Outer Limits 4x4 Board

hi i have a hj47 and it revs to about 3000rpm to get 60kmh out of it in third it has a 60 series 5 speed in it, whereas my parents 60 series both with 2h can reach around 75kmh in third i am just wondering how this is and if i can change my diff centre to the 60series will it be better on road

thanks Shane Mulcahy

from factory they are very likely to both have the same diff ratio (4.11), so there may be a difference in tyre size and/or speedo calibration to account for the speed difference. have a look at the build plate on the firewall in the engine bay; if the first two digits of the axle code are the same, they are the same ratio

Maybe its the gearbox
My old '47 series 4 speed
60 series 5 speed
also maybe difference in transfer ratio.
There is a lot that goes round before the diff.
most public libraries have repair manuals if you cant use or be bothered the links to get online manual

edit a bit quick on the uptake here sorry.
There is a couple of 5 speed boxes though are you comparing like with like.

It could be that your parents have 3.7 diffs while you have 4.11, which would give you something like the differences that you are experiencing, though not exactly when you do the numbers... however it could be a combination of that (diff ratio) and tyre sizes that is giving you the difference.... I don't know if 5 speeds came out with different 3rd gear ratios, but even if they did, they would be fairly close to each other numerically, so I can't see the gearbox (3rd gear) being the culprit, the rpm difference is just too big....

yeah i dono i have 31inch tyres and so do they my gearbox is a h55 which had the same 1st 2nd 3rd and 4th ratio as my old 4 speed when we rebuilt it but i put a newer model transfer case off a 1988 hj75 ute with the larger layshalft i don't no whether this makes the difference cause there car is faster in everygear i just used third as an example
thanks Shane Mulcahy

remembering tyre size alone (if box and transfer are the same) won't make a difference to the speedo reading of 60kmh, only to the actual speed (measured with gps for instance).
I have heard of older cruisers being re-geared with 3.7's, so check that.

Stackson45 wrote:remembering tyre size alone (if box and transfer are the same) won't make a difference to the speedo reading of 60kmh, only to the actual speed (measured with gps for instance).
I have heard of older cruisers being re-geared with 3.7's, so check that.

assuming the same speedo drive gear, same speedo etc.

the margin for error in speedo readings in older vehicles can be as bad as +-20% - two otherwise identical vehicles might display vastly different speeds for the same give roadspeed.

first step is to read the axle codes or jack up a wheel and WORK OUT the diff ratios. then get a GPS in each vehicle and test speeds in different gears. then calibrate the tachos to make sure it's all not just instrumental errors.

Mulcahy wrote:yeah i dono i have 31inch tyres and so do they my gearbox is a h55 which had the same 1st 2nd 3rd and 4th ratio as my old 4 speed when we rebuilt it but i put a newer model transfer case off a 1988 hj75 ute with the larger layshalft i don't no whether this makes the difference cause there car is faster in everygear i just used third as an example
thanks Shane Mulcahy

The transfer high ranges are the same at 1:1... the tooth count in the transfers in high range may be different but the actual ratio remains 1:1 (low ranges can be different tho)... if the vehicles are in the same locality, an easy check could be to drive them side by side (or one behind the other) at the same speed and see what each reads on the speedo and the tacho... mite give you some idea of what's going on.... I still say diff ratios are the most likely culprit...

so i am now thinking of pulling my diff out to get it rebuilt maybe drop in a locker and was wondering if anyone can tell me how to visually tell the ratio do i count teeth or do i have to check rotations

Thanks Shane Mulcahy

Mulcahy wrote:so i am now thinking of pulling my diff out to get it rebuilt maybe drop in a locker and was wondering if anyone can tell me how to visually tell the ratio do i count teeth or do i have to check rotations

Thanks Shane Mulcahy

Number of crownwheel teeth divided by number of pinion teeth = diff ratio.