[Vwdiesel] Re: Hydraulic braking system for trailers was: Rabbit towing t...

[pmdolan at sasktel.net]

There are NO direct hydraulic-to-hydraulic towing brake systems.  Due to bleeding issues, and today ABS concerns, will never happen.  What you saw would have been a vaccuum over hydraulic setup, pretty much all obsolete now since there are very few vacuum boosters left (they use another vac pump for these systems).  It may also have been air over hydraulic, but you would have seen conventional glad hands instead of inline quick-couplers.

Generally, if you want hydraulics on a small trailer, you use surge brakes, but these too have a limited future due to regulatory environment.  Personally, I like surge brakes, but you need to have a proper damper to make them work right.  I think in most places you can still use surge brakes on a car trailer.  Their biggest value is that any vehicle can tow the trailer and have braking.

In today's towing world, techno catch-up is taking place.  You have been able to buy electric over hydraulic actuators for a while, and over the last few years, actuators with enough line pressure to run disc brakes.  You can also now get full ABS on your electric over hydraulic trailer.  These systems store energy in a braking battery in the trailer, and charge it as the vehicle drives, since their actuator loads are well beyond what little wiring will carry.

All of the electric stystems need a controller in the tow vehicle.  Most are inertial devices (absolute junk).  The old system of using a tap into the brake line is also long gone (due to displacement limits on ABS circuitry).  The absolute top of the line is a controller that has a piezo transducer teed into the brake line at the master (no displacement issues, plus it reads the desired brake effort BEFORE ABS intervention) and a matching transducer in the trailer line.  The system (made by MasterBrake) compares the two digitally and communicates the driver's desired brake effort instantly to the trailer to match it proportionally to the ratio chosen on setup.

Pat 

----- Original Message -----
From: LBaird119 at aol.com
Date: Wednesday, January 12, 2005 9:29 pm
Subject: Re: [Vwdiesel] Re: Hydraulic braking system for trailers was: Rabbit towing t...

>  Of course then there's vacuum actuated and controlled hydraulic 
> trailer 
> brakes.  That went over to pressure and of course there's 
> commercial 
> type air actuated.
>     Loren
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