Terryallan wrote:
Truthfully. the trailer brakes should engage as soon as you pull the lever.
Operative word here is "should".
Often with IBC controllers, the manufacturers actually reduce the braking output at slow speed even with the "manual" control lever.
This may result in much less braking power than normal when using the manual lever.
However, the OP is using the trailer brakes to help assist disconnecting without wheel chocks and as pointed out by someone else, one should always chock the wheels before ever attempting to disconnect trailer from vehicle.
Granted the OP is dealing with a 5th wheel which means at least 20%-25% of the weight is on the front legs which would present a bit less potential of the trailer moving.. But that is a very risky and sketchy move regardless.
Not sure why folks do this, chock the wheels first, then disconnect, much safer and the life you save may be you or your family..