School Bus Hendrickson Suspension

Twenty years ago the suspension on a school bus was solid leaf springs which worked well but since the introduction of air bag suspension the ride has greatly improved. The rear suspension on the bus in the video is manufactured by Hendrickson International who have been in the suspension business for many decades.

I can remember the days when I was an apprentice cutting out or burning out walking beam bushings on highway trucks working the northern BC oil patch. It was a very stinky dirty job that had to be done so the junior mechanics always got the job. It was a rite of passage job for an apprentice mechanic back in those days.

The suspension on the bus in the video caused premature tire wear due to worn bushings on the main support members. The tires were scuffed and badly cupped costing us over 800.00 for recap tires. The next step is to replace the bushings and take the bus to an alignment shop. This all started when we received a call from another school district who were in town for a field trip. They noticed this bus was dog tracking and angling off of the road.

The misalignment doesn’t allow the drive axle to run in a straight line fighting the steering axle and doing nasty things to the tires. Once we issued a spare bus to the regular driver we brought the dog tracking bus into the shop and measured the distance between the center points from the steering axle to the drive axle on both sides. The difference was 1 1/2 inches.

This style of air bag suspension has a lot of great features. There is a torque rod that is bolted laterally from the differential to the frame that controls lateral forces while cornering increasing stability. Adjusting the the alignment has changed from torque rod shims to concentric washers that just need to be rotated one way or the other. It’s fitting that this new technology is called ‘Quick Align’.

The nice thing about air bag suspensions is the ride height adjustment while driving which compensates for load changes. The height control valve keeps the air bags at the best level for comfort. To this date I have never seen an air bag fail outright. Only air bags that showed signs of weather checks have been replaced.

The old school suspension days are gone with rock hard spring packs that had very little give. They worked for heavy loads but did not ride the best when the vehicle was empty. Once we get this suspension repaired and aligned I can see more of these jobs coming. There are many more buses with the exact same specs that will inevitably come due for repair as this bus did.