• Welcome to the Land Rover UK Forums

    You are currently viewing the site as a guest and some content may not be available to you.

    Registration is quick and easy and will give you full access to the site and allow you to ask questions or make comments and join in on the conversation. If you would like to register then please Register Now

Gearbox to go with Perkins 4.203

joncusch

joncusch

In Second Gear
Hi all, I am in the process of converting my S3 109 into an overland capable truck. It is currently fitted with a Perkins 4.203 which I love and it's original gearbox.. As a result, top speed is around 45ish mph on 7.50 tires.
I am considering fitting a newer gearbox (lt77 or r380).. Has anyone done this before?
 

Attachments

  • IMG_20240412_181722~3.jpg
    IMG_20240412_181722~3.jpg
    262.3 KB · Views: 11
I do long(ish) distances in my LWB S2A with a 4.203. A couple of months ago did London - N Yorks and back, 300 miles / day with a trailer. I run the standard S2A box but I have:
3.54 diffs
235/85-16 tyres
an OD.
This gives 30 mph/ 1000 revs so I'm at 2000 rpm at 60.
Sweet spot on the Perkins is about 1800 rpm so on long runs I tend to cruise at 55 - 57 which means I'm in convoy with the trucks which suits me and I still have to option to go up to about 65. This is with a roof rack, camper roof and all the gear. If we have all the stuff plus the Sankey the Perkins can't get us above 50-55 on the level and much less on a hill but it still pulls the 3.54 diffs fine.
I wouldn't swap the box, the old ones are strong and simple, but if you don't have an OD or 3.54 get some. Nice to see there is another 4.203 fan, they are lovely engines.
 
robwlondon said:
I do long(ish) distances in my LWB S2A with a 4.203. A couple of months ago did London - N Yorks and back, 300 miles / day with a trailer. I run the standard S2A box but I have:
3.54 diffs
235/85-16 tyres
an OD.
This gives 30 mph/ 1000 revs so I'm at 2000 rpm at 60.
Sweet spot on the Perkins is about 1800 rpm so on long runs I tend to cruise at 55 - 57 which means I'm in convoy with the trucks which suits me and I still have to option to go up to about 65. This is with a roof rack, camper roof and all the gear. If we have all the stuff plus the Sankey the Perkins can't get us above 50-55 on the level and much less on a hill but it still pulls the 3.54 diffs fine.
I wouldn't swap the box, the old ones are strong and simple, but if you don't have an OD or 3.54 get some. Nice to see there is another 4.203 fan, they are lovely engines.
Click to expand...
The diffs I'm not too keen on replacing, as I don't want to interfere with its low range offroadabilty. With regards to the overdrive, they are nice but very hard to find... Was considering a romerdrive but is it really worth the price? Where with half the cost of a roverdrive I can source an r380...
 
I think you will really like the Romerdrive. Those on here who have them are very keen on them and I will get one when my Fairey OD gives out. The 3.54 do raise low range (of course) but not enough to be a problem for touring or unmade roads. Off road is another matter but you don't want to be off roading in a an overland vehicle, its just a way to get stranded. We go around the Mercedes Benz off road track fine with our 3.54 diffs. The other option is a high ratio transfer box, these do come up used now and then. The Romer drive is expensive but it's bolt on which means a lot less time and hassle.
 
I had the Perkins 4203 in mine. Lovely engine.. But the torque was too much for the gearbox. And that was with 4.7 diffs.
Now adding 3.5 diffs will increase the torque resistance further, and would be multiplied again with an overdrive.
The Perkins puts a lot of added Stress through the gearbox and bearings.

Know about gear transmission torque | KHK Gears

'Know about gear transmission torque' is the page explaining some factors such as load, efficiency and number of teeth of gears to calculate transmitted torque.
khkgears.net khkgears.net

I would keep the 4.7 diffs, and add an overdrive. You then keep a decent low range and can choose when to reduce the leverage and stress going through the gearbox. Stress increases by raising the final drive ratios.
 
Back
Top Bottom