A useful voltage regulator.

Keywords. 12v DC voltage step-up regulator. Buck transformer. Under-voltage.

This neat little unit can sort out several problems or upgrades in the van - not just a Hymer, but any vehicle with 12v DC electrics.

What it does is take a variable voltage in, and delivers a steady output at a voltage set by the user. The input voltage can vary but the output voltage will remain constant.

There are two main uses in a classic motorhome.

The first is to fix any problem that is caused by equipment cutting out as the battery voltage falls. This can apply to old Truma heaters like the 2800. Although it runs on gas, it needs 12v to run the fans and safety circuits. As the voltage falls, they are designed to cut out at around 11.5v. However this can vary as the equipment gently ages - I ended up with a Truma 2800 that was randomly cutting out at above 12v so I installed one of these and it neatly solved the problem. I set it to a deliver a constant 13.8v.

The second common use is to power equipment that is DC powered, but needs more than 12v. In my case this was a really nice Samsung Smart TV. In the showroom I noticed that rather than the usual 220v AC power cable, it had a power brick and a DC plug. Closer inspection revealed that the TV ran on 19v DC. Using one of these modules I am running the TV directly from the leisure battery. There is a small conversion loss, but not really noticeable. There is a lot of equipment on the market that runs on 19v DC - using a unit like this enables you to use it.


There are many similar modules on Ebay, sometimes at a fraction of the price, but these mainly come from China and take weeks to arrive. You also need a meter to set them up properly. I found this one for around £8 from a UK supplier. It has a digital display which displays both the input and output voltage, so is really easy to set up. This unit also has quite a high power rating, up to about 10 amps or so, but I run at about a quarter of that so it runs cool to the touch.

If you are thinking of running/charging a 19v laptop (a common voltage for many laptops) then you must pay close attention to the power requirement. Most laptops are around 60 to 90w, and this unit is rated at around 65w, so is on the borderline. It would be OK for mini laptops - chrome books etc, but probably not man enough for a big laptop. Look on the power brick of the laptop for the power rating. If you need more power, then there are other higher power units available.

You should also note that a unit like this is not a universal cure all for a flat battery! ie you shouldn't expect it to bump up a battery that is going flat and deliver a constant 12v. It will help in situations as I have described, but you get nothing for free. As the battery voltage decreases, the unit will compensate and maintain a constant output, but the current will go up accordingly, and as you draw more current, the battery will flatten even quicker. You must not use a unit like this to camouflage an old battery that needs replacing anyway. But it works very well in similar situations to the two I have described.

The Ebay description for the one I used is "100W DC 3~35V To 3.5~35V LED Voltmeter Step-up Adjustable Power Boost Module"

Glowplugs

Glowplug failure is a very common problem on old Merc Hymers.

For those who don't actually know what they are ... don't confuse glowplugs with sparkplugs. Diesel engines don't have sparkplugs. But a diesel glowplug is not the equivalent of a petrol engine sparkplug. A glowplug is a pre-heater to warm up the cylinder and the fuel for the first few seconds until the engine comes fully to life. When you turn the key, the light should come on, you wait until it goes out, and then start the engine. What has happened is that the glow plug relay box sends power to the plugs for about 5 seconds which makes them glow red hot, which helps start a cold engine. After the engine is started, glowplugs have no function until the next time the engine is started again.

Glowplugs don't last forever - about 10 years in my experience. As soon as a single plug stops working, then the light no longer works as usual - which gives you a warning. However the other plugs will carry on working, and the engine will start OK, especially in summer. Once one plug goes, it is only a matter of time before others go, and ultimately if you ignore the problem you will notice that the engine becomes more difficult to start in cold weather, until one day it won't! If your plugs are acting up, and the weather is cold, best to count to 5 after turning the key to give the best chance to the remaining plugs. If you get stranded - ie the engine won't start because the plugs are not working, try not to flatten the battery. A "get out of jail card" is a can of "Easystart", available in Halfords etc. It is evil stuff and not good for the engine. You spray it into the air intake (you have to take the air filter housing off) and spray it into the filter while turning the engine over. It is a high octane chemical that will explode the engine into life. Breakdown guys use it - or they used to in the old days!

It's best to replace the whole lot as a set as soon as you get a problem. They are not expensive, but I have found that cheap plugs (a fiver or less on ebay) are generally a false economy. The best plugs are from Bosch or NGK and cost around a tenner each. Replacing them is best done by a garage - the front plugs are hard to get at - you need the right type of sockets and extensions to get a good purchase on them. They can be hard to get out, especially if very old. My mechanic tells me that you have to be careful with them - if you apply too much pressure or don't have the right tools it is possible (but rare) to break the plug, leaving the threaded part still in the engine block. It then becomes a nightmare of a job to extract and fix. But as I said this is quite rare and unlucky. A decent garage shouldn't charge more than an hour - less if you are lucky. I just had a new set fitted a month ago and it took 30 minutes.

