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Old 09-12-2011, 04:16 PM
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JCL JCL is offline
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That size of trailer will tow very well with a 3.0. I agree that the OE BMW hitch is the way to go. It does not need to be installed by a BMW dealer, but once it is installed coding will be required. That is simply to change a setting in the vehicle so that it recognizes the towing wiring module. That coding will require the dealer, or a shop with specialized tooling. I would get it installed elsewhere, and get the dealer to do the coding, unless the dealer is competitively priced. They usually aren't.

By way of background, there are two types of trailer brakes. Surge brakes have a mechanical application trigger built into the trailer hitch (on the trailer side, not the vehicle side). They work automatically, and no vehicle modifications are required. When the truck slows, the trailer coupling pushes back on the trailer brake trigger. They are not legal in all jurisdictions. They work fine IMO. The second type of trailer brakes are electrically applied. They are controlled by an electric trailer brake controller, which you need to purchase separately from the hitch kit. The controller has two ways of applying the brakes. The first is that when you put your foot on the brakes, the brake lights come on, and that circuit triggers the controller to apply the trailer brakes. The controller is connected to the Lighting Control Module, which controls the brake lights, to accomplish this. The second way is via a manual control that lets the driver apply the trailer brakes separately from the vehicle brakes. In both cases, the controller takes the signal, and feeds electrical power to the trailer brakes to apply them.

You can achieve a clean and safe install with either method. You will likely find that your BMW dealer knows little about trailer brakes; the experts are usually at trailer supply stores, not dealers. BMW has come out with a trailer brake controller for the E70, so it is easier than it used to be. Still, satisfy yourself that they have done the job before.

With that background, the many posts on trailers and trailer brakes may make a little more sense.

Jeff
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