On Mercedes 410D chassis variant gearbox options for higher cruising speed.

There were two boxes for this chassis. I don't know what the official name was but I have seen them called the city box and the country box. The city box.as fitted to all Merc Hymers has the lower ratios - 1st is a crawler that will pull down a house, and 5th feels like 4th needing a 6th! The country box - ie for the autobahn - is just what you want. Every gear is a speed higher. 1st becomes like the old 2nd and 5th is the gear you really desire now! But it's not all sweetness and light - Hymer do things for a reason, and the reason they fit the slow box is because a motorhome chassis is pretty fully loaded all it's life, and the engine, while it will go forever, is underpowered....realistically. With low gearing, any Hymer from a 550 to a 700 at 4.6 tons will tackle any gradient, anywhere.
I know this from experience, as I finally found and fitted a country box in my (turbo'd) S700 a couple of years ago. Basically I love it because it's quieter at speed on the motorway, which to be honest is where we spend most of our time. But I have also been in a few situations where I have smoked the clutch - for some weird reason even reverse is a higher ratio, and it just doesn't like reversing up steep turns! I have also found myself cursing it on certain steep gradients, where 2nd is too low and 3rd is too high.
But all in all I am happy with it, and an owner of a 5 series or 6 series with turbo should also appreciate it, as long as you take care off road, and in the mountains.
But the boxes are hard to find! But not impossible! The gearbox numbers are 711.110 (standard low ratio box) and 711.113 (high ratio box)
Others have solved the problem by fitting 16' wheels which, with the original box, gives about 10% extra rolling speed..... but I have also read of problems of rubbing on bodywork, and the 16" wheels that fit the Merc hubs are also hard to find - and replacing up to 7 wheels and tyres is more expensive than a box - my box cost £250, but I have no idea how good or bad that price is.
Others talk about the "coach diff" this is a higher ratio rear axle and diff which was fitted to minibuses based on the 4 series T1 - ie 410D - again to allow higher motorway cruising speed for minibuses. But I have never actually come across anybody who has actually done it.
So you have three options!


More notes on this subject from a recent discussion in 2017.

 I have done a lot of research over the years on trying to higher the gearing on the Merc (mine's a 700), mainly to lower the revs for a better motorway cruise. It has been discussed on here quite a lot, and also on the other forums before CH existed. 

There are 3 ways you can do it. 1. Increase the wheel size. 2. Change the diff. 3. Change the gearbox.

Changing the wheel size is not as easy as it sounds because it's hard to find a set (off a 508 I think) of 7, and even if you do, it's not cheap. I didn't look into the diff option much, but I do remember that some bloke on a forum told me that there were several diffs offered by Merc, in particular one that was known in the trade as the "coach diff", used on minibuses. This was about 10 years ago and I never actually got to the point of finding out ratios and part numbers for diffs because I chose to go the gearbox route.

I was told that there were two gearboxes available across the range - low and high. The high ratio box was fitted on light vans and trucks and was favoured for long distance work, and the low box was for the bigger vehicles and sacrificed top end speed for low end torque and pulling power. No prizes for guessing what Hymer specified! Effectively we got a crawler 1st gear that was hardly ever used but would pull a house down, and a top gear that felt like 3rd gear in a car and was screaming at 60mph.

Eventually I found a breaker in Cornwall who knew what he was talking about and I managed to find the part numbers of the boxes, and how to tell them apart. I bought a 711.113

box from him for £200, and had it fitted. It takes about 3 hours if you have a ramp and good tools. Less with no interruptions! It takes a bit longer if you are changing the box from LHD to RHD or vice versa.

I have been very happy with it. It performs exactly as expected. 1st is now a normal gear and 5th is now a motorway gear, and the van is much quieter on the motorway. However it is not all roses. As most of us know the Merc engine may be bulletproof, but it isn't a powerhouse. My van is turbo'd but even so the slightest sniff of a hill on the motorway and you are changing down. On cross country trips on A roads you have to work the box, and unlike the original box, which would climb most A road hills in 3rd, I am often to be found in 2nd at 20mph with a queue behind me. But this was a compromise I was always willing to make because I reckoned that 90% of journey time is motorway. You also lose the crawler, ultralow, first, which did have its uses. Occasionally in tight spots and extreme hill starts I have had to smoke the clutch. Hymer knew what they were doing I suppose. 

The comments above about gearing and speed and power are of course absolutely right. I did it as an experiment, and was willing to go back to the old box. But basically I am happy with the result - it's different, but usable, and quieter on the motorway. Although in my dreams about 50bhp extra would be lovely! 

I have no idea how you managed to end up with 2 diffs the same, but I am a bit doubtful that your van had already had a new diff fitted by a previous owner, surely that info would have been passed on from new owner to new owner. In 17 years in Merc Hymers I have never heard of anybody changing the rear diff. Wheel and tyre changes have been the most popular, especially on the earlier Hymers based on the 409, where the problem was even worse. And then me and a couple of others have changed the box.

The box I bought proved to had had a hard life. Syncro was dodgy into 4th and it was leaking a tiny bit of oil through the selector shaft oil seals. My mechanic said it wasn't worth the labour to fix them - it only needed topping up once a year. But it was a bit noisy too. But it had proved the principle, so all I now needed to do was to find another box in better condition. I set up an Ebay search 2 years ago, then forgot about it. Then last summer I suddenly got an email that there was a box for sale. £200 again, buy it now. I asked the guy for a photo of the plate, which he sent me by return. The serial number on the box was about a quarter of a million units newer than my box, and the guy told me it had come off an M reg 310 flatbed - so was probably one of the last ever produced. So I bought it. For various reasons it took me ages to get down there and pick it up, and the funny thing is, I only finally had it fitted last week! I am now a very happy bunny. The old box wasn't that bad, but the new one is lovely. It is quieter and syncro is lovely and smooth, and of course it is not leaking oil. Until I found this new box, I had been considering having it reconditioned, but that isn't cheap.

So if you want to continue the quest, despite the setback with the diff, then I hope this info is useful. Somewhere I have pics of the high ratio box and its plate with the numbers on. The guy I bought it off is a great guy - he only deals in Mercs and he breaks them up and sends the parts to Africa in containers. Nearly all the old Merc cars and vans from the pre Sprinter era have been exported to Africa. Occasionally he puts ads on Ebay because he knows there is still a following for them in the UK. He probably knows all about diff ratios too. His name is Mark, he works from a farm near Stowmarket. 07950 269508.