I pulled onto the freeway towing our 25-foot sailboat. I looked in my mirror, and I was shocked to see heavy smoke coming from all four trailer wheels. I quickly pulled to the side of the road, and slowly drove to the next off-ramp. The brake components were very hot, and the wheel hubs were starting to get hot. I inspected all visible brake components, but could find nothing amiss.
The next day I tried towing again to see if the problem would repeat, and it did, with all four wheels smoking. Since the brakes were getting hot before the hubs, the source of the heat must have been the brakes, not the bearings. I inspected all the brake components again, but still did not find anything out of the ordinary. I was stumped.
This was going to require more sleuthing. My trailer is equipped with a surge brake system, with disc brakes at each of the wheels. Determining the cause of the problem was going to require a good understanding of the theory of surge brake operation and the design of the actual hardware installed on my trailer.
After doing some research, I found there is a wide variation in the design of boat trailers and brake systems. Boat manufacturers generally do not make trailers for the boat. Rather, boat manufacturers utilize the many independent trailer manufacturers located throughout the country. Also, there is little standardization of trailer design. Manufacturers usually produce trailers by bolting together components they select from the many component manufacturers, including axles, brakes, actuators, wheels, fenders, lights, bunk boards, and rollers.
Further complicating the picture, not all states have the same legal requirements for trailers. Therefore, retailers may sell a single model of boat with different models or brands of trailers depending on location. As a result, a single model of boat can be paired with a variety of trailer designs and components. Moreover, the amount of information available about a trailer and its components varies greatly by manufacturer.
Surge brake systems are the most common type of brakes used on the 7 million boat trailers in the US. In contrast to travel trailers that ordinarily use electric brakes, surge brakes activate mechanically, operating independently of the tow vehicle brakes. This eliminates problems that water causes with electric brake components when submerging the trailer during launching.
Surge brakes use hydraulic pressure to activate the brakes. The system consists of an actuator/coupler assembly, where the front of the coupler attaches to the ball on the tow vehicle. The back of the coupler has a sliding connection to the actuator, and the actuator is permanently attached to the trailer frame. The actuator contains a master cylinder, which connects to the individual trailer brakes via hydraulic brake lines. The individual brakes can be either drum or disc, similar to a car.
Remind me not to go down a steep mountain road with you. I have never known anyone who lost their brakes like this, and twice? Do you ride the brake? Whoa!
Remind me not to go down a steep mountain road with you. I have never known anyone who lost their brakes like this, and twice? Do you ride the brake? Whoa!
A pendulum brake was a mechanism that attached a wieghted lever to a mechanical brake. When you applied the tow vehichle brake, the pendulum swung down and moved the mechanical brakes into position to rub shoe to drum. It seems there was a pendulum on each wheel and since I was just a kid, I do not really know if it was effective. They were on a light weight trail used to haul a 14' aluminum jon boat.
To Tool_maker: Thanks for the kind words. As far as suspecting the master cylinder early on, I actually did suspect it. But when I checked it, everything looked normal as far as I could tell (with what I knew at the time).
And yes, I was trying to avoid concluding the master cylinder was the problem. I didn't really want to disassemble such a major component without knowing what I was looking for, much less whether I could fix it or replace it. Without the benefit of hindsight, I could not think of what type of defect in the master cylinder could cause the symptoms I was experiencing. And as it turned out, it took a quite a bit of research to find a suitable replacement actuator/master cylinder, and it was a pain to install it on the trailer frame. And it was expensive to boot.
By the way, what is a pendulum brake? I haven't heard of that before. Is it an actual brake mechanism, or a brake controller, or something else?
This post put forth more information than I have ever read in one of these columns and I now know more about trailer brakes than I did before. Well done. However, once you decided that all four wheels were locked, why did you not go immediately to the only thing they all had in common? The master cylinder. It was almost as if you were avoiding the actual problem to find other things you could fix.
Just curious; does anyone know if pendulum (sp?) brakes are still used on smaller trailers?
Once upon a time I used DOT5 on my motorcycles. There's no issue with seals, since DOT5 is very inert and benign compared to DOT4. Everything must be thoroughly cleaned before changing between petroleum and Si-based fluid.
All brake systems collect moisture through the master cylinder reservoir. Since DOT5 is not hydro/hygro scopic, water will pool in the low points, usually the brake calipers. I would replace the DOT5 annually and overhaul the calipers, which would often have signs of corrosion at the bottom part of the piston and bores.
In their wisdom, the government came up with DOT5.1, which is petroleum-based and incompatible with DOT5 ! Talk about setting things up for human error....
To Jim_E, regarding the use of DOT5 brake fluid, it gets complicated. I believe you are correct that DOT5 is silicone based and therefore doesn't absorb water. In addition, it has a higher boiling point than DOT3 or DOT4, which is generally good.
But, the big factor is that silicon based fluids (DOT5) cannot be used for brake systems that are not designed for it, else it will damage the seals. Maybe someone with more specific knowledge about brake systems and fluids can chime in.
To bob from maine, those are good thoughts. My short answer is that since my boat is a sailboat, the trailer components have about an hour to cool after towing before they touch the water due to the time required to setup the boat (raising the mast, etc.). This is unusually sufficient time to reduce the temperatures to near ambient.
Also, I should have made it more clear that the extensive corrosion I found in the master cylinder occurred where the cylinder was exposed to air - behind the piston cup, not the front side where the hydraulic fluid is contained. The only protection the back of the cylinder had from moisture was a rubber boot covering the piston shaft and the back of the master cylinder. I haven't seen any problems (yet!) with corrosion in any parts of the system that are in constant contact with brake fluid.
When you haul a boat on a trailer, the wheel bearings get warm, possibly even hot. When you immerse the trailer into the water, the steel cools rapidly creating a partial vacuum in the wheel hub which draws water into the hub, diluting the grease. Expensive trailers have buddy caps which are spring loaded bearing grease caps that keep the grease under constant pressure during the colling period. The heat that is generated from rolling and braking also heats the calipers. When the brakes are not applied, there is no, or very slight movement of the pistons within the calipers, so when the fairly large caliper cools, it also tends to create a partial vacuum which, depending on the condition of the dust (dust, not water) seals will permit water to come in contact with the piston. The caliper on a trailer wheel is almost always steel and that small amount of water which is potentially ingested every time the trailer contacts water will create corrosion. I am not confident a "professional" would have found this problem within the budget of the boat/trailer owner. It was a good fix though, glad it wasn't me.
I wonder if it would make sense to use DOT5 brake fluid for boat trailers? If I understand correctly, DOT5 brake fluid is silicone based and non-hydroscopic (actually it's hydrophic).
I know that they don't recommend converting normal systems to DOT4, but maybe it would make sense for a boat trailer?
With regards to normal brakes, I have done a few "track days" in my Trans-Am, and once a season would flush the brake fluid. I use ATE Super Blue and ATE Gold for brake fluid. They have a high boiling point and are different colors (one if blue, one is gold) so when flushing the system, you know when all of the old fluid it out.
I've also flushed the fluid on my motorcycles too when upgrading to braided stainless lines.
Well, my 2000 Silverado truck also runs ATE super blue too, since the factory brake lines rusted out (!!!) and I had to install aftermarket stainless lines this year. One of the worst repair jobs I've ever done myself....
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