Troublesome Noise or Four-Alarm Problem?
The Portland Fire Department (PFD) was concerned about a strange rattling noise coming from one of their diesel trucks near the transmission area. Many heavy-duty fire trucks have an Allison Transmission 3000 Series EV (emergency vehicle) model.
The PFD brought the truck in, and although they took it to another dealer, no one could figure out the reason for the noise. With fire season looming, we needed to solve the problem fast.
New Truck with a Nasty Rattle
The truck had 3,000 miles on it. We ran a diagnostic, checking the fluid level, transmission health, and ran a clutch test. The results were normal, but we quickly zeroed in on the power take off (PTO). Specifically, the loud rattle was coming from a spot between the Chelsey PTO and the Allison Transmission 3000 EV. There we discovered the culprit: the builder had installed the wrong PTO gasket. We invited the PFD maintenance supervisor to come on-site and see the issue in person.
Investigating the Source
During the inspection, we recommended removing the PTO and inspecting the gears. The maintenance supervisor approved, so while he waited in the lobby, we removed the cover. On the gear and transmission, large chunks of metal were missing.
A Costly Mistake at the Assembly Factory
When the truck was assembled at the factory, the builder installed the incorrect PTO gasket – a cover gasket. What’s the difference? A PTO cover gasket has a thickness of 0.06 inches whereas a PTO gasket is 0.02 inches thick. This created a 0.04 inch backlash which caused catastrophic transmission failure.
Rescuing the Fire Truck
We updated the maintenance supervisor and recommended that we remove the transmission and go through the entire unit and clear it of any metal shavings that may be lurking inside the transmission. After replacing the PTO, installing the correct PTO gasket, and refreshing the transmission to ensure no metal shavings could cause further damage, we test drove the fire truck multiple times with no rattles or further issues.
The fire department was confidently able to get the truck back into production within three days.
