Checking gearing on LN130

[Rustinho]

I've checked on the VIN plate and the gearing is quoted as code G144 which should mean that it has a ratio of 4.88:1 (assuming I'm not getting my facts in a muddle there).

I'm not entirely convinced that this is the case, however. I expected some loss in mpg & overall cruising speed with changing to 33s but I've been quite surprised at how big a hit I've taken with it given the experiences I have read on the forum. Absolute top speed has dropped to a smidge under 70mph (from an indicated 90mph ish previously) and the mpg has dropped from mid 20s to late teens.

Is there something stamped on the diffs somewhere that I can use to identify whether I actually have what it says on the VIN plate or would it be a matter of me taking bits off and counting the number of teeth in order for me to make sure that I have what I thought I'd got according to the VIN plate details...?

Thanks in advance for any helpful info folks...

[TonyN]

You can lift one wheel, turn it 2 revs and count how many times the prop shaft goes round.


From 4Crawler...

If the differential is still installed inside an axle, then assuming you have open differentials, lift one wheel on the axle in question off the ground. Put the tranny in neutral, transfer case in 2H, e-brake off (if is the rear axle you are testing) and put a chalk mark on the driveshaft and on the tire. Now turn the tire in the air through 2 full revolutions, while counting the revolutions that the driveshaft makes. The number of which will be equal to your gear ratio. You can get a more accurate count by doing 10 or 20 wheel revolutions and dividing the driveshaft turns accordingly.

Why 2 wheel revolutions?
Because, the ring gear in an open differential turns at the average speed of the two axle shafts connected to it. Since one is on the ground (and thus not turning) the other axle shaft (i.e. the one you are turning) must turn twice as fast as the ring gear, so 2 revolutions on one axle + 0 revolutions on the other shaft averages out to 1 revolution on the ring gear.

If you have a limited slip or automatic locker, then you'll need both wheels in the air and you'll use just one wheel revolution to get the rear ratio. For better accuracy, you can use say 10 (or 20) revolutions and then divide your drive shaft revolutions to get the gear ratio. For example, the difference between 4.56 (a little over 4-1/2 revs) and 4.88 (a little over 4-3/4 revs) might be hard to distinguish, but if you did 10 times as many revs on the wheel, you magnify the difference at the driveshaft by 10 as well. So instead of say 0.32 revolution difference (4.88-4.56), you would now have 3.2 revolutions difference if turning the wheel 10 (or 20) times.

Personally, your findings arn't surprising, our 3.0 struggles to do 70-80 on any reasonable incline on a motorway with 33's and milage is 30-50 miles less a tank full on average.

I've always told people 33's WILL impact on the average trucks daily manners.

[dieselboy]

Don't be too disheartened. You haven't just fitted bigger tyres. To fit those tyres you will have needed to lift the Surf. When I first bought my Surf on the standard road tyres the "speedo" whizzed up to silly MPH (three figures (stupid of me but an example)), Now, with the lift and 33's it struggles to get to 90 and simply takes ages from then on. Even then the tyres aren't rated to much more so that isn't exactly wise.

I'm not sure what you have done to your truck but you can mitigate the result with little things like intercooler, higher boost and water injection. It depends on the money you are willing to invest for the gains. Most would say it's not really worth it.
My old 2.4 was purchased from Javars back in the beginning of '07. Even then achieving 90 was like losing virginity. You needed a decent amount of space and all of it flat. When you finished you realised the achievement and told your friends.

[Rustinho]

Thanks for the advice/comments folks.

Since starting this thread I have fitted a top mounted intercooler and it's made a hell of a difference, particularly on the motorway. It'll hold 60-70mph up most inclines now and mpg has improved a wee bit cos I'm not thrashing it to get up hills quite the same!

I'll report back once I sort out whats what with mpg, etc after a few runs.

[gwh200]

Thanks for the advice/comments folks.

Since starting this thread I have fitted a top mounted intercooler and it's made a hell of a difference, particularly on the motorway. It'll hold 60-70mph up most inclines now and mpg has improved a wee bit cos I'm not thrashing it to get up hills quite the same!

I'll report back once I sort out whats what with mpg, etc after a few runs.

Really rusty, the MPG problem is 33's. My old 2.4 was the same.

And the current one aint much better...but MUCH more fun

[an1mal_69]

If you pull the prop, the nut behind it will be/should be colour coded. Blue, I think is 4.88:1

[Rustinho]

Really rusty, the MPG problem is 33's. My old 2.4 was the same.

Absolutely - I was just going to report back the changes for anyone interested...

And the current one aint much better...but MUCH more fun

I'l bl00dy bet it is! I've dropped a few extremely unsubtle hints to the wife about putting a V8 lump into it and she said something along the lines of yes (when we can afford it).

If you pull the prop, the nut behind it will be/should be colour coded. Blue, I think is 4.88:1

Cheers matey! Useful info - I should get around to looking at that this week sometime now that I'm completely over the 'pox.