Gear Ratio Help R380/LT230

[RPR]

Sadly, after 20 years, 12 of which were behind the 3.5/3.9 V8 in my Series III, the Series transmission has given up the ghost. Multiple gear and shaft breaks, lots of metal shards. Would require a complete rebuild or new reconditioned box and, for the money, may as well go R380 and LT230. My Volvo portal axles are CV front joints, so full time 4WD is fine.

I'm trying to figure out gear ratios and need some serious rivet counting and math help please.

Currently:  5.99 axle (diff and reduction boxes), 1.15 t-case high range, Roamerdrive OD (x 0.28) and 35.5" tires, for:

4th OD: 4.59:1total ratio or 0.828 transmission ratio ; 60 mph @ 2823 rpm  3rd OD: 7.44:1 ; 30 mph @ 2112 rpm

With early RRC LT230 that I understand to be 1.03:1 high range. Question 1, is that the correct ratio?

5.99, 1.03, Suffix J R380 (5th 0.73:1 and 3rd 1.39:1), 35.5" tires for:

5th: 4.50:1 ratio or .0.752 transmission ratio ; 60 mph @ 2558 rpm     3rd: 8.57:1 ratio and 1.432 transmission ratio ;  30 mph @ 2436 rpm

With later V8 LT230 1.22:1 High range (is that correct ratio?)

5th: 5.33:1 ratio 0.891 transmission ratio ; 60 mph @ 3031 rpm   3rd 10.16:1 ratio or 1.695 transmission ratio for 30 mph @ 2883 rpm

 

So, the Tonka is not a daily driver, nor does it do highway miles, but on the county roads, it needs to do 60 - 65 mph. With the 1.22:1 high range LT230 that's 3000 - 3200 rpm. That seems pretty high rpms; higher than 4th OD with the Series box. Whereas with the early RRC ratio of 1.03:1 High Range, 5th gear is delivering 60 - 65 mph at 2558 - 2771 rpm. That's super comfortable. Fourth gear would be 40 - 50 mph at 2300 - 2900 rpm. It really seems that that 1.03:1 High Range ratio is perfect. So, questions:

 

Have I got the ratios right in the LT230 and gears right in the J Suffix V8 R380? 

Have I got the math right (using this rpm calculator: https://www.crawlpedia.com/rpm_gear_calculator.htm )

Am I missing something?

Appreciate your help on this. Thanks very much.

[Bowie69]

https://www.ashcroft-transmissions.co.uk/calc/ratio_calc.html

This will answer all your questions!

 

[lo-fi]

You'll definitely want the 1.003 LT230 with those diff ratios. I'm running that on my 109 with standard series 4.7 diffs and an LT85 behind a V8 and 30 something inch tyres and I'm really happy with it. You'll probably struggle finding an original 1.003 box, but Ashcroft do a conversion kit. https://www.ashcroft-transmissions.co.uk/lt230-ratio-changes/1-003-gear-set.html

[FridgeFreezer]

Guess I'm fairly well placed to comment

You want the 1.003:1 LT230 if you need to go any distance, even then with the V8 it might feel like you want an overdrive

Low range is always the same and will be nice & low especially on those small tyres

As lo-fi says, it was only the very early RRC's that had the 1.003:1 LT230 so they're relatively rare but Ashcroft do the ratio for newer boxes - the older ones had roller bearings on the intermediate shaft, the later ones use taper-roller so I don't believe the contents are swappable between casings.

Which R380 you choose is fairly academic - later ones are stronger, some have slightly different ratios, but you just need one that bolts to your V8.

[RPR]

Thanks very much!! Wish I'd known about the Ashcroft calculator first; that thing is fabulous. Luckily, I have a line on an LT230 with the 1.003 gears in it, and that is definitely what I want. That will make high range much more pleasant and means I don't need another Overdrive. First low crawl goes from from 64:1 to 73:1, which borders on silly slow. Mind you, loss of the Overdrive as a gear splitter will hurt. It was nice having 64:1 or 46:1 First low. I had been toying with 1100x16 tyres, but I think I'll stick with the little old Swampers.

