Text 27148, 275 rader
Skriven 2009-02-02 14:38:52 av Roy Witt (1:397/22)
  Kommentar till text 27102 av Michiel van der Vlist (2:280/5555)
Ärende: Trailer brakes
======================
02 Feb 09 10:56, Michiel van der Vlist wrote to Roy Witt:

 MvdV>>> A common misunderstanding, even among caravaneers. Engine braking
 MvdV>>> will help keeping the brakes of the tow vehicle cool, but it has
 MvdV>>> no effect on the brakes of the trailer. It does not matter what
 MvdV>>> method is used to control the speed of the tow vehicle: disc
 MvdV>>> brakes, drum brakes, engin braking or the Flintstone method; the
 MvdV>>> trailer brakes will activate when going down a steep slope.

 RW>> I think you misunderstand the concept. By alternating between
 RW>> systems,

 MvdV> You are the one who fails to understand.

No, you don't understand the difference between a surge brake and what
ever it is that you call yours.

 MvdV> There is just the one system: the suge brakes on the trailer.
 MvdV> Nothing to alternate between.

Wrong.

 RW>> the brakes of both vehicles will be kept at a minimum. Engine
 RW>> braking will keep both brake systems from engaging until they're
 RW>> needed, the trailer braking system being nuetralized by the speed.
 RW>> By shifting up a gear, the trailer brakes are then engaged, as the
 RW>> tow vehicle picks up speed.

 MvdV> You don't "pick up speed" when going down a prolonged 5-10% slope
 MvdV> with at camper trailer. That is suicide. 50 kph is the maximum safe
 MvdV> speed under those conditions.

If you pick up 2 or 3mph, what's the big deal, the brakes will still be
doing their thing.

 RW>>>> But as stated, in combination with low gearing and engine
 RW>>>> braking, disc brakes will stay cooler longer, even with a heavy
 RW>>>> load in the trailer.

 MvdV>>> No, see above. It seems to me you do not really have much
 MvdV>>> experience with trailers with surge brakes in combination with
 MvdV>>> prolonged steep descents...

 RW>> I have enough experience to know about it.

 MvdV> Obviously not. Or you would not claim that you can keep a surge
 MvdV> brake from activating by using engine braking.

I didn't make that claim.

 RW>>>> I beg to differ. Disc brakes are mechanically as simple as you
 RW>>>> can get.

 MvdV>>> They are more complex than drum brakes, if only for the
 MvdV>>> hydraulics.

 RW>> Drum brakes also have hydraulics,

 MvdV> Not here. Not on trailers behind passenger cars.

Too bad. If they had, you wouldn't have the problem of overheated brakes.

 RW>> Anybody who does is endangering their lives and those of others on
 RW>> the road.

 MvdV> Bullshit. Surge brakes with mechnicall linked drum brales are a
 MvdV> proven concept that is very reliable and safe.

Maybe. But I'm not so sure and not inclined to find out.

 MvdV>>> Recreational trailers do not make many clicks. The brakes do
 MvdV>>> not wear out. I have mine for 15 years now and I never had to
 MvdV>>> replace anything. I inspect them every spring through an
 MvdV>>> inspection hole in the drums.

 MvdV>>> With hydraulic disc brakes, there would be the rubbers that
 MvdV>>> crack, and oil that leaks.

 RW>> Maintenence of hydraulic brakes on you trailer would be no different
 RW>> than the hydraulic brakes on your tow vehicle.

 MvdV> The difference is that trailers are not subject to a mandates
 MvdV> yearly inspection.

You must have shrunk in height. That one went right over your head.

 RW>>  i.e. those 'neoprene' seals don't crack over a season. It takes
 RW>> many years before they deteriorate to such a state.

 MvdV> Trailers last much longer than cars. Mine is over 25 years old. The
 MvdV> seals can not be expected to last that lomg.

My 1956 Chevy is 53 years old. My 1988 Camaro is 21 years old. The seals
in both are in great condition for their age. Seals, btw, are not made of
rubber, but of neoprene. Neoprene is a synthetic type of rubber and lasts
far longer.

 RW>>  If you see oil, then you haven't done any maintenence on them.

 MvdV> There! They require maintenance. A pulling rod does not.

That pulling rod has to be held in by a clevice pin or perhaps just a hole
in the linkage and a bent rod. The hole, the pin and/or the rod end will
wear. In fact, it will wear faster since it is steel on steel and needs
some grease every now and then to keep it from wearing too fast. Even
putting a oiled bushing in the assembly will have wear, as the bushing is
made to do just that to save the rod and lever from wear.

 MvdV>>> It is the same with tyres. It is tear rather than wear that
 MvdV>>> limits their life. After 6 to 8 years, there is hardly any
 MvdV>>> visible wear.

 RW>> On a trailer with very little weight to tire ratio.

 MvdV> Again you show ignorance. Tires on camper trailers are nearly
 MvdV> always loaded to the maximum.

That's why they put bigger tires on them. The ignorance is yours, since
you obviously don't know that bigger tires will carry more load.

 MvdV>>> Profile is still perfectly ok, but little cracks develop on the
 MvdV>>> sides and then it is time to to replace them.

 RW>> Those cracks aren't from use, they're from environmental conditions.
 RW>> Tires age exponentially in the sun vs your garage.

 MvdV> I know that....

