rear gear ratio

[rambo]

hi all i am new to this site, i have a manual 91 nh pajero intercooled turbo diesel the car has done about 40-50k since engine build which was done way before i got it, when i brought the car about 8 months ago i took it to the local mitsubishi dealer for a service and a check over 1 problem they said that they found was that the rear diff would not lock in ( so both wheels would drive) apparently because my pajero was a fully imported unit from japan? they had no information on the extra bit's n pieces, he explained that when the switch on the dash is hit it runs a small compressor (under the back seat) that pumps air intodif to lock it into dual drive (which does not effect the front diff) he said that everything is working as should except for inside the diff, has any one cone across this problem before, what are my options also while i have your educated attention i am currently running 31x10.5 15 tyres i think that it rev's to high @ 100km it rev's @3100rpm i tried running 265 70 16 tyre & rim's and found that it didnt make that much difference to the rev's at 100 not sure what the gear ratio's are on the diff's , what are my options

[nj swb]

The two different tyre sizes you tried are essentially the same size; the 265/70R16 is essentially 31x10.5-16. Note that your speedo drive is taken from the gearbox output, so if you're comparing your speedo with your tacho the same indicated speed should always be the same revs in the same gear.

The NH had the 2.5 diesel, which I believe came with 4.875:1 diff ratio. If yours is an import, it might have 5.29, but I don't think your revs @ 100km/h are high enough for that. Taller tyres or diff ratio should allow you to drop your revs for the same road speed, but you'll need to correct your speedo. The V6 models had 4.625:1 (I think) which would alter your speed marginally - but there's a reason Mitsubishi fitted the shorter gears to the diesel.

The rear diff lock was available as an option in Australia , although not all that common. A Mitsubishi dealer should have all the information required to fix it. I guess the problem is a leak inside the diff. Are you sure the diff doesn't lock? There's a switch inside the diff to signal that the diff is locked - if that is broken the light on the dash doesn't work.

Good luck,

Scott

[rambo]

hi nj swb sorry you got it rongit was the 31x10.5 15 not 16 the 265/70 16 was a bit higher which has a fair bit bigger rolling diamater as far as testing the car with the bigger wheels on it it was a simple quick run out the road and back ,i was pretty disapointed when the rev's didnt change at all i was expecting to be going with the traffic but doing lower rev's as the car is mostly a town runabout lowering the rev's would lower the fuel bill a bit, as for the diff the spannerhaed said that the switch is working o.k. there is power going to the diff but it is not locking or engaging the locker the mitsubishi spannerhead said to start looking around for a new diff which seems a bit harsh to me , does the locker in the diff work electrically?? as you said a leak in the diff what do ya mean a leak ? a crack in the housing? as for the revs on the dash instrument panel dont the rev's work of the electric's and not the g'box which to me that should be less rev's at the same speed ?? reguardless what the g'box say's i am doing oorr maybe i'll shut up i fink iam confusing me self now........ cheers

[Gavin]

For NH models:-
LWB V6 GLS- 4.875, GLX- 4.625.
LWB 2.5TDI GLS- 4.875, GLX- 4.875.
LWB 2.5TD GL- 4.875.
LWB 2.6 GL- 4.875.
SWB V6 GLS- 4.875.
SWB 2.6 GL- 4.875.
Note- sometime in the NH 2.5TDI series a 5.29 ratio was introduced to help acceleration, these are rare, it was dropped with the introduction of the NJ 2.8TDI.

I do approx 3200 rpm at 100k and about 3600 at 110k in my 2.5tdi NH.