2009 Thomas Built Buses Saf-T-Liner C2

On June 18, 2019, the Office of Defects Investigation (ODI) opened PE19-007 to investigate instances of leaf-style suspension springs fracturing in various model 2008-2018 Thomas Built Buses (TBB) school buses, which could lead to a road hazard if a piece of the leaf spring detaches from the vehicle while driving. This investigation was prompted by ODI’s review of field reports in Daimler Truck North America's (DTNA) Early Warning Reporting (EWR) data, describing cracked rear leaf-style suspension springs in Thomas Built school buses. ODI contacted three municipal school bus fleets with subject vehicles. These fleets described similar failures where a fractured piece of leaf spring separated from the vehicle while driving. In addition, ODI contacted a nationwide school bus transportation service provider who identified several failures of this component. DTNA’s response to NHTSA’s Information Request (IR) in this investigation acknowledged that TBB school bus leaf springs may corrode and fracture. DTNA data provided in response to the IR did not show a high frequency of failures that result in portions of a cracked leaf spring detaching from the vehicle.In the response, the majority of the information concerned C2 springs. While the C2 represents approximately 71% of the sales, 136 of 141 warranty claims (97%) were for C2 buses, and 94% of all of the replacement parts sales were for C2 springs. In 2021, DTNA retained Exponent to assess reports of rear leaf spring fractures on TBB C2 school buses. As part of its assessment, Exponent inspected in-service buses and leaf springs, conducted material and metallurgical analyses of exemplar leaf springs, and analyzed manufacturer- and fleet-generated claims data. Exponent concluded based on its assessment that DTNA’s leaf springs are typical for the industry and within DTNA’s specification, and it found a low frequency of a cracked leaf springs detaching from vehicles. Exponent also asserted that it could not confirm any instance of detachment while driving, resulting in roadway debris. In 2022, in response to NHTSA’s ongoing investigation, Exponent conducted additional analysis of the metallurgical characteristics of new and used (in-service) subject leaf springs and reviewed data from a major nationwide school bus transportation provider that had obtained leaf spring replacements. Similar to its initial findings, Exponent determined that the leaf spring material specified by DTNA is commonly used for leaf springs and adheres to industry-adopted standards. Exponent’s metallurgical analysis also showed that DTNA’s springs are coated with a corrosion inhibitor. Exponent’s failure analysis of fractured leaf springs found that the fractures were due to fatigue crack initiation and growth, a common fracture mode for this component. Exponent’s inspection of in-service leaf springs found surface corrosion within the expected range. Exponent also found that corrosion pitting may play a role in fatigue crack initiation. Exponent’s analysis of DTNA warranty data found one claim in which part of the leaf spring was described as missing. Based on NHTSA’s investigation, including its careful review and assessment of the analysis provided by DTNA’s consultant Exponent, there is insufficient information at this time to conclude that a defect results in detached leaf springs creating a hazard for other roadway users. However, ODI does acknowledge that most roadway users encountering this type of debris would not know what it was or where it came from. For reporting purposes, using roadway debris as a measure could result in this issue being under-reported.  Additionally, leaf springs are generally considered wear components that need routine inspection. If signs of corrosion or fracture are present, leaf springs should be immediately replaced. During NHTSA’s investigation, DTNA did share messaging with school bus fleets reminding them of the importance of routine and required inspection of school bus wear components, including leaf springs. Considering the nature of this component and available information, including the metallurgical analysis of DTNA’s in-use components and low rate of broken or missing leaf springs for the subject population, this Preliminary Evaluation is closed. The closing of this investigation does not constitute a finding by NHTSA that a safety‐related defect does not exist. The Agency reserves the right to take additional action if warranted by future circumstances.

