Ron Bentham's Funky Mercedes Hymer S700 Motorhome blog: May 2020

One of the commonest repair jobs on classic Hymers is to replace the dashboard. This is a piece of plywood that sits between the van binnacle and the windscreen - ie the big flat shelf at the bottom of the screen, with two round air vents in it. Usually it is carpeted.

The reason it often needs replacing is that it gets loose and starts to move around. It serves a structural purpose in that it forms a part of the overall integrity of the front of the van, it plays an important role in binding the front fibreglass shell of the van to the front of the Fiat/Merc chassis. If you do see this movement, it is important to fix it, otherwise you end up with the whole of the front end of the van wobbling around which can cause all sorts of nastiness if left unfixed.

Although it looks like a big job - almost taking the front of the van to pieces, it is actually quite an easy job for the average DIY enthusiast - all you need are basic tools and a jigsaw, and the plywood is readily available from builders merchants. Or you may decide to have the job done professionally - there is a recommendation at the end of this article.

So how do you know if yours needs doing? It's quite easy - if it needs doing, you will visibly see it moving, especially on rough roads and cornering. If you look at the front of the board, under the screen, you will see the board moving out of sync with the screen. Another way of testing is to get two of you to rock the van hard from side to side, while watching in the same place. If it is loose, it is pretty obvious.

This old dash was rotten all along the front edge

So the first thing to know is how does it all fit together? It's not complicated. It is usually a single sheet of plywood, cut to shape. There are some differences between Merc and Fiat family vans, and also of different ages, and bear in mind that we are talking pre 95 vans here, which is the general (but quite loose) definition of a classic. Merc vans are usually all the same - a single sheet of plywood and 2 circular fresh air vents which are connected to intakes at the bottom of the front spoiler. On Mercs there is no connection to the heating system - the Merc demisting vents are in their original position just in front of instrument binnacle, and as such are quite far away from the windscreen, and consequently don't perform very well demisting such a large screen. On Fiat family vans, certain years and models have demisting vents mounted on, or integrated with, the front of the dashboard, and these are fed with hot air from the heater. This often takes the form of a plastic duct mounted on the front edge of the dash. Even more rarely you may find a multilayered dashboard that incorporates ducts - this is quite rare and may be the work of a previous owner. So as you disassemble it is most important, particularly on Fiat family vans, to note how everything is connected and mounted, so you can replicate it exactly when you reassemble the new dash.

Below the screen there is a lip of fibreglass about 30mm deep, and the front edge of the board is screwed to this. The rear of the board is screwed into the metal front edge of the Fiat or Merc dash/binnacle - basically where the original panel van windscreen would have fitted if it had been a van and not a coach-built motorhome. At each of the two ends there is a metal angle bracket that is screwed to the walls to form a lip for the board ends - see photos. Sometimes you will find rubber strip or foam, depending on the van, and also if the dash has been replaced by a previous owner.

Dash removed on a Merc - you can see the fibreglass lip below the screen

On the underside of the original board, Hymer installed foam insulation for soundproofing. Unfortunately after several decades most of this has turned to dust and has fallen away. This is another reason why many owners replace the dashboard - it is also a great opportunity to really upgrade the soundproofing, giving you a quieter van. I can tell you from experience that a new dashboard, using thicker ply, modern soundproofing, good carpet on top, plus an upgrade to the cab carpet with underlay .... all this can totally transform the sound levels in the front of the van.

Mounted in the dashboard there are usually two circular air vents. These are fed by ducts that are mounted in the lower part of the front spoiler and provide fresh air while driving. Don't be tempted to do away with these - used properly they are very useful - in all weathers. They have vane controls on them, and they rotate - they can be configured to provide anything from a trickle to a roar or air, and in any direction. To remove them the tops come off, and you will see tiny screws that are holding them into the holes, screwed into the edge of the plywood. The ducts are removed by unscrewing the small screws on the underside, and then pulling off. It's a really simple mechanism and can be cleaned and serviced at the same time.

Some van dashboards have had holes for speakers cut in them. Personally I don't think this is a good idea - especially for large speakers. Big holes can reduce the structural integrity of the board, and cab also let in more than their fair share of engine noise. This is less of a problem for small speakers of course, but small speakers are not really any good. The other thing you should think about with regard to speakers is that from an acoustic point of view, the front passenger space of a Hymer is a really crap sound stage. If your speakers are facing upwards, the sound is reflected off the underside of the bed, and it really doesn't sound very good. I found this out quite by accident when I took out the front bed in my S700 during a major upgrade, and was astonished at how much better the stereo sounded, both on the move and static. My advice with speakers, is to mount them in pods if you can, firing forward, or at least up 45 degrees. Also consider not having speakers at all - in these modern times of really high quality high power reasonably priced bluetooth speakers, there is much less need to install traditional car stereo speakers in the dash. Nowadays I use a pair of Ultimate Ears Megaboom 3 Bluetooth speakers, and they are fantastic, and can be placed anywhere, inside or out - and no wires. This is just background info - the choice is yours - but a dashboard replacement is also an opportunity for upgrades and new ideas.

