200tdi running 1.6 transbox swap to 1.2?

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Mac-1990

Mac-1990

Member
Posts
72
Location
West Yorkshire
Hi all,
Just wanted to ask for some personal experience of swapping a 1.6 transfer box to a disco 1.2 or 1.4.

I've got a 110 1985 ex mod landy. It's got a disco 200tdi and although no information can be found on my transfer box I belive it to be 1.6 which means anything over 50mph on the motorway is awfully loud and drones. Can also drive in 5th gear at about 25/30mph.

I'll never tow. She's my daily driver and I use motorways frequently enough that a long journey puts me off using the truck and going in the family insignia instead which isn't anywhere as fun!

I'm just looking for some personal thoughts on those who have done what I'm thinking about doing. Or anything to take into account.

Also just wondering what a second hand box miles ought to be at without being a lump of scrap and not worth buying. Is 150,000 miles to much unless its almost free of charge?

TIA
 
LT230 are tough, so long as no clanks and bangs, miles dont really matter.
I had a 1.19 in my 90 with 7.50 tyres and she struggled on long inclines, pretty much became a 4 speed gearbox, went back to std 1.4 and its much better
Best thing about 1.4 is they are cheap as everyone wants the 1.2 to carry out the so called upgrade to their defender!
Also worth checking as the LT77 also comes with different ratios, so you might actually get away with a 1.2.

1.6 is really deep ratio, might have some value for an off roader, might even find a swapper.

Ashcroft website has a calculator so tou can add tyre sizes/tfer/gbox ratios and work out speeds etc, very handy.
 
lynall said:
LT230 are tough, so long as no clanks and bangs, miles dont really matter.
I had a 1.19 in my 90 with 7.50 tyres and she struggled on long inclines, pretty much became a 4 speed gearbox, went back to std 1.4 and its much better
Best thing about 1.4 is they are cheap as everyone wants the 1.2 to carry out the so called upgrade to their defender!
Also worth checking as the LT77 also comes with different ratios, so you might actually get away with a 1.2.

1.6 is really deep ratio, might have some value for an off roader, might even find a swapper.

Ashcroft website has a calculator so tou can add tyre sizes/tfer/gbox ratios and work out speeds etc, very handy.
Click to expand...
Interesting! So how would I find out the lt77 ratio? It's a military green box but other than that I know nothing of its ratio. I had read somewhere about changing tyres can change the ratio but I couldn't get my head round the idea. Is it bigger wheels lowers or highers? To be honest not even sure what size I've got on mine without looking.

When you say you went back to a 1.4 what was your truck before you swapped it out? Also I've looked for 1.4 can't seem to find many?
 
Mac-1990 said:
Interesting! So how would I find out the lt77 ratio? It's a military green box but other than that I know nothing of its ratio. I had read somewhere about changing tyres can change the ratio but I couldn't get my head round the idea. Is it bigger wheels lowers or highers? To be honest not even sure what size I've got on mine without looking.

When you say you went back to a 1.4 what was your truck before you swapped it out? Also I've looked for 1.4 can't seem to find many?
Click to expand...


Give Ashcroft a ring they will advise you of the lt77 ratios

My 90 had the 1.19 when I bought it, and I went back to the 1.4 which it sill has in it now.

Larger diameter tyres raise the gearing so a 205 tyre would be lower geared than a 235, a 7.50 would be taller geared than the 235 and 8.25 even taller geared.

You have to bear in mind the engine is no power house, so to tall a gearing literally kiils what little power it has.
 
Ratio calculator here,https://ashcroft-transmissions.co.uk/ratio-calculator/

LT77 variants available, they list one as military so could be yours,
Screen Shot 2022-01-20 at 20.21.06.png


1.6 tfer box,
Screen Shot 2022-01-20 at 20.23.01.png


1.4 tfer box
Screen Shot 2022-01-20 at 20.23.40.png


1.2 tfer box

Screen Shot 2022-01-20 at 20.24.12.png
 
Yes black numbers are engine rpms, red means impossible rpms so ignore them.

Just compare all the 60mph rpms in top gear, but the best way it to mess around with the ratio calculator.
You will nee to measure the height of your tyres, as I just guessed at 30 inches.
 
lynall said:
Yes black numbers are engine rpms, red means impossible rpms so ignore them.

Just compare all the 60mph rpms in top gear, but the best way it to mess around with the ratio calculator.
You will nee to measure the height of your tyres, as I just guessed at 30 inches.
Click to expand...
And are dif ratios something to consider? Surely that wouldn't need changing aswell?
 
Mac-1990 said:
And are dif ratios something to consider? Surely that wouldn't need changing aswell?
Click to expand...

Nope, pretty much every 90/110/defender/200disco/300disco/td5disco has 3.54 to 1 diffs as std fit., so theres a 99.99 percent chance yours has 3.54 diffs as well.
 
lynall said:
Nope, pretty much every 90/110/defender/200disco/300disco/td5disco has 3.54 to 1 diffs as std fit., so theres a 99.99 percent chance yours has 3.54 diffs as well.
Click to expand...
Ok good to hear! Wasn't sure it being an 1985 military 110 if it might have had some bits from the series 3 line.
 
