<PAGE>

                                                                    Exhibit 4.14

                                ABC-NACO INC.,
              (formerly known as ABC Rall Products Corporation),
                                  the Company

                                      AND

                        U.S. BANK NATIONAL ASSOCIATION,
          (as successor trustee to First Trust National Association)
                                  the Trustee

                             ____________________

                         THIRD SUPPLEMENTAL INDENTURE
                         Dated as of September 1, 2000

                             ____________________

                          Supplementing that certain
                                   Indenture

                          Dated as of January 15, 1997

                                by and between

                         ABC Rail Products Corporation

                                      and

                       First Trust National Association

<PAGE>

                         THIRD SUPPLEMENTAL INDENTURE

     THIS THIRD SUPPLEMENTAL INDENTURE (this "Supplemental Indenture") is made
and entered into as of September 1, 2000 between ABC-NACO Inc., a Delaware
corporation (the "Company"), and U.S. Bank National Association, a national
banking association, as successor trustee to First Trust National Association, a
national banking association (the "Trustee").


                                   RECITALS

     WHEREAS, pursuant to that certain Indenture dated as of January 15, 1997
(as amended, supplemented or modified from time to time, the "Indenture"),
between the Company (formerly ABC Rail Products Corporation); and U.S. Bank
National Association (successor trustee to First Trust National Association),
the Company executed (i) an officer's certificate, dated January 28, 1997 (the
"9 1/8% Officer's Certificate"), establishing a series of securities known as
the 9 1/8% Senior Subordinated Notes Due 2004 in the original principal amount
of $50,000,000 (the "9 1/8% Notes") and (ii) an officer's certificate dated
December 17, 1997 (the "8 3/4% Officer's Certificates") (the 9 1/8% Officer's
Certificate and the 8 3/4% Officer's Certificate each, an "Officer's
Certificate" and together, the "Officer's Certificate"), establishing a series
of securities known as the 8 3/4% Senior Subordinated Notes, Series B, due 2004
in the original principal amount of $25,000,000; (the "8 3/4% Notes" and,
together with the 9 1/8 % Notes, the "Notes"):

     WHEREAS, the Company requested that the holders of the Notes consent to the
amendment of the Operating Coverage Ratio covenant under Paragraph 10(d) of each
Officer's Certificate and established pursuant to Section 301(17) of the
Indenture;

     WHEREAS, pursuant to Section 902 of the Indenture, the holders of not less
than a majority of the aggregate pricipal amount of the outstanding Notes
(voting as one class) have consented to the modification to the Operating
Coverage Ratio covenant under Paragraph 10(d) of each Officer's Certificate and
established pursuant to Section 301(17) of the Indenture;

     WHEREAS, the Company requested that the holders of the Notes consent to the
amendment of the interest rate under Paragraph 4(a) of each Officer's
Certificate and established pursuant to Section 301(5) of the Indenture;

     Whereas, pursuant to Section 902 of the Indenture, the holders of not less
than a majority of the aggregate principal amount of the outstanding Notes
(voting as one class) have consented to the amendment of the interest rate under
Paragraph 4(a) of each Officer's Certificate and established pursuant to Section
301(5) of the Indenture;

     WHEREAS, the Company desires to change the titles of the 9 1/8% and the
8 3/4% Notes, respectively, to reflect the amendment to the interest rate
provision;

     WHEREAS, pursuant to Section 901(4) and 901(8) of the Indenture, the
Company and the Trustee may, without the consent of any holders of the Notes,
change any provision of the Indenture or correct any provision that may be
inconsistent with any other provision of the Notes, provided that such action
does not adversely affect the rights of the holders of the Notes or any other
security in any material respect; and

     WHEREAS, in order to effectuate and formalize the aforementioned
amendments, the parties hereto desire to amend the Indenture and each Officer's
Certificate as set forth below and to enter into this Supplemental Indenture.

     NOW THEREFORE, the parties hereto, intending to be legally bound, and in
consideration of the premises and other good and valuable consideration, the
receipt and sufficiency of which is hereby acknowledged, do hereby amend the
Indenture and the Officer's Certificates and further agree as set forth below:

<PAGE>

     Section 1. Definitions.  All terms capitalized but not otherwise defined in
this Supplemental Indenture shall have the meanings assigned to such terms in
the Indenture.

