UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the

Securities Exchange Act of 1934.

Date of Report (Date of Earliest Event Reported): August 7, 2012

MONRO MUFFLER BRAKE, INC.

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code (585) 647-6400

Not Applicable

(Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions (see General Instruction A.2. below):

On December 17, 2012, Monro Muffler Brake, Inc. (the “Company”), amended its Amended and Restated Credit Agreement (the “Amendment”), originally entered into on June 13, 2011, between RBS Citizens, N.A., as administrative agent; Bank of America, N.A., as syndication agent; JPMorgan Chase Bank, N.A. and Branch Banking and Trust Company, as co-documentation agents; and a syndicate of other lenders (the “Credit Agreement”).

The Amendment increases the borrowing capacity by $75,000,000 to a total of $250,000,000, and allows the Company to request an increase of an additional $75,000,000 to its borrowing capacity. The Amendment also extends the maturity date to December 17, 2017. All other unchanged terms under the Credit Agreement remain in full force and effect. A copy of the Amendment will be filed as an exhibit to the Company’s Quarterly Report on Form 10-Q for the quarter ended December 29, 2012.

The description of the Credit Agreement provided in Item 1.01 hereof is incorporated herein by reference.

As previously disclosed, in April 2011 the Board of Directors of the Company created the position of Lead Independent Director and established the duties of the Lead Independent Director in a charter adopted by the Board. On August 7, 2012, the Board of Directors authorized an amendment to the Company’s By-Laws to add Section 2.12, which updated the By-Laws to reflect the power the Board of Directors of the Company (the “Board”) to designate a Lead Independent Director in circumstances where the Chairman of the Board is not independent. Section 2.12 further confirms the power of the Board to authorize the Lead Director to coordinate the activities of the other independent directors and to perform such other duties and responsibilities as the Board may determine. Such duties include, without limitation, the right to call meetings of the independent directors of the Board by written request to the President or Secretary of the Company. A copy of the amended By-Laws is attached to this current report as Exhibit 3.02 and incorporated herein by reference.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the Company has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

Exhibit Index