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Old 05-22-2020, 09:58 AM   #1
tech740
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Trailer brake issues

Helping my father with his trailer and I am stumped. He asked if I would help adjust the brakes on his toyhauler because he didnít feel they were working while driving. We jacked up one wheel and the brakes had a slight drag like they should. Pulled the pin and it locked up. We did this to each wheel and they worked as they should. We checked continuity at the umbilical and all the wires were good to ground. We then switched to the truck and we have 12 volts when the brake controller is activated. Does this mean the controller isnít working correctly when the brakes are applied with the pedal? How do you check voltage while hooked up and moving to see if power is being supplied?
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Old 05-22-2020, 11:00 AM   #2
chuckster57
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What brake controller? Some wonít show much if any voltage going to the brake if your not moving.
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Old 05-22-2020, 11:14 AM   #3
travelin texans
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The newer trucks the brake controller is proportional, meaning they apply more at different speeds & brake pedal pressure.
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Old 05-22-2020, 11:28 AM   #4
flybouy
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Most after market controllers here than 20 years old have a "inertia sensor" to provide proportional breaking. But if you are getting 12v at the truck 7 way it should be ok. Every brake controller I know of has an "intensity" adjustment also.
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Old 05-22-2020, 11:58 AM   #5
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Itís a Primus IQ. Itís older. Last year seemed to have good brakes. This year you can barely feel them. Like I said they are adjusted and show good voltage.
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Old 05-22-2020, 01:53 PM   #6
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Here's how proportional electric only brakes work:
The activators are electromagnets that when activated by an electrical current are attracted to the side of the rotating brake drum. The friction between the brakedrum and the magnet face pulls the magnet which is attached to an actuating lever that applies some force to the brakes.
To vary the amount of force, the controller tries to vary the amountof friction between the magnet and the drum. To vary the amount of friction, the controller has to vary the amount of magnetic attraction. Since the controller can only supply up to 12 volts and the coils in the magnet are fixed, the magnetic force can only be varied by varying the current through the magnetic coils (voltage and current are like pressure and flow rate of water).
When you disconnect the trailer and measure the voltage at the trailer connection, there is no current flow so you will always see 12V when the controller is active (unless the output transistors are completely dead). However, this doesn't indicate the controller's ability to control the current through the brake magnets.
The best way to test your controller is to remove the back shell from the trailer side connector and connect the trailer to the truck. Then, with the engine running and the brake controller set to full, apply the brakes in the truck hard and measure the voltage going to the brakes. It may still not reach the full 12V because of voltage drops in the wiring and the fact that the magnets have fairly low resistance and are wired in parallel, but it will propbably be near that figure. If it's zero or very low, like 2-3V then your controller might be toast.
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Old 05-22-2020, 01:56 PM   #7
sourdough
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Did the controller maybe get "readjusted" somehow"? Here's a link showing how to adjust it in the event it's not set up correctly.

https://www.google.com/search?source...2isAX5vaqABQ39
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Old 05-23-2020, 09:43 AM   #8
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Quote:
Originally Posted by sourdough View Post
Did the controller maybe get "readjusted" somehow"? Here's a link showing how to adjust it in the event it's not set up correctly.

https://www.google.com/search?source...2isAX5vaqABQ39

We have it maxed out and there is little braking when we use the pedal and stronger when we use the manual over ride. Thinking the controller may need replaced.
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Old Yesterday, 04:18 PM   #9
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Make sure the controller is level side to side. There should be two dials gain and delay.
With both to max and the lever fully engaged is the only time you will see max voltage. Pulling the lever about half way should give 8-9 volts. On the proportional controllers there is a pendulum that will swing, so the controller will only give max voltage at about the same time you coffee spills out of your cup holder with the brake pedal engaged. My bet is that the pendulum is all gummed up with dust and moisture. Blow it out or replace the truck with a 2020 f450, they come from the factory with a truly awesome brake controller.
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Old Yesterday, 05:13 PM   #10
tech740
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I wish dad could do the 2020. May have to try the cleaning this weekend.
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Old Yesterday, 06:52 PM   #11
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Does the Primus IQ have a pendulum? If it does, save the cost of a new truck and just get a prodigy brake control. No pendulum and all it cares about is being ďin lineĒ with the tow vehicle front to rear. My prodigy is old (2nd gen) but still works as good as day 1.
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Old Today, 01:47 AM   #12
tech740
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When we talked about replacing it prodigy series either 2 or 3 were the only ones I told him to look at. I will see him again this weekend and see if he has made any changes yet. I appreciate all the suggestions. Thanks guys.
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