 RW>>>> If so, they have far less braking power than a hydraulic system.

 MvdV>>> Another misconception.

 RW>> Wrong again. It is a proven fact that mechanical brakes will not
 RW>> have the stopping power of a hydraulic system. That's why mechanical
 RW>> brakes were outlawed here in 1939...

 MvdV> You are comparing apples and oranges.

Hmmmm. That's what I thought this thread was about. Only I'm comparing a
known safe braking system to one that isn't as well known, nor has it been
approved for use, in you own words.

 MvdV> For _trailer surge brakes_ the hydraulics are just another way to
 MvdV> link the sliding part on the coupler to the moving parts on the
 MvdV> brake.

The only moving part on a hydraulic surge brake is the rod that applies
the pressure to the master cylinder. And of course, the pistons that apply
the brakes of the trailer.

 MvdV> It has no effect on the stopping power as the forces remain the
 MvdV> same

Wrong. The more force applied to a hydraulic surge brake, the more force
is applied to the actual braking pistons. They work the same as the
hydraulic brakes on your car. Wanna stop sooner? Apply more pressure.

 MvdV> fir a direct mechanical link or an indirect mechanicak link
 MvdV> via hydraulics.

The only way to get more stopping power out of a mechanical braking system
is to increase the length of the levers used to apply the brakes. Even
then, more pressure applied to the rods means they will have more of a
tendancy to bend under pressure. Of course, that only applies to Ford
mechanical brakes, as was proven by the US Govt back in the 30s. If all
you have is a pulling rod, then it will have a tendancy to stretch, as was
also proven by the US Govt in the 1930s.

 RW>>>> That was the difference between getting insurance on my 1937
 RW>>>> Ford vs my 1940 Ford. The former had mechanical brakes, while
 RW>>>> the latter had hydraulic brakes. The latter being considered the
 RW>>>> safer system by the insurance companys.

 MvdV>>> Apples and oranges.

 RW>> Mechanical vs hydraulic brakes. Hydraulic known to be superior.

 MvdV> As Bob Bashe explained to us: that depends on your perception of
 MvdV> "superior".

Bob is not, in my opinion, known to be a mechanically minded person. Had
Henry Ford not been so stubborn to suggestion by those who were already
using hydraulic brakes in the 30s, he wouldn't have been so embarrased
when the Govt proved him wrong. GM and Chrysler were using hydraulic
brakes as far back as 1930. It took Henry ten long years to do so.

 MvdV>>> No, that is not he problem. One problem is "spots" where the
 MvdV>>> brake pads rest on the disc.

 RW>> Pads don't rest on the disc. They're always a few mm away from them.

 MvdV> Look again.

I don't have to. I know they don't.

 MvdV> The space is much less. And if they are not in perfect rder, the
 MvdV> pad can touch the disc.

Ok, I meant nm. If your pads touch the rotors, your braking system is in
need of some maintenence. They're not supposed to ride on the rotor.

 RW>> If you find that they're touching the disc, you haven't done
 RW>> your maintenence.

 MvdV> I prefer systens that require no maintenance at all.

Unfortuanately, there is no such system.

 MvdV> Anyway this is leading nowhere.

Yeup.

 MvdV> I was discussing going dwnhill in the Alpes. With a camper trailer
 MvdV> behind a passenger car. And that means surge brakes. With
 MvdV> machanical drum brakes. Because that is what is in use here.

Unfortunately.

 MvdV>>> Here the automatic speed traps detect vehicle length. If it is
 MvdV>>> over nine metres, it assumes it is a truck or a combination and
 MvdV>>> it triggers at the lower speed allowed for trucks and trailers.

 RW>> Meanwhile law enforcement is having coffee and donuts at the local
 RW>> donut shop.

 MvdV> Maybe in your part of the world. Here the spped traps are handled
 MvdV> by robots,

Hmmm. 1984 began early in Holland.

 MvdV> while the real cops are busy catching real criminals.

There is safety in numbers. We have task forces dedicated to catching
criminals and others dedicated to traffic control. Besides, robotic speed
traps are not what is used in a free society.

 RW>> By the same token, the surge brake will engage when the vehicles are
 RW>> going down a steep grade, whether the tow vehicle applies its brakes
 RW>> or not.

 MvdV> As I have been saying all along...

That's the way they work.

 RW>> This system is inferior to the electronic controlled system

 MvdV> That depends on your POV on "inferior".

I know. When there's no alternative, your system is the best you can get.

 MvdV>>> Certification is a long and slow process. Much red tape to be
 MvdV>>> cut. Let us hope the manufactures of the "caravan Descent
 MvdV>>> Control", as it is called, will not go broke before it gets
 MvdV>>> officially certified for use on public roads.

 RW>> If it works and is safe, then it should be certified.

 MvdV> Agreed in principle, but who decides if it is safe? Surely not the
 MvdV> manufacturer. Transport authorities do not make decisions like that
 MvdV> overnight and for good reasons.

Here, such things are required to be demonstrated by the manufacturer to
be what they claim it to be. The US DOT (Department of Transportaion) will
certify that it is safe upon an investigation and testing of the system.
The maker pays a fee for the service, so they have an incentive to make it
as good as their claims. Some states also have a DOT (TXDOT here in Texas)
and also require such things be submitted to them as well. Along with the
proper fee, of course.

                R\%/itt



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