HDX School Bus Tips

imported_John Whelan - March 23, 2014

Thomas HDX School Bus Tips and Advice

I want to share some areas of the HDX Thomas school bus that our shop has experienced that you may have already dealt with or have not seen it happen yet. They are a very comfortable bus to drive mainly because of the engine weight in the back end that smooths out the suspension even more which is a Neway air bag system.

Another plus with these models is the driver visibility using the mirror system. These buses are very easy to spot because of the extended drop mirrors that they have designed that gives the driver excellent vision. Highway driving is ideal... you just have to glance back and forth to each side. One disadvantage is driving in congested traffic in the city making a turn.

Drivers need to be very aware of pedestrians being blocked out by the mirror body hanging down in front of them. Also these mirrors are less than six feet from the ground so I hit my head on them many times when we first got them. My mind is fully aware of them now :) The following content covers areas that will give you important information on the Thomas HDX school bus.

Navigating The Electrical System

Knowing where the electrical panel is and how to navigate it will help you troubleshoot problems. The access door is below the driver's sliding window and has an electrical diagram that will show you where the fuses and relays are located and what circuits they control.

The LED lights are very useful on the panel. The amber LED indicates there is ignition or battery power getting to the relay while the green LED tells you there is power getting to the load. This could be a heater motor, Loading light or signal light. This panel runs mainly the body electrical accessories.

Avoiding Radiator Failures

The radiators were failing on a regular basis because of debris (mainly rocks) getting in to the rad core area. The turbulence inside the shroud from the engine fan would cause the rock or anything else to damage the radiator core. One major service call told us we had to make an improvement.

The radiator is mounted transversely from the engine so it is sideways related to the rear drive axle tires. Everything that gets kicked up from the highway is liable to get into the core area. In the video you saw the mudflap addition in front of the radiator. This has really helped and we have had no problems since then.

Main Body and Chassis Battery Power Switch

In certain HDX models we were experiencing battery power failures because of a main power switch mounted along the frame. It is turned on from the ignition and supplies the body and chassis battery power. It's location was not convenient nestled inside the frame beside the transmission.

Thomas bus came out with an updated control switch that solved the problem so the work to replace it was well worth it. There have been instances where the switch would either go dead or turn power on by itself. This is something that had to be addressed with quickly being the main power source.

Vehicle Interface Module

The VIM is mounted above the steering axle so it caused problems with some of the HDX accessories due to corrosion building up inside the module. Circuits would run on their own without switch activation. For instance the back up lights were coming on by themselves because the connection inside of the VIM which runs accessories that are linked to the transmission.

These accessories are the exhaust brake, B/U lamp and high idle circuits. The only way to fix this problem is to replace the VIM and insulate the metal cover that protects the modules. Thomas recommends the insulation spray foam that is used for the home. It has to be used conservatively so the modules can still be worked on.

Rear Emergency Window Wiring

The original wiring from the factory caused the window alarm to come on when ever moisture was around the ground terminal on the frame. We ended up using the old “Vandalock” switch assembly to ensure that this problem would not occur. The window has to be removed to replace the wiring and run new wiring to the Vandalock switch.

This was a regular fix when ever a new HDX cam on the lot and worked for us every time. However I heard there is an electrical harness with a diode or something attached to avoid this problem. The Freightliner bus dealer should know about this and it would be worth it to contact them to save you the work we went through.

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