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.

 

[aczlan]

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?

Ummm, if you are backing DOWN a hill (or boat ramp) and the trailer is PULLING on the truck, how will it lock up the brakes?
I understand on flat ground, if you hit a bump, or are backing uphill, but if you are backing down hill?

Aaron Z

 

[xtn]

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?

Um... it is too correct. At least my basic description is correct. It's not part of their very nature to activate when backing up. That can happen, but it's because their very nature is to activate when the hitch is compressed. There are conditions under which you can be backing up without compressing the hitch.

Now I only have experience with one boat trailer that has surge brakes. And the fact that you think having the electrical harness plugged in makes any difference confuses me. Perhaps there is a system I'm not familiar with wherein the reverse lights trigger a mechanism that prevents the master cylinder being operated?

Regardless, you want to know why a set of surge brakes on a boat trailer might not operate when backing up. Either they're faulty, or you're backing trailer-first down a hill (or otherwise not causing the hitch to compress and activate the master cylinder).

xtn

 

[bamboozled]

Discs and surge brakes you either have a lockout pin or a reverse lockout solenoid energized by the reverse lights from the tow vehicle.

As said above, the brakes are not going to engage going in reverse, downhill. Flat ground, or reverse uphill, and they will engage.

 

[Diamondpilot]

Ummm, if you are backing DOWN a hill (or boat ramp) and the trailer is PULLING on the truck, how will it lock up the brakes?
I understand on flat ground, if you hit a bump, or are backing uphill, but if you are backing down hill?

Aaron Z

You are correct but if you look at the original post he his talking about flat land in which case it should activate the brakes.

On all disc brake systems I have seen they incorporate a back up solenoid activated by the reverse lights.

Chris

 

[aczlan]

You are correct but if you look at the original post he his talking about flat land in which case it should activate the brakes.
On all disc brake systems I have seen they incorporate a back up solenoid activated by the reverse lights.

I was responding to post 9 where Coyote machine said that xtn was incorrect in saying that the brakes wouldn't activate when backing down a hill or boat ramp because gravity would keep the actuator from being compressed.

Aaron Z

 

[Coyote machine]

Ok. Sorry! It seems I was wrong about IF I were backing DOWN a ramp, but that is NOT my question. I have four wheel disk brakes actuated by a tongue surge brake controller attached to the trailer. My original and still pending answers as to why question is this: Flat driveway, putting my trailer with boat on it into temporary storage, backing up with the wiring harness NOT connected the brakes should lock and not allow me to backup. They are allowing me to backup and shouldn't be. Why and what is likely allowing this to happen?
Sorry for any confusion, I have never dealt with disk/surge brakes on a trailer before this season. My prior trailer was drum and surge~ no issues with backing up due to inherent design. :confused3:

Thanks to all contributors to date....

 

[timswi]

Not familiar with disk brakes on a surge, but are you sure that the surge is adjusted correctly?...I rented a surge car trailer once and the surge was set so tight that it would only engage with a shock, not normal braking...That was fun with a '66 big block El-Camino on the trailer.

 

[bamboozled]

Depends how much the actual boat and trailer weigh, but it's possible you could reverse on flat ground if the load is light enough and you don't gun it in reverse. They could be actuating some but not enough to be noticeable at such a slow speed.

You did verify that your master cylinder has fluid in it after the line replacement?

 

[Jim Shooz]

I think you need to check that the wiring harness has a connection to some part of the braking system. How many wires in the harness and where do they all go. If they all go to lights (turn indicators, stop lights etc) then connected or not they wont lock out the brakes when reversing.

 

[aczlan]

Depends how much the actual boat and trailer weigh, but it's possible you could reverse on flat ground if the load is light enough and you don't gun it in reverse. They could be actuating some but not enough to be noticeable at such a slow speed.
You did verify that your master cylinder has fluid in it after the line replacement?

Good point. I'll bet that if he chocked the wheels and backed up with a spotter watching the tires, it would try to skid the them if the brakes are bled. If not, my first bet would be that they didn't get the line fully bled and it has an air pocket in it.

Aaron Z