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Defender TD5 high Ratio Transfer box gears


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Hi, I believe the general consensus is its easier to get hold of an old Discovery box than to open the box up. I have been watching a few on ebay, but they seem to go for silly sums - especially the TD5 ones with diff-lock (later Disco's didn't have diff-lock or at least the lever to engage it).

As far as towing/pulling power - the independent dealer I bought mine from said that the transfer box swap was best done in conjunctions with a remap.

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when i had a td5 i looked at these options, in the end i went for an overdrive (i had a GKN one, but roverdrive still do overdrives. one for sale on D2 forum currently) the benefit being a 6th gear without losing the low down grunt for towing.

having said that a 1.2box in a disco doesnt sturggle for towing in hilly areas but then RD of tyres is less.

another solution fit bigger tyres to see what it would be like, it would be similar to fitting a1.2 over a 1.4 box if you get the OD right for the increase.

last 1.2box with difflock i sold for £50.

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What sort of weight will you be towing?

And under what sort of conditions?

My standardly-ratioed 90TD5 has seen plenty of "fast-road" towing [motorways etc] with 2.5 tons of twin-axle flatbed behind it. I can happily go up the entireity of Shap Fell in 5th at 60MPH. If/when the transfer-box dies I'll be fitting the highest ratio I can find - OK, I may need to downshift to 3rd more often when towing on hills, and occasionally do the start-off-in-low-2nd-then-shift-to-high-1st double-lever-shuffle but that will be a minor inconvenience compared to the reduction in noise when not-towing on open roads at 75-80MPH.

Truth is, I reckon in the 100,000-odd miles I've driven, low-ratio's only ever been used on-road for about five miles. The Ashcroft option which keeps the low-ratio as-is but raises high-ratio significantly is worth looking at.

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I have a 1.2 (disco 1) box in a 300tdi 110, and I tow a horse trailer, with 2 horses the trailer weighs probably more than 2 but less than 2.5 tons, and has considerable wind resistance. Solo it's excellent, you can engage the clutch at tickover, and I think it gives less gearchanging than with a 1.4 box. Towing it's fine, even in 5th (it has a full width intercooler) but 1st feels just a wee bit high setting off on much of a hill or crawling with it in traffic, but then I just use low. I also have a standard 90 and that feels a bit manic by comparison, but it does set off with the trailer more easily. A td5 should find it easier. However I think if I was pulling say 3.5 tonnes it might be a different story

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It's only very rare does it called in to tow something most of the time it's just on the road. It is completely standard apart from snorkel and a hannibal rack an overdrive does seem best all round solution but obviously most expensive! Thanks for your advice, is a 300 Tdi disco transfer box the same as they have diff lock right?

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It's only very rare does it called in to tow something most of the time it's just on the road. It is completely standard apart from snorkel and a hannibal rack an overdrive does seem best all round solution but obviously most expensive! Thanks for your advice, is a 300 Tdi disco transfer box the same as they have diff lock right?

Yes, but it won't have the diff-lock switch that your Td5 needs. You can do without it, but the ECU uses the high/low range signal to apply a different throttle map so you'd lose that feature.

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Very helpful advice here. RustyNissanPrairie thanks for that its exactly what i was worried about sounds like i would definitely require a remap with a high ratio transfer box and think i would always be limited to standard tyres. Shame theres not a cheaper overdrive available!

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Roamerdrive DS is a lovely bit of kit. I've had one for the last 9 months or so.

Seems very well engineered, some very nice touches like the mounting bolts being machined for O rings to prevent leaks.

Very easy to install, with the new gearshift mechanism, probably a leisurely 3 hours work.

Not completely silent in use, but only just noticeable.

You'll need to find EP90 in GL4 spec (the handbook contains dire warnings on the subject of GL4/5 and GL5 oils). Given the cost of the O/D, the fully synthetic GL4 from Castrol seems worth the cost - especially since I couldn't find anywhere with GL4 in stock but Ha****ds had the Castrol on the shelf.

If only I'd known how good it was, I wouldn't have wasted my money on that complete **** from GKN years ago. In fact, the only reason I did was that I couldn't be sure the 'old' shift mechanism on the Roverdrive would fit in the Ibex.

The new one should fit anything with the correct shift housing on the main box.

Dave

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My GKN lasted about 35k behind a TGV, and approx 1 warranty plus 1 week.

It jammed leaving me with no drive at all. It also never shifted in smoothly, and always seemed to be wet with ATF.

When stripped the oil pump showed significant wear (steel piston running in ali barrel), and both filters were full of swarf.

The big screen filter wasnt too bad, having been off and cleaned more than once, but the internal one was completely full.

I stripped and rebuilt with new seals. The rough shift appeared to be due to a missing spring in the solenoid.

However it either jams or the clutch slips when warm, it works fine when cold, but when disengaged coming off the motorway it takes about 1/2 sec to get drive through it (feels a bit like an auto).

Wasted enough time on it, will probably flog it for spares when I get around to it.

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