If you have not read the thread from the start, I have a 2012
Pacific, 3 axle boat trailer with surge disk breaks on the forward 2 axles. I use this trailer to tow our Nor'Sea 27 sail boat that has a spec of something like 8,600 pounds dry. With gear and fuel aboard I am sure I am a bit over this. BUT, I do drain the fresh water tanks before a tow.

I used the trailer to tow from Guaymas Mexico to the Phoenix Az. Area. https://youtu.be/9FcG4H_dQyQ
We then towed to and from the Napa Valley for a cruise. https://youtu.be/tcat84ORW1A
We then towed to New Orleans for a cruise over to Pensacola Fl. And back to Az. https://www.youtube.com/watch?v=n69SgRyZ2b4&list=PLnA9GMvTHKta6ceNDwrPIsyES050HXvlv

we were towing from the Phoenix area to the Tampa area. A longer trip, but no mountains to cross.

During the week before we departed I checked all tire pressures and we did a complete change of break fluid. This was the 3rd change of fluid. I used a hand vacuum pump to draw the fluid through the system into a quart jar at the break caliper. In doing this, you are advised to use a heavy coat of thick grease around the base of the bleeder fitting in order to block any air from entering the bleeder fitting. I used a bit of grease I had at hand. It was a winch grease. In retrospect this may have added to my problem as it is not a “high temp” type grease. I also did not thoroughly clean all the grease away.

When we first hooked up to the trailer in the storage yard, I did a check of each tire/wheel/brake to look for problems. I used my bare hand to check for any leaks.

After the first 5, then again at 25 +/- miles we stopped and I again checked all components of the system. I felt each bearing to insure I could hold on to it with NO discomfort from heat build up. I found no leaks and checked each disk for even wear. I checked each tire for proper pressure.
NOTE; the tires say to fill to 60 PSI when cold. After running for about an hour at 55~60 MPH, then checking the tire pressure (mid 70's F day), the pressure was up to almost 70~75 PSI. So I removed enough air to bring them all to 55 PSI when cold, the start of the second day.

NOTE: Time & Mile data is from our towing log book.

At the first fill up of the second day, (1007 AM, mile 273355) the right front tire was a bit low. I decided I may have blundered during the morning fill, so added air to get back to 55 PSI. I decided that if it showed low on the next fill up, I would change it out for one of the spares I have along. It did NOT make it to the next fill. I was looking in the mirror just as it parted! (1430 PM mile 273577) So we pulled over and I put on the spares. YES, I used my torque wrench. I know it may not be recently calibrated, but I am no longer working on aircraft or spacecraft. I did a check of all the other items but do not remember anything amiss. We made one more fuel stop that day and everything checked good.

The next AM (0815 mile 273711) did a pre-launch check and all was good, including air pressure and break fluid.

At 11:07 AM, mile 273821 we did a fuel stop and I did my all around touch & feel and ALL checked good.

At approx. 1:40 mile 273927 the brake fire took place. It was the right front caliper ONLY. Once more I was glad I was watching closely! Jill manned a pump water sprayer we keep handy for any need and kept the flames down as I got the fire bottle out. 2 quick squirts and it was out. NO damage to any other parts of the trailer or boat. Not even the brake lines were damaged.

The fire took place after we were in a long line of stop & go traffic. It was maybe half an hour of this and we were just getting back up to speed.

I called Boat US as we have a tow policy with them and it says it covers trailer assistance also! WE LOVE IT!!!!!! I may be a member for life!

Our boat on our trailer is about 12. 5 feet off the ground, so they could not find any assistance that could put our system on a trailer and still go under any overpasses. They found a mobile mechanic to come out to assist us. Once he arrived, he removed both right calipers. The aft one had maybe 10~12 % of the pad remaining. It showed a lot of heat, but no fire. The forward one had 0 % pad remaining. It was down to the metal backing plate. The two on the left had 85~90 % remaining, almost like new??

With the lines tied up, and no brakes on the trailer we went back about 5 ~ 10 miles to the only hotel we could get a spot in. WHO knew all the rooms fill up so fast in mid Texas??

The mechanic took the 2 calipers back to his shop and started a search for replacements. I talked to them on the phone and requested that if he found them, get 4. I wanted to replace them ALL as we were 45 miles shy of half way to Tampa.

The mec found the parts and installed all 4. When we (YES I WAS HELPING ALL THE TIME!) tried/// to bleed the system, we could not get any fluid through it! So, we removed the surge box and it was taken to Magnum Trailers. As we were disconnected any way, we drove to Magnum and went over the box with the mechanic there. We decided to go ahead and replace the master cylinder (a $45 part) and as long as it was open, change out the solenoid shutoff also. We then took it back, attached it to the trailer and...... and....... and.... the brake line would NOT snug up on the solenoid! I called and suggested I tow the 25 miles to the shop. The next day, I did a white knuckle no trailer brake drive. Turns out there are 2 solenoids that can fit, but each has a different output fitting. That difference is almost invisible to the human eye!

They changed out the wrong one, put on a power bleeder and pumped about a quart of DOT 3 through the system! It was now working as new, as MOST of it was NEW!!!

The rest of the trip, I made about 55 to 60 MPH and stopped every 100 miles or so, doing the same checks. We are now in the Tampa area and getting ready to splash for some sailing. As a note, At each fuel stop I check the MPG and it remained about the same before and after the caliper change.

SOOOOO, WHAT HAPPENED? I talked to each of the people we worked with. NONE had a definitive cause that could be verified. But the trailer mec said he felt that I “might” have had a small air bubble in the caliper that burned. As that system heated during the stop & go the bubble heated and expanded to lock that one???
That plus my use of less than high temp grease and not cleaning it ALL off could have added to the problem.

At this point, I do not know for sure. But I can say, that thanks to some good input from this and other forums, before I do another long tow, I plan to purchase the following;
1. A brake fluid test pen. It checks for water in the system and gives a positive feedback.
2. A power brake bleeder kit.
3. A system to remotely read the tire PSI & temp.

One last item, we talked to a couple of people who deal in trailers. NOT in trailer tires. They said that if your tires are over 5 years old, EVEN if they have not rolled 5 feet on a highway, REPLACE THEM. NOT my word, info for you to use as you see fit.

Hope this helps some one to avoid the problems I had.

Greg