Ron's Tech Tips number 3.5 billion ......
Fun and Games with your Brakes!
A couple of other members have recently posted about brakes, so here are a few pointers about van brakes in general, and Merc brakes in particular.
Fiat and other owners, please chip in with your experiences and comments.
The Merc 310 and 410 (and earlier 309/409) chassis have discs on the front and drums on the rear.
I have had very little problem with fronts. In 15 years in a S700 I have had occasional front pads but otherwise the fronts have been fine.
But the rears are a different story. I have had to have the rears serviced and sometimes replaced, and have spent quite a lot of money over the years.
The 4 series chassis have double back wheels, so the brakes on these have quite a lot more to do, but the designs are similar on all Mercs of this generation.
It is worth pointing out that on Merc Hymers (and I suppose all vans) the rear brakes are responsible for a much greater percentage of the total braking effort than in other vehicles, so it is important the rears are in good order.
There is also a component mounted on the rear chassis, just in front of the rear axle, with the rear hydraulic pipes going to it. This is called the load balancing sensor. It mechanically senses, via a lever and pivot mechanism, how low the back of the van is, and therefore how heavily laden it is. It increases and decreases the braking force at the back accordingly. It is a service item often ignored by regular garages and as a result becomes responsible for many braking problems. These include "snatching" - where the brake action is too sudden and "fade", where you don't get the braking action you expect!
So when having brake work done on a Merc you should specify that the LBS is checked, and if you get a blank stare, act accordingly! I have always found that I get better service from truck and light commercial specialists, rather than car garages.
On my recently acquired second S700, my garage man said that the LBS was completely seized, and hadn't been touched for years - a new one was 2 weeks from Germany, but he was good enough to take it off, soak it, and coax it back to life to his satisfaction, so that saved me over £200.
After brake work at the garage, your handbrake should be tight and start working after the first click - this is a sure indication that the brakes have been attended to.
Winter storage is the enemy of all brakes, and Merc rears in particular. For those that may not know - brakes should be off for storage, whees chocked if necessary, linkages should be lubed, and care taken for the first few hours of driving after storage. There is usually a light covering of rust on the discs and drums, which is no problem as long as you take it easy until it wears off.
I have found out the hard way that you only usually find you have a brake problem at the worst possible time! We all tend to drive our vans sedately and carefully, and emergency stops are pretty rare.
Occasionally, usually in hot weather and abroad in the Alps or wherever, you might experience the dreaded "foot to the floor" brown trouser moment. This usually caused by the brake fluid getting hot - sometimes as a result of a fault, like a binding brake cylinder, or sometimes just caused by too much braking and everything just getting too hot - Alpine passes and multiple hairpins are just about the most stressful times for the brakes - and these are old vehicles, not racing cars. So if you are on a really big descent, change your braking technique. Apply the brakes well before the next hairpin, and as you descend compare each braking action with the last. Use engine braking as much as possible. By expecting the worst, you will be prepared if it actually happens. The handbrake will always work well in an emergency, so don't be afraid to grab for it. If it does happen, don't necessarily immediately head for the garage. Let the brakes cool, and keep a close eye on them for the next few days - it could have just been a "one off" under extreme conditions. It has happened to me twice, once in Morocco and once in the Alps - both times the van was fine and needed no work. But of course it's up to you, it could equally be the vans way of telling you that the fluid is twenty years old and it's time for a good service. Don't forget that all vans are designed and tested to cope with the worst roads in Europe, fully laden.
At least once a month, or whenever I think about it, I choose an appropriate moment to test the brakes. Make sure there is nobody behind you, that stuff in the van is well packed, and most important of all that you warn the wife and the dog! Then, as you approach a junction or roundabout on a nice dry, empty road, apply the brakes much harder than you would normally....don't stamp on them as if a child had just run out, but brake hard and progressively. And that's what you should get - hard and progressive. If you feel snatch - which is caused usually by the front brakes coming on before the rear, or vice versa, then you need attention. If it doesn't stop the way you would expect in an emergency, ditto.
The next test is to apply the handbrake only - from about 30 or 40 mph - you should get a strong braking action. If you don't, then get the rears checked.
Finally, on a straight road, with minimum camber, lightly apply the brakes and feel the steering wheel - you are looking for wandering left or right, which indicates uneven braking action at the front. A gently wander to the left is usually OK, due to the natural shape of the road.
Before the health and safety brigade go bonkers.....you are responsible for your own actions! There are plenty of deserted roads you can do this - industrial estates at the weekend for example, or if you are really paranoid....book a track day at a racing circuit. If you do please take a video and post it here!
Although I am a Merc owner, I reckon these comments should apply to all other makes. All makes have their idiot sync crassies ..... so other owners please post your brake comments.
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