     Section 2. Effect Of This Supplemental Indenture.

     (A)  Except as expressly supplemented or amended by this Supplemental
Indenture, all of the terms and provisions of the Indenture and the Officer's
Certificates shall remain in full force and effect.

     (B)  To the extent of any inconsistency between the terms and provisions of
this Supplemental Indenture and the terms and provisions of the Indenture and
the Officer's Certificates, this Supplemental Indenture shall control.

     (C)  The rules of construction stated in Section 1.01 of the Indenture
shall apply to this Supplemental Indenture.

     Section 3. Amendment To Paragraph 10(d) Of Each Officer's Certificate.
Subparagraph (d) of Paragraph 10 of each Officer's Certificate is hereby
amended, effective beginning with the first fiscal quarter ending after the date
of this Supplemental Indenture, in its entirety to read as follows:

     "The Company will maintain, at the end of each of its fiscal quarters, an
Operating Coverage Ratio with respect to the four consecutive fiscal quarters
then ended taken as a whole of at least 1.8:1.0; and".

     Section 4. Amendment To Paragraph 4(a) Of Each Officer's Certificate.
Subparagraph (a) of Paragraph 4 of each Officer's Certificate is hereby amended,
effective beginning with the first interest payment date after the date of this
Supplemental Indenture, in its entirety to read as follows:

     "(a) the rate at which the Notes shall bear interest if 10 1/2%."

     Section 5. Amendment To Paragraph 1 Of The 9 1/4% Officer's Certificate.
Paragraph 1 of the 9 1/4% Officer's Certificate is hereby amended, effective
beginning with the first interest payment date after the date of this
Supplemental Indenture, in its entirety to read as follows:

     "Pursuant to Section 301(1) of the Indenture, the title of the Securities
of the series established by this Officer's Certificate is "10 1/2% Senior
Subordinated Notes, Series A, Due 2004.""

     Section 6. Amendment To Paragraph 1 Of The 8 3/4% Officer's Certificate.
Paragraph 1 of the 8 3/4% Officer's Certificate is hereby amended, effective
beginning with the first interest payment date after the date of this
Supplemental Indenture, in its entirety to read as follows:

     "Pursuant to Section 301(1) of the Indenture, the title of the Securities
of the series established by this Officer's Certificate is "10 1/2% Senior
Subordinated Notes, Series B, Due 2004.""

     Section 7. References To Indenture.  All references in the Indenture to the
Indenture shall hereafter be deemed to refer to the Indenture as amended by this
Supplemental Indenture and as may be further amended, modified, restated or
replaced from time to time.

     Section 8. Other Terms In Full Force And Effect.  Except as expressly so
amended, the Indenture and the Officer's Certificates shall remain unmodified
and in full force and effect.

     Section 9. Counterparts.  This Supplemental Indenture may be executed in
any number of counterparts with the same effect as if all parties hereto had
signed the same document. All such counterparts shall be construed together and
shall constitute one instrument, but in making proof hereof it shall only be
necessary to produce one such counterpart.
<PAGE>

     IN WITNESS WHEREOF, the parties hereto have caused this Supplemental
Indenture to be executed as of the day and year first above written.

                                        ABC-NACO INC.


                                        By: /s/ James P. Singsank
                                            -------------------------
                                            Name:
                                            Title: SVP/CFO

ATTEST:

/s/ Vincent V. Rea
--------------------------------
Name:
Title: VP & Corporate Treasurer

                                        U.S. BANK NATIONAL ASSOCIATION,
                                          as successor trustee

                                        By: _________________________
                                            Name:
                                            Title:


ATTEST:


________________________________
Name:
Title:
<PAGE>

                             OFFICER'S CERTIFICATE
                             ---------------------

     WHEREAS, this certificate is delivered pursuant to Section 102 of the
Indenture dated as of January 15, 1997 between ABC Rail Products Corporation
(the "Company") and First Trust National Association, as trustee (the "Trustee")
(as supplemented and amended through and including the First Supplemental
Indenture dated as of January 15, 1997, and the Second Supplemental Indenture
dated December 1, 1997, the "Indenture"), in connection with the execution and
delivery of the Third Supplemental dated as of September 1, 2000 (the
"Supplemental Indenture"). Each capitalized term used but not defined herein
shall have the meaning assigned such term in the Supplemental Indenture; and

