Differential Surgery for Lower Gearing

Hi all, so I've got this D90 fitted with a 3.9V8 and an LT95 4-speed manual gearbox out of an early Rangie, and as soon as I got it running and out on the road, I noticed that I have to shift gears at very slow speeds to keep the rpm down, and that the gearbox whines louder than expected at the vehicle's rather slow cruising speed.

The D90 originally came with a four-cylinder engine and a five-speed gearbox, and I mention this in case that engine/gerbox combination defines the factory differential gear ratios that came with such models.

Basically I'd like find out if it is possible to modify the front and back differential gear ratios so that I can get a wider acceration band before each successive gear shift. In other words, I'd like to change from first to second gear later than I do now, and with the engine running at much lower rpms than it does now, sacrificing a little low-end torque to gain quieter acceeration and a bit higher of a top speed.

I would be grateful to hear from anyone who has modified differential gear ratios in this way, hopefully explaining whether such conversions can be done by swapping the internal parts of the diffs, or if it would be necessary and practical for the entire front and rear axles to be replaced with those of a different Defender model. Forgive me if this question sounds stupid, but my knowledge of gearing and such is very limited.

Any help would be much appreciated. Thanks.

All defenders, 90's 110's, discos and RR classics have the same 3.54:1 diff ratio. The difference lies in the transfer box.

With the engine-gearbox-diff ratio it is correct as standard for RR classic which should be just fine. You cant change the diffs because as far as I know 3.5:1 was the closest ratio there was so. I dont believe your gearing is to low at all. I Think your gearbox is pretty tired and your worried about the noise at higher RPM.

You are in luck tho. You can get an overdrive to fit the LT95 gearbox In fact I may well have one in a couple of weeks that has been fitted to a recon box reconditioned a few years ago and kept in dry storage that I have been promised for some beer tokens.

Overdrive is the way to go uping your diff ratios will make low box undrivable. Alternative is to change your tyre size for slightly taller tyres.

Wow, I'm all ears, Jai Landrover. Never heard of this Lt95 overdrive unit before. Are they sold new on the net anywhere that you know of ? I do appreciate the offer to buy one from you, but I work in Africa and visit the UK infrequently, which would complicate the logistics of acquiring the one you have.

Regarding the need to sacrifice low range capability when installing the overdrive, I don't ever do any hard-core offroading, and so won't miss the low range crawl of my LT95 gearbox, should I adopt this fix.

Hughesy I thank you for your confirmation about the standardized gear ratios on all those Landy models. It is odd though, that my D110 pickup, which I fitted with the same engine and gearbox combo, doesn't crawl as though in low range like this D90 does. Till I read your post here, I just assumed that there had to be a difference in the gear ratios to account for the contrast between the gear-change speeds of two Defenders.

Much obliged fellas. I'm about to run a google search on LT95 overdives.

do check to make sure somone hasn't put series 4.7 ratio diffs in your mota that could account for it being slow. If you fit an overdrive the low range is not affected. Its only if you change diff ratios so its all good

Grasshopper,

Try Ashcroft Transmissions... they changed the ratio in my transfer box, to make is more driveable at highway speeds... low ratio is standard so off road capability remains. They will ship anywere I'm sure, and have heaps of good advice.

When I was in Zambia Foleys in Livingstone were really hepfull... and even helped with shipping me out a new motor for my old series III... I seem to remember a Bearmach stockist in Lusaka. Which part of Africa are you in?

Good luck

The Gribbin said:

Grasshopper,

Try Ashcroft Transmissions... they changed the ratio in my transfer box, to make is more driveable at highway speeds... low ratio is standard so off road capability remains. They will ship anywere I'm sure, and have heaps of good advice.

When I was in Zambia Foleys in Livingstone were really hepfull... and even helped with shipping me out a new motor for my old series III... I seem to remember a Bearmach stockist in Lusaka. Which part of Africa are you in?

Good luck

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Ashcroft transmissions would be the way forward if you had an LT230 transfer box but I don't think they d owt for the LT95 gearbox and intergrated transfer box from memory thy are 2 mins up the road frm me and the LT95 is the old 4 speed manual. If you had an LT230 transfer box you can get various ratios to suit. For the LT95 an overdrive is the way forward but a new one would be a lucky find becaue of their age.

I may be totally wrong but I think the early 3spd auto RRc's,(Chrysler Torqueflite box) had a higher ratio gearset in the transfer box which would fit the LT95 box/tbox.(If you could find one.)

again early 3 speed autos have an almost 1:1 ratio transfer box. Unfortunatly these are again LT230 transfer boxes. These are like rocking horse poo I got one for my 90 but they aint easy to get and will not fir the LT9 box.

ive got a nice 5 speed lt85 santana gearbox proper v8 defender box with a disco t box behind it. might let it go if you talk to me nicely.......and offer me the right dough for it any got a 3 speed auto don want the t box just gearbox???