Trailer brakes

[JDP]

14 hours ago, Gordmac said:

What operates the disc brakes on the trailer? When they started fitting disc brakes to cars they had to fit servos to get the pedal force down.

Galvanised break callipers, with cables to a piston that moves and pulls the breaks when you break, much like drums . Like suzook mentioned though, the disk that comes in contact with the pads will get a light coat of rust. However spraying the breaks with saltaway or any other saltwater remover stops this and gives a coating to stop rust. Also if you dont use any of these cleaning products, simply using the breaks removes that coating of rust very quickly. Ive only ever needed to replace disk pads and cables in the last 20+ years of towing boats this side of the pond. My boats in the UK didn't have braked trailers but in saying that most were on moorings.

We also need to have Ellectric break away breaks that will break the trailer if it comes unattched from the tow vehicle but only in rigs over 2 tons.

[GPSguru]

1 hour ago, Andy135 said:

 

However, I believe the brake coupling is currently in the compressed (reverse?) position. I suspect it's stuck in that position. Not sure if this is relevant?

Yes, that is why the shoes don't fit.

In the compressed position the trailer brakes are applied, via the rod and cables. You need to pull the coupling completely forward and make sure the cables are not seized. The cable equaliser should sit square. If it is pointing to one side when the coupling is forward then that side cable / brake is not moving freely.

When the coupling is uncompressed there should be a 3 - 5mm gap at the coupling end that operates the rod.

Effectively, right now, even with the adjusters backed off, it still thinks the brakes are on, therefore the drums wont fit ..............

Edited April 20, 2021 by GPSguru

[Andy135]

Just now, JonC said:

So basically the problem isn’t the brakes or the new parts, it’s the guy who is trying to fit them doing it wrong?

I think we all suspected that from the start. 

Lol, not quite, but nice try.

[Andy135]

4 hours ago, GPSguru said:

Yes, that is why the shoes don't fit.

In the compressed position the trailer brakes are applied, via the rod and cables. You need to pull the coupling completely forward and make sure the cables are not seized. The cable equaliser should sit square. If it is pointing to one side when the coupling is forward then that side cable / brake is not moving freely.

When the coupling is uncompressed there should be a 3 - 5mm gap at the coupling end that operates the rod.

Effectively, right now, even with the adjusters backed off, it still thinks the brakes are on, therefore the drums wont fit ..............

Thanks. Will see if I can free off the coupling. Might have to take it apart rather than use brute force given that the trailer is up on blocks.

[Gordmac]

9 hours ago, JDP said:

Galvanised break callipers, with cables to a piston that moves and pulls the breaks when you break, much like drums . Like suzook mentioned though, the disk that comes in contact with the pads will get a light coat of rust. However spraying the breaks with saltaway or any other saltwater remover stops this and gives a coating to stop rust. Also if you dont use any of these cleaning products, simply using the breaks removes that coating of rust very quickly. Ive only ever needed to replace disk pads and cables in the last 20+ years of towing boats this side of the pond. My boats in the UK didn't have braked trailers but in saying that most were on moorings.

We also need to have Ellectric break away breaks that will break the trailer if it comes unattched from the tow vehicle but only in rigs over 2 tons.

They are mechanically operated then. I wouldn't think you would get much braking with mechanically operated disc brakes without some sort of assistance. Is there a solenoid helping?

You see motorhomes towing cars, they must have some sort of legal way of operating the car brakes.

[suzook12]

1 hour ago, Gordmac said:

They are mechanically operated then. I wouldn't think you would get much braking with mechanically operated disc brakes

There were a few bikes around in the 80's and on that had cable operated disc brakes, and can definitely say they were an improvement over drums. Obvious disadvantage would have been how difficult the arrangement would be for twin discs compared to hydraulic.

Back to trailers, an overrun brake uses the energy from the trailer to apply force to the brakes, so should be more than possible to apply adequate braking to each wheel as long as its matched to the right damper.

[Gordmac]

Legally the car being towed is a trailer and will need brakes to be legal if over 750kg. They generally run on their own wheels.

There is next to no weight in a bike, won't need a lot of force at the disco work compared to a trailer.

[suzook12]

11 minutes ago, Gordmac said:

There is next to no weight in a bike, won't need a lot of force at the disco work compared to a trailer.

You seem to have missed the point. The point is you don't need a servo, it's all about leverage and ratios.

A trailer wouldn't need servo assisted brakes becayse the trailer is the energy source. No overrun =No brakes required, if the trailer is pushng the tow hitch with 1 tonne of force, that's 1 tonne of braking force available as it is transferred via mechanical coupling to the brakes. As long as the damper is suited to the loads required it will work just as drum brakes do. Servos were around long before disc brakes were the norm....

[Gordmac]

What makes you say there is a one ton braking force? Not often you would be looking for 1g deceleration. Thing about levers is to get a lot of leverage you need a lot of movement. Drum brake normally have a self servo action on at least one shoe which increases the braking considerably. Servos did exist before discs but that made them necessary.

 

[Andy135]

11 minutes ago, Gordmac said:

What makes you say there is a one ton braking force?

As the vehicle pulling the trailer slows down, the weight of the trailer (and boat) moves forward and compresses the coupling damper to provide the energy required to activate the brakes. This is the force that Zook is referring to I think, which is why servos aren't necessary on trailer brakes. In effect the weight of the rig provides all the energy needed for braking and probably more. So not quite 1 ton of force at the brakes (drums couldn't do that) but 1 ton of force to activate the brakes.