The relay box is generally quite reliable, but occasionally they do go. I have had to replace one in my old van. It is easy to check - if you take the plug off you will see 5 big pins - you should get 12v on each of these when the key is turned. There is also a 60amp strip fuse mounted on the top of the box - this is easy to see if it is blown. It rarely blows unless there is a good reason. The boxes are available on ebay for about £70 - I have known Merc garages charge a lot more, so shop around. However the £70 ones are generally pattern parts - the original Bosch/Merc ones are dearer. The same box was used in loads of merc cars and vans from the 80s and 90s. Very occasionally you will get a break in the wiring, but this is rare, unless the engine has been worked on and the wiring has been disturbed. It's easy to check with a meter.

Glowplug relay box with the cover removed. Pull off the plugs to expose the pins. The strip fuse is on the left in this picture.

Glowplugs!

ABS notes on the 410D and 310D Mercedes

ABS was an option on vans with these chassis - so there is a light on the dash if fitted, and no light if not - a separate red light that says "ABS".

See photo - the bottom left red light isn't fitted on non abs vans.

The ABS system fitted is made by Bosch. The control box for it is in the passenger foot well behind the trim and the fuse box.

The system is very reliable, and in practice in a motorhome, which is generally driven quite conservatively and emergency stops are quite rare, you can go for years without ever hearing or feeling it. Occasionally you will feel it in snow, on on a loose gravel surface.

When you turn the key, the ABS light will come on, and it should go out when the engine starts and the system self tests. If the light stays on, the brakes will still work as normal, but with no ABS.

The problem is that the MOT rules say that if fitted, abs must work. But the only indication to the tester is that the light comes on and then goes out. If it stays on, there is a fault, and the van fails. 
I have seen several vans over the years where ABS is fitted, but not working, but the light has been taken out, or even modified so that it looks as though it's working when it isn't - just to get through the MOT - very naughty! This is usually because most folk have no clue how to fix these old ABS systems, and neither do garages. 

However this isn't always the case. The commonest abs fault that makes the light stay on is nothing more than a £100 voltage control relay - an easy fix. The second commonest fault is the reluctor rings, and while Mercedes will scratch their heads and say "obsolete, no spares available", there are specialist companies that can supply them. There is a company in the UK called reluctorrings.com. The sensors on the wheels are also replaceable - you just have to find a garage who know these old vans.
See photos for more info.

Behind the fuse panel is the ABS control box (if fitted!)

Mounted on the left is the voltage control relay - this is the commonest reason for the ABS light staying on, and is easily replaced - a good tip is to find another owner and swap their relay for yours to prove if yours is faulty, before you order one.

If you don't have this red ABS light, lower left, then you don't have ABS!

Roller blind fix

We fixed a blind the other day! I always wondered if it was doable like this, and if you are careful, it can be done.

When you squeeze the button, the blind should disengage and be moveable up or down. But sometimes, with old age or abuse, this doesn't happen. The tiny pip of plastic that connects the buttons to the sliders has broken off.

If you very carefully drill a small hole, at a slight angle, you can put a small screw in there (see photos) which remakes the connection.

Ok it's not pretty, but it's cheaper than replacement parts - if you could even find them.

Musings on the 410D cooling system

The fan is on a viscous coupling. You can see the vanes in the middle. The vanes sense the temp of the air coming through the rad. As the engine works hard, the coolant temp rises, and so does the temp of the air flowing through the rad. The vanes on the fan sense this, and at a given point the fluid in the vanes expands and engages the fan, which until then had been turning freely. It is arranged this way for fuel economy - you lose a few horsepower when the fan kicks in.

The good news is that if you can feel the fan kicking in and out, then at least it's working. The viscous coupled fan doesn't last forever and many old vans have worn out fans but don't know it. In a cool country like the UK you may never notice - then you go to Europe in a heatwave and climb up the alps ... and overheat. The Merc cooling system is designed for all climates and has a lot of spare capacity.

The other issue is the state of your rad. Again, they don't last for ever, and get clogged up with road dirt, and the vanes get damaged by stones etc. The vanes on the Merc rad are quite close together, so tend to easily get clogged. I fitted a new rad last year and it was interesting to see that there was more space between the vanes on the new rad. If you have a dirty rad, then it's efficiency is reduced, and so the temperature will climb quicker, cutting in the fan. It's a positive feedback loop - and each component of the system needs to be in good condition. So inspect your rad, and have it blown out with a high pressure airline from back to front. If a lot of crud comes out, then that's good!

