Thread: Material differences btween a NPR 4BD1T and a ex-army 4BD1?

Of course klr recommended keeping the r380, thats what they do. The 380 is the torque rating in nm of the box, my 4bd1t is up in the 650nm range, i doubt the r380 would last.
I would have a talk to Sheldon at Cor Conversions as well.

He posted some great info the other day on facebook in regards to both gearboxes, i will see if i can find it and paste it here.

I wouldn't deem myself as a critic per se. The '380' in the R380 designates the torque loading in Nm of the gearbox. A naturally aspirated 4BD1 has 245Nm of torque. It's possible to get upwards of 600Nm if a turbo and intercooler is fitted to the 4BD1. Even the KLR kit says it near doubles the output by adding a turbo Turbo Systems - KLR Automotive Double 245NM is 490Nm. Which is more than the 380Nm the R380 was designed for. 5th gear on a LT85 is hung out the rear of the main case - ie not between the main bearings. 5th gear on a R380 is hung out the rear of the main case - ie not between the main bearings. The difference in arrangement is that the R380 also has rear support bearings, where as the LT85 did not. It is the two rear support bearings that Ashcroft upgrade. Ashcroft Transmissions quoted from their site 'then as the bearings wear it allows the 5th gear on the layshaft and 5th gear on the mainshaft to come a little out of mesh, then 5th also gets noisy and often results in the teeth coming off one or both of the 5th gears'. The other difference is that the R380 has a smaller 5th gear (as are all gears in the R380) compared to the LT85 - so therefore higher tooth loading in this critical area. So 5th is still an issue with the R380 - certainly that's what Ashcrofts personal experience has been. I have no personal experience of the R380 behind a 4BD1. I am a degree qualified mechanical engineer, with 20 years engineering experience, so engineering fundamentals play a big part along side practical experience for me. If a R380 is working for whoever has it then great. Great that there are options out there. The R380 is derived from the LT77 which was originally designed for the Rover SD1 - a 1,500kg car. gearboxes2 and upgraded over the years into the now R380. The Isuzu box is designed for the NPR turbo trucks with a Gross Combination Mass of 9,000kg - designed for something heavy from the get go. Not a typical landrover 'make something work from what parts are lying out back'. For reasons already mentioned it is a much stronger box than any landrover 5 speed. I know of someone who had a LT77 behind a 6BD1 (yes that is a 6 not a 4) in a series landrover until they wrecked the vehicle, it worked for them. In my Mechanical Engineering Degree qualified personal experience I wouldn't recommend that for long term reliability. Stronger will always be better. If a R380 works - go for it. If it's cheaper to fit (how much is it anyway?) and gets you going - go for it. I'm certainly not a critic. Everything for a price. If a stronger drive-train is desirable and available, then perhaps that is a better option. At the time when I had gotten over replacing a worn out LT85, I wanted to fit a turbo/intercooler and get the most out of what the 4BD1 would give, so went down the path of designing a bullet proof replacement. The logical choice was a gearbox designed and in worldwide use behind the 4BD1T. That's where I have personal experience other than the LT95 and LT85. If someone doubts that the Isuzu MSA 5 speed is stronger than a R380 then I'd love to hear their personal experience.

I'm the person behind COR Conversions and the Isuzu MSA 5 speed conversion (amongst other conversions in the pipeline) - just wanted to state that out in the open.

Pros/Cons in general (as I see it) for the easily available options there are at present for manual boxes;

LT95 - cheapest/no overdrive

R380 - overdrive, most cost effective means to get a 5 speed fitted/strength and longevity issues.

The R380 has a lay shaft to main shaft separation of 77mm (same as the LT77). Hence dictates the physical size of the gears inside the box. LT85 and LT95 are 85 and 95mm respectively. The bigger the gears the less force loading on gear teeth.
The R380 (and all other Landrover 5 speeds) have 5th gear hanging out the rear of the main case - not between the main bearings. I suspect this is one of the main reasons Ashcroft's upgrade the rear support bearings in their upgraded R380 build. Combine higher gear teeth loading and premature wear of these bearings - increase risk of failure. High loading 5th gear in a Landrover 5 speed, Ie. up hills and towing heavy loads not advisable.

Isuzu MSA - overdrive, distance between main and lay shaft is 97mm (bigger gears than even LT95 and dare say better Japanese quality over Landrover stuff), 5th gear is between main bearing centres (and the bearings are bigger) - no dramas towing and loading in 5th, upgraded input shaft and LT230 input gear in the conversion (with the MSA and LT230 this interface would otherwise be the weakest link and is now approx. Double the strength) this also reduces a lot of driveline slop caused by the original 10 spline interface, readily available pto attachment, increased oil capacity (MSA standard is 2.5 litres, the rear adapter housing adds 1.25 litres for 3.75 litres, compared to R380 of 2.6L)/cost? Basic kit is $3500 right now. Plus gearbox $2000 rebuilt, plus LT230 transfer plus fitting.

Patrol 5 speed - overdrive, main to lay shaft 100mm, not so hard to adapt to 4BD1/5th is not between bearings, probably be a similar cost to an MSA conversion



Then there are overdrive auto option(s)

Just a bit of info i found interesting, gives people a bit of an idea on the difference.
This was cut and pasted from a post from Sheldon

Originally Posted by Vern

Just a bit of info i found interesting, gives people a bit of an idea on the difference.
This was cut and pasted from a post from Sehldon

Excellent info to consider as I progress down this path......WRT to torque figues I'd really just want to replace 'like for like'. I'm happy with the Td5 performance and as you point out the R380 is designed for <380Nm, I'm very mindful of bumping up my output past the R380 limits and having problems manifesting further down the driveline. It's a bit of a balancing act......but one I'll be discussing with KLR taking into consideration the points you rightly raised.

I'm on a pretty steep learning curve with the 4BD1(T) and appreciate the input.

Originally Posted by Fubar

Excellent info to consider as I progress down this path......WRT to torque figues I'd really just want to replace 'like for like'. I'm happy with the Td5 performance and as you point out the R380 is designed for <380Nm, I'm very mindful of bumping up my output past the R380 limits and having problems manifesting further down the driveline. It's a bit of a balancing act......but one I'll be discussing with KLR taking into consideration the points you rightly raised.

I'm on a pretty steep learning curve with the 4BD1(T) and appreciate the input.

As i said, give Sheldon a call as well. Klr aren't the only people dealing with 4bd1's.
Sheldon. Cor Conversions 0488 474020

A couple of comments.
1. A lot of the issue with the 4BD1 is that it has high torque at very low revs - and has only four cylinders, so that the torque impulses will be seen by the transmission as impulses, not steady torque. In other words, it gets a hammering! (If you drive like that - the 4BD1 pulls well right down to a stall if you let it, but doing so is not being mechanically sympathetic, and doing it in fifth is asking for trouble.)

2. I seem to remember that the LT77, and hence the R380, started life as a pre-war four speed Jaguar box, with fifth gear a later modification; which is why fifth gear is outboard. (reminiscent of the Series gearbox, which started life in Rover cars in 1932)

Given the cost of doing this conversion, the engineering costs, possible issues down the track and as you say you really just want to match the performance of the TD5, then why not either rebuild the TD5 or get a short engine - will work out much cheaper and easier. If you want a bit more zoom zoom then as part of the process get the TD5 chipped, intercooler etc. (even a 2.8 upgrade but I have not heard they are all that good).

Garry