[Andy135]

2 minutes ago, JonC said:

Tons being a measure of mass? Can we work in Newton’s of we’re talking about force please as it’s a different thing. 

Quite right. 9800-ish Newtons of force available for braking from 1 ton of mass being towed.

[Andy135]

8 minutes ago, JonC said:

Thanks, now I understand. 

Happy to help 😉

[GPSguru]

1 hour ago, Andy135 said:

Quite right. 9800-ish Newtons of force available for braking from 1 ton of mass being towed.

Not quite that simple. The force applied is dependent on the inertia, i.e the faster the rate of speed decline of the towing then the inertia of the trailer is increased.

you need to draw up a vector diagram to see the full effect, as it is not linear.

[Andy135]

1 minute ago, GPSguru said:

Not quite that simple. The force applied is dependent on the inertia, i.e the faster the rate of speed decline of the towing then the inertia of the trailer is increased.

you need to draw up a vector diagram to see the full effect, as it is not linear.

Agreed but I have to keep it simple for Jon, remember. Frankly I'm surprised he's managed to read this far down the thread...

[GPSguru]

7 hours ago, Andy135 said:

Agreed but I have to keep it simple for Jon, remember. Frankly I'm surprised he's managed to read this far down the thread...

In its most basic form it is really just Newtons second law, which is F= m a.

However with a declining acceleration (retardation / deceleration) then the formula is more complex. I will post it up later.

Edited April 22, 2021 by GPSguru

[GPSguru]

11 minutes ago, JonC said:

I’m sure we are all on the edge of our chairs waiting for that. 

Well, you should be, it is the same formula for wave acceleration and mass, so you can calculate at what deceleration rate is needed to avoid a wave over the stern !

[GPSguru]

@JonC, @Andy135 , @suzook12 , @Geoff

 

Here you go............

Decelerating mass is almost a sinusoidal function, which is why it is similar to wave mass calculation.

u(x, t) = 2a²·sech²(a(x + 4a²t))

u is the vertical displacement from equilibrium, t is time, x is horizontal distance and v is velocity,  sech(z) is the hyperbolic secant function and is equal to 2/(exp(z)+exp(−z)

 

[suzook12]

27 minutes ago, GPSguru said:

@JonC, @Andy135 , @suzook12 , @Geoff

 

Here you go............

Decelerating mass is almost a sinusoidal function, which is why it is similar to wave mass calculation.

u(x, t) = 2a²·sech²(a(x + 4a²t))

u is the vertical displacement from equilibrium, t is time, x is horizontal distance and v is velocity,  sech(z) is the hyperbolic secant function and is equal to 2/(exp(z)+exp(−z)

 

I often wondered......

What does that actually mean in real life?

[GPSguru]

5 minutes ago, suzook12 said:

I often wondered......

What does that actually mean in real life?

In simple terms ........

It means the quicker you slow with the tow vehicle, the trailer mass becomes greater, thus exerting more pressure on the brakes from the damped over-run actuator.

[suzook12]

5 minutes ago, GPSguru said:

In simple terms ........

It means the quicker you slow with the tow vehicle, the trailer mass becomes greater, thus exerting more pressure on the brakes from the damped over-run actuator.

Ok, now it makes sense. I pretty much knew that, just couldn't put it as simply as that

[Saintly Fish]

6 hours ago, GPSguru said:

@JonC, @Andy135 , @suzook12 , @Geoff

 

Here you go............

Decelerating mass is almost a sinusoidal function, which is why it is similar to wave mass calculation.

u(x, t) = 2a²·sech²(a(x + 4a²t))

u is the vertical displacement from equilibrium, t is time, x is horizontal distance and v is velocity,  sech(z) is the hyperbolic secant function and is equal to 2/(exp(z)+exp(−z)

 

I used to think that BK was the god of googling. But that takes it Ian....... top googling that man. 👍🏻

[Geoff]

8 hours ago, GPSguru said:

In simple terms ........

It means the quicker you slow with the tow vehicle, the trailer mass becomes greater, thus exerting more pressure on the brakes from the damped over-run actuator.

As you all know, my own school days and Newtons laws are now a long way off, but I do not think the trailer mass can change - forces yes, but mass? Geoff.

[GPSguru]

2 hours ago, Geoff said:

As you all know, my own school days and Newtons laws are now a long way off, but I do not think the trailer mass can change - forces yes, but mass? Geoff.

 

Yes, you are correct Geoff, the mass remains constant (because ' it is what it is') but the force is variable, but is there not another scientific name for it ? a 'something mass'

[Andy135]

3 minutes ago, GPSguru said:

a 'something mass'

You're thinking of Sunday mass. Definitely Sunday mass. 😁

[GPSguru]

4 hours ago, Saintly Fish said:

I used to think that BK was the god of googling. But that takes it Ian....... top googling that man. 👍🏻

 

🤣

It was more to illustrate that the forces of towing a trailer are definitely not simplistic. However, not the sort of complex math that I would remember without reference

TBF the only formulas I remember are those I used to use at work, like calculating my commission, formula based around satellite orbit, and several formulas related to Global positioning (GPS).

Google (and others) are a great resource, but you have to know what you are looking for as there is also a ton of shite on there. However, it beats going into the loft to find the right reference book.