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Final Drive Ratios


EdF
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I've bought yet another 90 TD5.. On my last two I got Ashcrofts to change the transfer box final drive ratios to the Discovery gearing, which made a good difference (15%) lessening the revs at speed. (Why DO LR over gear them?? Not everyone wants to pull a trailer load of sheep everywhere..). However, I felt with the last two motors that a greater difference would be more comfortable and less noisy as there was still a tendency to 'look for another gear' at speed. Both of them had performance chips, this one has had a remap. The only other gearing option, apart from an overdrive which I don't want, is to change the differential ratios. KAM make crownwheel and pinion sets of 2.83:1 (standard gearing is 3.54:1) and there seems to be a bit of conflict over what percentage difference this makes, Dave Ashcroft says 32% and thinks it's too much of a change, a company called Rakeway who use KAM products say 24%, KAM says 'up to 25%'. Anyway, I suppose the best opinion would be from someone that has done it already as guessing one way or the other is not like driving it... Any takers?? It's a bit expensive to get it done and find out it IS too much.. Thanks!

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When you say discovery gearing, do you mean 1.222:1 or the 1.211:1 "Q" gears? You could go for an old transfer box from a 3-speed Range Rover Auto which is 1.003:1, they can be had cheaply. They're also known as LT230R or Roller boxes because the intermediate gear runs on roller bearings, not the later taper ones.

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I gather from your answer that the RR gears won't fit the 90/Disco transfer box, hence fitting the entire 'box.. I did ask Dave Ashcroft if there was another ratio option other than the Disco one and he didn't mention the 1:1003 which is listed on his site as an option, but maybe not for a 90. I'll ask him specifically about it. I would have thought that if a RR V8 can pull that ratio, then a 150bhp TD5 (with more torque) could as well.. I'd like to find out if the vehicle is driveable using the KAM crownwheel and pinion ratios.. I'm going to contact KAM to see if they can tell me of anyone who has had it done so I can speak to them. Rakeway, a company in Staffs, who also do this sort of work, have put many KAM diffs into Landys with big 6.5 litre GMC diesels but that's a bit different to a TD5! Price inc. everything is about £1000 plus vat.

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Doh, okay how do you know??!! Anyway, I've had contact with KAM and they say several 300TDi owners have fitted their crownwheels and pinions successfully and reckon a TD5 should be okay too, although they don't know any TD5 owners who have fitted them. They do make a 25% difference, not 32% and it sounds about right to me. The downside is that KAM are out of stock and won't have any for about 6 months.. I'm on their waiting list.. At Rakeways, the diffs are £432 a pair, fitting the crownwheels and pinions is £90 for each diff and £360 for removing the difs from the vehicle and replacing them.. They will only fit 90's, not 110's..

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:( Ive no doubt you could do better than that!

Back one is no sweat, but the front is no doubt trickier, though the KAM man says there's a trick to it without disconnecting everything on the hubs.. No doubt someone on here knows it. An option of course is to send Rakeways the diffs by carrier, all depends on personal spannering ability. I have heard from Jon Kelly who runs Venture Overland and who owns my previous 90, that a new overdrive is soon to be introduced by'Overdrives'. Jon has a shiny 110 DC pick-up so the diffs are not an option.

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As Jericho says, unbolt the hub from the ring of bolts on the axle. Pull the shaft and hub out and it's done. I recently fitted new diffs to my Discovery using this method.

HTH

Ivan

Being in the early stages of senility, I couldn't remember what Kevin at KAM said! It's one job I have never done so I'm not familiar with the in's and out's (or the shake it all about) but I knew someone on here would! Incidentally, I've had an email from Jon (Venture Overland) who says that a certain Land Rover specialist he spoke to debating the pro's and con's of the various gearing options had half of the overdrives he has sold returned faulty - due to the electronics mostly. We're going to wait to see what this new overdrive will be like.

One of the best magazine cartoons I ever saw was about Jericho (the city). A bunch of guys pole up at what's left of the city wall and one at the front says, "we've had buglars."

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instead of spending £1000 on diffs ( :o ) why not fit the disco gears for next to nowt and spend £400 on some 33" tyres.

then you'll get your 15% increase from the disco gearing and on top of that 5% from a larger rolling diameter.

20% overall increase is a nice intermediate step between the option you've done before and the super expensive diff option.

Changing the diffs to 2.8s will seriously affect your low range gearing, doing the above will only raise it 5% from the tyres.

If you bust a diff, its expensive to replace and there wont be a 2.8 diff lying around at a mates house you can just bung in, like you can with a standard diff.

fitting 33"s will make your truck look nicer!

you can spend the £600 you save on more shiny pressies to yourself.

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