So you have detected movement, and have decided to do the job, then it's time to proceed! The first job is to expose the board. Remove the carpet and any other layers, but before you remove any vents or speakers, or anything underneath - inspect the board. In many instances you will find the board in decent condition, and all that has happened is that the screws have come loose. In which case, if you are really happy that the board is otherwise solid and strong and not damp along the front edge, then you can leave it in place and refix it with new screws - or nuts and bolts - as discussed later. Even if you find that your board is reusable you might still want to take it out entirely to replace insulation. But in most cases, you will probably find that the front edge of the board has gone rotten or damp, and is loose all along the front edge. This is usually caused by a lifetime of use and vibration, coupled with condensation running down the inside of the screen and soaking the board. So it's time for a new board.

Once you decide that it has to come out - do your best to remove it carefully - this is important because it is your template for cutting the new board, so don't break it up - get it out in one piece!

You will also have to remove the two gadget trays either side of the dash - the square ones made from soft plastic. These are fixed by 4 screws - the screws are under the plastic dome covers - if they are still there. On the drivers side, there is often a ventilation duct - this has to be pulled out also. Look for a small fixing screw.

What board do you buy? Purists will say - marine grade plywood - and there has been some online discussion about this. It's up to you, but personally I, and others, don't think it's worth the extra for marine ply - as used on yachts - what your local builders merchant sells as "plywood" should be more than enough. I have also seen a grade sold known WPB, or waterproof board. This is what I used. It's about £30 a sheet if I remember correctly (about 2017). What is worthwhile upgrading is the thickness. The original was around 9mm and most owners replace with 11 or 12mm. This is pretty much the standard procedure nowadays - you get a much stronger and quieter job that should also last longer. The only slight problem with using thicker board is that it might stand up just a mm or so higher on the front lip, and catch the underside of the window-screen rubber, preventing a snug fit. So offer it up and check, and if necessary toy have to chamfer the front edge of the board - ie file a bit off the corner. Using a power tool makes this a job of a few minutes, but even with a hand file it only takes 10 minutes. Don't be tempted to use any sort of MDF, chipboard or blockboard - it must be some form of laminated plywood.

Next job is to cut the board with a jigsaw. Lay the old board on the new, and trace round with a pencil or felt tip. I can't teach you in writing on how to actually do this - but it's just common DIY skill - if you are unsure, get help from a friend. If you are really unsure, you can just take the original dash to a local wood shop and ask them to make you one - it won't cost a fortune.

A new dash being prepared for a customer by Peter Curry at North Cotswold Motorhome Services

So now you have a new dash board, cut and shaped and chamfered - don't forget the ventilation duct holes! Now is the time to prepare it. At this stage you should glue your chosen insulation to the underside. What to use is another much discussed topic (check out the Facebook Group for specific recommendations). Insulation varies from cheap and cheerful, right up to weapons grade dedicated sound insulation as used by professional sound engineers, that costs twice as much as the plywood itself! Basically it's up to you and your level of OCD perfection desire. But there are plenty of basic insulation products on the market at reasonable money - if it looks a bit thin - use 2 layers - that's what I did, and was very happy. Another good idea is to apply a coat of varnish - this gives you an extra layer of waterproofing. However it is not mandatory - the old dash lasted over 20 years and the new one will last even longer, and a coat of varnish, while belt and braces, won't really shorten the life of the job, so if you are needing to do the whole job in a day and don't want to wait for varnish to dry, then fine. I did mine on a summers day and I found that a reasonable coat of polyurethane varnish was almost dry to the touch in about an hour.

Now we come on to the most important aspect of the job - fixing it. General opinion nowadays is that Hymer were lazy in only using simple self tapping screws to fix the board to the front lip. Along the back lip, you are screwing into metal, so it doesn't matter as much, but at the front you are screwing into fibreglass and over the years it has become obvious that simple screws are not enough - they work loose with time. To be fair to Hymer, maybe they didn't really expect their vans to last 30 years!

Offered up, prior to fixing - check everything!

