Motorhome enthusiast Funkyronster (Ron Bentham) has completed over 250,000 miles over 20 years in his classic 1990's S700 Hymer Mercedes motorhome, all over Europe and N Africa. Along the way falling in love with the "classic" Hymer motorhome, probably the most robust standard motorhome ever made. This blog details the majority of technical problems and issues that owners of these classic vans may encounter.
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On extreme descents with a lot of braking, the brakes can get hot and start to fade, sometimes the pedal can go right to the floor.
Question - Hi Hymerers - today's request revolves around brake fade after 8km down a 28degree incline with lots of switch backs in Guatemala
So we reached the bottom safely. We used engine braking - but for some reason out auto box won't stay in first when first is selected, so it almost immediately changes up to 2nd and stays there - so still pumping brakes sporadically to keep speed down. So on Monday will replace brake fluid and bleed using continuous pour and pump pedal method. Anyone got any suggestions for additional steps/actions? Should say no leaks and correct level in reservoir although when we stopped level was 15mm higher than normal and 2 hours later back to normal. Also 2 hours later brakes returned with no spongy pedal and worked normally. S700 1993 merc.
Answer - Yes I have experience of this in the Alps and the Atlas mountains. In extreme continuous braking situations the brakes will show their age. They get hot, the fluid gets hot, and you lose braking. Pumping helps, and careful use of low speed and engine braking, but it only really ever happens in extreme situations. Sometimes you just have to pull over and let the buggers cool off a bit. Of course it helps to keep the brakes in top condition, but in my experience thre is very little you can do other than change the fluid every few years. All that can happen is that pads wear out and pipes and callipers and cylinders spring leaks suddenly, and these things tend to happen suddenly not gradually. I now have enough experience to sit at the top of a mountain pass, having slogged up the bugger with one eye on the road and the other on the temperature gauge, and look down and think - right! I've got the bloody van up here in one piece, now I have to get it down the other side ditto. You just use the gears and eye up the hairpins well in advance, and ignore the traffic behind.
Last year in the French alps we went over a real hum dinger. Coming down I applied all the experience and expectation of previous descents, and was quite happy with the progress, no brake fade - I always open my window so I can smell the brakes. We got to the bottom, and there was a gentle descent into the village, and we were hunting for croissants. As I pulled into the parking area in the square, having spotted a bakery. I almost piled into a parked car, because the brake pedal went to the floor, being still boiling from the descent, even though it hadn't done that during the actual descent.
Unless you are completely uncertain when the fluid was last replaced, then don't necessarily rush to service the brake system. Do regularly check for the obvious, but it just occasionally happens on long descents, and you will come to recognise the potential situations before they give you a shock. Our mercs are resilient, but doing a transcontinental trip does tend to work them hard, as you have found. The first time it happened to me years ago, I had the brakes completely checked over, and there was nothing wrong. They then worked perfectly again until the next extreme situation a few years later. It's old technology, and it has its limitations. Nowadays a modern van would have a sensor that just bullied you into limp mode and gave you no option but to stop and call breakdown, and by the time they got there the temp would have dropped and they would find nothing wrong. At least with old tech you get the option! Mountain ranges are a challenge to any van - did you see my video last year of the Transfaragsan in Romania? Never seen so many hairpins! Just wait till you get on that crazy cliffhanging "road of death" in Chile or Peru wherever it is.
A technique I use is not to pump, but to apply braking in spurts of about 5 seconds, slowing down to a speed where engine braking will be able to keep me slow for another 5 seconds, during which the brakes have 5 seconds to cool down - so its a 50% duty cycle. As opposed to having your foot on the brake all the time, which keeps the pads in constant contact and allows the heat to build up. The worst possible thing is to allow the van to increase speed too much on the straights between hairpins, as you would in a car, because then you have to brake hard before the bend as well as during it. If you use the gears you can give the brakes a rest between hairpins. many is te time I say to my wife - it's quicker going up in first and second than it is coming down! If the pedal hits the floor, it will come back to normal if you just stop and let it cool. Don't panic!
Other comments -
MW
Hi Ron - thanks for the vote of confidence from your experience. We had the same. totally fine all the way down, got to the flat 50m later total failure at 20mph. Our problem is the autobox wont hold 1st gear when selected- it selects 1st fine but as soon as speed hits 13mph on speedo or I lift foot off accelerator it changes up to second and then stays there so engine braking is limited to 30mph on Speedo ... fine for rolling UK Cotswolds ... but not what you and us have experienced. So the big question then: Fluid changed 27000kms ago. Should I change it again? Would you? Pads about 50% discs smooth no grooves drums smooth no grooves. Pedal solid no eventual loss with continuous pushing. In fact all round no evidence of any problems. Just the sudden loss of trust in the brakes and many many more steep inclines to plummet down. But seriously Ron would you bother to change fluid?
