OK, following responses to my earlier question about Ashcroft high ratio transfer box mod, it seems that it may be too high for the standard 2.25 petrol engine.
I know lots have changed to 3.54:1 diffs - how is this mod for normal day-to-day driving?
I would use an overdrive but am reluctant to pay over the odds for a Fairey unit which seem to be kinda fragile, the Roamerdrive seems a better bet.

Thanks

I've not changed diffs so I can't really help but I am a big fan of O/Ds.

Not only does it give you a 28% higher top gear but the split between 3rd and 4th makes so much difference on hills and when loaded and towing.

Fairey unit do have a rep for being fragile but I've used them hard Inc in 2nd when needs must (not recommended) and even managed to strip a layshaft without harming the O/D.

The worst I could say about them is a worn one will scream like a banshee.

If I had the readies I wouldn't think twice about fitting one to the ambulance, preferably with a warranty or if I win the lottery a Roamerdrive.

I have both an overdrive and 3,54 diffs on my 109 albeit with a 200tdi conversion.

The 3.54 diffs are higher geared than the high gear transfer box and will affect low range as well. You will also need a new speedo of the right tpm. And will also reduce handbrake efficiency by 33%
But if you want to try it buy a high ratio diff and fit it in the rear and drive about and see how it feels. Just don't engage 4wd. If you like it get one for the front if you don't swap it back to standard diffs.

The overdrive is the best as it can be selected unlike the other options. It's easy to fit and doesn't require different speedos and such.

The other issue is how good is your petrol engine? The series gearbox and transfer box with higher diffs and 7.50 16 tyres is almost the same gearing as a disco which came with Tdi power or v8 power.

If your petrol isn't as healthy as factory or you haven't modified it slightly for more power then you may find your engine unwilling to pull with the higher gearing and if you tow anything or carry much stuff in the vehicle the problem will be amplified.

You can get higher gearing with a larger tyre choice or by looking at different series gearbox suffixes as some had lower 1st and second gears which would be good if you go for higher gearing and some had higher 3rd and 4th gears.

However to make best use of the gearing you want a different engine.
2.25 petrol may have been used in the first 110's and 90's that had the 3.54 diffs but the gear ratios were lower.

If you do go for diffs you'll need the 10 spline variety.

I wasn't aware of different Series ratios except for lower 1 Ton transfer box ratios?

X1 109inches. I run a SWB 2.25 petrol, with 750's and a Bearmach O/D and FWH's. The gear change is feckin rough but OK as long as you're exceeding 40mph when you change. It gives better top speed and fuel economy. Good for 3rd/ 4th driving on county roads with hills etc, but not very effective when towing weight. No insight on diff changes but suppose that depends on what driving you want to do. FWH's will also help to reduce axle drag on the road.

blue beasty said:

I wasn't aware of different Series ratios except for lower 1 Ton transfer box ratios?

Click to expand...

They aren't stupidly different like 1 ton ratios but are different depending on the suffix. You can mix and match however to get an ideal ratio gearbox if you can strip and rebuild a gearbox. I don't know the exact figures but id take a guess at 6% difference between the highest 4th gear and lowest fourth gear similarly to all gears in the box.
I think I read something about it on the series 2 forum.

I tried 3.54 diffs in an 88 with a good rebuilt 2.25 diesel. It was bloody awful and lost all driveability I soon went back to 4.7s.
All the above not helped by having to change down the gearbox a lot more, no nice on an old tired box. As said above you need at least a 200TDI or V8 up front.

I have the 3.54 diffs in my 88 pick up with 2.5 nas diesel and they work well. Used to have 7.50s on and it struggled a little on the hills had to drop to 3rd. If you use motorways and want to keep up with traffic I would recommend them. I have the overdrive and never use it, scary if I do. I think ideal would be normal diffs, 7.50 tyres and a good overdrive for everyday driving.

Mines a 88 with 2 1/4 petrol on Weber dtml with 3.54 diff's 235/85/16s .I wouldn't go back to 4.7s ,only time I've struggled is with my 1000kg boat and family of four all aboard was still able to cruze at 80 kmhr in top gear at 2500 rpm .I might try some 205 16 tyres for towing

Many thanks for all your replies, some good points to ponder on while I hunt for an affordable overdrive!