Exhibit 10.28

FIRST AMENDMENT TO THE STOCKHOLDERS AGREEMENT

This FIRST AMENDMENT TO THE STOCKHOLDERS AGREEMENT, dated as of May 8, 2013
(this “Amendment”), is made by and among Allison Transmission Holdings, Inc., a
Delaware corporation, and each of the other signatories hereto.

W I T N E S S E T H:

WHEREAS, the parties hereto have entered into that certain Amended and Restated
Stockholders Agreement, dated as of March 12, 2012 (the “Stockholders
Agreement”);

WHEREAS, Section 8.8(a) of the Stockholders Agreement provides that the parties
hereto may amend the Stockholders Agreement; and

WHEREAS, the parties hereto desire to amend the Stockholders Agreement as set
forth herein.

NOW, THEREFORE, in consideration of the foregoing and the mutual covenants and
agreements herein contained and other good and valuable consideration, the
receipt, adequacy and sufficiency of which are hereby acknowledged, the parties
hereto hereby agree as follows:

Section 1. Amendment to the Stockholders Agreement. The definition of
“Restricted Management Stockholders” provided in Section 1.1 of the Stockholders
Agreement is hereby amended and restated in its entirety to read as follows:

“Restricted Management Stockholders” shall mean Lawrence E. Dewey, David S.
Graziosi, Michael G. Headly, Randall R. Kirk and David L. Parish.

Section 2. Effectiveness of Amendment. Upon the execution and delivery hereof,
the Stockholders Agreement shall thereupon be deemed to be amended and restated
as hereinabove set forth as fully and with the same effect as if the amendment
and restatement made hereby was originally set forth in the Stockholders
Agreement, and this Amendment and the Stockholders Agreement shall henceforth
respectively be read, taken and construed as one and the same instrument.

Section 3. General Provisions.

(a) Miscellaneous. This Amendment may be executed in one or more counterparts,
all of which shall be considered one and the same agreement and shall become
effective when one or more counterparts have been signed by each of the parties
hereto and delivered to the other parties hereto. This Amendment shall be
governed by, construed, applied and enforced in accordance with the internal
laws of the State of Delaware.

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(b) Stockholders Agreement in Effect. Except as specifically provided for in
this Amendment, the Stockholders Agreement shall remain unmodified and in full
force and effect.

First Amendment to Stockholders Agreement

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IN WITNESS WHEREOF, each of the parties hereto has caused this Amendment to be
executed as of the date first written above.

 

ALLISON TRANSMISSION HOLDINGS, INC. By:    /s/ Lawrence E. Dewey

Name: Lawrence E. Dewey

Title:   President and Chief Executive Officer

 

CARLYLE PARTNERS IV AT HOLDINGS, L.P.

By: TC Group IV Managing GP, L.L.C., its general partner

By:    /s/ Brian A. Bernasek

Name: Brian A. Bernasek

Title:   Authorized Person

 

ONEX ALLISON CO-INVEST LP

By: Onex Partners II GP LP, its general partner

By: Onex Partners Manager LP, its agent

By: Onex Partners Manager GP ULC, its general partner

By:    /s/ Robert M. Le Blanc

Name: Robert M. Le Blanc

Title:   Senior Managing Director

By:    /s/ Donald F. West

Name: Donald F. West

Title:   Vice President and Secretary

 

ONEX ALLISON HOLDING LIMITED S.Á R.L. By:    /s/ Donald F. West

Name: Donald F. West

Title:   Type A Manager

By:    /s/ Olivier Dorier

Name: Olivier Dorier

Title:   Type B Manager

First Amendment to Stockholders Agreement

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ONEX PARTNERS II GP LP

 

By: Onex Partners GP Inc., its general partner

By:    /s/ Robert M. Le Blanc

Name: Robert M. Le Blanc

Title:   President

By:    /s/ Donald F. West

Name: Donald F. West

Title:   Vice President

 

ONEX PARTNERS II LP

By: Onex Partners II GP LP, its general partner

By: Onex Partners Manager LP, its agent

By: Onex Partners Manager GP ULC, its general partner

By:    /s/ Robert M. Le Blanc

Name: Robert M. Le Blanc

Title:   Senior Managing Director

By:    /s/ Donald F. West

Name: Donald F. West

Title:   Vice President and Secretary

 

ONEX US PRINCIPALS LP By:    /s/ Donald F. West

Name: Donald F. West

Title:   Representative of the General Partner

 

1597257 ONTARIO INC. By:    /s/ Christopher A. Govan

Name: Christopher A. Govan

Title:   Managing Director

By:    /s/ Andrea E. Daly

Name: Andrea E. Daly

Title:   Vice President and General Counsel

First Amendment to Stockholders Agreement