Thread: Which gearbox, & how to fix?

Originally Posted by mike_ie

Bearman - I'll not be running anything bigger than 265/75/R16's, and after plugging that into the gear ratio calculator, the Rangie TC looks pretty good in the numbers. Any recommendations on your end???

Mike, I reckon you will need the 1:1003 transfer ratio to match the Isuzu characteristics. This is what was standard in Isuzu LT85/LT230 from factory. Sounds like Matt has one you could use.

Originally Posted by slug_burner

What about one of the grubs Isuzu MSA boxes?

Would absolutely love to, and that was the original plan, but the emergency $$$$$ got burned up with the whole Alice adventure, so I'll be making do with what I have. Best I can do now hopefully is to pick up a secondhand MSA gearbox and chuck it in the back of the Defender before shipping home (can't get them in Europe), and see if the_grubb can ship the adaptor kit to me sometime in the future. Have seen his kits and they really are the proper solution.

rovercare and Bearman - I didn't realise that the Isuzu was usually mated to the 1:1.003 TC - I thought they were for auto boxes. Other than dropping down the engine rpm required per gear in high range, what other effect does it have, when you say "match the Isuzu characteristics"?

Unless you are using larger diameter tyres that is the ratio I would use. Isuzu characteristics, where do I start??? Hmmmm, bulletproof, simplicity, long lasting, next to nil maintenance, no electronics, economical running, but most of all slow revving and low down torque. Max revs is 3200 -3500 rpm depending on which motor you have so if you can keep top gear around 2000-2400 at 100kph that is a good range to aim for.

Originally Posted by mike_ie

[snip]

Other than dropping down the engine rpm required per gear in high range, what other effect does it have, when you say "match the Isuzu characteristics"?

What Brian is trying to say in the post above is that the torque curve is a lot lower down the rev range than a Tdi, they have torque to burn off idle rather than nothing off idle until you get to 15-1750 RPM with the boost bringing the power on as with a Tdi.

Originally Posted by rick130

What Brian is trying to say in the post above is that the torque curve is a lot lower down the rev range than a Tdi, they have torque to burn off idle rather than nothing off idle until you get to 15-1750 RPM with the boost bringing the power on as with a Tdi.

Thanks for the explanation. I was curious what the advantage of the 1:1.003 was over the 1:1.222, seeing as the 1:1.222 will give me 100kph at 2216RPM with the tyres I'm currently running, which sits it square in the middle of Brian's parameters. Makes more sense now.

Originally Posted by mike_ie

Thanks for the explanation. I was curious what the advantage of the 1:1.003 was over the 1:1.222, seeing as the 1:1.222 will give me 100kph at 2216RPM with the tyres I'm currently running, which sits it square in the middle of Brian's parameters. Makes more sense now.

Probably bugger all in that, but I haven't worked out the gearing either.

I think the original Landy fitted engines were industrial spec too, which IIRC have a slightly lower rev range than truck engines ?

Some Isuzu fitted county's came with 1.2:1, most had 1:1

It will drive better with the 1:1 case, I thought old mate might of said it had 1:1 gears? I can't remember, maybe give him a bell or get the gear counts got the lt230 and confirm

1.2:1 is to short I think, even on 35's and 5 speed, I drive tonys when I was up nsw it had 35's, 1.2 case lt85

I only have the lt230r, yours if you want it

I have had both ratios in my county,1:1 make 1st gear a bit high if your loaded up taking off up hill etc.but on 235/85 5th is good on highway.
I now have 1:1.2 and 255/85,I find this to be a much better ratio.
Most low speed tracks 2nd high is good with a gear lower if track gets steeper
I think the ratio you need depends on if your fully loaded all the time the lower but if traveling light and a lot of highway the higher ratio.
Jim.