By Chuck Aulgur
The material presented on the following pages represent the design of a surge brake system that I designed for our 1990 Geo Tracker. General Motors Corporation has not approved this system for use on their Geo Tracker Vehicles, nor has D. O. T. or any other State or Federal Agencies approved it for use on public highways. The design is presented for information only, to show how such a surge brake system could be used on a Geo Tracker. You are free to use this information in any way you want, at your own risk. I make no guarantee that this information is correct and what you do with this information is totally your responsibility. Just keep in mind, if you are involved in a serious accident, and it is shown that your vehicle brakes have been modified and not tested or approved to meet D. O. T. guidelines, you are opening the door for potential Legation. Same as when you modify the OEM brakes on your GMC. For my own protection I Cary very high liability insurance.
The drawings for this design are located at:
The Geo Tracker, which is the GM version of the Suzuki Sidekick, is designed such that it is very easy to adapt a Surge Brake System for towing.
The Geo Tracker has a hollow tube crossmember at the front of the vehicle frame. A round metal plug is placed in each end of the hollow cross member tube. The welded base plate assembly is bolted to these two plugs, which act as a bearing, to allow forward and aft rotation of the base plate.
The air shock is pressurized to hold the assembly against the forward towing position stops. When the brakes are applied on the tow vehicle (GMC Motor Home for my Tracker), the tow bar bushes back on the base plate, causing it to rotate aft against the force of the air shock. The aft rotation pushes back, via an adjustable linkage, on the bottom of the brake lever on the side of the vehicle frame. This aft rotation of the base plate causes the top of the brake lever to move forward, which applies the Tracker brakes via a linkage connected directly to the Tracker brake pedal.
The sensitivity of when the Tracker brakes are applied is controlled by the amount of air pressure in the horizontal air shock. The shock absorber dampens the motion of the braking system to prevent any rapid application or releasing of the Tracker brakes. With about 70 psi in my air shock, I can do light braking on my GMC without the Tracker brakes being applied, and the Tracker brakes will not be applied when coasting down steep hills. Any more than light braking of my GMC will cause the Tracker brakes to be applied and the harder I brake the GMC the harder the Tracker brakes are applied. The aft rotation of this surge brake mechanism is limited by adjustable stops to control how much force is applied to the Tracker brake pedal. I use an electric vacuum pump on the Tracker so the power brake system is functional, same as when driving.
The forward linkage rod is adjusted so there is no slack in the chain links connecting to the brake pedal, with the base plate in the forward "towing" position. The aft stops are adjusted by having someone push on the tracker brake pedal as hard as they can (with vacuum assist) while the braking mechanism is manually rotated aft (no air in the shock) to where all the slack is out of the chain links. The chain links allow the Tracker brakes to be applied when it is driven, without being affected by the surge brake system. There is only one task that has to be done when connecting the Tracker for towing other than the normal function of connecting the tow bar, safety chains, and electrical plug. The additional task is checking the pressure of the air shock (I have a pressure gage located behind the Tracker grill that is permanently connected to the air shock).
The beauty of this system is that is a totally mechanical system, using direct mechanical linkages, with no electronic components, hydraulic hoses, or other widgets that can fail. And there is nothing that has to be done when connecting or disconnecting other than the normal functions of connecting a tow bar. If the air shock fails the Tracker brakes will still be applied. The base plate tow bar connection points can be positioned to attach any of the modern tow bar assemblies that stay connected to the rear of the tow vehicle.
The front frame configuration on the 1996 and later Trackers were modified slightly, however, this same surge brake system can be modified to work on them by making the cross bar and the two vertical end bars slightly longer to mate with the revised frame and lowered bumper facade. They also welded a strap across the end of the round hollow frame cross member, to support the bumper façade. This bracket has to be removed, and the facade support modified, so the rotation bearing plugs can be installed. The affects of this change can be adjusted out by slightly increasing the pressure in the air shock.
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