Trailer hydraulic-reverse lockout solenoid

[Paul]

Heh guys.  Both of my trailers have hydraulic brakes with an 'over-run coupling'.  These work really well when going forwards, but the brakes engage when reversing - especially when reversing up a hill.  There is a brake-disable latch you can flip over, but is a PITA and sometimes won't drop in if under load.

So, I want to use an electric solenoid that hydraulically vents the line pressure back to the header tank when reverse is selected in the car.  Below are two examples of three-port reversing solenoids that are available in the USA that would work.  The first one is slightly annoying, in that it is single wire, so the solenoid 'earths' via the trailer chassis (so I'd need to add a trailer chassis earth connection).

[Paul]

Here in NZ, I've only found a two-port (non-bypass) reversing solenoid and all that does is lock the brake line.  So if you have no line pressure it will work, but if you already have line-pressure it does NOT get vented out, thus the brakes remain locked.....

[Paul]

So, does anyone know of any three-port reversing valves for sale in NZ?

[Jeff B]

What's the big deal with earthing the single wire solenoid back to the trailer light earth wire?
Will it blow the fuse in the rover?

[Warwick Marflitt]

Does this have to be certified by LTNZ and designed by a registered engineer to allow VTNZ to sticker trailer to pass WOF inspection? You know how they love to complicate simple things. At least with stupid electric trailer brakes you don't have this problem.
The trouble is that if you ring and ask them for their ruling they're like chooks all running for cover. No one wants to give you an answer for fear of being held responsible if you have an accident and the brakes are under suspicion of failure? Make sure that the insurance company will cover it with a non factory modified brake system?

[Warwick Marflitt]

So, does anyone know of any three-port reversing valves for sale in NZ?

I thought old Rovers where Positive earth Jeff

[Paul]

What's the big deal with earthing the single wire solenoid back to the trailer light earth wire?

Nothing, but where would you connect the earth to on the solenoid?  Or do you mean add a wire between trailer chassis/coupling, across into the lighting loom (- thus using parts of the braking system for the earth connection)?  I haven't known of a trailer chassis being earthed before?

I've never bought from ebay before.  I was trying to buy local if available.

[Paul]

Does this have to be certified by LTNZ and designed by a registered engineer to allow VTNZ to sticker trailer to pass WOF inspection?

The 3-port USA ones, are 'fail safe' - i.e. a system failure just means they don't release when going in reverse - forwards still has full braking available.  The local 2-port ones can 'fail deadly' whereby they stop braking effect in forwards AND/OR don't release the brakes in backwards.

Re WOF inspection, the brakes are basically not tested now.  The tester just gets you to press the handle to see if it will stop a wheel when they spin it by hand - there is no performance/ balance testing on the trailer brakes.  However, any vehicle & trailer combo is covered by an overall performance check - it has to be able to stop within 7m from 30kmh.

[Jeff B]

Yeah just run an earth from mount lug to trailer earth loom? Or do you not want to earth trailer chassis to your rover chassis?
I don't see any issue with running an earth wire back to the car? You have to run a switch wire to activate it anyway (hooked up to reversing light?)
If you don't want to earth trailer chassis then insulate the valve from chassis? Mount on rubber block and have rubber hose joiners??

[Jeff B]

Or you could go down another path and hook up a pull solenoid (outboard electric choke activator or old commodore electric boot release solenoid) to flick the little reversing tab to lock over ride coupling?
Or make the mrs get out and do it...

[Paul]

Yeah just run an earth from mount lug to trailer earth loom? Or do you not want to earth trailer chassis to your rover chassis?
I don't see any issue with running an earth wire back to the car?

Earthing of a trailer chassis, isn't something I'd had to think about before - it just sounded unnecessary so was trying to avoid it.  I guess adding an earth near the solenoid sounds feasible.  Now just need to sort out an ebay account..

You have to run a switch wire to activate it anyway (hooked up to reversing light?)

The car/ trailer-socket/ flat-bet trailer is already wired for reverse.  The light clusters are off a Hilux or something, so reverse on the trailer lights up white already - quite good at lighting driveways at night. 

[swifty]

Flip the brake-disable latch over on flat ground,problem fixed .

[Jimmy Jet]

I've had the complete master cylinder and lockout valve from Trailequip on 2 x heavy boats.
Mint system and hard to live without. Power and earth comes from the std 7 pin using the reverse light.
Normally open so unless there is some crazy short you can't lose braking.

[Paul]

Flip the brake-disable latch over on flat ground,problem fixed .

Not always that easy Matt.  There are often times when getting the disable-latch engaged is a - an example being when you go down a driveway and then have to reverse out.  You end up doing stupid stuff, like having to chock up the trailer, drive forward (- to stretch out the coupling), disable-latch drops in, reverse, remove trailer chocks, then reverse out.  PITA, but when you've got a 2T digger on your trailer, not having brakes is not an option.

[Jimmy Jet]

Or you can apply handbrake on trailer, drive forward a bit, swing latch, take off handbrake and back up.
Has worked for me before.