Gearbox Upgrade

Gearbox Upgrade Overview

Upgrading the 5th Gear Ratio in the H Series Landcruiser transmission will improve fuel consumption, extend engine life and reduce cabin noise substantially.

The H Series gearbox is fitted to many Toyota Landcruiser 70, 80, 100 models from 1990 on.  The H150f, H151f and the H152f have different gear ratios, particularly 5th gear. The LTG 4×4 5th Gear Conversion can be fitted to the earlier gearboxes, converting them to the later H152f which was introduced in the 70 Series from August 2016 on.

The 70 Series has had a multitude of model changes and upgrades since its inception in 1984, but one of the more significant changes was the gearbox change from 2007-16 (H150f) to 2016-on (H152f). The easiest way to note the change is it is synchronous with the introduction of the DPF and the larger air scoop in the bonnet. There are a number of other changes at the same time, but the taller 5th gear improved fuel economy, extended engine life and reduced cabin noise. See table

The extra RPM is completely unnecessary, the 4.5Li V8 turbo intercooled engine has loads of power and torque, even for heavy towing, so the extra fuel useage and noise is completely unnecessary.

The Toyota H152f gearbox is interchangeable with the H150f. The clutch is also interchangeable. The clutches are known to be adequate, without being exceptional, so they are often upgraded when a GVM has been fitted, it has any significant power upgrade or performs heavy towing.

As you can see from the above list of ratios, the H152f has a taller 5th gear, and 2nd gear. The taller 2nd  gear helps to reduce the gap between the higher gears leading up to 5th.

The benefit of the 5th ratio change, the reduction in highway RPM, is engine life and fuel economy.

The later H152f transmission results in around 20% extra fuel economy, for highway use.

Regarding engine life, consider the reduction of component movement over a 5 hour highway drive.

Driving at 100kms/hr with 285/75/16” tyres, the RPM in 5th is 2420 with the earlier gearbox. With the same configuration, the RPM is 2060 with the later transmission fitted.

That’s RPM, Revolutions Per Minute. That saving of 360 RPM = 21,600 Revs per hour. Over a  5 hour drive that equates to 108,000 less engine revolutions.

A trip from Sydney to the Kimberley and back is going to save 1.81 million revolutions!

So, there are a couple of upgrade options you can do for the H150f models. You can source, new or used, the later H152f gearbox and swap that out with the older one. Or LTG 4×4 sell a 5th Gear Upgrade Kit for the H150f transmission, which has a ratio 0.736, slightly taller than the H152f at 0.75, saving 2.01 million revolutions on that trip to the Kimberly and back.

An automatic conversion to 6 speed automatic, reduces the RPM more than twice as much as either of the manual upgrade options. It calculates to a reduction of 4.06 million revolutions on that trip to the Kimberly and back.

Can you believe it? What a huge difference in engine wear!

NOTE: If you’re buying a second-hand 70 Series, this demonstrates the odometer reading is pretty much meaningless when considering engine life. Of course, there are other significant reasons as well, but this is one that is rarely considered!

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The earlier model is a H150f transmission. The later model is the H152f.

Table of Ratios
GearH150fH150f 5th ModH151fH152fAB60
6th    0.588
RPM in 5th or 6th Gear
GearH150f*H150f 5th Mod*H151f*H152f*AB60*
6th    1615
* RPM @100kms/hr with 285/75/16″ Tyres taken aat 32.7″ in diameter

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