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Old 04-29-2016, 03:02 PM   #1
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Tow dolly surge brakes going down hill

I was reading a thread recently about tow dollies and the subject of braking going down hill came up. I rarely tow in the mountains, but when you do and are going down, are the surge brakes of the dolly constantly engaged? Some people had made comments about the brakes overheating in this situation.

It sort of makes sense, the toad & dolly are headed down hill, the coach is coasting, probably engine braking. Why wouldn't this stress the brakes in a surge dolly (like my EZ Tow)? I know I could put the little break defeat plug in, but that sort of defeats the purpose of having brakes on the trailer.

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Old 04-29-2016, 03:22 PM   #2
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I just did 2 days of driving the Blue Ridge Parkway with my surge brake dolly and toad.

A few times, when I stopped, at one of the overlooks, I would feel the the dolly brakes. It is a NON issue !!

I don't have a temp gun, but I could put my hand on the caliper.

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Old 04-29-2016, 04:33 PM   #3
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When we towed with a dolly that had surge brakes going down hills NEVER applied the brakes on the dolly. The coach had to slow so momentum would override the built in safety spring on the surge mechanism before the dolly brakes would apply. Just coasting downhill or using the engine brake on the coach would not cause the surge brakes to apply.
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Old 04-29-2016, 08:24 PM   #4
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When we bought our KK-460 I was also worried about it. Called Demco and they asked if there was a coiled spring in a certain spot. There wasn't so they sent me one. It's job was to stop the actuator from coming on going down hill with the exhaust/engine brake on.
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Old 04-30-2016, 09:06 AM   #5
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The only effect of the downhill is that the coach is braking much of the time, which can trigger the surge brakes (as it is supposed to). If the dolly brakes are overheating, it's only because they are doing their job. However, they are not easily adjustable by the driver, whereas electric brakes can be increased or decreased using the controller at the driver seat. If you know enough to do that.

Like the others here, I think this potential problem is far overstated on RVing sites. Sure, you can have a problem if the brakes are not in proper adjustment, or the surge mechanism is awry for some reason, but generally they should work fine. As with any trailer brake system, it is wise to spot check the wheel temperature occasionally to test for possible overheating, which indicates a brake or wheel bearing problem with the trailer.

This etrailer.com article may help:

Be aware that the same problem occurs with electric brakes unless the controller is set for very low gain. However, doing that prevents the dolly/trailer from doing much braking, which simply makes the coach brakes work harder. Some people always set the electric brake control for very light braking, but at some point that defeats the whole purpose for having the brake in the first place.
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Old 04-30-2016, 06:07 PM   #6
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I spoke at length with UFP, who manufacture trailer brakes including those used on the ACME dolly, about this since last fall when pulling into a rest stop after using the motor to hold back the coach on a long grade just prior to pulling into the rest stop which resulted in extremely hot brakes. Below is a bulletin they sent me. Note that in other threads I did inquire about running aluminum wheels. Note also that the article focuses on boat trailers and the issue of immersing electric brakes, which is not an issue for a dolly.

In general, I don't think it is something to be alarmed about but it is something to be aware of. I plan to keep a closer eye on things this year and apply some of the principals recommended in the below bulletin.

Boat Trailer Brake Operation and Potential Effects of Long/Steep Downgrades

Every time you brake, you create friction between the disc brake pads and rotor. This friction is by design intentionally transferred into heat and can't be avoided. The better the braking, the more heat generated. The ventilating action of the rotors and aluminum wheels on many trailers absorbs and transfers heat very efficiently which helps dissipate heat away from the hub and bearings. However, when brakes are continuously applied, as such can occur on long downgrades, how much heat generation is acceptable (on a long downgrade) is a common question. Idler (non-brake) hubs run at about 180 degrees F during normal towing. Disc brake rotor hubs will run hotter depending on the amount of braking. Temperatures of up to 250 degrees F on the nose of brake rotors are not uncommon on long downgrades. These temperatures, even on the nose of the hub, are certainly too hot for the touch in many conditions. Normal braking temperatures on the rotor surface can be so high as to be only measurable with a hand held infrared thermometer. If you are concerned that the temperature of your hubs may be running too hot, a good rule of thumb is to compare it to the temperature of the front brakes of the tow vehicle.

