Contaminated brake shoes need replacing

Hey there, time traveller!
This article was published 02/03/2012 (5321 days ago), so information in it may no longer be current.

QUESTION: I have a 1999 Ford F-350 dually. The rear brake cylinder is leaking and I am going to replace it. The brake shoes are not very worn, however, they have brake fluid on them. Can I clean the shoes with a cleaner like brake parts cleaner and continue to use them or will I have to replace the shoes also?

ANSWER: Small amounts of contamination on the pads of disc brakes can often be cleaned and the brake pads reused, but contaminated brake shoes on drum brakes must always be replaced. No matter how much you clean the brake shoes, some of the brake fluid will remain in the linings. This fluid will boil out of the brake lining during braking.

Disc brakes allow the contamination to be thrown off, but brake drums trap the contamination and may cause the shoe linings to glaze, which reduces braking efficiency. The brake shoes can also start to “grab” which causes uneven braking and a possible loss of vehicle control during braking.

Don’t take a chance with contaminated brake shoes. Replace them to ensure good brakes. If you are changing the shoes on one side of the truck, replace the other side as well. The coefficient of friction can differ between lining materials, so it is important to always replace both sides even if one side is good. This is necessary to ensure balanced braking.

QUESTION: I have a 2005 Dodge Grand Caravan with a V6 engine. The vehicle also has rear heat. During cold weather (-10C and cooler), there is barely any heat coming out the main vents. The fan works fine and the rear heat generates pretty good heat.

When we drive at speed, either in town or on the highway, there is a reasonable amount of heat. When I take my foot off the gas or come to a stop, the heat diminishes to almost nothing. The difference when it’s really cold outside is very noticeable (according to my wife!) The degree of warm air is like a yo-yo. When I turn the vehicle on to warm it up, I usually leave the heat off because it never warms up inside the van at idle.

Could the problem be the thermostat? I had been told that was likely not the problem as these engines come with a 190-degree thermostat. I hope you have some ideas, because we still have lots of winter left here!

ANSWER: Your wife is undoubtedly correct in stating the temperature drops when you take your foot off the gas. A problem with aluminium engines and fuel injection is that they don’t produce a lot of heat. The aluminium dissipates engine heat to the outside air very rapidly. The fuel injection shuts off the fuel during deceleration so very little heat is produced inside the engine. A lack of heat in the winter can be noticed in passenger cars and trucks, but vans have the biggest interior space to heat and therefore the biggest problem.

The thermostat is the first place to start. If the thermostat opens too soon or sticks open even a little, then the heater works poorly. Test a new thermostat before installing it; I have seen faulty new thermostats many times.

I test thermostats by placing a fine wire in the valve and heating the thermostat in water. Hang the thermostat in the middle of the container and measure the temperature of the water when the thermostat falls off the wire. A candy cooking thermometer works fine for measuring the temperature but it is fragile. A good thermostat should just start to open at its rated temperature and be fully open about five degrees higher.

Another possible reason for poor heating performance is the amount of air passing over the heater core. Most drivers place the heater fan on high when warming up the vehicle, but the interior will warm up faster if the fan speed is set on medium. When the fan is on high, there is so much cold outside air flowing over the heater core that it cannot all be heated. The cold air entering the van forces any warm air out the air exhaust vents at the rear of the van. Place the heater controls in RECIRC mode for faster warm-ups when nobody is in the van.

Finally, a weather-front will help keep heat in the engine while driving so the heater will perform better. This has little effect while sitting still however. There are no magic answers on how to get heat in today’s aluminium engines, but I would try a new thermostat first, and perhaps use one with a 195-degree rating.

Jim Kerr is an experienced mechanic, instructor and member of the Automobile Journalists’ Association of Canada.