I have a 300tdi in my ex-military 110, running 750x16 tyres. I fitted a Discovery 1.2:1 transfer box as it came with the dead Discovery that donated the engine.
Prior to this it had a 1.6:1 transfer box and although it accelerated like a scalded cat, it was screaming its boll0x off at 50mph.
The Discovery box definitely makes motorway driving far more civilised, but does feel a bit over-geared at times, particularly on very steep hill starts or whn towing on long hills.
I use my 110 to tow a horsebox and there is one particularly steep junction (about 1 in 4) that I have to pull out of occasionally and I use low ratio to save slipping the clutch. Low ratio is the same on all the transfer boxes.
The serial number on your transfer box will tell you what ratio it is, on the early boxes it is on the passenger side facing the inside of the chassis, later boxes have it on the rear face near the filler plug. Make sure that you check the ratio of any box you buy, as some from V8's and some automatics are even higher geared and would be unsuitable for tdi's.
I think Discovery transfer boxes are more plentiful and cheaper due to the fact that Discovery's fall apart in the rain I imagine that most Discovery transfer boxes will have done less hard work than Defender boxes as well, but Land Rover chose the 1.4:1 ratio for Defenders for a reason.
 
Rougharse Racing said:
I have a 300tdi in my ex-military 110, running 750x16 tyres. I fitted a Discovery 1.2:1 transfer box as it came with the dead Discovery that donated the engine.
Prior to this it had a 1.6:1 transfer box and although it accelerated like a scalded cat, it was screaming its boll0x off at 50mph.
The Discovery box definitely makes motorway driving far more civilised, but does feel a bit over-geared at times, particularly on very steep hill starts or whn towing on long hills.
I use my 110 to tow a horsebox and there is one particularly steep junction (about 1 in 4) that I have to pull out of occasionally and I use low ratio to save slipping the clutch. Low ratio is the same on all the transfer boxes.
The serial number on your transfer box will tell you what ratio it is, on the early boxes it is on the passenger side facing the inside of the chassis, later boxes have it on the rear face near the filler plug. Make sure that you check the ratio of any box you buy, as some from V8's and some automatics are even higher geared and would be unsuitable for tdi's.
I think Discovery transfer boxes are more plentiful and cheaper due to the fact that Discovery's fall apart in the rain I imagine that most Discovery transfer boxes will have done less hard work than Defender boxes as well, but Land Rover chose the 1.4:1 ratio for Defenders for a reason.
Click to expand...

Thanks mate this is exactly the kind of answer I was hoping for. Have you driven a 1.4 with a tdi?
 
Mac-1990 said:
Hi all,
Just wanted to ask for some personal experience of swapping a 1.6 transfer box to a disco 1.2 or 1.4.

I've got a 110 1985 ex mod landy. It's got a disco 200tdi and although no information can be found on my transfer box I belive it to be 1.6 which means anything over 50mph on the motorway is awfully loud and drones. Can also drive in 5th gear at about 25/30mph.

I'll never tow. She's my daily driver and I use motorways frequently enough that a long journey puts me off using the truck and going in the family insignia instead which isn't anywhere as fun!

I'm just looking for some personal thoughts on those who have done what I'm thinking about doing. Or anything to take into account.

Also just wondering what a second hand box miles ought to be at without being a lump of scrap and not worth buying. Is 150,000 miles to much unless its almost free of charge?

TIA
Click to expand...
I think I can answer most of the questions.

Most likely is a 1.6:1 transfer box. But if you didn’t get it straight from the Military then it might have already been swapped for a 1.4:1

Do you know what sort of top speed you can get currently?

As for changing the gearing. The transfer box is the easiest and cheapest option for the most part. Although you could change the diffs as an alternative. You could also fit an Overdrive unit like Roamadrive. But they are pricey. But would essentially give you an extra cruising gear.

What tyre size are you running? And do you plan to run bigger at any point? The bigger the tyre the taller you overall gearing will be. So short gears can be good.

Also do you off road?

I know you said no towing. Not sure on your age. But if under 40, then the law has changed so everyone can tow 3.5t. A 110 would be good for this. So I guess you might want to consider it for the future.

BTW - for motorway use. Taller gearing will allow lower rpm at cruising speed. And to some extent higher cruising speeds. But there is a point this becomes untrue as you’d need to drop a gear to maintain the speed due to lack of power & torque.

This means you will get less rpm noise. But if I’m honest, most of the noise in a Land Rover. And esp an ex MOD one is not the engine rpm. Just don’t expect it to completely transform the noise levels.

Is your engine tuned?

Personally I’d suggest a stock power Tdi running normal 235/85 or 7.50 tyres would be under powered with a 1.2 transfer box. A tuned one will pull the gearing fine. But will feel less perky than your current setup.

My recommendations would be a 1.4:1 transfer box.

Or retain the 1.6:1 and fit an Overdrive. You can use the gearing calculators to see how they would compare at say 65mph in terms of revs.
 
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