Overdrive or high ratio transfer case?

[Klusenhusen]

I wish to try to reduce the engine noise, what would be the best way to go?
The 109 will only be driven on normal roads, no serious rock crawling with this camper.
I would guess that the Ashcroft transfer case is the one which requires the least maintenance.
I am sourcing parts for the rebuild, so advice as to what that works, is always welcome.
Anyone with experience from both possibilities out there?

[RMS]

Hi Jan,

As you've got the VW/Volvo 6 pot Diesel, you have enough power to consider using Discovery/Range Rover differentials.
However, that would give you a higher ratio overall, 3.54:1 instead of 4.7:1, so some steep hill starts could require you to use low ratio for setting off.

It is by far the cheapest option though - over here a set of early Disco diffs are around £30-£40 each, though if your rear axle is a Salisbury you would need a rear differential from a Defender 110 (around £50-£75).

We have 3.54 diffs in both our heavyweight Carawagons, with 200TDi engines, and we also have overdrives
However, we cannot use the overdrives until we are doing around 50mph as the engine would be turning too slowly

Although the 200TDi is more powerful than your 6 pot, your engine will have better torque at low revs as you haven't got a turbo strangling the engine. The 200TDi is a bit gutless until the turbo picks up


If money were no object, I would say a new overdrive (Roamerdrive) would be perfect as it allows you to 'split' the gears, for example when climbing long hills and 4th is too high and 3rd is too low.

An Ashcroft high ratio box works out about the same as a Roamerdrive, I think, but has one less lever to play with compared to an overdrive

HTH,
Robin.

[Wildwoodflower]

May I offer an observation?

Overdrive units are a pain. They can be noisy (not always, but often), are a nuisance to rebuild and have interesting tricks that can include siphoning oil out of the main box when the front seal blows or spouting their own oil out of the breather hole so that the prop and rear axle get an impromptu 'rust-proofing' [French bystanders never cease to marvel at la femme anglaise crawling around under her vehicle in a service station car park ... and they never offer to help, either].

They get incredibly hot on a long motorway journey - and, lacking any cooling fins, will cook many oils.

Don't get me wrong - having 20 gears can be useful. Probably.

My next gearbox - whenever that may be - will be getting an Ashcroft high ratio transfer box and if it already has an overdrive then that will be sold to fund it.

Apart from that, they're great - and I couldn't contemplate a long or motorway journey without one. Tried that ... not good.

[Klusenhusen]

Thank you both; when you say overdrive, I am led to believe that there is a significant difference between the old Fairy type OD and the Roamerdrive.
Do the Roamerdrive create the same amount of heat as the old type? I am also told that the Roamerdrive does not make so much “noise” as the old type of OD.
As of now I think that the Ashcroft HRTB will be the winning solution, but they are both costly.
Wishing you all a happy Easter.

[RMS]

Hi Jan,

Exactly - the Roamerdive (Roverdrive) is a totally different animal to the old Fairey overdrive.
It uses an epicyclical (sp?) drive system, and shares the transfer box oil.
It's much more rugged than the Fairey, and supposedly a lot quieter (though I haven't heard one in operation).

Check out Rocky Mountain for the UK distributer, and HERE for the full description

Personally, if I had to choose, and if I had the money, I would go for the Roamerdrive because of its flexibility and ease of fitting, but it does cost significantly more than the Ashcroft kit

Cheers,
Robin.

[Rangie]

Depending on your uses there are a few options.....

My 109 daily driver does a fair bit of heavy towing, I opted to keep the 4.7 diffs but fitted a Toro Overdrive to handle commuting at high revs, these are stronger with large oil capacities and handle sustained motoring better. It's fitted with a Nissan LD28 non-turbo at 95hp which suits the setup well and I get 32mpg.

The Ambulance is also 4.7 diffs, with a Fairey Overdrive behind a standard 2.25P. The lower power of the 2.25P gives me confidence with the Fairey, despite the nearly 3-tonnes of Ambulance. When out and about roaming the west coast its generally trundling about 30mph looking at scenery, the Overdrive gets used on the main-road runs/dashes. It evens out the use and suits the vehicle. 23mpg gentle cruising, 18 on the hilly west coast.

A breakdown I have had for years and am currently re-chassis-ing, I went with RR 3.54 diff in the front, 110 diff in the salisbury rear and used the gearbox output to power the front winch. This is powered by a Mazda-Perkins 3.0 Non-turbo (previously an asthmatic Perkins 4236). Again this satisfies the requirement for sensible cruising speed, winch and power for towing. I get about 28mpg with it.

I didn't go down the route of the high ratio transfer box conversion or gearbox swapping as they require mounting repositioning, modifying tunnel, modifying propshafts, etc. If something breaks I can use common standard parts to repair them. If the Fairey prolapses, I have the gear, locktab and carrier plate in the Ambu spares compartment to whip it off in 1/2 hour also!! The biggest risk I have is the LD28 which is a nightmare to get parts for, I have amassed a range of spares for it over the years to give me confidence but its reliability is very good!

Hope info is of some use in helping you select your combination.

Alec.