<PAGE>   1

                                                                    EXHIBIT 4.3



                 TRANSPORTATION MANUFACTURING OPERATIONS, INC.

                                AMENDMENT NO. 2
                                       to
                                CREDIT AGREEMENT
                            AND OTHER LOAN DOCUMENTS
                            Dated as of May 23, 1997


     This Amendment No. 2 to Credit Agreement and other Loan Documents (this
"Amendment") is dated as of May 23, 1997 and entered into by and among
TRANSPORTATION MANUFACTURING OPERATIONS, INC., a Delaware corporation (the
"Borrower"), the guarantors set forth on the signature pages hereof
(collectively, the "Guarantors" and individually, a "Guarantor"), the banks set
forth on the signature pages hereof (collectively, the "Lenders" and
individually, a "Lender"), NBD BANK, a Michigan banking corporation ("NBD"), as
the resigning Administrative Agent for the Lenders and as the exiting Lender,
Swing Line Bank and Issuing Lender, and THE FIRST NATIONAL BANK OF CHICAGO, a
national banking association ("First Chicago"), as the new Lender, Swing Line
Bank and Issuing Lender and the successor Administrative Agent for the Lenders.

                                R E C I T A L S:

     A.  The Borrower, the Lenders and NBD, as Swing Line Bank, Issuing Lender
and Administrative Agent, are parties to that certain Credit Agreement dated as
of September 30, 1996, as amended by Amendment No. 1 thereto dated as of
December 17, 1996 (the "Credit Agreement").

     B.  In connection with the Credit Agreement, the Guarantors executed the
Subsidiary Guaranty dated as of October 1, 1996 (the "Guaranty") in favor of
the Administrative Agent for the ratable benefit of the Lenders.

     C.  The Borrower has requested changes in certain of the covenants
contained in the Credit Agreement and a release of BusLease, Inc., one of the
Guarantors, from its obligations under the Guaranty, and the Lenders are
willing to agree to such changes and such release on the terms and conditions
set forth herein.

     D.  NBD desires to assign to First Chicago, and to be released from, all of
its rights and obligations under the Credit Agreement, the Guaranty and all
other documents executed and delivered in connection with the Credit Agreement
(collectively, the "Loan Documents"), excepting only certain Retained Rights
(as defined below) with respect to the outstanding Letters of Credit specified
below.


<PAGE>   2


     E.  NBD further desires to resign as Administrative Agent under the Credit
Agreement and all other Loan Documents, and First Chicago desires to replace
NBD as Administrative Agent thereunder.

     F.  The parties hereto desire to amend the Credit Agreement and all other
Loan Documents in certain respects as hereinafter set forth so as to take into
account the foregoing.

     ACCORDINGLY, in consideration of the premises and the agreements and
provisions contained herein, and for other good and valuable consideration, the
receipt and sufficiency of which are hereby acknowledged, the parties hereto
agree as follows:

     Section 1.  DEFINED TERMS.  Capitalized terms used herein and not
otherwise defined herein shall have the meanings attributed to such terms in
the Credit Agreement.

     Section 2.  AMENDMENTS TO CREDIT AGREEMENT AND OTHER LOAN DOCUMENTS.

     2.1 (a) Effective as of the Amendment Effective Date (as hereinafter
defined), NBD shall hereby sell and assign to First Chicago, and First Chicago
shall hereby purchase and assume from NBD, all of NBD's rights (other than the
Retained Rights) and obligations under the Credit Agreement and the other Loan
Documents, whereupon, except as set forth in subsection 2.1(b) below, (i) NBD
shall cease to be a Lender, the Swing Line Bank and an Issuing Lender under the
Credit Agreement and all other Loan Documents and shall relinquish its rights
and shall be released from its obligations under the Credit Agreement and the
other Loan Documents, and (ii) First Chicago shall for all purposes be a Lender
party to the Credit Agreement and each other Loan Document executed by the
Lenders and shall have all of the rights and obligations of a Lender, the Swing
Line Bank and an Issuing Lender under the Credit Agreement and the other Loan
Documents.  This Amendment shall be deemed to satisfy all the requirements of
Section 8.07 of the Credit Agreement with respect to such assignment from NBD
to First Chicago.

