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I think I'm right in saying that the disco box is a higher ratio than the 90. If so, and bearing in mind that I have 300tdi and am running 235/85's at the mo, how much difference will the taller gears make on and off road. Would the transfer box be swapped or split ?
The transmission has gone up in volume and could be said to be whining.
Stop rubbing your hands together Matthew, but will be coming if and when I need help.
If it ain't broke, I'd be bloody suprised.
To be honest Nick, I would just swap it and give it a try, you can always swap the transfer box later if it is a problem. I can't see it though as plenty of Disco's run 235x85's on and off road without issues and they weigh considerably more than the 90.
5/4 of people admit that they’re bad with fractions.
I think you'll find that if they're both R380 gearboxes out of 300Tdi vehicles then the gearboxes will have the same ratios. The difference, if there is any, will be in the transfer box, with the disco being most likely 1.22:1 and the defender 1.41:1
This link might help you work it all out:
Discos have more horsepower as standard than a defender though and are more aerodynamic (and possibly also smaller diameter tyres?) so to me it makes sense that they would have a 1.22:1 box compared to a 1.41:1 in a defender. The link I put in my previous post suggests that too.
Thanks guys, I hope that this will all be for the future. So if I'm lucky (which I never am) the gearbox is the same so will swap straight over, it is however the transfer box which alters the ratios. Of cousre I will find that it is the transfer box which has had the volume turned up to eleven.
It would be nice to find out what all the numbers mean in the real world: it will be fast/slow on road, too fast/slow in low box off road etc etc
If it ain't broke, I'd be bloody suprised.
Ok, I'm sad and have too much time on my hands sat in front of a computer.
Here's a spreadsheet than will show road speed for given transfer and gearbox ratios and tyre diameter.
Assuming both gearboxes are R380s and from Tdi vehicles they will probably be the same, so the only difference will be in the transfer box.
I think I'm right in saying that low box on all LT230 transfer boxes is the same, so it won't make any difference when you're playing in the mud.
If your existing transfer box is 1.41:1 and you swap it for one that is 1.22:1 then when in high box everything will be faster than before. This will mean lower engine rpm at cruising speed which on the plus side will probably make it quieter but on the minus side might mean that you have to change down from 5th to 4th on every little hill which can soon become a nuisance.
I'm not sure tbh. I can't see it making any difference round town as you'll just tend to be in a lower gear to compensate. On a long higher speed run you might find you get a few more mpg if you have enough power to keep it in 5th but if you're forever going between 5th and 4th every time you get to any kind of a hill then I would guess any gains on the level will be lost there.
At the end of the day if it was going to be better all round with a 1.22:1 box then they would probably have fitted one in the factory so I would guess that unless you have had the engine tweaked for a few more bhp then you'll probably find it less than ideal.
ISTR that when DaveW first built the 100" and put the box from his Rangie into it that it had a 1.22:1 box and he changed it for a 1.41:1 because the auto box was forever changing down from 4th to 3rd when cruising. You would probably end up with the same problem in yours, especially as you will probably have less horsepower than Dave's 3.9V8i.
you cant just slot the r380 from a disco into your 90 - or the gearstick will be where your tranny tunnel meets the seat box. However you can swap over the lever and gubbins on the top of the box with the one from your defender box. Bit of hassle setting it all up so all the gates work and you can get all the gears i believe.
transfer box will bolt straight on though. it will raise your gearing 10% in high range only. Low range will be the same.
Unless your tdi is poorly you wont have any problems pulling that extra 10% on the road. Mine will accelerate up the big hill on the M62 going towards manchester in 5th from 60mph without needing to change down. So with taller gearing it might mean i cant accelerate up that long slogging hill, but i would imagine it would at least maintain speed. If mine ever goes pop, i'll be looking for a disco transfer box as a replacement as i would like the extra gearing.
Another bloody dent...
I've kept quiet a while so now for my 2npce hapenny .
1 Disco 1.2 transfer box will drop straight into a 90.
2 1.2 gear ratio's designed for 205/80/16 tyres not 235/85/16's ,
If you've got a TD5 it'll pull the 1.2 ratio no problem , drop it in a 90 (2 or 300TDI) on 235/85's and you'll spend all your time thrashing your engine in 4th as it won't hold 5th on anything other than flat and downhill. A 90/110 becomes an airbrake over 60mph a Disco doesn't.
Stick with the 1.4.
On a similar note those of you running Disco's on 235/85's or bigger should be looking at dropping a 1.4 ratio box into them as it'll improve drivability no end .
I run a 1.6 BTW as I've got 35" tyres on at the mo and the autobox won't hold top with anything lower, could get away with a 1.4 in the 110 but the V8 revved to 6500K smoothly (the diseasel wont).
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