     WHEREAS, pursuant to that certain Indenture and certain Supplemental
Indenture"), between the Company (formerly ABC Rail Products Corporation); and
U.S. Bank National Association (successor trustee to First Trust National
Association), the Company executed (i) an officer's certificate, dated January
28, 1997 (the "9 1/8% Officer's Certificate"), establishing a series of
securities known as the 9 1/8% Senior Subordinated Notes Due 2004 in the
original principal amount of $50,000,000 (the "9 1/8% Notes") and (ii) an
officer's certificated dated December 17, 1997 (the "8 3/4% Officer's
Certificate") (the 9 1/8% Officer's Certificate and the 8 3/4% Officer's
Certificate each, an "Officer's Certificate" and together, the "Officer's
Certificates") establishing a series of securities known as the 8 3/4% Senior
Subordinated Notes, Series B, due 2004 in the original principal amount of
$25,000,000; (the "8 3/4% Notes" and, together with the 9 1/8% Notes, the
"Notes"); and

     WHEREAS, the Company requested and obtained the necessary consents to amend
the Indenture and Supplemental Indenture as set forth in the Third Supplemental
Indenture attached hereto as Appendix A.

     NOW THEREFORE, James P. Singsank, Senior Vice President and Chief Financial
Officer, and Vincent V. Rea, Vice President and Corporate Treasurer of the
Company, have read the Indenture (including each covenant or condition with
which compliance is required in connection with the execution and delivery by
the Company of the Indenture and related definitions), the Supplemental
Indenture and the Officer's Certificate and are duly authorized by the Company's
Board of Directors to execute the Third Supplemental Indenture to reflect the
amendments. The undersigned officers of the Company have also examined originals
or copies of such corporate records and agreements, certificates and other
documents as in their judgement were deemed necessary as a basis for the
certification expressed herein. In the undersigned officers' judgement, such
officers have made such examination or investigation as is necessary to enable
them to express an informed opinion as to whether or not all such covenants or
conditions have been complied with.

     Based on the foregoing examination, the undersigned officers of the Company
hereby certify that each covenant or condition with which compliance is required
in



<PAGE>

connection with the execution and delivery of the Supplemental Indenture has
been complied with.


           [the remainder of this page is intentionally left blank]

<PAGE>

     IN WITNESS WHEREOF, the undersigned duly authorized officers of the Company
have caused this Officer's Certificate to be executed in their names as of
September 1, 2000.

                              ABC-NACO Inc.


                              By: /s/ James P. Singsank
                                 ---------------------------------
                              Name:   James P. Singsank
                              Title:  Senior Vice President and Chief Financial
                                      Officer

                              By: /s/ Vincent V. Rea
                                 ---------------------------------
                              Name:   Vincent V. Rea
                              Title:  Vice President and Corporate Treasurer


<PAGE>

                            SECRETARY'S CERTIFICATE
                            -----------------------

     I, Mark F. Baggio, Secretary of ABC-NACO Inc. (the "Company"), a Delaware
corporation, in connection with the Consent Solicitation for the Indenture for
the Senior Subordinated Notes (the "Consent"), DO HEREBY CERTIFY on behalf of
the Company, solely in my capacity as an officer of the Company, as follows:

     Attached hereto is a true, correct and complete copy of the resolutions
adopted by the Board of Directors of the Company with respect to the Consent
Solicitation for the Proposed Amendments to the Indenture for the Senior
Subordinated Notes which was duly and validly adopted by the Board of
Directors on July 10, 2000. Such resolutions are in full force on the date
hereof in the form in which adopted relating to the transaction contemplated
thereby.

     IN WITNESS WHEREOF, the undersigned has caused this Certificate to be
executed on and as of the 31st day of August, 2000.


                                                   Mark F. Baggio
                                                   ---------------------
                                                   Name:  Mark F. Baggio
                                                   Title: Secretary

     I. JON C. VIGANO, Assistant Secretary of the Company, DO HEREBY CERTIFY on
behalf of the Company that MARK F. BAGGIO is the duly elected or appointed,
qualified and acting Secretary of the Company, and the signature set forth above
is his genuine signature.


