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Transfer Boxes And Gearing


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Does anyone have a 300Tdi and run a Disco transfer box in a Defender, or 235/85 tyres on a Disco? I'm interested in a Disco xfr box for my Ninety to improve the road 'volume' but I'm worried it won't have the legs for the bigger cogs - it'll nearly indicate 100mph at the moment (at 22mpg) but I'm worried I won't see any improvement if it'll sluggishly pull to 70mph with my foot on the boards in 5th.

Am I right in thinking the 1.2 box would raise high but leave low unchanged?

Cheers

John

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Am I right in thinking the 1.2 box would raise high but leave low unchanged?

Yes

I would have thought with those tyres on it would have been a bit over-geared - my 90 feels dead on 33" tyres with 1.4 gearing... and 32" tyres on 1.2 gearing would be a lot higher than that.

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It's certainly sprightly on the 235/85s but it's certainly revving hard to keep me at 70mph. I'm hoping for a noise and fuel consumption decrease but obviously it'll burn more fuel if my foot's on the floor to maintain 70... Anybody know the ratio of the GKN Defender overdrive?

JB

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There was some discussion at the old place (defender forum IIRC) about fitting a 1.2 box to a 110.

I think it all comes down to what you want from the vehicle, acceleration and towing ability or nice 'relaxed' cruising. Some people like it some don't.

Also helps if you have a tweek or two.

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Spot on, Mark - cheers. For anyone else, the old thread is here.

Summary: Looks like the setup works and is more economical although it's sluggish; there's always 4th gear to get the 'zip' back. The difference between 4th and 5th is 30%, and the difference between the transfer boxes is 15% so 5th@1.4 is a higher gear than 4th @1.2, meaning the 'new' 4th would be about halfway between 4th and 5th now, and 5th beyond that. The only potential problem will be an overgeared 1st for car parks etc. Hmm.

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Got a 1.2 transfer on my 90 300tdi and 235/85 tyres. Still does 70 up the steepest motorway hills and a lot more on the flat. Got an Allard intercooler and a very mild pump tweak and it can still "perform" better than some drivers expect at the traffic light Grand Prix :P

1st has never been too high even when towing on a hill start. It also allows you to join the motorway at 70mph in 4th and then change up rather than running out of steam about 55mph and having to change into 5th as you get to the end of the slip road... :blink:

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Simon - thanks for the opinion, I'll have a think about whether I want another gear above 5th, in return for less below 1st, bearing in mind I also have a set of 33" tyres for offroading.

Budgie - yes, email arrived nicely and the price seems good - I need to inspect my xfr box to make sure the PO hasn't welded the splines up first though! Piccies would be lovely though.

Cheers

John

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John, I've recently done quite a bit more driving in a standard 300tdi 110 and its very interesting to compare it to my 90 running 33" tyres compared to 31s. The 300 feels dead and laggy compared to the TGV but it feels better on the motorway even though its down on power. Although the TGV is much much better on hills than the 300 I had in before it does still struggle on the steepest hill. The biggest hill near me is the one heading north on the A34 a few miles after the M4 junction. If I start at 70 at the bottom my trucks ususally at 55 by the top, the 110s at about 60-65. Part of this is gearing but some will also be the extra resistance of the tyres on the road and the air resistance and weight of the cage, bumper, lights etc. I, personally, wouldn't go for any higher gearing on a 90 like yours. Although the engine's a little louder with a 1.44 a lot of the noise comes from the wind and the gearbox so its not as noticable as you'd imagine. This is why I'm going for a 1.66 t.box with the auto, it'll just make the truck more spritly at low speeds and it'll make life easier on 35s.

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