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Swapping transfer boxes


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Just now my 1986 90 has a 300TDi fitted with the standard LT77 and LT230 box. As far as im aware it's still got the standard gearing set. The tyres are AT2's 235/70/R16. I do a lot of motorway driving and anything over 55mph just sounds scary, like it going to take off! I was wondering about changing it to a discovery transfer box with the 1.2 ratio in the hope it would make the car a little quieter and maybe slightly more fuel efficient.

I've been looking at transfer boxes and have come across plenty but does it have to be a particular kind from a certain discovery or will any lt230 box be a direct swap? I know the handbrake will all need modified to work if i go from a rod operated system to a wire operated system.

Cheers

Stephen

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Thanks for the speedy reply western, how do I know what box I have fitted? Can I tell this from the serial number? I know it may have been changed inside previously so it doesn't match and I sadly don't have that much detailed information to know if it has been.

Cheers

S

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Take the pto cover off mark the shaft, mark the prop flange then roll the truck forward one revolution of the prop and see where the other mark has got to. The other will then be roughly a 1/4 turn on (1.2), half a turn on (1.4) or a bit further still (1.6) from a full turn. I think that's the right way round.

Mike

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Thanks for the speedy reply western, how do I know what box I have fitted? Can I tell this from the serial number? I know it may have been changed inside previously so it doesn't match and I sadly don't have that much detailed information to know if it has been.

Cheers

S

It's probably hugely unlikely that you have a 1.6 transfer box.

Personally fitting a 1.2 isn't the way to go, it'll blunt performance.

If you really are doing lots of motorway miles, the reality is, you are using the wrong vehicle. You'd probably be much better off buying yourself a Discovery of some kind. They have far superior NVH to "any" Defender.

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Will have a look this weekend, got the handbrake to sort so I will be around the transfer box. When I say a lot it just feels like a lot its maybe 20 miles a day. But its at least 5 days a week sometime more and it would be nice to have it cruising with the rest of the traffic and not holding up the HGV's!

When you talk about it blunting performance I take it that refers to how fast I can get up to speed? Cant say I'm to worried about that, my days of racing things at red lights are behind me (for now anyway!)

In terms of changing the box if its a 1.4, will any 1.2 box fit? Ive found a couple from 300Tdi discoveries but wasn't sure how much of a straight swap that would be.

Cheers

S

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If you really are doing lots of motorway miles, the reality is, you are using the wrong vehicle. You'd probably be much better off buying yourself a Discovery of some kind. They have far superior NVH to "any" Defender.

Not completely true - i have an overdrive and do lots and lots of motorway journeys. I often take the 110 in preference over the D2. The OD reduces the noise (ok, not to D2 levels, but then i am comparing a tdi to a TD5 in my case), increases the comfortable cruise speed and the suspension in my 110 is in good order, so i wouldn't describe it as harsh. So, if you want to own a defender and also use the motorway, you can do a lot to make it more comfortable before recommending selling it.

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As they said, the first thing to try would be 235/85 tyres - they're better for just about everything. It should have a roughly comparable effect to the transfer box swap, just a bit less, but would be much easier and will give a more comfortable ride as well as improving ground clearance off road.

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I have thought about the tyres and I have 2 reasons to be against them, I just bought some new ones and changing all 5 (including the spare) would probably be £450 keeping it with AT2's and a random for the spare. Also just now my car just fits into the multi-storey at my shopping centre, by just I mean there is maybe 3/4cm in it!

Will get the numbers posted up ASAP, will try and do it tomorrow morning before work. The thought of doing 75mph sounds exciting!

S

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Haven't checked the speed with a GPS, will do that tomorrow on my way to work, using the signs at the side of the road that flash your speed at you 30mphish on the speedo seems to be about 25/27, also haven't got any speeding tickets or anything. But will check tomorrow and see whats actually happening!

Thanks

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Out of the factory the speedo should slightly over-read - for example mine reads about 65 when doing 60 on a GPS. They're not allowed to under-read at all. For example if your speedo is saying 30 and you're actually doing 35 for example it means you've got the wrong drive gear in the transfer box for the size of tyre fitted. But it sounds like yours is correct (slight over-read).

Without meaning to sound rude, is it a new car to you? A Tdi engined car without any soundproofing is a horrible place to be when you get the thing up to speed noise wise, might be a case of perception?

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I would say my speedo over reads, guessing its got the standard drive gear installed but with smaller tyres. Ive had the car for 2 and a bit years now. The previous owner done the engine swap. I guess it could be just noisier than what I think it should be. Hard to tell, it will do 70/75 or so the speedo says but thats flat out on the accelerator and wouldn't say its comfortable for the engine but it could be I guess.

S

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Sorry this info took longer than planned but here it is! Doing 60mph on the speedo is about 55mph on the GPS. Found the gearbox and transfer box numbers. Gearbox is 3615 LLR and the transfer box is 22D197619D/220197619D. Was struggling to tell. Also under lots of dirt was a label that said 1.410. So guess it's a 1.4 transfer box.

Would fitted a 1.2 disco box help? Along with a new speedo gear so all the numbers are right!

Cheers Stephen

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That is not the gearbox serial number. It will Start with a 50 or similar.

22D is definitely a 1.4

A 1.2 might help and should work fine with those tyres. But... there is something else very wrong if the engine is screaming at 55 mph. As above, that is only 2600 rpm and that should be a comfortable and relaxed speed for the engine.

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A 1.2 Disco box is one solution. You may need to use the gearbox a bit more to keep the engine/turbo 'on the boil' so to speak - but what's wrong with snicking down to 4th at the beginning of a long hill and letting the engine rev a bit?

[TBH I've always thought that the best match to a turbodiesel is an autobox with a 'slippy' torque-converter and a hairtrigger kickdown]

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You really just have standard gearing then as 235/70's are similar to 205's personally I would advertise your current tyres forsale for a disco owner and purchase some 235/85's or even 255/85's.

My 300 would do an indicated 85 on 205's.

Just my 2p.

Will.

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I have a 1.2 transfer box fitted, had it 6 years now, but I used to have higher gear ratio diffs, now these are gone I want to put the standard back 1.4.

As said earlier, the 1.2 is good at low speeds, more grunt, but on the motor way it's hard to get up to speed, mostly 4th is good, but you have to really push it to change to 5th, then your flat out again.

Could just sound bad due to something else in the drivetrain, but if you have no sound proofing then that will not sound so nice.

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So I think going to a 1.2 transfer box is the best option for me. When I was out today I took more notice of the noise and how it sounds when I push it up to 70mph on the speedo, the car isn't soundproofed at all and when I listen now I think a lot of it is road noise and not engine noise. So now all I need a LT230 transfer box with a 1.2 ratio! (and need to work out how to change them...

S

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From a Disco owners POV.

Fit the 1.2 TXB

get a recon exchange 1.2 from ashcroft rather than the lotto boxes off egay and enjoy trouble free motoring.

My reasoning being, a 1.2 TXB & 235/70 tyres are std for 200Tdi/300Tdi and give ample road performance, and as you also state that taller tyres mean you no longer fit in your car park.

My Discovery runs 235/85 16 tyres with it's 1.2 TXB, I find it a ball ache round town, ball ache on country roads and I find down shifting on motorway hills very necessary and parking is always problematic when going in to the city.

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