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Old 12-17-2013, 01:40 PM   #1
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A possible solution for the Hensley "bump"

A cheaper solution to changing tow vehicles or hitches to stop the Hensley bump actually exists. I learned the following talking to an electrical engineer at Tekonsha today.

I used a Tekonsha Prodigy RF brake controller bringing the 2013 25FB International Serenity home from the selling dealership using my Mercedes as there was no easy way short of removing the complete interior to get a brake controller installed.

There are two parts to the unit. The actual brake controller mounts onto the street side of the trailer A-frame. It has a seven pin cable to plug into the tow vehicle socket. The trailer seven pin cord plugs into the brake controller. Inside the brake controller is also an accelerometer.

Inside the vehicle, one plugs the cigarette pack sized remote control into a 12Vdc power socket like you would a CB or cell phone charger. No other wires are attached or altered to or in the towing vehicle. This is NOT a Bluetooth device so will not interfere or be interfered with by these devices. In addition to programming the brake controller, it also has a slide switch for manual application of the trailer brakes with increasing force as the slide is moved. The remote control can be placed wherever the driver wants for easy access instead of feeling for the factory brake controller slide switch somewhere below the driver's left knee cap on my Dodge.

The Control head interrupts the brake signals coming from the tow vehicle and generates it’s own brake signals to the trailer. The trigger for the brake controller is when the TV brake lights come on. This is the important point.
Those lights come on when the brake lights micro switch opens within the first ½ to one inch or brake pedal travel and BEFORE the tow vehicle brakes get energized.
Thus the trailer brakes can be energized first even before the tow brakes come on.

The hand held remote control can set the brake controller into enhanced mode and the accelerometer can sense deceleration from the diesel engine brake and apply the trailer brakes as well.

This action can help preclude the side lateral movement of the Hensley hitch head to it's stops (thus generating the bump) on one side of center or to the other side when under deceleration from the tow vehicle and before application of the trailer brakes which has been an issue on some recent model Dodge Ram 2500 pickup trailer brake controllers.

The Tekonsha Prodigy RF brake controller was on Amazon today for around $308 versus the suggested retail of $400.

I plan to install my existing Tekonsha Prodigy RF unit when the new trailer gets here and try it out. Nothing to loose at this point.
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Old 12-17-2013, 01:58 PM   #2
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Very interesting, and please keep us informed on how this controller performs.
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Old 12-17-2013, 02:16 PM   #3
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Does the Ram factory controller use input from the brake light system? We've not had the "bump" with our ProPride and 2012 Ram 1500 using the factory controller. I don't even know if it uses an accelerometer, which may have a slight delay.

I also wonder of the trailer brakes were not evenly adjusted, or worn, for whatever reason, if that could pull the trailer to one side slightly causing a "bump"?
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Old 12-17-2013, 02:17 PM   #4
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The Tekonsha Prodigy RF worked well on the Mercedes and I never felt the bump. I have felt the bump with the Dodge with the factory controller, but was unaware initially as I thought the Hensley was wearing in since it was relatively new in terms of miles of use.

The new trailer gestation is 9 to 15 January. I have to wait until the 27th of January when I return from the factory build trip or mid February to try this out as I have to await the delivery of the new unit to Arizona from Jackson Center. I will be out of Arizona the first few weeks of February.
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Old 12-17-2013, 04:14 PM   #5
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Do you still have proportional brakes proportional to the deceleration of the TV? Do the brakes come on just a little when the brake light switch makes contact and then get stronger as you brake more? I do not have a Hensly so I do not care about the bump. Thinking about one of these because the current controller(the cheapest Tekonsha) on my Dodge is mounted by my knee also and I know I will never find the lever if I really need it. I am going to replace it but not sure yet with what.
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Old 12-17-2013, 06:03 PM   #6
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You don't have to go to such lengths to avoid the Hensley bump. It's simply a matter of setting the trailer brakes to be a bit more aggressive. With the Tekonsha Prodigy (non-RF version) you add some "boost" in and the dial in the correct max voltage. My combination (Mercedes GL, Hensley, Safari Bunkhouse, disc brakes) works well at about 10.0 volts max with Boost Level 1.

The point is to get the trailer to "lead" the tow vehicle enough that in normal braking the trailer isn't able to push the tow vehicle. The bump occurs when the trailer brakes less than the tow vehicle, which is not a good thing anyway.

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I used a Tekonsha Prodigy RF brake controller bringing the 2013 25FB International Serenity home from the selling dealership using my Mercedes as there was no easy way short of removing the complete interior to get a brake controller installed.
Switz, I think you also got bad info from the dealer about the installation of a brake controller. This is common. I guess MBUSA hasn't done a good job of educating their dealers about towing issues, because my local dealer said something similar when I asked about a brake controller. The Service Mgr actually wanted to remove half the interior to run a dedicated power line from the battery (under the front passenger seat) -- at a cost of $1200!

The truth is that there's a simple pin kit sold in the Parts Dept that costs about $15 and allows connection of a brake controller quite easily. I had the Tekonsha Prodigy installed with this kit at a local RV dealership for about $100 in labor, and it's not that hard of a DIY job either. Mercedes even publishes the procedure, so any dealer should know about it. See attached TSB.

If you've got a driver's side knee airbag (like mine) then you need to fabricate a little mount for the Prodigy so it can mount on the dash at the correct angle. I made mine out of a little piece of cherry wood and double-stick tape.
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Old 12-17-2013, 06:27 PM   #7
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I've never experienced the Hensley bump with my setup. I use a Prodigy II controller, braking a 34' triple axle trailer.
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Old 12-17-2013, 06:55 PM   #8
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My 2007 ML 320 CDI was built in October of 2006 as one of the first (to America's knowledge) diesel versions released and the first at the Indianapolis Mercedes stand alone dealership (they hd been made at the Alabama plant with diesels for the rest of the world since the design was first made). The connections for the brake controller were all in the right rear of the car. After the first three months of production, the required cables were routed to the driver's wheel well. And yes, I saw the "kit" but the wires would all have to go to the front requiring interior removal for a proper job.

Thus the use of the wireless brake controller from Tekonsha which worked well.
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Old 12-18-2013, 09:45 AM   #9
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I find the 2-speed setting on my Direclink controller quite helpful in controlling the Hensley bump...supports fine tuning the braking force at high and low speeds.
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Old 12-26-2013, 11:07 AM   #10
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I have a 2010 ram 2500 with 3p hitch - have only drove the Tv/TT a couple times now and can only produce the bump at low speed heavy braking

I've had decent success at preventing it with controller set higher bit have not had a chance to fiddle much with it but plan on doing so soon before canopener rally coming up

I'm hoping my adjusting the controller alone will do the trick but so far it seems the low speed heavy breaking reliably produces some lateral play with the TT - which I presume means the controller not telling TT breaks correct timing and magnitude of breaking and/or some setup issue of the hitch itself...

Keep us informed Switz et al
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Old 12-29-2013, 08:27 AM   #11
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"brakes", not breaks, please

How does the electrical circuit for brake lighting initiate. A contact switch (as in the old days) or . . . .?

.
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