                                                   Jon C. Vigano
                                                   ---------------------
                                                   Name:  Jon C. Vigano
                                                   Title: Assistant Secretary



<PAGE>

The ABC-NACO Inc. Board of Directors hereby adopt the following Resolutions:

               CONSENT SOLICITATION FOR THE PROPOSED AMENDMENTS
              TO THE INDENTURE FOR THE SENIOR SUBORDINATED NOTES
              --------------------------------------------------

WHEREAS, the Board of Directors of ABC-NACO Inc. has determined that it is in
the best interest of the Company and its stockholders that ABC-NACO Inc. engage
in the Consent Solicitation for the proposed amendments to the Indenture, dated
as of January 15, 1997 (as amended, modified or supplemented from time to time)
for the Company's Senior Subordinated Notes upon substantially the terms and
conditions presented to the Board of Directors on July 10, 2000, an outline of
which is attached hereto as Exhibit A;

NOW, THEREFORE, BE IT RESOLVED, that the Consent Solicitation for the proposed
amendments to the Indenture for the Company's Senior Subordinated Notes by ABC-
NACO Inc. is hereby ratified, confirmed and approved by the Board of Directors
and that all actions taken by the officers of ABC-NACO Inc. in connection with
the Consent Solicitation for the proposed amendments to the Indenture for the
Company's Senior Subordinated Notes upon substantially presented to the Board of
Directors on July 10, 2000 are hereby ratified, confirmed and approved by the
Board of Directors.

     FURTHER RESOLVED, that the close of business on Monday July 10, 2000, and
it hereby is, fixed as the record date for the determination of the stockholders
entitled to receive notice of the Consent Solicitation for the proposed
amendments to the Indenture for the Senior Subordinated Notes and to vote
thereat.

<PAGE>

     Exhibit A
     ---------


                         CONSENT SOLICITATION SUMMARY
                         ----------------------------


The following summary is not intended to be complete. Holders are urged to read
the more detailed information set forth elsewhere in the Solicitation Documents.
Each of the capitalized terms used in this Summary and not defined herein has
the meaning set forth elsewhere in this Consent Solicitation Statement.

ABC-NACO Inc. hereby solicits Consents to the Proposed Amendment to the
Indenture, dated as of January 15, 1997 (as amended, modified or supplemented
from time to time, the "Indenture"), between ABC Rail Products (predecessor
organization to ABC-NACO Inc.) and First Trust National Association (predecessor
organization to U.S. Bank) as Trustee (the "Trustee").

The following is a summary of certain Consent Solicitation terms:


                           The Consent Solicitation
                           ------------------------


Consent Fee                   For each $1,000 in principal amount of Notes, a
                                  cash payment of $10.00. No accrued interest
                                  will be paid on the Consent Fee.

Interest in Coupon Rate       The coupon interest rate will be increased from 9
                                  1/8% to 10% on the Series A notes and from 8
                                  3/4% to 10% on the Series B notes, effective
                                  as of the Consent Achievement Date.

Record Date                   5:00 p.m., Chicago time, on July 10, 2000.

Consent Achievement Date      The time and date on which ABC-NACO Inc. publicly
                                  announces that the Requisite Consent has been
                                  achieved.

Expiration Date               The Consent Solicitation will be open until 5:00
                                  p.m., Chicago time on August 10, 2000, unless
                                  terminated or extended by ABC-NACO in its sole
                                  discretion. The time and date of expiration of
                                  the Consent Solicitation are herein referred
                                  to as the "Expiration Date".

                              ABC-NACO Inc. expressly reserves the right for any
                                  reason (1) to abandon, terminate or amend the
                                  Consent Solicitation at any time prior to the
                                  Expiration Date by giving oral or written
                                  notice thereof to the Information Agent, and
                                  (ii) not to extend the Consent Solicitation
                                  beyond the Expiration Date whether or not the
                                  Requisite Consent has been received by such
                                  date.


<PAGE>

Eligibility for Consent Fee
And Increase in Coupon             Holders whose properly executed Consents are
                                      received (and not revoked) prior to the
                                      Expiration Date will be eligible to
                                      receive the Consent Fee and Increase in
                                      Coupon promptly after the Expiration Date
                                      if the conditions for payment described
                                      herein have been satisfied or waived. Any
                                      subsequent transferees of Holders, and any
                                      Holders who do not timely grant (or who
                                      revoke) a valid consent (and their
                                      transferees) will not be eligible to
                                      receive the Consent Fee even if the
                                      Proposed Amendments become effective with
                                      respect to the Notes held thereby and, as
                                      a result, become binding thereon.

