Thread: Ideal LT230 for 4bd1T?

Originally Posted by Dougal

I look forward to it.
I'm very happy with my 1:1.003 high range with 3.54's, 29" tyres and .0.77 overdrive. Even if I get bigger tyres later on (will require a taller garage) I won't be going lower in gear ratios, I've got plenty of torque for 5th gear passing duties.

What motor are you running?
In Defender with 300Tdi, faster high fifth and /or overdrive would be good for some high speed work. However faster gearing after the gearbox would be a disadvantage for some situations Land Rovers are used for with first and reverse high being too fast. Reckon for my purposes going to 1.003 is overdoing it.

The six speed gearbox in combined with approx 1.2 high in Pumas have slightly lower first and reverse gears and higher top than R380's. So probably owners will feel less inclined to use non standard transfer and diff ratios.

Mick

Originally Posted by Bush65

The down side of this is that you effectively halve the life of intermediate gear. That may or may not be an issue.

Gear ratings are based on strength and wear for 12000 hours. Gear strength is for fatigue strength of the teeth, gear wear is basically for pitting of the surface of the teeth flanks.

Because load is applied twice to each tooth on every revolution you halve the fatigue life and double the load cycles for wear.

If the gears were to be designed for this in the first place then the material and hardness of the intermediate gear could be selected to suit.

Generally the pinion (small gear of a set) has the lowest strength and wear rating if both gears are manufactured from the same material, so usually the pinion is made from higher strength material and the larger gear is made from lower strength material so their ratings are more or less matched.

The above factors are undoubtedly important with reasonably high loads and much more so when they approach or exceed that designed for, especially shock loads. However, I doubt it is an issue with an LT230 unless considerably more torque is applied than can be generated by a standard Rover motor and gearbox. Or in Series transfer boxes, where the input gear drives what is also high gear on the cluster like my LT230 modification.

Reports of these transfer boxes being busted seem very rare compared with those for Land Rover gearboxes, diffs and axles.

When there is a large factor of safety regarding gear strength, other than rapidly wearing them out and /or overheating by running without oil, a major destroyer of gears is failure of bearings causing them to not mesh properly. Normal loads can then then cause very heavy wear and /or stress and breakages.

In many gearboxes the cost of a complete set of new bearings may be similar to the price of one typical gear in it. Therefore if there seems any risk of bearing failure, it is good insurance to replace them.

One of the rare instances I have come across gears breaking - after relatively short periods of heavy load is final drive bull gears and pinions in my header (ie combine harvester). This was harvesting summer (growing ) crops in heavy muddy conditions in winter in the early 1990's. (Seems to me that will be our turn to have wet seasons and floods again in Murray Darling Basin in not too distant future despite record recent droughts. One effect - more uses for Land Rovers!)

Header was on rice tyres which were larger than standard ones on the machine and treads are much longer and further apart than tractor pattern. Loads encountered would have been far in excess of those considered by the designers. However, it is interesting to note that most of the trouble was with the left side final drive. Probably because the gearbox was close to it , with only a short drive shaft. The long right side drive shaft would have flexed a lot more, acting as a shock absorber to reduce fatigue and failure in final drive gears.

Note regarding Land Rover axles which are prone to breakage - usually next to the spline, "waisted" ones where the diameter of the axle is similar to the inner rather than outer diameter of the spline seem to be more reliable. They are more inclined to flex over their whole length and less likely to develop fatigue in one or two areas.

Mick