2012 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.

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 INSIDE THE BUS BODY INCREASING THE RISK OF INJURY TO THE PASSENGERS. THE BUS IS GENERALLY IN MOTION AND HEATER ON WHEN THE FAILURE OCCURS. *DT*JB

NHTSA ID

11160748

Incident

Dec 5, 2018

Mileage

122,860 mi

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

NHTSA ID

11153141

Incident

Nov 6, 2018

Mileage

153,203 mi

THOMAS BUILT BUS - SAFE-T-LINER C-2: TWO INSTANCES IN LAST 4 MONTHS OF CHILDREN SLIDING FORWARD OUT OF THEIR SEATS AND BECOMING WEDGED ON THE FLOOR BETWEEN THE BOTTOM OF THE SEAT SUPPORTS. EACH INCIDENCE REQUIRED APPROXIMATELY 3 MINUTES TO EXTRICATE THE TRAPPED ELEMENTARY SCHOOL CHILD. I BELIEVE THAT FRONT TO BACK SEAT SPACING IS TOO TIGHT. IN AN EMERGENCY, THIS COULD BE A CONCERN. *TR

NHTSA ID

10500700

Incident

Dec 12, 2012

Mileage

15,000 mi

Revised Thomas Built Buses Service Bulletin for Vehicle Starts in Pretrip Mode With Vandalock Active. Minor note: added an update of document previously submitted. The related VMRS codes are added

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.

Revised Warranty Policy Letter for Alliance/Mascot Aftermarket Warranty and Claim Filing. Revisions are in blue. With Mascot now in partnership with Detroit Reman and Alliance Parts, DTNA is pleased to announce that Mascot coverage has been added to OWL. Remanufactured Alliance/Mascot parts include transmission, differential, steering gear, and steering pump used in an on-highway vehicle applications. The Alliance/Mascot aftermarket warranty coverage period has not changed: depending on the part, coverage is for one (1) or two (2) years and current parts, labor, and reimbursement policies apply.

Warranty Policy Letter for Alliance/Mascot Aftermarket Warranty and Claim Filing. With Mascot now in partnership with Detroit Reman and Alliance Parts, DTNA is pleased to announce that Mascot coverage has been added to OWL. Remanufactured Alliance/Mascot parts include transmission, differential, steering gear, and steering pump used in an on-highway vehicle applications. The Alliance/Mascot aftermarket warranty coverage period has not changed: depending on the part, coverage is for one (1) or two (2) years and current parts, labor, and reimbursement policies apply.

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