Requisite Consent                  Holders must grant (and not revoke) valid
                                      Consents in respect of a majority in
                                      aggregate principal amount of all
                                      outstanding Notes to approve the Proposed
                                      Amendments. For purposes of the foregoing
                                      calculation, any Notes held by ABC-NACO
                                      Inc. or any of its affiliates will not be
                                      counted as being outstanding.

                                   As of the date of this Consent Solicitation
                                      Statement, the aggregate outstanding
                                      principal amount of the Notes was $75.0
                                      million (of which $50.0 million were
                                      Series A and $25.0 million were Series B)
                                      none of which was held by ABC-NACO or any
                                      of its affiliates.

Consequences to Non-
Consenting Holders                 If the Requisite Consent is obtained, and
                                      the Consent Fee is paid, non-consenting
                                      Holders will be bound by the Proposed
                                      Amendments but will not receive the
                                      Consent Fee.

Procedure for Delivery
Of Consents                        Consents must be delivered to the Tabulation
                                      Agent prior to the Expiration Date. DTC
                                      is expected to grant an omnibus proxy
                                      authorizing the DTC Participants to
                                      deliver a Consent. Only registered owners
                                      of Notes as of the Record Date or their
                                      duly designated proxies, including, for
                                      the purposes of this Consent Solicitation,
                                      DTC Participants, are eligible to consent
                                      to the Proposed Amendments and receive the
                                      Consent Fee. Therefore, a beneficial owner
                                      of an interest in Notes held in an account
                                      of a DTC Participant who wishes a Consent
                                      to be delivered must properly instruct
                                      each DTC Participant to cause a Consent to
                                      be given in respect of such Notes. See "
                                      The Consent Solicitation"-Consent
                                      Procedures".

Revocation of Consents             Revocation of Consents may be made at any
                                      time prior to the Consent Achievement Date
                                      but only by the Holder (or a duly
                                      designated proxy). Each Holder, by
                                      delivering its Consent, will agree in the
                                      Consent Letter not to revoke its Consent
                                      after that time, even if the Consent
                                      Solicitation is extended beyond that time.
                                      See "The Consent Solicitation-Revocation
                                      of Consents".

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<PAGE>

Solicitation Agent            Robert W. Baird is serving as Solicitation Agent
                                 in connection with the Consent Solicitation.

Information Agent;
Tabulation Agent              ADP or Georgeson??? is serving as Information
                                 Agent and Tabulation Agent in connection with
                                 the Consent Solicitation.

Note Depository               DTC Company is serving as Note Depository in
                                 connection with the Consent Solicitation.

U.S. Federal Income
Tax Consequences              For a discussion of certain U.S. federal income
                                 tax consequences of the Consent Solicitation to
                                 beneficial owners of Notes, see "Certain United
                                 States Federal Income Tax Consequences".

                            The Proposed Amendments

Payment Provisions
Affected                      Other than the interest coupon rate, which will be
                                 increased to 10% for both Series A and Series B
                                 Holders, none of the maturity date, payment
                                 provisions, redemption provisions, guaranty
                                 provisions or any other similar terms of the
                                 Notes will be amended as a result of the
                                 Proposed Amendments.

The Proposed Amendments       The Proposed Amendment to modify the Company's
                                 Operating Coverage Ratio covenant would: (i)
                                 enhance ABC-NACO's future operating
                                 flexibility, (ii) give the Company greater
                                 latitude to pursue its newly announced
                                 profitability improvement initiatives, and
                                 (iii) provide the Company sufficient time and
                                 latitude to execute its balance sheet de-
                                 leveraging strategies.

Terms of Proposed
Amendments                    The Proposed Amendment consists of a modification
                                 to the Minimum Required Operating Coverage
                                 Ratio from a minimum of 2.40 to a minimum 1.80
                                 (or 2.00 ?). If Consent is achieved, this
                                 modification will become effective for all
                                 fiscal quarters ending after the Consent
                                 Achievement Date.

Effectiveness                 The Proposed Amendment will be effected by
                                 execution of one or more supplemental
                                 indentures (collectively, the "Supplemental
                                 Indenture") between the Company and the
                                 Trustee.

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