     (b) NBD shall retain all of its rights as an Issuing Lender under the
Credit Agreement with respect to the outstanding Letters of Credit described on
Schedule I hereto (the "NBD Letters of Credit") as against the Borrower with
respect to, among other things, reimbursement obligations under Section 2.04(c)
of the Credit Agreement, fees, interest and other charges under Section 2.04(e)
of the Credit Agreement, and indemnification under Section 2.04(h) of the
Credit Agreement, and as against the respective Lenders as purchasers of
participations in the NBD Letters of Credit, provided that First Chicago shall
not be deemed to have purchased a pro rata participation in the NBD Letters of
Credit pursuant to Section 2.04(a) of the Credit Agreement.  All such retained
rights of NBD with respect to the NBD  Letters of Credit are referred to herein
as the "Retained Rights," and NBD shall continue to hold the Retained Rights
until all of the NBD Letters of Credit shall have expired in accordance with
their terms or shall have been surrendered to NBD for cancellation and all
reimbursement obligations, fees, interest, charges, indemnities and other 
obligations of the Borrower with respect to the NBD

                                     -2-

<PAGE>   3


Letters of Credit shall have been paid in full.  NBD shall have no obligation 
to, and shall not, issue any Letters of Credit after the effective date of this 
Amendment.

     2.2  Effective as of the Amendment Effective Date, (i) NBD shall resign as
Administrative Agent under the Credit Agreement and the other Loan Documents
and First Chicago shall replace NBD as Administrative Agent under the Credit
Agreement and the other Loan Documents, and (ii) except as contemplated by
Section 7.11 of the Credit Agreement, NBD shall have no further rights or
obligations as Administrative Agent under the Credit Agreement or any other
Loan Document.  In furtherance of the foregoing, for all purposes of Section
7.11 of the Credit Agreement, effective as of the Amendment Effective Date, NBD
shall be deemed to have resigned as Administrative Agent and First Chicago
shall be deemed to be the successor Administrative Agent appointed by all the
Lenders, and this Amendment shall constitute (i) the notice of such resignation
to be provided by NBD as Administrative Agent to the Lenders and the Borrower,
(ii) the instrument by which the Lenders appoint First Chicago as the successor
Administrative Agent, and (iii) the instrument by which First Chicago accepts
such appointment.

     2.3  The reference to "NBD BANK, as contractual representative" set forth
in the introductory paragraph of the Credit Agreement is hereby amended to read
as a reference to "THE FIRST NATIONAL BANK OF CHICAGO, a national banking
association, as contractual representative".

     2.4  The definition of "Business Day" set forth in Article I of the Credit
Agreement is hereby amended to read in its entirety as follows:

          "Business Day" means a day other than a Saturday, Sunday or other day
     on which the Administrative Agent is not open to the public for carrying
     on substantially all of its banking functions, and, if the applicable
     Business Day relates to any Eurodollar Advances, a day on which dealings
     are carried on in the London interbank market.

     2.5  Article I of the Credit Agreement is hereby amended to add thereto the
following defined term:

          "Consolidated EBIT" means, for any period, the sum (without
     duplication) of the amounts for such period of (i) Consolidated Net
     Income, (ii) Consolidated Interest Expense and (iii) provisions for taxes
     based on income, all of the foregoing as determined on a consolidated
     basis for the Borrower and its Subsidiaries in conformity with GAAP.

     2.6  The first sentence of Section 2.01 of the Credit Agreement is hereby
amended by adding after the reference to "Section 8.07(c)," therein the
following: "or, in the case of First Chicago, on the signature page of
Amendment No. 2 dated as of May 23, 1997 to this Agreement,".




                                     -3-

<PAGE>   4


     2.7  All references to the "Administrative Agent" in the Credit Agreement
and the other Loan Documents shall be deemed to refer to The First National
Bank of Chicago in its capacity as Administrative Agent.

     2.8  Except as provided in Section 2.1(b) hereof, all references to "NBD"
or "NBD Bank," whether as a Lender, the Swing Line Bank, an Issuing Lender or
as Administrative Agent, in the Credit Agreement and the other Loan Documents
shall be amended to read "First Chicago" or "The First National Bank of
Chicago," as appropriate.

     2.9  All references in the Credit Agreement and the other Loan Documents to
any address for notices to NBD, NBD Bank or the Administrative Agent shall be
amended to read: "The First National Bank of Chicago, One First National Plaza,
Suite 0634, Chicago, Illinois 60670, Attn: Sharon Bosch, Facsimile No.: (312)
732-4840, Telephone No.: (312) 732-7112."

     2.10 Section 5.02(c) of the Credit Agreement is hereby amended by deleting
from clause (iv) thereof the figure "$15,000,000" and substituting therefor the
figure "$25,000,000" and by adding at the end of such clause (iv) the
following:

     provided, further, that such aggregate outstanding amount may include
     up to $20,000,000 of Investments by the Borrower in an entity formed for
     purposes of operating as a finance company ("Newco") in which Dina or any
     of its Subsidiaries may also be an investor, which Investments may consist
     of debt or equity interests or a combination thereof and the consideration
     for which may be cash or other property valued at fair market value;

     2.11 Section 5.02(e) of the Credit Agreement is hereby amended by adding
to clause (iv) thereof, after the phrase "limited recourse basis" the first
place such phrase appears therein and before the semicolon, a comma and the
phrase "including, without limitation, such sales to Newco".

