Have a early 2000 model E-ONE F550 mini pumper/rescue. We currently are having issues with it being very unstable at any speed over say 40MPH. We have weighed the truck and according to the specs on the chassis it isn't over weight. Someone suggested the baffles in the water tank could be broken but we drove it empty and its even worse. Shop says tires are to spec so we are kinda at a loss as to why this truck is so unstable. Anyone with knowledge of this issue would be fantastic. We'll try anything this point as we have to poke this thing to the scene to keep from wrecking it.
New tires? Air pressure? Are the tires from the same manufacturer? I have had problems with new tires with too much air pressure. The truck would just drift across a lane of traffic. How about the steering box? I have had steering boxes almost break off of the frame rail.
Check the tire manufacturer's recommendations for weight and air pressure.
First, check the APPARATUS manufacturer's tire pressure rec. A tire can be mounted on a wide variety of rigs and the tire pressure found on the sidewall is almost always the MAXIMUM pressure for that tire. The apparatus builder has determined the appropriate tire pressure for the weight and intended use of each rig. There are several good articles on-line that cover this subject.
Second, check every nut, bolt, shackle, and bearing. I once inspected a near-new engine and found 3 of the U-bolts that mounted the rear body to the frame were loose.
Also, the steering is power assist. Is there a kinked line, a faulty pump, a loose belt ?
I agree with Tad Check your tire Pressure and did you replace the tires with the same load range as the previous Tires.