[lo-fi]

You'll get good money for your series overdrive if it's in good condition, which will go a fair way to funding an overdrive which would fit the LT230 if its something you decide you want. 

Do you have a thread running somewhere? It sounds like an interesting vehicle

[FridgeFreezer]

I'd hope you wouldn't need overdrive in low box, you've got 5 gears to choose from after all

If you do go overdrive, get a Roamerdrive - the GKNs just seem to explode for a pastime.

[Snagger]

2 hours ago, lo-fi said:

You'll get good money for your series overdrive if it's in good condition, which will go a fair way to funding an overdrive which would fit the LT230 if its something you decide you want. 

Do you have a thread running somewhere? It sounds like an interesting vehicle

The existing marketed LT230 overdrives only fit 1.4:1 versions, as far as I’m aware.  Certainly the case for the GKN and Roverdrive.

[FridgeFreezer]

28 minutes ago, Snagger said:

The existing marketed LT230 overdrives only fit 1.4:1 versions, as far as I’m aware.  Certainly the case for the GKN and Roverdrive.

Good point!

I guess if you need higher gearing you either just fit bigger tyres or see if anyone has any of the 5:1 gears for the Volvos.

[lo-fi]

Interesting... Any idea why? I'm pretty sure there are two sizes of input gear; the very early ones being a different size. The difference between the various ratios on suffix C onwards (which Roamderdrive fits) being between the intermediate and main shaft high gear. An input gear is an input gear regardless of high ratio. Suffix G boxes are different again, having different pressure angle, but that's beyond the scope here. Maybe the size of the intermediate gear on the higher ratio boxes interferes with the overdrive?

[Snagger]

I’m not sure about the LT230, but I think it’s like the Series unit in that the input gear meshes with the high range gear on the intermediate cluster.  The Series unit only had one ratio for high range throughout production (ignoring 1-ton and V8 models, which don’t accept the overdrives that fit the standard unit).  I suspect the LT230 is similar, and so their overdrives will only mesh if the intermediate gear cluster (and thus high range output shaft gear) are of the “standard” Defender size of 1.4:1.  The 1.6, 1.22 and 1.003 models presumably have not only different intermediate clusters and output shaft gears, but input gears too.

If the input gear drives the low range gear of the intermediate cluster, then I don’t know the answer as I thought the low ratio was consistent across the different versions, but that may also have differing ratios.

Im pretty sure about the overdrives only fitting 1.4s, though.

[lo-fi]

Ah, it's actually a different design. The intermediate cluster has three gears cut in, the middle of which meshes with the input gear. The forward-most gear is low range, the rear-most is high range. Aside from the A and B suffix, the input gear and middle on the intermediate cluster stay the same regardless of high range ratio, with the change being to the rearmost gear and the corresponding gear on the mainshaft. In the higher ratio boxes, the high range intermediate gear is larger that the driven input gear - I suspect this may be the deciding factor. 

Sorry for going off on a bit of a tangent, but I'm happy it's at least relevant to the theme of the thread

 

[RPR]

Based on the numbers run in the Ashcroft calculator, with the 1.03 HR LT230, there should be no need for an Overdrive.

[Snagger]

In a transmission that is working hard, and I think yours would be, I’d be hesitant to add another stage that would be a weak link and also contribute to heating the rest of the transmission and it’s oils anyway.

[FridgeFreezer]

4 hours ago, Snagger said:

In a transmission that is working hard, and I think yours would be, I’d be hesitant to add another stage that would be a weak link and also contribute to heating the rest of the transmission and it’s oils anyway.

RPR's transmission shouldn't be working that hard - it's a light truck with low gearing. His only problem might be heat depending on the local climate but if RR's and Disco's with the same engine & box & transfer aren't struggling I'd hope a little 88 wouldn't have a problem.

I've worked the 109 fairly hard on occasion and none of my oil temp tell-tales have ever shown an issue either with high speeds or heavy loads over long distances. And we proved the LT230 is good for ~400hp with zero mods.

[Daan]

I'd say that the v8 R380 is going to be a tight fit in an 88". The short case 380 or LT77 with a v8 conversion kit may be better to package behind the series grille, while maintaining reasonable propshaft length.