To swap or not to swap (transfer box)

Lots of conflicting views on this when you do a search, the reason for possible swapping is to improve motorway travel other than that I am happy with the gearing.
I have a 96 defender 90, 300tdi (tweaked) running on 35”tyres (not used for towing), currently the transfer box is (1.4:1) considering replacing it with a disco item (1.2:1).
What I don’t want is the gearing to be too high in 1st that I have to rev the nuts of it when starting off.
Any advice appreciated.

I have done it on my 200tdi and my TD5, best mod I have ever done

As it is

Ashcroft Transmissions - Ratio Calculator

Swap to 1.2

Ashcroft Transmissions - Ratio Calculator

Leave it as is with 35'' tyres otherwise it will be too low geared

I've just fitted a Disco one in mine but my tyres are no where near that size, If I was using 35" tyres then I would keep the 90 box.

Your tyres are to tall for the disco tfer box, mine has 34 inch tyres and it did have an early r/rover t/fer box 1.19, kin nightmare pulling away up steep hills etc, back to a 1.4 t/fer box and its lovely.
With the 1.19 box on long gradients it would lose speed no matter what I did, basically way to high geared.

Don't do it. My disco (on standard gearing) is a bit of a nightmare to drive atm and I'm only on 33's. Gearing is definitely too high.

Stick with the 1.4 transfer box!

I'm running 305/70/16 on a 200tdi 110 with a disco transfer box and it's on the limit. I certainly wouldn't want to go any bigger with tyres and this ratio. It was perfect when I had 265/75/16. It does make motorway drives a lot better though.

Sounds like yeeee all got no power!!!!!!!! Put ya's right foot down!
Running 35 fedimas on my 200tdi 90 with disco box and still pulls like a train. Only time I notice it is pulling up long duel carridgeway hills then it's a 4th gear job but still doing 55 odd so not bad, 5th is more of an overdrive with the big tyres on but still pulls good.

Like mentioned 265's is ideal as can still pull big hills in 5th without having to drop a gear but it makes everyday use so much nicer, top speed flat out is around 95 but only on private roads like and normal 65/70mph you can do at a nicer less rpm.

I've got to change boxes before a Wales offroading week and I'll be putting a disco one back in!
If you do any towing Id leave it for defender as Imagine anything more it will be too much!

Thinking about doing this mod myself with 265 special tracks fitted is the 12.1 T/Box ok to use with these tyres

used for very light towing, offroading and accasional mway use

Yes matey its ideal with 265's

I done it and motorway travelling a lot more enjoyable, not much difference driving on a and b roads except i do not use fifth as much. But i do not tow , i am very happy with the mod.hope this helps, btw 90 with 265/75 on.

Does anyone have a overdrive on a defender . heard mixed reports on em . some say they trash the transmission ?

Weird everyone recommends it as an excellent mod, BUT then go on to say they dont use 5th as much, so change your tfer box and end up with a 4 speed defender sweet:crazy:

Thanks all for your replies, I think on balance the don’t do it wins (with my 35” tyres), the next option then is fit a overdrive!!

We have a 110 tipper with disco box on 235\85\16's and you use low box setting off loaded . I wouldn't recommend it like

I had a drive in mine yesterday for the first time since the rebuild. It cruises a lot more comfortably with the disco transfer box and seems a lot less stressed. Other than the wind noise 75 is quite comfortable. That is with 265s though. Acceleration seems the same as it has always been.

Just a quick update I have purchased second hand GKN overdrive (not been delivered yet) but will let you know when fitted what I think.

steve999 said:

Just a quick update I have purchased second hand GKN overdrive (not been delivered yet) but will let you know when fitted what I think.

Click to expand...

think this is the right move I have 33" tyres with disco tbox 300tdi normal driving is ok and still tows well but if the box dies I will be putting the standard gearing back.