Thread: LT230 tooth count and ratio questions

Ben, the following from Maxi-drive, may help. I haven't time at the moment to digest what you have posted.

John beat me to it.

I actually have those pages uploaded in the files section on here.

Thanks. So it seems that apart from the gear width and cross drilling, all input gears on LT230Ts are 26, 28 or 32 teeth??? So can any 26 tooth input gear be interchanged with any other?

That helps me out with replacing the input gear on the 1:1 Rangie case.

It seems I may have miscounted and the MD case is 41/40 not 40/40 - which then makes the ratios make sense. However from the case serial number it should be a 28T input gear.

Originally Posted by isuzurover

Thanks. So it seems that apart from the gear width and cross drilling, all input gears on LT230Ts are 26, 28 or 32 teeth??? So can any 26 tooth input gear be interchanged with any other?

That helps me out with replacing the input gear on the 1:1 Rangie case.

It seems I may have miscounted and the MD case is 41/40 not 40/40 - which then makes the ratios make sense. However from the case serial number it should be a 28T input gear.

There could be a problem interchanging the different 26T pinions. Especially if one was mated with a 40T wheel and the other with a 41T wheel. Even if both pinions were mated with 40T wheels.

AFAIK, the centre distances between the input and intermediate gears doesn't change in any LT230 gear case. But there are options on the ratios/tooth counts. Now that is a common situation with gearing, it simply requires a correction to the addendum of either or both the pinion and wheel. Also it is common to apply a positive addendum correction to the pinion, for strength reasons.

There is no guarantee the both 26T pinions have the same addendum correction, even if both mate with a wheel having the same number of teeth. The amount of addendum correction is, within reason, a matter for the gear designer, to balance the issues of centre distance and tooth strength.

Another issue is that depending upon the model, Land Rover have changed not only tooth widths, but (as told to me by Mal during a telephone conversation) the helix angle and the pressure angle of the gear teeth. While the tooth width affects strength, it is not necessary to be the same for the gear and pinion, but it is normal practice for the pinion to be wider than the wheel, though not a show stopper. However, mismatch of either the helix angle or pressure angle is most definitely a show stopper.

The best you can do is assemble just the intermediate gears and the pinion and spin them together to check backlash and how smoothly the mating teeth roll in and out of mesh. They need to be very smooth. I would check this with both boxes, before pulling the pinions from them, i.e. when the correct mating pinion is meshed with its original mate, to get a feel for what to expect, before changing the pinion to mesh with the other wheel.

Be aware of how wear could affect the meshing. Wear does not occur uniformly over the tooth profile, but changes the accuracy of the profile, which besides being the source of noise, increases dynamic loads that reduce the strength and wear capacity.

Originally Posted by Bush65

...I would check this with both boxes, before pulling the pinions from them,...

Thanks John. The only problem with this is the 28D case (MD Low conversion) was received in a dismantled state, so I can't check, and has 2 pinion/input gears in the box.

From the list you posted, it seems 26T inputs were always paired with 41T gears, so I may have miscounted - it was late at night...

I should have mentioned in my last post, that if the outside diameter of both 26T pinions is the same, then they will have the same addendum correction.

If the OD's are the same (same addendum correction) and the pressure angles are the same, the thickness of the tips of the teeth will be the same. if the PA is increased the tips will be thinner.

Note the tips get thinner as + addendum correction increases. This is what limits how much + addendum correction you can have, because the thickness of the case hardening will extend too far and eliminate the tough core we want.

Also there may be some profile correction applied near the tips. Profile correction is needed in some circumstances. It is done to prevent the tip interfering with the flank of the mating teeth when the tooth deflects under load. A good visual inspection should detect if there is any profile correction, at least with a new pinion. I mention this because it affects the thickness of the tips.

To dispell any myths,

it is possible to remove and refit a 26 tooth input gear on a 1:1 t-case through the pto hole. Removing and refitting the wider cross drilled gear is a bit harder but still possible, probably 0.2 mm in it though, so on some cases it may not be possible.

However, whether they are interchangeable...

Old 26T input gear:
OD 95.0 mm
gear width: 27.1 mm
root thickness: 7.4 mm (hard to measure with a vernier)
Tooth height: 7.6 mm
Distance between bearing seats: 79.9 mm

New 26T cross drilled input gear:
OD 96.6 mm
gear width: 32.8 mm
root thickness: 7.4 mm Edited (hard to measure with a vernier)
Tooth height: 8.2 mm
Distance between bearing seats: 80.0 mm

The new gear fits in the case and turns smoothly, but doesn't quite seat down fully in the rear bearing race - however that is using old mismatched bearing and race at this stage.

Does anyone have the torque figure for the intermediate shaft nut to hand?

[QUOTE=isuzurover;1959589]1.192 is not an LT230 ratio, so I suspect the input gear may be incorrect for the t-case (it is disassembled so I cannot check...)



Hello. Just reading thru this and you say that 1.192 is not an LT230 ratio option.... It is, just not here I believe. 1.192 was found in factory V8 90's I believe, and its a transfer ratio I'm after as it is ideal behind a TDi in a Series Land Rover running a 5 speed and 3.54:1 diffs.. I'd be keen on owning those gears if you have the full set....

The available ratios that I've played with in the UK are as follows.. 1.667:1:- army 110's with naturally asmatic 2.5 d, 1.410:1:- most 110's and 130's with 200,300 and Td5 engines. 1.222:1:- 200/300/Td5 90's Discos and Tdi powered Rangies. 1.192:1:- Factory built V8 90's (there were not many but I owned a chocolate poo brown one for a while!), and 1.003:1 which is almost direct drive and found behind the older Torqueflight 3 speed auto in Range Rover Classics. The boxes marked 'R' have standard Needle roler bearings on the intermediate shaft which is held in with a small locking plate and from memory an M10 Nyloc nut. The boxes marked 'T' have taper roler bearings on the intermediate shaft, and have the shaft preloaded with a huge nyloc nut that holds it and the casing together! That's the expanse of my LT 230 knowledge, but if anyone know more please enlighten me. Hope this helped!