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1987 110 2.5 NA Transfer Box Ratio


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Doing a recommissioning job on my 1987 110 ex-military. That means stopping up the leaks and making sure everything works. 18J engine with its bountiful 67 BHP is coming along just fine, LT77 box likewise, and attention turns to the transfer box. I'm weighing up the pros and cons of changing the gearing on the final drive from 1.667 to 1.41 as on the 90. I can't be the first person to consider doing this on an NA engine, but I can find anything here on the subject. Please point me in the right direction if I've failed to find.

The vehicle has only done 3,500 miles ish. Engine looks great, gearbox internals look like new - except some idiot has slammed it into reverse and chipped the teeth. New gears on order. So I'm not in the business of swapping in a more powerful engine. I want the reliable slog of the good old NA to take me long distances without having to worry about the mechanicals. Typical cruising speed on faster roads, I really only need 60MPH. Long distance means Turkey, Middle East, North Africa etc. Oh - and back home again.

Here's my logic - please shoot holes in it if it doesn't make sense or is just plain wrong. Living in the far west of Cornwall we don't have any motorways, and no real dual carriageway until you get past Hayle (otherwise known as up-country), so my limited driving experience of the 110 prompts my request for thoughts, advice, and maybe even actual experience. Sorry this is a bit of an essay.

Returning to the logic. The 110 hard top weighs in at 1796kg kerb weight, the 90 1685kg - according to Mr Haynes. I assume these are EU defined kerb weights, i.e. full of juices but no people. This puts the 110 at 111kg over the 90. Changing the 110 ratio to 1.41 would then be like driving around in a 90 with two 9 stone people in the back.

The 110 has a 1,154kg payload capability against 715kg for the 90 - again based on Haynes data. Different sources give different numbers, but for where I'm going it's a little academic. I'm never going to get anywhere near the sort of load weight capability of the 110. If I put in the extra weight of the 110 at 111 kg, two people at 150kg, I have 454kg available for tents, cooking, kit and caboodle, spare parts, tools etc until I'm up to the weight of a fully loaded 90.

My first look into the LT230 shows a unit in pristine (but leaking) condition. The 1.41 kit from Ashcrofts looks like a natural. Using their ratio calculator 60MPH at 1.667 means RPM at 3,192 in 5th, and at 1.41 an RPM of 2700. That sounds more comfortable, and a better driving experience?

So...

Q1: Have I got my sums right?

Q2: Whats a 90 with a 2.5 NA diesel like to drive at the sort of loading I'm talking about?

Phill

P.S: Yeah - I know a stock 2.5NA 110 is a bit of a lorry. A 1950's one at that.

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I know it is kind of different with my 200 Tdi, but worth telling the experience. I bought a 1.1 LT230 from Ashcroft for my Oneten (MY'83, LT77, LT230: 1.2), The 200 Tdi is very slightly tuned.

I don't have revs, but it was really worth it. Up to 80 km/h it runs like a car with 4 gears. The fifth is not usable from 80, but there is a lot less noise in the car from 80 with 5th. For me it was a real good buy, but a little bit of an experiment. I quess it will be an experiment for you too. I made a spreadsheet with all ratios and the real resulting speed and revs. Power diagrams of the engine I used to estimate, if this could work.

Important: Use and check different possible tire diameters

With the long LT230 entire ratio is a little bit shorter now as with a GKN Overdrive.

 

Edited by Sigi_H
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Good morning Sigi - many thanks for your insights. You have an additional 44+ BHP over me, so I'm obviously not able to go as far as a 1.1 ratio. Hey-ho. I have been secretly wondering what would happen to mine if I put a 1.3 ratio in there though. Unlikely to be practical though.

Your calculations on power/gears/ratios? A man after my own heart. I've been setting up the spreadsheets even as we speak. If you or anybody else can point me in the direction of power and torque graphs for the 12J diesel engine I'd be very grateful. I can see why you would want to do it though, we've passed through Switzerland on some very beautiful roads a number of times on trips to Croatia and Bulgaria and you certainly know all about challenging hilly roads. 

Many thanks

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I wasn't going to recommend the 1.1 ratio. The gist is, if you are happy with a 4-speed auto up to most used speeds (not towing regularly ie), it is worth having a longer ratio for the LT230 (in terms of engine power) because noise will be much lower.
It is noticeable that I have to let the clutch drag longer when starting uphill. In LO ratio everything is like before. That means if towing heavily i can start in LO gear as well. Makes it a bit more complicated, but max once a year 🙂

 

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It's not a huge job to change a transfer box so why not buy a 1.4 box and try it. Personally I don't think it'll be too much of a problem but as they say, the proof of the pudding is in the eating.

