed if the none v6 ird had changed.
     
  17. matko

    matko Member

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    Very interesting mecanical theory!

    We gona try next monday and tuesday to go to fix the freelander. My plan:

    -> We quit the gearbox AND the IRD at all. Once on the floor we try to put the IRD in the gearbox in order it fit in well. If it don t go in, we try to "eat" the teeth that are worst. Then clean the female with Gazoil and a magnet to capture all the little opiece of metal (i know it s a **** that inside there still could be little pieces of metal... we will see)
    Let dry it and put some oil to lubrificate. (transmission oil)?
    -> Once we suceed to put the IRD inside the gearbox (i read to put the 4 on the gearbox can help... i didn t know that.) We reassemble the all thing.

    -> Little question: Is it possible to reassemble the gearbox and IRD on the floor and then to fix it in the car, like both together already attached?? (if we quit the large metal car cradle?) I think would be easier. Then is it possible to put the two little tube of water easy?
    I know this is a lot of question :cool: ... and next time i would write here before to destroy it all... :mad:

    I hope my english is still understandable.
    Thank you a lot ;)
    See you
    Mateo
     
  18. Nodge68

    Nodge68 Well-Known Member

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    No. The IRD needs to be put in once the gearbox is bolted to the engine. Fitting the IRD isn't difficult. You just need to turn the shafts so the splines line up. Fit the front left driveshaft before the IRD, so you can turn the shaft to line up the splines when fitting the IRD. You'll also need to turn the IRD rear propshaft output, so the larger spline lines up too.
     
  19. Avocet1

    Avocet1 Well-Known Member

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    Thanks again, both. So imagining it was on steel railway wheels of the same rolling radius at each end, the engine driving the powertrain would cause the front wheels to cover a slightly greater distance than the rears? (Say, for every 1m the front wheels cover, the rears cover (say) 0.98m?

    If we then swap the "railways wheels" for a new set of tyres all round, all at the same pressure, the drop in rolling radius on the front wheels due to the weight difference, are we saying that in the example above, for the same number of engine revolutions, both the front and the rear wheels now cover 0.98m?

    If we then have half-worn tyres on the front and new tyres on the rear, all at the same pressure, are we then saying that in the example above, for the same number of engine revolutions, the front wheels now cover (say) 0.95m and the rear wheels cover 0.98m?

    (Obviously, in reality, the car itself travels only one distance and the tyres at both ends just slip a bit)!
     
  20. Avocet1

    Avocet1 Well-Known Member

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    I wasn't actually interested in driving in the wet, only in understanding the different gear ratios at each end of the car. I don't disagree with anything you say about driving in the wet, but it's not the thing I was interested in.

    OK, and this suggests that either:
    1. The difference in rolling radius because of the extra weight on the front is exactly compensated by the different gearing at each end or
    2. The front and rear tyres just each scrub a bit and the VCU doesn't allow any relative movement of the front and rear halves of the propshaft or.
    3. By sheer rotten luck, 100m is the right distance for one half of the propshaft to have turned exactly one turn more than the other half?

    If 1 is true, then putting new tyres on the back and half-worn on the front won't be any different to putting new on the front and half-worn on the back. Either way, you'll still have the either the VCU absorbing the difference, or tyre scrub absorbing the difference, or a bit of both. I'm guessing that 2 being true is unlikely? As for 3, have you tried it again with different tyre pressures front-rear or over a different distance?

    Agreed. The comment was simply that it seems odd to go to the trouble of having different gearing at each end of the car when you could just run the front tyres a few PSI harder to compensate!

    Understood, but this is just curiosity on my part. I'm sure most owners DON'T care or worry what the gear ratios are! I just want to get to know the system a bit better, and tapping into your and Nodge's knowledge is very useful to me - thanks!
     
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