Motorhome Maintenance with Mike (PT.7)

If you own a coach with a retarder you likely already know some or all of the benefits that come with the device. The main one is: the ability to descend a grade without heating up or possibly overheating your service brakes. Hot brakes are less effective than cool brakes and the hotter they are the less effective they become, ultimately to the point of being incapable of stopping the vehicle. Proper use of the retarder should eliminate that dangerous and harrowing experience.

Getting acquainted with the amount of drag your retarder is capable of is important, so are your driving experiences using the retarder. 

Here's why: Steepness and length of grades varies. At the beginning of a grade that requires the engagement of the retarder you, the driver, must determine at what speed you will be able to safely descend. Steeper grades require slower transits, therefore more retardation and/or lower transmission gear selection will likely be required. Once you have mentally set this desired speed it becomes the drivers job to select the amount of retardation that does not allow the coach to build speed too rapidly. The object is not necessarily to maintain a certain speed but to prevent the rapid increase in speed.

Let’s say that you have determined that 45MPH would be a comfortable speed on a particular decline. You slow the coach to 40MPH, select the degree of retardation that you think will hold you and then you see how long it takes to get back up to 50MPH. If that happens very quickly, select more retardation or downshift to the next lower gear. If it takes a good while to get up to 50, apply the service brake and slow yourself back to 40. You are set about right. Once you find this sweet spot, don't change the settings when you come to that level spot or a climb before the next drop in elevation. Just either turn the retarder switch to "off" or push the accelerator pedal. That way you can regain your setting when the next descent comes.

In the same scenario, if your coach won't get above 40 or slows below that speed when you first select your settings, select less retardation or a higher gear.

It's ok to use your service brakes in conjunction with the retarder. You just don't want to be using them so much that they get hot and lose effectiveness. You want to keep full braking capacity in case you need to make a panic stop. Retarder use also extends the life of your brakes dramatically. Brake shoes, pads, drums and rotors don't like heat. Remember that speed equals heat. Keep the speed down.

Some types of retarders are also affected by speed/heat. Transmission retarders will heat the transmission fluid and in extreme use can destroy the fluid and the transmission right along with it. Most coaches that have transmission retarders have a transmission temperature gauge. If it indicates an overheating condition it will be necessary to select a lower retarder setting, downshift to a lower gear or a pull to the side of the road and fast idle until the temperature is reduced to a safe level. Coaches with engine compression release "Jake" brakes will not have this issue but are slightly less effective. Exhaust brakes fall into the latter category also and are less effective still. There also is the rarely used driveline retarder. In effect a huge, heavy electromagnet that has been installed in the drive shaft. If it gets too hot it will require lubrication.

With the use of these common sense practices all of these retarders, at times, used in conjunction with transmission gear selection, can bring you and your coach down the scariest mountains with you and all of your hair still intact.