The Office of Defects Investigation (ODI) received a complaint alleging brake fluid loss caused by a ruptured brake line that had chafed against a wire harness in the engine compartment of the complainant?s vehicle.It was determined that the chafing was caused by contact between the convoluted tubing covering the fuel supply line and the metal brake lines.This issue only affects units with a Caterpillar (CAT) C7 engine and a fuel water separator mounted in a specific location on the frame rail.Not all units with CAT engines were equipped with fuel water separators, but all units with CAT engines and a fuel water separator have them mounted in the same location.Units with other engines have a different fuel supply line routing and are not affected by this defect.Daimler Trucks North America (DTNA) submitted a recall notice on 18 October 2011 involving seven-hundred (700) model year (MY) 2005-2009 vehicles.In its notice, DTNA provided an explanation that MY2010 vehicles were not built with CAT C7 engines and, that of the model years that were built with C7 engines, only 700 had fuel water separators.All 700 such vehicles are included in this recall.DTNA's announcement of a safety recall addresses ODI's concerns.The recall remedy involves replacement of any damaged brake lines and rerouting as needed.This investigation is closed.The ODI report cited above can be reviewed at www-odi.nhtsa.dot.gov/owners/SearchNHTSAID under the following identification (ODI) number: 10383939

This investigation was opened after ODI was contacted by a fleet alleging that in certain situations, such as a light brake peal application during a low speed operation, the brake lamps fail to illuminate on the rear of the bus.ODI confirmed the problem with two fleets.On April 29, 2010, Daimler filed a defect report concerning this issue. The stop lamps may be intermittent during light brake applications.They are still evaluating the remedial program and will furnish this information to ODI when it is available. This safety recallresolves the issue raised by this investigation. Hence, this investigation is closed.

This investigation was opened after ODI received a complaint from a school bus fleet stating they had experienced warning lamps failing upon opening the front entrance door. After completing their evaluation, Daimler Trucks North America, the parent company of Freightliner and Thomas Built Buses, decided to conduct a safety recall to replace the reed switch on the front entrance door with a more robust switch. All repairs will be made by Thomas Built Buses dealers and direct warranty customers. The action taken by Daimler and Thomas Built Buses resolves this investigation. Accordingly, this investigation is closed.

THIS SCHOOL BUS USES A PLASTIC ELBOW TO CONNECT A COOLANT LINE TO THE REAR HEATER INSIDE THE BUS. THE ELBOW IS CRACKING AND OR FAILING WHICH ALLOWS HOT COOLANT IN THE BUS BODY INCREASING THE RISK OF INJURY TO THE PASSENGERS. THE BUS IS GENERALLY IN MOTION AND THE HEADER ON WHEN THE FAILURE OCCURS.*DT

NHTSA ID

11171958

Incident

Jan 24, 2019

Mileage

190,664 mi

THIS SCHOOL BUS USES A PLASTIC ELBOW TO CONNECT A COOLANT LINE TO THE REAR HEATER INSIDE THE BUS. THE ELBOW IS CRACKING AND OR FAILING WHICH ALLOWS HOT COOLANT IN THE BUS BODY INCREASING THE RISK OF INJURY TO THE PASSENGERS.. THE BUS IS GENERALLY IN MOTION AND THE HEADER ON WHEN THE FAILURE OCCURS. *DT*JB

NHTSA ID

11171951

Incident

Jan 23, 2019

Mileage

171,651 mi

Service Solution for C2 Window Retrofi t (New StyleWindow in Old Style Bus)

Warranty Information letter announcing that DTNA is increasing the Standard Diagnostic Times (SDTs) shown. The updated after treatment system (ATS) diesel exhaust fluid (DEF) pump times will be applied to repair orders opened on or after April 12, 2021.

Thomas Built Buses Service Bulletin for Axle Flange Gasket Replaced with O-Ring. Daimler Trucks North America has released a new axle shaft to hub rubber O-ring (part number 11-30728-000) as a replacement for the paper gasket (part number 11-14418-000). The new O-ring will provide better sealing and is reusable. It is quicker and easier to use compared to the paper gasket, because using a paper gasket requires cleaning the hub when the axle shaft is removed.

Thomas Built Buses Product Awareness Bulletin on RH 3 POS Switch for Electric Operated Entrance Door

Thomas Built Bus Service Bulletin for When troubleshooting powernet issues, use the BCT-460DTNA PowerNet Assessment Tool. As of May 29, 2018, the AutoMeter® is the only Daimler-approved tool for troubleshooting vehicle powernet issues.

Thomas Built Buses Product Awareness Bulletin on Lettering Changes - Notification