The answer is to use nuts and bolts, and clamp the plywood firmly to the fibreglass lip. But even this isn't enough - you have to incorporate some form of locking washers to prevent them shaking loose. I have been involved in at least 4 dash replacement jobs over the years, and even nuts and bolts can work loose after a few years. You probably know that there are several methods to prevent nuts coming loose - nyloc nuts are very popular and common, but I have known even these to come loose. Another problem is what style of bolt to use, what head, and what washers? As I write this I know that there are several vans out there using different variations of fixing nuts, bolts and washers, and the jury is still out as to what is the best. Another problem is that the original screws were screwed in from the top, and were countersunk - resulting in flush heads. If you upgrade to bolts, the heads will be proud. Usually you can't notice this under the carpet, but just bear it in mind.

The next problem is how to tighten them - if using screws, all Hymer had to do was screw in from the top - nice and easy, which is probably why they did. But if you are going to do a proper job and use nuts and bolts and washers, then this means that you have to get a spanner or socket on the underside to hold the nuts as you tighten from the top. This is quite easy for those in the middle, but if you are doing a really strong job, you need strong fasters at the sides as well, and getting a spanner or socket on the underside of these is a real contortionist stretch in through the front access panel - so be warned - it's a 2 man job. But don't be put off - it's doable. I'm just explaining things I found out the hard way. Also see below about an alternative method using teenuts.

For fixing the front lip and the sides to the angles (more on the angles later), you should use minimum 5mm fasteners - many have used 6mm. The length should be enough to get through the 12mm ply, and the lip, with a bit extra - this makes it easier to find the bolts when you are stretching - but bear in mind that if you make them too long, then you won't get a standard socket on them - but whether you use sockets or not depends on your tool kit. You may be using spanners - if you use spanners, then ring spanners are better. 25 or 30mm long bolts should be about right.

In terms of bolts - you have to choose a head. This will either be a screw head - slotted or pozi, hex heads - these need a spanner or socket and will stand proud, or even hex socket - ie allen screws. The choice is yours, each has its merits and demerits. Screw driver heads mean you might not get them tight enough, but can be used if you just hold the heads with the screwdriver from the top, and tighten from below with a a socket driver. You can use hex heads (normal bolt heads) but these will stand proud, and will also dig into the ply wood, which isn't actually a bad thing. My personal favourite is dome head hex bolts, with large washers. If fixing from below, screwing up into the board, you must use either hex head or socket head - screw heads - pozi or slotted will be impossible to get to from underneath - you need something that you can do by feel because at the sides you will be at full stretch.

On the underside you want nyloc nuts and large washers - but not so big as they stick over the edge. If you can get your hands on serrated washers - those with teeth that stick into the wood, so much the better.

Serrated washer

Conventional bolts, washers normal nuts and Nyloc nuts

Teenuts - clever stuff!

Yet another method, used successfully by several owners is to use "captive nuts" - the commonest of these for use in wood is called a teenut. This is a threaded socket mounted in a metal collar that has sharp teeth - or tangs - that enable it to be hammered into the wood and fixed. The picture explains it better than words! The beauty of using these is that you don't have the problem of the whole bolt rotating when you are trying to tighten them up - this also makes it into a one man job - you don't need somebody holding the screw from the top. The down side is that you need just that little bit more preparation. You have to decide in advance where the holes are going to be, then drill the board, and knock in the teenuts. Then you have to drill through the teenuts into the fibreglass lip and the end angles, making sure that everything lines up. Then you have to widen the holes so that the M5 bolts pass through, and up into the teenuts - don't forget to put washers under the heads to spread the load and prevent shaking loose - preferably use serrated shake proof washers. You have to be very careful with your measurements because the teenuts are close to the edge of the board, and there is only so much space on the fibreglass lip - so make sure everything lines up and looks good before you commit.

You may think I am going into too much (confusing) detail here - this is because the job has been done by many owners over the years and each one swears by their system! So I really have to explain all the options. I am also going into deep detail to hopefully help you avoid mistakes - you only want to be doing the job once. The first time I did it, it was loose again in a year and needed a days work to re-fix - that's how I discovered that screws were useless and nuts and bolts were needed. Don't underestimate the power of the front of your Hymer to shake those fasteners loose! All I want to stress is that you want to clamp that new board as tightly as possible, using fasteners that have the least chance of shaking loose with time. And diary to check them a year later!

But having said all that - if you have understood all the discussions about the different ways of fixing, my personal advice is to use teenuts, but the alternative of conventional (nyloc) nuts and bolts is almost as good ... but definitely avoid using self tapping screws as the original.

