Trailer Brakes -how do they work?

lakelandterrier · 12 August 2013, 20:36

A simple question, probably due to my ignorance of most things mechanical, but how to brakes on a braked trailer work? Is it like inertia reel seat belts, or some other mechanism?
What applies / disengages them?

mister p · 12 August 2013, 20:52

Momentum of the trailer against a braking car pushes a plunger mech between the trailer nose and the rest of the trailer. This action activates the brakes in the same way a brake pedal acts upon the master cylinder. The more the car brakes the more the trailer pushes against it, the more the trailer brakes are activated. It can be mechanical or hydraulic.

PeterM · 12 August 2013, 20:59

Quote:

Originally Posted by lakelandterrier

A simple question, probably due to my ignorance of most things mechanical, but how to brakes on a braked trailer work? Is it like inertia reel seat belts, or some other mechanism?
What applies / disengages them?

Its magic - like Harry potter etc . Ok its not that -Its actually hundreds of brake pixies run round the inside of the drum like people on a very very very small treadmill running the wrong way. These are very similar to the pixies in your engine that run very very fast to turn your prop.

Or is it really the push of the hitch on a bar which pulls a cable, which pulls the shoes onto the drum ?

Sorry its been a long long day here .....

wavelength · 12 August 2013, 21:38

Quote:

but how to brakes on a braked trailer work?

on most trailers dunked in sea water they work at first, then degenerate to working sometimes, a detour into sticking on when left alone despite handbrake being off, quickly followed by not working at all
! *!*!* trailer brakes - spawn of the devil!

colcreate · 12 August 2013, 21:44

Over-run brakes, as the others have said (except no pixies)

Here's a link to an interactive drawing to keep you amused (for about 8 seconds...)
Car-technolgy, valuable informations, simulation, questions, tasks

It's the auto-reverse mechanism that really baffles the brain until you see it close up in action, simples!

mister p · 12 August 2013, 21:54

Aaah yes, those "reversing without disengaging trailer-brake" moments. Pure genius for others' amusement.

lakelandterrier · 12 August 2013, 22:00

Quote:

Originally Posted by PeterM

Its magic - like Harry potter etc . Ok its not that -Its actually hundreds of brake pixies run round the inside of the drum like people on a very very very small treadmill running the wrong way. These are very similar to the pixies in your engine that run very very fast to turn your prop.

Thanks Pete,
bur I'm not that ignorant of how engines work - I know there are no pixies in it - pixies are who you have on computer screens / digital cameras

My engine works like this: I exchange hard earned cash for a liquid - not produced by the government, but who take most of the money I pay for it. Liquid goes in tank. I turn key. liquid eaten by engine. Boat goes through water. When I want to go fast / through waves the engine decides to eat more liquid. Pixies don't come into it!

Anyway, coming back to the trailer, why don't the pixies drown when I submerge them in the water? Not sure you've explained this simply enough for me - or is this why the brakes stop working - they're gummed up with drowned pixies?

PeterM · 12 August 2013, 22:07

Quote:

Originally Posted by lakelandterrier

- they're gummed up with drowned pixies?

exactly! the pixie magic only keeps them going for a while, then they 'turn' (like gremlins when they get wet) . They then glue your brakes together or pull them apart depending on what you need the trailer to do on that day...if you need to tow more than a mile they glue, if it's a distance where brakes won't be needed they allow a wheel to fall off!

bloody pixie magic!!!!!:/

rossymtb · 12 August 2013, 22:37

That's a really good point. How do they not activate when in reverse?
I'm talking more towards the older style hitches with rods.

mister p · 12 August 2013, 22:55

Some have a reverse lockout that needs to be manually activated. On drums they are usually leading shoes so will slip in reverse anyway.

colcreate · 12 August 2013, 23:10

My old 1 ton trailer has manual lockout for reversing (its been rebuilt more times than triggers broom). Bit of a pain having to jump out and lock the brakes off when reversing. Good thing about a 4x4 though is I just put my foot down in reverse and the trailer doesn't have much say in the matter.. it still goes backwards!

lakelandterrier · 13 August 2013, 11:53

Quote:

Originally Posted by mister p

Momentum of the trailer against a braking car pushes a plunger mech between the trailer nose and the rest of the trailer. This action activates the brakes in the same way a brake pedal acts upon the master cylinder. The more the car brakes the more the trailer pushes against it, the more the trailer brakes are activated. It can be mechanical or hydraulic.

Thank you mister p for this quick and clear explanation.

I now understand.

9D280 · 14 August 2013, 08:06

Quote:

Originally Posted by mister p

Some have a reverse lockout that needs to be manually activated.

Which as wel las being a nuisance can also prove interesting 50 miles later down the motorway when you realise two things simultaneously as the car in front E-stops:

1) you forgot to de- activate it.
2) you should be wearing brown trousers......

Auto reversing brakes - PITA to set up, but genius when working properly!

As an aside - because the trailer brakes are essentially "overrun" brakes you will only ever get something like 80% of "full braking" on the trailer, because as soon as the brakes come on the drawbar extends again & they release, by which pioint the car has slowed down a bit more so they come on again...<repeat> That's why they have dampers in the drawbar - it reduces the surging.

tehguy · 16 August 2013, 14:31

The only other viable alternative in a normal road car is electric brakes though which is the de facto standard in North America. The problem is the vehicle must be fitted with the brake controller, and I do not believe electric brakes are allowed on UK trailers due to not reacting fast or proportionally enough with the vehicle braking. If you don't have a brake controller in your car then the brakes on the trailer will not work - at least with overrun brakes you can hitch it up to any car and they will work.

I think the mechanical overrun brake system is all round the best and most foolproof braking system for light (up to 3.5ton) trailers. Because as said you don't need to do anything except hitch up and make sure the breakaway is connected and it will work. Due to the nature of them the pressure is self-adjusting too depending on the rate of the vehicle braking and the load in the trailer.

The other option is certain vehicles e.g Land Rover can be fitted with close coupled (air) brakes. The Defender can legally tow 4ton when fitted with this option.

9D280 · 26 August 2013, 12:59

Although as has been discussed before here - electric brakes in salt water is a failure waiting to happen!