I Imagine that siggi gets away with a 1.1 box because he probably has an earlier LT77 with lower gearbox ratios. Those that were introduced with the 200 tdi, G and H suffix had higher gearbox ratios to better suit the increased power of the new engine.

HTH

Mo

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1 hour ago, Mo Murphy said:

because he probably has an earlier LT77 with lower gearbox ratios

No, I don't. The later LT77 in the 200 Tdi is stronger and this is why I still use it, even though the LT77 before is shorter

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Thank you Sigi - good points well made. Wish I'd twigged the LT230 ratio thing before I started dismantling, I could have worked it out experimentally. At least at the top end of the speed range. And I'm of sufficient age to remember when cars only had 4 gears. Some only 3.

I agree Mo, about whacking in a 1.41 box to see what happens. Thing is somebody will have done this already and will have the voice of experience. Anybody?

Still searching for a 12j torque curve...

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You have some good hills on the A30 between Hayle and Bodmin. My advice is do a few trips up country to Bodmin and see how you find your set up powered by the mighty 12J. Its all down to personal preference. The 12J is quieter and smoother than a clattery tdi unit but I think you'll be changing down through the gears up hills as a 12J is down on both power and torque compared to a tdi. I've heard that 12J engines really don't appreciate high revs. 

I was happy with the 19J doing just small local trips, but now I am doing more and more miles I'm wanting more than the 19J is able to offer. A few good long trips will tell you how happy you really will be with a 12J.

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22 hours ago, Sigi_H said:

No, I don't. The later LT77 in the 200 Tdi is stronger and this is why I still use it, even though the LT77 before is shorter

What size tyres are you using Sigi ?

Mo

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Ok - thanks Monkie, some good thoughts there...

Think I've worked out what I'm going to do. I'm going to change the LT230 to 1.41, this will give me good enough hill starts. I'll test it up Bowjey Hill in Newlyn. Give it a go next time you're down this way. Also I'm going to up the 5th gear ratio to 0.77. The peak power/torque figures (with a bit of guesswork and general diesel engine behaviour) should mean that on level ground, no wind, I should be able to cruise comfortably at 60MPH at 2,500 RPM on my standard 13" tyres. I don't have a problem with needing to change down to 4th when crossing Bodmin moor. Or the Swiss Alps.

I'll do a tooth count on the internals of my LT77 tomorrow to double check what I've got and figure out what gears I need for a 50A box.

A bit more expense than I'd hoped for, but it will be worth it in the long run.

Unless anybody can tell me differently....

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3 hours ago, Mo Murphy said:

What size tyres are you using Sigi ?

Mo

Summer BFG MT 255

Winter Nokian Hakablahblahblah 235

I can feel the difference

 

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Hi Phill,

My 110 is also an NA. I'm changing the entire power train and putting in a V8 because I need to go to petrol (thanks, TFL) and if I've got to do it then a V8 is the obvious way to go.

What I will say is that around here, which surprisingly isn't that different to around there as far as hills and fast roads go (I used to be based at Culdrose so I do know where you are), my Landy performs...adequately. I think if the gearing was much longer then it would struggle on hills (I'm thinking some of the drags up to Bodmin for instance) and might be frustrating. And in truth I don't think you'd notice a significant reduction in noise or fuel consumption because you'd be using a heavier foot to maintain momentum.

But I also recognise that I'm relatively new to all this and may be talking rubbish. 

Cheers,

Simon

Edited by Junglie
The system changed an inappropriate word so I no longer needed to apologise...
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On 4/25/2021 at 6:26 AM, monkie said:

...I've heard that 12J engines really don't appreciate high revs. 

 

You've heard right. Slow and noisy or slow, smoky and noisier, depending on how hard you rev it.

In my experience anyway.

The weird thing is...I still love it. It should drive me insane and yet somehow it's just so right. Does that make sense? Or is it just Land Rover ownership in general? (Actually I think I've just answered my own question...)

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On 4/25/2021 at 3:21 PM, Phill S said:

I should be able to cruise comfortably at 60MPH at 2,500 RPM on my standard 13" tyres.

