help on diffs and transfer boxs

[damo]

hey there i keep hearing people going on about swaping diffs and tranny boxs could any1 tell me what this does if i was to put a diffrent sized diff and transfer box in my sj413?

[Tramp]

It would just change the gear ratio, if you have big wheels or you want more torque and less speed you lower the gear ratio, if you want to go faster and. have less torque you go higher, i can't remember figures off the top of my head but the 410 transfer box has a lower gear ratio this gives more torque and is better for offroad

[dazerede]

If u put 410 diffs and a 410 t box in it 413 this will make the gearing lower so its better for off-road
Some one else will explain better

[damo]

my wheels are 235x75x15 would that make my sj go slower than the standard sized wheels if it has the standard diffs etc

[dan_2k_uk]

those tyres aren't that far from standard size.

in theory bigger tyres will increase your top speed but in the real world with drag, aero dynamics, and the fact there is a limit to what the engine can turn it doesn't work out like that.

are you having a problem with top speed?

[damo]

yes mate does 55 mph flat out wagons go round me on the motorway been told its probly the carb but im no good wi stuff like that im alright at simple jobs lol

[dan_2k_uk]

Would have a look at tuning mate. Fuel/air mix or timing. Either that or somethings causing extra drag.

How aggresive is the tread pattern on the tyres?

[ScottieJ]

Your SJ should be able to hit 70 easily with that size tyre fitted, my 970cc used to hit 70 with 31" tyres.

I would give it a service (fuel filter, dizzy cap, rotor arm, plugs, leads etc.), timing set and a tune up, if you don't know how to set up the carb yourself then maybe take it to a garage.

As for Gearing, when larger tyres are fitted it makes it harder for the engine to turn them, by lowering the gearing it makes it easier for the engine to turn the wheels. As those tyres aren't much bigger than stock a 410 Tbox would be perfect, however a Rocklobster would be better as then you'll have a lower ration in Low box for offroading; helps with engine braking down hills and more torque going up!

Dazerade: SJ410 diffs do not fit 413 or samurai axles