GB
Sounds text book
. The fluid expanded with heat, ossibly boiled. You could expect old contaminated fluid to expand more than fresh fluid. It returned to its original level after cooling. There may have been a slight difference if you were back in Europe but id imagine moisture levels are low over there so it doesent get to take it on. The spongyness would have been from the reduced density of the boiled fluid. Try to have it vacuum bled Mark. Pumping an old master cylinder can damage the end seal and cause a leak. The normal stroke length of the shaft is clean however when you pump beyond that the corrosion or debris built up over years sitting on the shaft can tear the seal. I know it's another expense but it would save a future delay waiting for a new cylinder. Pressure bled from the top is fine too. Reverse bleeding can in some circumstances reverse the lip of a piston seal.
My S700 Merc has the same problem in 1st, having driven big hills in heavy 4x4 not being able to drop to and hold 1st gear in the auto box worries me. The gear selector just won't go in..
Ron
I agree with George - unless you know for sure your brake fluid is recent, then have it changed. I can't comment on the gearbox issue, my limited experience is that if manually selected they should stay in that gear. Even with a manual box, descending really steep passes, the weight of the van plus gravity was too much for engine braking to work in second, and first is just too low to be practical - so it is always for me a mixture of constant brake and engine braking. The brakes are fine - it's a solid reliable system - but if circumstances lead to the fluid getting hot then you have to be aware of it, and allow cooling time, or adjust driving technique. Don't forget that your handbrake is mechanically connected to the rear drums, which are pretty effective. I have had to use my handbrake on several occasions in the past, and as long as it is properly adjusted, it is a very useful and reliable emergency brake, and it's good to know you can grab it if you are unlucky enough to get unexpected pedal fade on a steep hill.
Wish they had that twenty years ago when went from revving in Neutral and selected first. It wasn't pretty.
RB
Mine will go into first, but you have to be going slowly
CS
I checked this today on a steep descent having read your post. My OM602 Auto (S550) stays in first if I select first on the selector, it doesn't up shift. When you are trying to select 1st you bring the selector all the way back and then push to the right, The "1" indicator the dash should light.
MW
Thanks everyone for your input.
CS
thanks for doing a test drive for us. It seems that although I have now fixed all the leaks in the autobox and found the correct fluid and figured out the correct filling temp and levels that there is a problem with it holding first gear. Thanks for the info on changing the fluid. I will get a manual vacuum pump and brake fluid for a complete fluid change. I will re-learn my downhill braking style and also pay more attention to the distance down the mountain and the angle of descent and make driving decisions accordingly. Much appreciated everyone. Here's to many more safe descents down Guatemalan mountains.
RB
still jealous! be safe!
GB
Guatemalan roads. You're heros
CS
Been a very useful thread, coincidentally we've been exploring Exmoor this weekend and we had our first experience of pedal to the floor brake fade after a series of steep twisting lanes, we were nosing about for a wildcamp spot and so had the brakes on more than might be usual. This thread came at a perfect time! (Thanks to
In the event of a total loss - ie a write off, the insurance company will appoint a loss adjuster, who's job it is to value your van at the lowest possible figure that you will accept without going to court, and this is regardless of what you tell them what you think your van is worth when you take out the policy. In the case of an old van, that is difficult if not impossible to replace, like for like, then heartache can ensue. The only way round it is to do what the classic car people do, and that is to have an "agreed valuation" with the insurance people from the outset. They will usually ask for a written valuation to support this, and such a valuation isn't too difficult to get, although I can't at the time give you a definite contact - I'm working on it. I am in the process of doing this myself. It would cost me around £18k to find a similar van, and then to add the extras that I have, to get an exact replacement - but a loss adjuster would probably offer me £10k. So I have spoken to my insurer (NFU) and they have said no problem - they just need a written valuation, which I am in the process of obtaining. Only by agreeing this valuation in advance and in writing with your insurer, will a classic owner have any chance of recouping a realistic figure in the event of a total loss. Owners of "tatty" or "tired" vans need not worry so much, as they will usually be able to negotiate a figure that will enable them to buy a half decent replacement. But owners of lovingly restored or highly modified vans should take note.