The first absolute answer is that if your normal towing area includes any hilly areas with anything over a short 5% down grade, your trailer should have brakes installed on all axles. It is unfortunately common for tandem or triple axle trailers to be built with one or more idler (non-braked) axles. Having a combination of brake and idler axles on a trailer may be acceptable for light duty/level ground use, but it is UFP’s strong recommendation that all trailers requiring brakes to have brakes on all axles. Incidentally, trailer brakes on all axles may not be required by your state’s laws but are required in a number of states, and many foreign countries.

Second, most boat trailers are equipped with “Surge” operated brakes. The standard “Surge” brakes apply when the brakes are applied on the tow vehicle and the trailer then tries to outrun the tow vehicle, compressing the master cylinder in the tongue and applying the trailer brakes. In 95% of customer situations, they work extremely well, are simple, and require little input from the tow vehicle driver. The issue arises when a customer travels in a location with long downgrades of several miles, and say a 5% or greater grade. In that case, if the tow vehicle is downshifted at the top of the summit to use engine braking down the grade, and the trailer brakes are automatically and continually applied by the surge actuator on the trailer tongue, the effect is the same as riding your vehicle brakes all the way down the hill. Eventually the brakes will overheat.

This issue can be handled in most cases by the tow vehicle driver using the following procedure:
1. Decelerate to a slower speed before cresting the hill.
2. If using engine braking when coming down the hill, every half mile or so, accelerate the tow vehicle slightly away from the trailer so the trailer brakes are released.
3. The ventilated disk brakes will cool right down and the brakes can then be reapplied.
4. Continue down the hill a half mile with the trailer brakes applied, and then repeat the trailer brake release procedure.

Assuming your trailer has brakes on all axles/wheels, and the above operating procedures are being followed, in the majority of cases, downgrades will not be a problem. However, if the terrain in your area still creates a concern about heat buildup in the brake system, then the question becomes whether to use the standard “Surge” applied hydraulic disk brakes, or to upgrade to an electric over hydraulic brake application system to allow total control of the trailer brakes from the tow vehicle cab. We generally do not recommend the use of fully electric drum brakes (like a camping trailer) for the marine (boat) trailer application, as the electric components in the drums may work ok in fresh water, but are subject to rust during storage after marine use. Fully electric brakes do allow independent control of the trailer brakes from the cab, but are not the best solution.

Thus, if steep grades in your area are common, or are such length and level of descent that the above apply/release method is neither desired or adequate, an electric over hydraulic system is suggested. Electric over hydraulic is typically used in the Rocky Mountains in the western US, for example, or on heavier trailers (over 12000 pounds gross weight) in less hilly areas. With these setups, a fixed non-braking coupler is installed on the trailer tongue. The electric over hydraulic pump unit is a very high speed hydraulic pump that can generate 1000 psi of hydraulic pressure in a fraction of a second. It is turned on and off by the electric brake controller in the tow vehicle. The system includes the pump, a set of backup batteries, and a “breakaway kit” if your trailer was to come uncoupled from the tow vehicle. There are several Electric over Hydraulic pump units available in the marketplace. UFP is most familiar with the Titan EHB unit. In addition to the components above, the Titan unit uses a signal converter box on the trailer to work with Ford/Chevy in cab controllers. The Titan pump unit is “water resistant” but is usually installed by the trailer manufacturer on the trailer tongue, sometimes on a small pedestal to keep it out of the water when launching. The installed system then gives you the benefits of ventilated hydraulically operated disk brakes, but total control of the trailer brakes from the truck cab. The brakes are either directly applied by the electric brake controller when you press the foot brake in the truck, or sometimes can be applied alone with a lever on the brake controller (in the unusual case of needing to straighten out a skidding truck/trailer on snow or ice).
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Old 05-04-2016, 04:18 PM   #7
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Originally Posted by Mr_D View Post
When we bought our KK-460 I was also worried about it. Called Demco and they asked if there was a coiled spring in a certain spot. There wasn't so they sent me one. It's job was to stop the actuator from coming on going down hill with the exhaust/engine brake on.
You know, I should have said this: " It's job was to stop the actuator from coming on too soon or too hard going down hill with the exhaust/engine brake on.

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