23E079 – Transmission May Separate from Driveshaft – Allison Transmission B3400 xFE & B400R

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October 11, 2023 NHTSA CAMPAIGN NUMBER: 23E079000

Transmission May Separate from Driveshaft

A sudden loss of drive power can increase the risk of a crash. Additionally, a disabled bus may require an evacuation procedure in an uncontrolled traffic situation, increasing the risk of injury to passengers.


NHTSA Campaign Number: 23E079

Manufacturer Allison Transmission, Inc.

Components POWER TRAIN

Potential Number of Units Affected 8,498



Allison Transmission, Inc. (ATI) is recalling certain models B3400xFE_R and B400R, with part numbers B3400xFE_R and B400R. The transmission yoke may separate, resulting in driveshaft separation and a sudden loss of drive power.



Dealers will inspect the output yoke bolts, and if necessary, tighten loose output yoke bolts, free of charge. Owner notification letters are expected to be mailed October 27, 2023. Owners may contact ATI customer service at 1-317-242-5000. ATI’s number for this recall is 2023FA04.



Owners may also contact the National Highway Traffic Safety Administration Vehicle Safety Hotline at 1-888-327-4236 (TTY 1-800-424-9153), or go to www.nhtsa.gov.


Chronology :

– June 26-27, 2023: ATI learned of potential loose output yoke bolts and separated drivelines in Canada involving Nova Bus vehicles and that Nova Bus conducted a field survey that identified loose output bolts.

– July 10, 2023: ATI began noise, vibration, harshness (NVH) testing on select Nova Buses jointly with Nova Bus.

– July 12, 2023: Nova Bus submitted a defect information report to NHTSA related to the issue. See Recall No. 23V482.

– July 19, 2023: ATI Opened a formal investigation.

– Jul. – Sep. 2023: ATI investigated potential causes of the Nova Bus reports and collected data related to torque specifications for the output yoke bolt. ATI learned of complaints of driveline cases for transit buses manufactured by another vehicle manufacture. ATI investigated the additional claims and conducted a field survey of transit buses to inspect transmissions for loose output yoke bolts.

– Sep. 25, 2023: After confirming reports of loose bolts in buses produced by additional vehicle manufacturers, ATI escalated the issue to its Field Performance Evaluation Review Committee (FPERC).

– Sep. 26, 2023: ATI’s FPERC made its recommendation to ATI’s Executive Field Action Decision Committee (EFADC).

– Oct. 4, 2023: Based on the information developed during the investigation, ATI – through the EFADC – agreed that the condition constituted a safety-related defect.

ATI is not aware of any accidents or injuries related to this condition.


2 Affected Products




3 Associated Documents

Recall Acknowledgement

RCAK-23E079-5909.pdf 646.387KB

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Defect Notice 573 Report

RCLRPT-23E079-4966.PDF 216.95KB

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Manufacturer Notices(to Dealers,etc)

RCMN-23E079-0536.pdf 387.788KB

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