All the above concerns fixing the front and sides of the board. Along the back lip, where it joins the instrument panel, you will see the original holes that Hymer used. Just make sure that you use a good quality screw - maybe go up a size. The rear screws are not so prone to shake loose - but make sure you get a good fix on them.

Now lets talk about the metal angles at the sides. Take a good look at these, and you will probably shake your head and wonder. They certainly don't look very strong do they. So what you must do is to re-fix them, using extra fasteners if necessary, and make them as strong as you can. Then you want to fix the new dash board to them using at least two good solid nuts and bolts - but be warned these are the really hard ones to get at.

Location of metal side angles.
Also note the little black box, on many vans this is the amplifier for a wire loop radio antenna that goes around the windscreen hidden in the rubber.

Now I will tell you about a modification that you can do to give even more strength, courtesy of Peter Curry, who as you might know, is an expert. There is no actual fixing of the angle bracket to the side wall - this has been a criticism of the design. But there is a way of doing this, but you have to be keen and careful. It is only worth doing if your van has suffered more than most from a loose front end - it may be high mileage or had a hard life and you just want to make it as strong as possible. What you have to do is to locate the aluminium trim of the outside wall (see photo) and remove the plastic strip. then you have to carefully drill a hole through the trim, through the wall, then through the bracket, so you can get a 5mm bolt all the way through. But it won't be any bolt - you will use a countersunk head bolt that you will file carefully so it just fits snugly in the bottom of the aluminium trim, so that when the plastic strip is re-fitted, you can't see anything. Then you bolt it all together from the inside. This has the effect of clamping the angle bracket to the wall, and adding to the strength of the end fixing of the dashboard. Now I must stress that this is not a "necessary" modification, but if you are either engineering minded, or have a particular problem and need to beef up your front end, then this is a useful mod. But for most vans that are in decent condition for their age, it isn't necessary - just make sure the angle bracket is fixed as strongly as you can, with good quality fasteners that have a good chance of not shaking loose.

I don't have a photo of this mod to hand - I will add one soon.

Another thing to take into consideration is the area where the windscreen wiper motor is fitted. You will notice from the photos that you have to cut out a small bit of the wood to allow for the bolts that fix the motor bracket. Dashboard replacement time is the ideal time to service, or even replace your wiper motor and mechanism. These jobs are 4 times harder with the dashboard in place, so if you have any issues at all with your wipers, then you should get them fixed at the same time.

Other things you can do at the same time while the dash is out are have a look at the washer bottle, which is hard to access. Check the wire and tube connections and service as necessary. Also take a peer with a torch right down to the are near the wheel arch where the Hymer fuse box is located. On many vans there is a lot of road water and dirt thrown up here and it can benefit from a bit of TLC. Non of this is mandatory - just things that you should look at while the dash is out. Also check the rubber boots, if you can see any, that keep the water out where the wires go through the bulkhead. It's all common sense really - it's quite fascinating being able to peer into the engine compartment from the top!

Once the dash is back in and looking like a masterpiece of modern construction, all that remains is to upholster it with the trim of your choice. A tip here is to use a dark material, otherwise you might get to much reflection from a lighter material. If in doubt, test it first before glueing - also ask yourself - do you really need to glue? Was it a real mess taking off the old stuff? Get creative!

Finished!

So that's about it - All the above isn't just my opinion, it is the collective wisdom of many other owners too - I am just the guy collating it all into one place. There is no definitive correct way to do the job - but as long as the result is solid and will remain that way for many more years, then that is the main objective. You can get creative and you may have special skills, but I must stress again - all you need is a drill, a jigsaw, basic tools and basic household DIY skills to do a good job.

For those owners who would prefer to have the job done by a professional, I have a recommendation for you. Peter Curry is one of the UKs leading experts in all things Classic Hymer. His company, North Cotswold Motorhome Services, will replace your dashboard, insulated and trimmed, for between £400 and £500 inc VAT (2020 prices), depending on model and final finish required - there are options. NCMS is near Stratford on Avon and is a pretty place to visit out in the countryside. info@northcotsmotorhomeservices.com or 07917 863703.

If in doubt and for further info, ask on the Facebook group "Classic Hymers Technical". Join this group, and then look in the index for "dash board replacement". There you will see a link back to this blog, but also you will find links to the discussions that were had in writing this article. There will be more photos, and also suggestions of what people have used for insulation, and suppliers, and lots more photos.

https://www.facebook.com/groups/297054424534823/

Gallery - here is a gallery of photos of different jobs and methods - sent to me by various owners.