Trailer brakes

[JD6230P]

If you have a trailer that has hydraulic and air brakes do you have to use both at the same time or can you use hydraulic on their own?

 

[Ormond]

Either or......plug in the hydraulic brake pipe to use that , leave air hoses not connected .....make sure all air is dumped out the tank on the trailer. Or just hook up the red and yellow air hoses.....is the common term.... Air over hydraulic with that type of system........

 

[Weare Cham]

If you have a trailer that has hydraulic and air brakes do you have to use both at the same time or can you use hydraulic on their own?

One or the other. Air is best.

 

[snarling bee]

NEVER both.

 

[melted welly]

NEVER both.

what happens if you do?......asking for a friend

 

[Andrew]

NEVER use both at the same time.

what happens if you do?......asking for a friend

Then you basically double the braking force and the wheels will lock.

 

[snarling bee]

Or you break the brakes. Which is a) expensive and b) means you potentially have no brakes, at least on one wheel.

 

[e3120]

Whilst I wouldn't advise using both, there won't be double force, as the air and hydraulics are in series, not parallel. The one with most force will dominate and force the oil/air out of the other.

 

[Munkul]

With air over hydraulic, does this mean you have no parking/failsafe brakes? Since if you're using hydraulic only, you aren't releasing the parking brake... how does this work? Just out of curiosity.

 

[ollandroverman]

Either or......plug in the hydraulic brake pipe to use that , leave air hoses not connected .....make sure all air is dumped out the tank on the trailer. Or just hook up the red and yellow air hoses.....is the common term.... Air over hydraulic with that type of system........

With air over hydraulic, does this mean you have no parking/failsafe brakes? Since if you're using hydraulic only, you aren't releasing the parking brake... how does this work? Just out of curiosity.

Ag trailers can have air and/or hydraulic brakes.

Air over hydraulic brakes is a different thing altogether, and could be found an smaller HGVs.
It is a system where air pressure is modulated through the foot-brake to control an air slave cylinder/hydraulic master cylinder combination, that in turn controls a hydraulic wheel braking system.

 

[Lincsman]

I think you can use both as its the same rod thats pushing the arm, whether its 50/50 or 30/70 it wont matter as the driver will press to the required braking needed.

Dual Supply Air - hydraulic trailer brake actuator type 20 - 25 mm piston | eBay

Find great deals for Dual Supply Air - hydraulic trailer brake actuator type 20 - 25 mm piston. Shop with confidence on eBay!

www.ebay.co.uk

But I only use Air as its more sensitive, and stops the tractor having to do much... pre mother regs.

 

[Munkul]

Ag trailers can have air and/or hydraulic brakes.

Air over hydraulic brakes is a different thing altogether, and could be found an smaller HGVs.
It is a system where air pressure is modulated through the foot-brake to control an air slave cylinder/hydraulic master cylinder combination, that in turn controls a hydraulic wheel braking system.

Sorry, wrong terminology on my part.
So... with Ag trailer air and/or hydraulic brakes, my question - Is there a failsafe/park brake? I can't see how there can be, unless you have air pressure to release it.

 

[Andrew]

Sorry, wrong terminology on my part.
So... with Ag trailer air and/or hydraulic brakes, my question - Is there a failsafe/park brake? I can't see how there can be, unless you have air pressure to release it.

Yes and no.
Every trailer must have a park brake of some kind. This is normally a ratchet and steel cable.

Hydraulic single line brakes have no failsafes.

Hydraulic brakes with an accumulator / electric cable / breakaway cable are designed to apply the trailer brakes automatically if the trailer becomes disconnected. You can sometimes press a button to apply the park brake.

Tractor trailer air brakes work in the same way, but normally the park brake is applied with the tractor handbrake. Drain all the air out the system and there will be no brakes. This is why they must have a park brake as above.

Both systems are failsafe in that they stop the trailer in a breakaway situation, but not failsafe in that a leak in the pipe to going to the actuators will cause brake failure.

HGV trailer airbrakes failsafe in that the brakes are applied by a spring, so if air pressure throughout the trailer is lost then the wheels will be braked. This is why they don’t have cable applied handbrakes.

 

[Munkul]

Right, so basically Ag spec trailer axle brake air actuators don't have the secondary park brake mechanism in the air side, so have a separate mechanism to apply park or breakaway.
The hydraulic component is in series with the air actuator, rather than in parallel.

Thanks

 

[Andrew]

Right, so basically Ag spec trailer axle brake air actuators don't have the secondary park brake mechanism in the air side, so have a separate mechanism to apply park or breakaway.
The hydraulic component is in series with the air actuator, rather than in parallel.

Thanks

The ‘breakaway‘ on ag spec air is like older truck trailers, and relies on the drop in air pressure on the red line upon separation, to air apply the brakes.
Some manufacturers fit combined air / oil actuators, some fit separate ones so could be in series or parallel if that makes sense.