The way to cut down the noise is by insulation. Most classic Hymers need the dashboard sorting out after 20 odd years - it's a common thing. If you can see the windscreen move slightly in relation to the dash when the van rocks from side to side, then it needs doing. There have been plenty of articles about this. When doing this job, it pays to have the new dash well insulated - thick soundproofing on the underside, and good carpet on top. I also have an extra jacket on the inside engine cover. I did mine 2 years ago, and am very pleased with the results. I reckon my van now drives as quietly as practicably possible.

Musings on the Merc 410D suspension and springs

The Classic Hymer 6 and 700s are on the Merc 410D commercial chassis. It's a good solid platform. But in commercial use - either van or flatbed, it would be lightly loaded when empty of goods, fully loaded (up to 4.6 tons!) when full. Most of the time it would be between the two. But in a motorhome configuration, the caravan body is load, so it comes out of the factory well over half fully loaded, and by the time it is full of people and all their gear it is usually over 4 tons. As a result, in my opinion, the duty cycle of the springs, and in particular the rear springs, is higher than in general commercial use. So they wear out quicker. I have had 2 S700s over 18 years, and my last van I hammered all over the place, clocking up 350,000k on some tough tough roads in Morocco etc. I broke rear leaf springs on 2 occasions, and for most of it's later life suffered from saggy bottom. So it is my opinion now, that after 25ish years it is no surprise than on many vans, depending on use of course, end up with worn springs. So there is a fair case to be made that new springs are a decent investment - certainly on the rear. I think that a 25 yr old van on original springs and shocks is now a completely different driving experience compared with when it left the factory. The problem is that we tend to drive our vans sedately - we don't push them hard, so we don't really notice. I believe that new shocks and springs would transform any old 410 based van dramatically.

It also pays to inspect your springs carefully - you may have a broken leaf, or the U bolt retainers can be broken, plus the springs front and back are mounted to the hangers with heavy duty rubber bushes, which wear out over the years. All these things are easy fixes. I had a new single leaf custom made and fitted in Turkey a few years ago. It took 2 hours and cost £75! I replaced the bushes on my old van and was amazed at the difference.

As for air suspension - Well when I got my second van 3 years ago, I decided to go to town on it, no expense spared. Top of my list was air suspension. It's hard to find the bits nowadays - there are very few left in stock anywhere. It's not the bags, it's the metalwork that goes with them - it's quite a complex fitting on the rear axle of the 410. In the end I ended up having VB air suspension fitted by Conrad Anderson in Birmingham. They told me that I was lucky to find a set still in stock in Holland. It wasn't cheap! Overall I have been pleased with them. But I can't help but think it would have been cheaper to just have had new springs fitted. And shocks. Many vans are still on original shocks - and they are also getting hard to find.

All these experiences, and those of others over the years have led me to conclude that I would rather spend money on new springs (and maybe shocks) than on air suspension. But that is my personal opinion.

As an interesting side story ... last year I bought a 670 in Germany and imported it over here. On the drive back I was amazed at the difference compared with my 700. It handled like a saloon car! On closer inspection I found that it had been fitted with Koni shocks, and the tyres were 205R14 as opposed to the usual 185R14s. The springs looked good - it was quite a low mileage van, obviously well looked after. To me, this was proof that these vans can handle well in old age, if you are willing to put in the effort.

Contacts - As well as Conrad Anderson (they are not cheap!) I have heard that the guy at Marcle Leisure is an authority on air suspension. Also Goldschmitt the German company, but I know nothing about them. For springs, new Merc springs are out of the question - they cost telephone numbers! Midland Road Springs, Jones Springs and Rossendale Springs all have a good reputation. There is also a company in Cheshire that does coil spring assisters for motorhomes, but I can't see the point in assisting tired leaf springs with coils.

Tyre pressures are also important. You need the rears pumped up to the max - 65psi. Personally I run my fronts at 50psi, which is below the recommended.

Fwd: Cam lock window stay repair

Look what I've been repairing today!

Took me a while to work out why 2 of my window stays were sliding free and not locking. I had to take a working one apart to see that there is a piece of 5mm o/d steel rod that acts as a cam lock roller, and that this was missing - how, I'll never know!

I replaced it with a bit of 5mm threaded bar that I hacksawed off a bolt. If anything it grips better now because of the thread.

It's a fiddly job, but once you get it apart it is pretty easy. All you need is a philips screwdriver.