"Vegascpl" presented a question about the use of a RoadMaster braking system on his 2006 Ford Escape Hybrid in the "Physics of Towed-Vehicle Braking" thread. This is an important topic to be sure, but in an effort to keep the afore mentioned thread devoted to generic towed-vehicle braking, I have started this new thread.
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">
...I'm now thinking about the Roadmaster which is similar and installed for about the same price as the purchase price of the SMI. http://www.roadmasterinc.com/product...r/brake_m.html
Anyone have any experiece with this system?
Thanks for the information on the thread. It convinced me I should add a breaking system.
2005 Dutch Star 40' 4 slide
2005 BMW K1200LT motorcycle on lift
2006 Ford Escape Hybrid </div></BLOCKQUOTE>
I would caution you not to use a RoadMaster system on your Escape Hybrid. They (RoadMaster) implicitly tell you NOT to use any of their braking systems on this vehicle. Here is the link Roadmaster Vehicle Guide
. Select you vehicle in the top of the page and click the "Braking System" tab in the middle of the page. Here is what it says...
The following information relates to the installation of the supplemental braking system selected above.
Every reasonable effort has been made to verify the accuracy of this information; however, ROADMASTER, Inc. does not warrant its accuracy and disclaims liability for any claims or damages which may result from errors or omissions.
At This time there is NO braking system for the H3 Hummer, the Lexus GX470, any Ford Escape Hybrids or Mercury Mariner Hybrids.
The bottom statement is a little misleading. There are braking systems available for all of the vehicles, just not from RoadMaster. I have personally installed many of our systems, both Air Force One and Stay-IN-Play, in all of those vehicles; and have heard nothing but 100% positive feedback. Why does SMI work? SMI systems are designed to work a vacuum-assisted brake pedal at a little over half boost or a hydra-boost pedal at no boost. Your Hybrid has hydra-boost brakes. Here is the difference in the two configurations.
Vacuum-assisted braking decreases the pedal effort of a vehicle by using a lack of atmospheric pressure generated by the engine to assist in moving the hydraulic fluid from the master cylinder to the brake calipers/drums. The vacuum level in the booster varies depending on the vehicle, the RPM at which the engine is running, and the load on the engine. An average value is ~20 inHg. SMI systems are engineered to operate the brake pedal of the towed properly at 12 inHg. A fully boosted vacuum pedal would be next to impossible to properly modulate, and would greatly amplify any user error.
Hydraulically boosted braking (or hydra-boost) decreases the pedal effort of a vehicle by the use of hydraulic pressure (similar to power steering). Typically this pressure is attained from the power-steering pump, although some newer vehicles (H3, Vue Hybrid, Escape Hybrid) use a completely separate hydraulic system.
Why do the SMI systems work the same in both applications? What is the difference?
A vacuum-assisted pedal is very stiff when it is not energized because the pedal is actually fighting air pressure (from compressing the brake booster which is now at atmosphere) and braking fluid pressure. A hydra-boost pedal does not have the resistance of the brake booster, and it takes 60-70 full depressions before it is completely "unboosted." This is why RoadMaster (designed to ram a dead vacuum pedal) has this disclaimer stating that they do not work on hydra-boost brakes. The system would burn the brakes (and tires eventually) off the car in no time.
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