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Andrew95

Member Since: 27 Jul 2022
Location: Midlands
Posts: 75

1997 Defender 110 300 Tdi SW Corris Grey

R380 / LT230 Ratios

Now I have started doing a lot more overseas trips I am looking at improving the motorway handling of my 300tdi 110. Currently on 285/75's, fairly well tuned engine, with a moderate to heavy load. Not looking for increased top speed, just better manners - reduced revs, less stress on the engine, quieter etc.

I am looking at replacing the gearbox soon, so my original thought was when the T-box is out as part of this, replace the gearing to 1.3 (I don't want to go as high as 1.2) which from what I have read sounds ideal for what I am after and has really good reviews.

But, I only replaced the T-box a couple of years ago, its perfectly fine. So to save on cost and effort, do I keep the T-box as 1.4 and instead get the V8 5th gear in the R380.

There are pros and cons for both - I am wondering if anyone has any real world experience of either (ideally both!) and can comment?

15th Oct 2025 9:36am

el sid

Member Since: 06 Sep 2025
Location: devon
Posts: 21

1996 Defender 90 300 Tdi CSW Barolo Black

My 300tdi has a Romer overdrive,it reduces revs by 28%in all gears including low range,they cost quite a lot ,but mine came with one.im very pleased with it,just another option for you.

15th Oct 2025 10:19am

Andrew95

Member Since: 27 Jul 2022
Location: Midlands
Posts: 75

That was my original though (has been for a few years), but they are so expensive and difficult to get hold of.

15th Oct 2025 10:24am

bankz5152

Member Since: 02 Feb 2017
Location: South London/North Kent
Posts: 2237

Higher 5th is an excellent choice. Low rpms in 5th and better mpg.

I had 33s, 1.3 box and higher 5th on my old 110, new 110 has 33s and stock ratios. Everything else is pretty much the same.

Old 110 got almost 50miles more per tank!

15th Oct 2025 4:42pm

TexasRover

Member Since: 24 Nov 2022
Location: Paris
Posts: 1357

2002 Defender 110 Td5 DCPU Chawton White

The strain on the engine would actually be higher with lower rpm. You do need to watch for labouring the engine too much with high gearing hence an overdrive makes it easier to stay in the sweet spot.

15th Oct 2025 7:16pm

jst

Member Since: 14 Jan 2008
Location: Taunton
Posts: 8473

2011 Defender 110 Puma 2.4 USW Stornoway Grey

This was the point I was going to make. Lower rpm might increase thermal load and engine stress, as alot of m57 conversions are finding out. Run the ashcroft calculator to get the correct rpm for rhe speeds you want. Cheers

James
110 2010 XS Utility
130 2011 M57 bespoke Camper
90 2010 Hardtop
90 M57 1988 Hardtop

15th Oct 2025 9:52pm

L110CDL

Member Since: 31 Oct 2015
Location: Devon
Posts: 11082

Andrew95 wrote:
That was my original though (has been for a few years), but they are so expensive and difficult to get hold of.

I have one, i bought it from Trebro, but please read this . . . .

https://www.defender2.net/forum/topic51558...drive+sale

I fitted this unit in Millie and it was noisier than i thought it would be, so after a week i got the unit took out and it has been stored away ever since. If it doesn't sell sometime, i'm going to get it fully serviced and try it again in Millie

I'm open to a very sensible offer

Clayton.

1996 Golf Blue 300Tdi 110 Pick up.
Keeper.

16th Oct 2025 10:15pm

MarkBrown

Member Since: 03 Oct 2022
Location: Mid Wales
Posts: 599

1983 Defender 110 Other HT Auto Keswick Green

I had a Triumph 2500 with an overdrive, it was brilliant! Essentially you got gears 3.5 and 4.5, along with 2.5 if the inhibitor switch was modified ( which mine was ), so seven speed in total. It was operated by a switch on the gear knob.

I had a high 5th gear in an Lt77 V8 once, following advice, but it was useless in most situations as it was just too high and the engine couldn’t pull it.

I’ve read that the 1.3 transfer box is about the best overall. 1983 110 automatic OM606

17th Oct 2025 7:41am

TexasRover

Member Since: 24 Nov 2022
Location: Paris
Posts: 1357

L110CDL wrote:
Andrew95 wrote:
That was my original though (has been for a few years), but they are so expensive and difficult to get hold of.

I have one, i bought it from Trebro, but please read this . . . .

https://www.defender2.net/forum/topic51558...drive+sale

I fitted this unit in Millie and it was noisier than i thought it would be, so after a week i got the unit took out and it has been stored away ever since. If it doesn't sell sometime, i'm going to get it fully serviced and try it again in Millie

I'm open to a very sensible offer

The R380 Roamerdrive can be noisy on overrun, supposedly improving after running in for a few 1000km.

I bought one direct from Canada two years ago as no-one in the EU/UK was stocking them anymore (additional shipping was not a big deal like $50-100 more). It has been totally quiet and yes there is a slight whine on overrun but barely noticeable and my Td5 is quiet overall.

It's only really useful on the motorway where it makes a big difference, but you find yourself shifting down when you get a decent hill.

17th Oct 2025 8:18am

leolito

Member Since: 07 Jul 2025
Location: Sofia
Posts: 38

Is it true on a Td5 using an overdrive the cruise control function is lost?
Sorry for the half-off topic question ...

17th Oct 2025 8:22am

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