#1429: Click and Clack Vs Electric Brakes

Jul 19, 2014
This week on Car Talk, can Tom and Ray help Paul fix the electric brakes on his cattle trailer? Will the fact that they’ve never even heard of electric brakes stand in their way? Of course not! Elsewhere, Kate can’t get her mechanic to take her Acura’s brake problem seriously, and Alice and her husband can’t agree on whether to take the high road or the low road to go visit their daughter. Also, Marian’s truck is having trouble adjusting to life in Cleveland; Army Captain Rob may have to go AWOL to get out of a Summer road-trip with his in-laws, and should Erin ease her husband’s descent into Minivan Land by letting him keep his BMW? All this and more, this week on Car Talk.

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As Read on Car Talk


electric brakes

As a long time listener, this is probably the third time in as many years as I've heard Tom say he has no idea how electric brakes work. This is the simplest explanation I can offer. Imagine the trailer has drum brakes with an emergency brake cable and handle that come up all the way to the car. When you step on the car brakes you simultaneously pull the handle to give pressure to the trailer brakes. Now, take away the handle and the cable and replace the cable mount inside the drum with a pivot arm with a small electromagnet mounted on. The handle in the car is replaced with a DC servo control that is connected to the vehicle brakes. The servo gives a varying amount of DC power to the electromagnet. The magnet then starts to cling to the inside of the steel drum, providing resistance and pushing the pads out to slow the trailer. The servo provides varying power so that you are not just turning the magnet on full and totally locking up the wheels. There is no motor drive, as Tom suspects, it is magnetic driven. It sounds like Paul either has a blown bulb (as Tom said) or a loose ground wire and the magnet is grabbing when the signal flashes because the circuit is looking for a replacement ground. Hope that helps!
Favorite Moment: 

Break problem

A second thought. Had the same problem even changed out the master cylinder and problem continued. Problem turned out to be o rusted bolt along the break line that was heating up the break fluid making it appear to be the master cylinder. Mechanic had never seen in 25 years.
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Can't cha help out ol Paul?

Looks to me like Paul has wired the trailer brake wiring to the parking light wire instead of the brake light wire. Have Y'all thought to have an occasional guest mechanic to help to the guys solve some car problems?
Favorite Moment: 
Correctly guessing that a retired engineer was involved with the last call.

Take the high road or the low road

Alice and her husband should get themselves a hybrid car that puts the breaking energy back into the battery. Then they should definitely take the shorter high road over the hill to visit their daughter.
Favorite Moment: 

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