Backing up with disc trailer brakes

[Coyote machine]

My new trailer has disc brakes on both axles. What mechanism allows the brakes to lock if the wiring harness is detached when trying to back up?
Even though brand new, the trailer came with a bogus brake line from the tongue to the first caliper. For whatever 'reason' someone decided to put a brass splice in the line, and it was leaking from the getgo!?:confused2::shocked:
So, after talking to the trailer manufacturer I got them to send me a replacement brake line. Then I had my mechanic install it, which including checking bearings for proper throwout on one wheel which seemed to be running hot, took 2.5 hours.
Since then I've run the trailer a couple of times. IIRC, when I went to park it most recently I realized as I was backing up that the wiring harness was not connected and thus should have made it impossible to backup without hooking up the harness or using the bypass 'key'. Assuming what I said is true, what would allow me to backup without the brakes locking?

I have not received any reimbursement from the trailer manufacture for the $150 I am out for the line replacement. I included a copy of the bill with the line when I returned the original. Brakes are guaranteed for a year from date of purchase, materials and workmanship.:confused3:

TIA for any thoughts/ideas/answers.

CM

 

[sdef]

Just reread your post. So your problem is brakes locking when backing up? That is proper operation. To allow disengagement, you need to lockout the master cylinder as mentioned below:

If you have hydraulic surge brakes, as you are probably already aware, they are activated by pushing backwards with the tow vehicle or when the trailer is moving forward faster than the towing vehicle- same force applied at the master cylinder at the trailer hitch assembly. There are only two ways I know to backup a hydraulic system like this, 1) to engage the manual lockout for the master cylinder engagement or 2) to electrically do the same thing with the solenoid engagement.

Since there is not a wiring connection between the trailer and vehicle, only the mechanical lockout would do this, as far as I am aware.

 

[Coyote machine]

Suggest one more read.:confused3: The problem is the brakes are NOT locking when backing up with the wiring harness DISconnected.

 

[Diamondpilot]

Is the trailer loaded? If light it will not lock up. Also, did your mechanics bleed the system properly after replacing the faulty hose?

Chris

 

[Coyote machine]

It's loaded with my boat. It locked up before I loaded it, prior to the brake line replacement. I usually spray the bunks with bunk roller spray- like Teflon and wet them with a hose; last time I forgot. I launch it off the trailer by backing up and slamming on the brakes to make sure it slides off.

 

[Diamondpilot]

Sounds like there is a issue with the system. It needs to be seviced. My guess the mechanics who changed the line did something to it.

Start by checking the brake fluid level.

Slamming a boat off is not the way to do it. Tough on your truck and dangerous. Back it off using the motor.

Chris

 

[xtn]

Surge brakes operate when the tow vehicle and the trailer are shoved together. For example... when you're slowing the tow vehicle on the highway, or when you try to back up.

So they aren't going to operate if you're backing up down a hill (boat ramp). That is pulling the tow vehicle and trailer away from each other. It's not going to pressurize the master cylinder.

 

[Coyote machine]

Sounds like there is a issue with the system. It needs to be seviced. My guess the mechanics who changed the line did something to it.

Start by checking the brake fluid level.

Slamming a boat off is not the way to do it. Tough on your truck and dangerous. Back it off using the motor.

Chris

I'm going to check it out soon and make sure what I think is happening actually is. I agree it's not best to ram the boat off the trailer. unfortunately this particular ramp was perpendicular to a very narrow waterway to launch into and the trailer was high/dry out of the water for most of it's length.

 

[Coyote machine]

Surge brakes operate when the tow vehicle and the trailer are shoved together. For example... when you're slowing the tow vehicle on the highway, or when you try to back up.

So they aren't going to operate if you're backing up down a hill (boat ramp). That is pulling the tow vehicle and trailer away from each other. It's not going to pressurize the master cylinder.

That's NOT correct. A surge brake cylinder will lock up disc brakes backing up. It is part of their very nature that it does so. The only way to prevent that is by inserting a release key into the tongue mechanism to prevent this for occurring, or to have the electrical harness plugged into the towing vehicle. This should be and was happening before but now it seems to not be occurring. This IS the question: WHY is it NOT locking, as it should, when backing without the harness connected?

 

[trktrman]

Surge brakes operate when the tow vehicle and the trailer are shoved together. For example... when you're slowing the tow vehicle on the highway, or when you try to back up.

So they aren't going to operate if you're backing up down a hill (boat ramp). That is pulling the tow vehicle and trailer away from each other. It's not going to pressurize the master cylinder.

This is how I thought it worked.