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Series transfer box VS R380 torque capacity?


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Hi folks.


(if you just want to quickly add a reply, nip to the end of the thread for the final question)


I understand that it is somewhat unfair to compare the torque capacity of a mainbox and transfer box (torque multiplier effect etc) and I'm also aware that the 5-speed to series transfer box adaption is unloved by many, many people (just fit an LT230! its stronger and quieter I hear them cry). That being said….


As some of you know I already have the parts to build a hybrid R380/Series T-case gearbox (an Ashcroft LR380 adaptor kit, a R380 stumpy conversion kit, a Defender R380 ready for rebuild to 050-ratio and a late series transfer case for rebuild (2.35:1). To this I'll be adding a Series V8 adaptor ring. A nice, incredibly-compact, relatively-tough little transmission… and exactly the same recipe as the ECR 5-speed - which I shamelessly ripped-off - and which they used behind many-a-3.9EFI. This one is going in one of my LR specials.


Now, in the US - the land of the strong truck top loader gearbox - the series transfer case is actually considered to be pretty tough. Allegedly equal or superior to its contemporary Right Hand drop transfer boxes (D18, Land Cruiser, etc). I'll take it with a pinch of salt, but its certainly up-there and not considered to be weak. This was a bit of a surprise to me as, like most people I naturally think "series transmission = weak".




Yes, there are breakages on both sides of the pond behind everything from 2.25s to 6BTs and it would be difficult to conclude which were down to excess torque, which to worn, poorly-maintained 40-year old components and which to driver flamboyance. But there's a couple of well respected US off roaders who have used local boxes mated to the series T-case behind some incredibly torquey motors - Terriann of course with the Green Rover (300lb-ft of ford 302 V8) and Matt Jackson (330lb of 350SBC). I understand that Timm Cooper has run a few set-ups too (and managed to break some). These are figures I would never dream of running through a Land Rover mainbox (or a series transfer box for that matter).


The factory torque capacity of the R380 is 380NM (280lb-ft). Yet Land Rover never factory-fitted it behind the 4.6 V8 (280 lb ft@ 2,600 rpm) - instead they allowed a margin for safety and only used it behind the 4.0 (236 lb ft (320 Nm) @ 2,600 rpm) - which seems very sensible and something I will emulate. In diesel form it was used in the Disco II TD5 up to 221lb-ft (they offered a higher output 250lb-ft but this was auto-only).


(finally, the question)

So, rather than asking anyone to guestimate a torque figure, could I simply ask… "all things being equal - Suffix L R380 and Suffix C/D Series Transfer case (if it were possible to get both brand-new from the factory) - which is the weak(er) link? If I put enough torque through them and drove sillily enough - which would fail first?

(I actually suspect that the R380 would fail before the series transfer box. I ask as I will build a V8 to sit in front of the weaker unit  with a considerable margin for safety - if it is the R380, that makes life simple and I'll pop in a 38A 4.0 as this was factory proven. If its the transfer box I'll be looking towards a less torquey iteration of the old RV8 - aiming for 'showroom-acceptable strength' rather than anything extreme. But sincerely hope the R380 is the weaker link - the 4.0 38A RV8 with its short timing cover measures perfectly for the project)


Appreciate your help on this. And yes… I'm aware that a LT230 would have been better, cheaper and easier.

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Can't answer directly, but plenty of people run RV8's behind Series transmissions without major regular issues. Accepted, many of these are often trials motors. But they often give them some grief.


On this note, I would really worry and certainly wouldn't be trying to engineer the motor to run worse or make less power.

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I ran a 3.5 carb V8 in front of a series 3 main and transfer boxes in my 88". It took a fair bit of abuse and never failed me.


If you run your R380 with the optional oil cooler it will help.

I know of one particular heavy tower that used to kill R380s (in a 4.6 engined Defender) for a past time. Once the cooler was added they lasted a good deal longer.

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I don't think it's ever just torque that kills boxes, it's abuse, driving style, shock loading, and big lumpy diesels that create massive torque spikes.

Also wasn't aware the Series transfer box having a particularly bad rep, although the LT230 is undoubtedly stronger (as we know it will handle 400hp happily)

I'd say just bolt it all together, don't drive like an ar5e, and see how it goes. Some people can break anything, others can make anything last forever, it's up to you.

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From everything I have seen and heard, first and second hand, from club users to LR technical staff and instructors, all strongly suggest you'll kill any LR gear box before you kill a transfer box.  I have also been told by LR technical people and one of their tech drivers and prime instructors that the Series transfer box is considerably tougher than an LT230.  Frankly, from the work I have done on mine and what I have seen of LT230s, I'm inclined to believe it.

Ask yourself how many people on here enquire about R380 faults and rebuilds, or look for second hand ones, versus how many ask about Series transfer box faults, and make allowance for how many more R380 vehicles are about, you'll still see a very heavy bias towards R380 failures (and LT230s too).

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3 hours ago, Snagger said:

Your weak spots are going to be the diffs (can be made far stronger by pegging) and, if driving an 88", rear half shafts.  Are you uprating them too?

Yep. "LR380" hybrid box, 4.7 4-pin open diff (ashcrofts own) and 24-Spline shafts on the back. Front I have a choice of stock in my barn - either late 24/10 SIII take out stubs or I have a pair from a Stage 1 if I lose confidence in the UJs.

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I can't speak to the R380, but the Series transfer case is plenty strong. There are several examples of Series T-cases running behind Small Block Chevy and Ford V8s (you reference a number of them above). I cannot envisage economically building an offroad friendly Rover V8 that would generate so much torque that it would cause the Series tcase to fail and leave the R380 in one piece. I have been running a 3.5 V8 in front of a Series main box and t-case with Suffix B low range for 10 years - 2 or so carbed and 6 under a NAS90 top end and Lucas Hotwire injection. Other than having chewed up the synchro on Second (driver error), I have not had a problem. Mind you, I don't thrash it.

You'll be fine with a Rover V8 and if the objective is massive power, a clapped out old SBC 350 from the breakers with fresh oil will deliver more power than a bells and whistles Rover V8, in which case, something other than a Land Rover might be a better choice

As advised above, the half-shaft will be the fuse in this system...


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I have been running a r380 and lt230 behind a 3ltr TDI BMW remapped at 420nm for over a year now

the 380 was built by ashcroft with big bearing conversion , and has pumped cooler , and uses Redline

synthetic , in a heavy 110 . doesnt seem to bother it at all , max temp seen hot day on autobahn up long hill 130c on the guage just over half danger level .  As previous posters think axle is the most likely weak point if not full time 4wd from personal experience with V8 and large diesels  in series .

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