Mark V
Member
Lessons Learned to share-
If you have a Demco surge-brake actuator on your trailer and the brakes aren't working, you may have a composite (black plastic) master cylinder that Demco told me they know is prone to having its piston stick in the bore.
My piston had permanently stuck at about mid-stroke in its composite bore, so Demco sent a new aluminum master cylinder, reverse solenoid, and push rod to me for free. I changed it all myself and they work great now.
My rig is a 07 Tundra w/5.7 liter V8 and the boat & trailer combined are about 8000 pounds. the trailer is a Vanguard with 2 axles/4 wheels and four disc brakes.
Things I learned as an amateur trailer brake actuator mechanic:
a) It's somewhat hard to really know if your trailer brakes are working if it's your first trailer rig like this. My first clue was excessive clunking/severe banging as I accelerated AND decelerated with my truck.
b) When the surge brakes are properly set up, they should not clunk or bang much at all as you brake or decelerate. Your ball mount and hitch may have some slop between them, resulting in minor clunking, but the actuator should have almost zero clunking when braking occurs. The main reason there should be no clunk is that the actuator should NEVER reach the end of its stroke in the compressive direction...ie it should NEVER reach its hard-stop when it is compressing during braking.
In addition, on mine, 2 hydraulic shock absorbers and a spring on the push rod help cushion the motion as the actuator is compressed and transfers the compressive load to the master cylinder piston, which in turn pressurizes the brake fluid...etc..and applies the brakes...smoothly.
b) I confirmed mine wasnt working by temporarily disconnecting the 2 shock absorbers (to eliminate their resistance) and working the actuator by hand. It was obvious (and visible) that the actuator was hitting its hard stop when compressed, and there was ZERO resistance as I compressed it. This was because the master cylinder piston was stuck so far back in its bore that the actuator push-rod never contacted it.
c) I bought a $30 MityVac brake bleeder and it is well worth the $$. I now have absolutely no doubt, that there is no air, in my brake lines at all. Using this thing is the ONLY way to do it right if you are bleeding them by yourself.
d) My surge actuator still clunks significantly upon accelerating from a stoplight unless i am very gentle with the gas pedal. This is because the actuator will ALWAYS reach its hard stop when it is extending - telescoping longer- and releasing the brakes.
This still happens on mine despite the two mini-shock absorbers attached to the actuator, resisting its motion. There would probably be less clunk if they were more resistive, slowing down the actuator extension more, but the actuator will still always reach its hard stop when extending. (makes you wonder why Demco hasnt done something more to cushion that "event").
e) Now that its all working well, I can literally feel the boat trailer braking and slowing down my Tundra versus feeling the Tundra brakes doing all the work. A good way to tell....in safe traffic of course, is to start at about 50 mph, brake moderately hard (activating the trailer brakes), then let your foot OFF of your brake pedal..and let your truck coast....dont accelerate yet...in this mode, the trailer brakes will still be lightly applied and you should feel the trailer brakes slowing down your rig. The trailer brakes should not release completely until you accelerate enough to extend the actuator ..and get ..."The Clunk".
I hope this saves you some diagnostic time if you are struggling with your trailer brakes !
If you have a Demco surge-brake actuator on your trailer and the brakes aren't working, you may have a composite (black plastic) master cylinder that Demco told me they know is prone to having its piston stick in the bore.
My piston had permanently stuck at about mid-stroke in its composite bore, so Demco sent a new aluminum master cylinder, reverse solenoid, and push rod to me for free. I changed it all myself and they work great now.
My rig is a 07 Tundra w/5.7 liter V8 and the boat & trailer combined are about 8000 pounds. the trailer is a Vanguard with 2 axles/4 wheels and four disc brakes.
Things I learned as an amateur trailer brake actuator mechanic:
a) It's somewhat hard to really know if your trailer brakes are working if it's your first trailer rig like this. My first clue was excessive clunking/severe banging as I accelerated AND decelerated with my truck.
b) When the surge brakes are properly set up, they should not clunk or bang much at all as you brake or decelerate. Your ball mount and hitch may have some slop between them, resulting in minor clunking, but the actuator should have almost zero clunking when braking occurs. The main reason there should be no clunk is that the actuator should NEVER reach the end of its stroke in the compressive direction...ie it should NEVER reach its hard-stop when it is compressing during braking.
In addition, on mine, 2 hydraulic shock absorbers and a spring on the push rod help cushion the motion as the actuator is compressed and transfers the compressive load to the master cylinder piston, which in turn pressurizes the brake fluid...etc..and applies the brakes...smoothly.
b) I confirmed mine wasnt working by temporarily disconnecting the 2 shock absorbers (to eliminate their resistance) and working the actuator by hand. It was obvious (and visible) that the actuator was hitting its hard stop when compressed, and there was ZERO resistance as I compressed it. This was because the master cylinder piston was stuck so far back in its bore that the actuator push-rod never contacted it.
c) I bought a $30 MityVac brake bleeder and it is well worth the $$. I now have absolutely no doubt, that there is no air, in my brake lines at all. Using this thing is the ONLY way to do it right if you are bleeding them by yourself.
d) My surge actuator still clunks significantly upon accelerating from a stoplight unless i am very gentle with the gas pedal. This is because the actuator will ALWAYS reach its hard stop when it is extending - telescoping longer- and releasing the brakes.
This still happens on mine despite the two mini-shock absorbers attached to the actuator, resisting its motion. There would probably be less clunk if they were more resistive, slowing down the actuator extension more, but the actuator will still always reach its hard stop when extending. (makes you wonder why Demco hasnt done something more to cushion that "event").
e) Now that its all working well, I can literally feel the boat trailer braking and slowing down my Tundra versus feeling the Tundra brakes doing all the work. A good way to tell....in safe traffic of course, is to start at about 50 mph, brake moderately hard (activating the trailer brakes), then let your foot OFF of your brake pedal..and let your truck coast....dont accelerate yet...in this mode, the trailer brakes will still be lightly applied and you should feel the trailer brakes slowing down your rig. The trailer brakes should not release completely until you accelerate enough to extend the actuator ..and get ..."The Clunk".
I hope this saves you some diagnostic time if you are struggling with your trailer brakes !
