Workhorse Brake Temperature Monitor
This describes a brake temperature monitor I built and installed in my motorhome - a 2004 Sea Breeze LX on a Workhorse W22 chassis.
Why a brake temperature monitor? In the first 36,000 miles of driving this motorhome I had to replace all four brake rotors after three of them developed serious cracks. There have been numerous complaints about overheating brakes and cracked rotors on Workhorse W20 and W22 chassis. An ongoing NHTSB investigation has documented over 650 complaints and over 3,780 unique warranty counts related to the problem. NHTSB has not released any findings but sticking calipers have been identified as a possible candidate.
I remain hopeful for a solution. In the mean-while this monitor will enable me to watch for overtemperature conditions and perhaps shed some light on the cause.
The monitor
is based on digital temperature controllers typically used for things
like industrial ovens. Size and cost is reduced by using just two of
these single-channel devices instead of one per wheel. A programmable
digital timer cycles between the front and rear brakes every 8, 16,
32, or 64 seconds, or switching can be done manually.
Two programmable alarms are available. When the first level is reached
on any wheel an amber LED is illuminated. The second (higher) level
activates a red LED and an optional buzzer. Initial settings are 300
and 400 degrees Fahrenheit. These values will be adjusted if necessary
based on experience.
The controllers run on 120 VAC so an inverter is necessary to provide
power in the RV. 12 VDC is used by the timer module, LEDs and buzzer.
That can be supplied by the RV battery or by an integral converter.
Temperature sensors are commercial Type K thermocouples. They are attached directly to the brake pad backing plates using holes drilled and tapped to accept #10 machine screws. Pigtails are connected to thermocouple extension wire going to a junction box under the dash.
Initial road tests showed that temperatures normally run below 200 degrees F, with the rear brakes 50 to 100 degrees higher than the front. The maximum "normal" temperature observed to date is about 350 degrees, seen on the rear brakes after an exended period of driving in city expressway traffic with frequent braking. In one instance which I believe to be associated with a dragging caliper on the left rear wheel the temperatue reached 450 degrees.
Click on the schematic for a larger image
All of the parts were bought at local stores or online. Total cost was $250 - $300.
| Controllers (2) | Dual Digital F/C PID Temperature Controller | Cold Fusion (eBay) |
| Timer Kit | Timer Kit 1 8 to 8192 s |
Electronics123.com |
| Relay | Relay, 4PDT 12VDC KH | All Electronics |
| Relay Socket | 14 Pin Screw Terminal Socket | All Electronics |
| Thermocouples | Bolt-On Washer Thermocouple Type K | Omega.com |
| Thermocouple Extension Wire | Type K | eBay |
| Thermocouple Connectors | HMPW-K-MF | Omega.com |
Construction Notes For The DIYer:
Thermocouple instrumentation requires special wiring techniques. If measurement accuracy is to be maintained compatible wire and connectors must be used throughout. Soldering, if any, should be done with high-temperature silver solder. I am not able to do that well so used screw-terminal (HMPW series) connectors.
There is a good tutorial on DIY TC instrumentation here . This is an Adobe PDF file.
The monitor described here is probably way too geeky for most people but I am an engineer an enjoy such things. For a simpler solution consider a hand-held thermocouple meter. This one has the ability to monitor and display the temperature of all four brakes simultaneously and to store the maximum value for each one. It is easy to use and reasonably priced. The only negative is that it requires continuous visual monitoring because it lacks the ability to sound an alarm if the temperature gets too high.
For more information please email me at my Yahoo address; davegoss47 (name@yahoo.com).