You've got some odd size tyres there fella :P

I would assume zero problems running a 1.4 transfer box behind a healthy 2.5NA in good fettle, and I'd also point out that 1.6 gears / transfer boxes are more sought after by the bigger boys who've fitted silly size tyres and ruined their gearing so don't bin the old bits.

I guess the cruising thing is up to you - the 2.5NA is never going to be a motorway cruiser, 2500rpm at 60mph is a fairly loud and steady way to travel long-distance.

On 4/23/2021 at 10:38 AM, Phill S said:

I want the reliable slog of the good old NA to take me long distances without having to worry about the mechanicals.

The Defender drivetrain in good nick will reliably live with a lot more power so I wouldn't let that stop you.

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4 hours ago, Junglie said:

My 110 is also an NA.

Hi Simon - is your vehicle running or have you started taking it to bits already? Have some questions for you if it's still running. You might want to fib.

So a couple of items update. Apparently the 0.77 ratio can't be put into the suffix E LT77 and earlier boxes. Also my tooth count shows my LT77 gear ratios are way lower than I was expecting. My first gear ratio comes out at 3.985. That's 4 to you and me. To eliminate any other surprises I checked the LT230. That's still in one piece but I was able to eyeball it at 1.6. Similarly the front axle (still on the vehicle) comes out at 3.5 - everything as expected there at least.

So it's spreadsheet time to work out the next steps....

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Hi Phill,

Happy to answer anything, I've got nothing Landy related to hide ;)

Mine's still running - I haven't had the time to do everything (anything) yet short of stripping the new LT230 to refurb it.

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Posted (edited)

Hi Simon - started writing it out but it started looking like the Merlin ship recovery flight test programme.

I'll carry on with with my estimation methods

Thanks anyway

20210427_102555.jpg

He's hoping for something good to be dropped in there

Edited by Phill S
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If you still have the original LT77, military 110s had lower ratio 1st & 2nd gears than standard which will help if you change to a 1.4 box

I've used 12j's on 1.4 boxes and it's fine, though slight inclines have you dropping down the gears.

You will help yourself a lot if you avoid roofracks, lots of bolt-on ironware and aggressive tyres

I've done lots of overlanding in n/a defenders - 60mph cruising speed is a bit wishfull, think mid 50s with occasional downhill thrills and lumbering tortuous uphill slogs.  There are some pluses to the n/a, long road trips aren't a strong suit though and even changing the ratio won't help much other than lower the engine rpm a tad. 

my last trip in one I had to get it to Florence in 24hrs, ragging it flat out through the night all the way on motorways without stopping - I managed an average speed of less than 40mph.  

The engine & transmission noise gets very intrusive on long journeys and I'm pretty sure has contributed to my tinitus, so have a think about lining the floor panels, closing floor gaps and using heavy mats etc.

 

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20 hours ago, Phill S said:

...started looking like the Merlin ship recovery flight test programme.

Don't you start brandishing that modern stuff. I'm a Wessex man originally, though I ended up on The Mighty Sea King before going to Lynx.

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22 hours ago, FridgeFreezer said:

You know the ratio calculator exists right?

Yup - been using that, although it told me my 50A box had different ratios than the Mil-spec that it actually has. I'm as certain as I can be that I'm the first person inside there. Lost a little confidence in it after that, but then maybe my box is some kind of "special"?

4 hours ago, Eightpot said:

military 110s had lower ratio 1st & 2nd gears than standard which will help if you change to a 1.4 box

As Junglie has said above, great to hear your experiences. Another good reason to replace the massive 24v alternator I've currently got then. But no Radio 4?

Just before I start ordering up the Ashcroft 1.4 gears, what did you think of my logic in the opening blurb about ending up with the driving characteristic of a 90 with two 9 stone people in the back? The machinery can only do what the machinery can do, but with the Mil-spec LT77 and the LT230 1.3 ratio gears, first gear upper ratio comes out pretty much identical to the 2.5NA 90. What sort of a monster would that create I wonder...

Gotta ask

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You really won't notice a huge difference with the 1.4, it will just drop engine rpm, there's enough torque in a good engine to disguise the gearing difference but you won't necessarily go any faster as there isn't the hp to overcome the wind resistance.  

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7 hours ago, Junglie said:

Some good experience there...

Florence in 24 hrs though? That's hardcore.

Had to drop of a customers car & make the last flight home before xmas - never want to be that tired again..

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