how do trailer brakes work?

[matt 2LT]

well i need to fit a towbar to my E46 to tow a (braked) trailer.

it has just occured to me, how do the brakes work on the trailer?

and will i need any extra electrics for a braked trailer, or will the single electrics be all that i need?

cheers,
matt

[varsas]

I believe most operate off the tow bar, when the trailer moves toward the car (e.g. because the car slows down) it compresses a lever which applies the brakes. You will still need electrics for the brake (and other) lights.

[Jem0911]

The Brakes are called overrun brakes.
As the car slows down the trailer brakes are operated by a piston in the drawbar.
Compressing the front piston pulls a rod acctivating the drum brakes on each wheel.
The electrics you require are for the road lights on the trailer.

[Ozzie Osmond]

Jem0911 said:

The Brakes are called overrun brakes. Compressing the front piston pulls a rod acctivating the drum brakes on each wheel.

which is why the people you see belting up the motorway at 80 mph with a trailer are completely bonkers. If there's one certainty in life it is that modern car brakes are MASSIVELY more effective than the trailer brakes. If they slam the brakes on the car will stop -
but the trailer WON'T! It'll either go round, over or through the car. Keep a good distance away if you can.

The back half of an articulated lorry or a trailer towed by a lorry is completely different. Full braking system on every wheel operated directly by the tractor unit's braking system. They stop very effectively.

[netherfield]

In reply to the original question.

A lot don't because people can't be bothered to adjust,service or reline trailer brakes.

It can be very frightening when a trailer decides to start overtaking the towing vehicle,once helped a mate to fetch some lawn turf from York,almost home when some twunt decided to overtake another car coming up a hill,our Land Rover slowed down but the trailer weighing about 2 tonnes had other ideas and started to jack-knife,letting go the brakes brought it back a bit but not before ripping the front wing off the overtaking car.

[rallycross]

Yeah the piston in the draw bar activates the brakes.

Having towed with lots of trailers including some with no brakes (ie not working) the difference is huge, a 4 wheeled trailer with working brakes has surprisingly good stopping power with a car loaded on it, they really work well.

[Stubby Pete]

Jem0911 said:

The Brakes are called overrun brakes.
As the car slows down the trailer brakes are operated by a piston in the drawbar.
Compressing the front piston pulls a rod acctivating the drum brakes on each wheel.
The electrics you require are for the road lights on the trailer.

What he said.

Juwt make sure that they are seviced and working. he slightest "brake test" on an unladen trailer should lock the wheels immediately (don't do this in traffic!!) so more cre is required than when pulling a car/boat etc.