     2.12 Section 5.02(j) of the Credit Agreement is hereby amended by deleting
clause (ii) thereof in its entirety and substituting therefor the following:

          (ii) as long as no Event of Default or Potential Event of Default     
     shall have occurred or be continuing, or would result therefrom, the
     Borrower may (A) declare and pay ordinary dividends on its outstanding
     common stock in such amounts as may be determined by its Board of
     Directors and (B) make other distributions (including, without limitation,
     dividends on preferred stock and payments for the redemption or repurchase
     of common or preferred stock), provided that the aggregate amount of all
     such dividends and distributions from and after the date hereof does not
     exceed 50% of cumulative Consolidated Net Income determined for all fiscal
     quarters ending after January 1, 1997 but prior to the date of such
     distribution.



                                     -4-


<PAGE>   5

        2.13 Section 5.03(a) of the Credit Agreement is hereby amended by
deleting the table set forth therein in its entirety and substituting therefor
the following:


<TABLE>
<CAPTION>
------------------------------------------------
Applicable Period                  Maximum Ratio
------------------------------------------------
<S>                                <C>
Effective Date - March 30, 1997    4.25 to 1.00
------------------------------------------------
March 31, 1997 - June 29, 1997     3.75 to 1.00
------------------------------------------------
June 30, 1997 - March 30, 1998     3.50 to 1.00
------------------------------------------------
At all times thereafter            3.00 to 1.00
------------------------------------------------
</TABLE>

        2.14 Section 5.03(b) of the Credit Agreement is hereby amended by
deleting it in its entirety and substituting therefor the following:

             (b) Fixed Charge Coverage Ratio.  The Borrower will not permit
        the ratio ("Fixed Charge Coverage Ratio") of (i) the sum of
        Consolidated EBIT plus Consolidated Rental Payments to (ii) the sum of
        Consolidated Interest Expense plus Consolidated Rental Payments,
        determined as of the last day of each fiscal quarter for the four
        fiscal quarter period then ended, to be less than 2.50 to 1.00 as of
        the last day of any fiscal quarter.

        Section 3. RELEASE

        The Lenders hereby release BusLease, Inc. from any and all obligations
under the Guaranty.

        Section 4. CONDITIONS TO EFFECTIVENESS.

        This Amendment shall become effective as of the date hereof (the 
"Amendment Effective Date") upon the receipt by First Chicago, as the new
Administrative Agent, of the following items:

        (i)   Counterparts of this Amendment duly executed by the Borrower, the
     Guarantors, and the Majority Lenders (determined immediately prior to the
     occurrence of the Amendment Effective Date).

        (ii)  A Promissory Note in the principal amount of $20,000,000 and a
     Swing Line Note in the principal amount of $5,000,000, each payable to the
     order of First Chicago and executed and delivered by the Borrower (the
     "New Notes").  Immediately upon receipt by First Chicago of the New Notes,
     NBD's Promissory Note and Swing Line Note shall be deemed canceled,
     provided that all accrued but unpaid interest thereon shall be deemed
     accrued and unpaid on the respective New Notes.


                                     -5-


<PAGE>   6


        (iii) Such other documents as the Administrative Agent or any Lender
     may reasonably request.

        First Chicago and NBD shall make mutually satisfactory arrangements for
payment of the consideration for the assignment under Section 2.1 hereof.

        Section 5. REPRESENTATIONS AND WARRANTIES OF BORROWER.

        To induce the Lenders to enter into this Amendment, and to amend the
Credit Agreement and the other Loan Documents as provided herein, the Borrower
and each of the Guarantors hereby represents and warrants that:

        (a) The Borrower has full power, authority and legal right to execute,
deliver and perform this Amendment, the Credit Agreement as amended hereby and
the New Notes, and each of the Guarantors has full power, authority and legal
right to execute and deliver this Amendment.  The Borrower has duly executed
and delivered this Amendment and the New Notes, and each of the Guarantors has
duly executed and delivered this Amendment.

        (b) This Amendment, the Credit Agreement as amended hereby and the New
Notes are the legal, valid and binding obligations of the Borrower enforceable
against the Borrower in accordance with their respective terms, and this
Amendment is the legal, valid and binding obligation of each of the Guarantors,
enforceable against each such Guarantor in accordance with its terms, in each
case as enforceability may be subject to the effect of applicable bankruptcy,
insolvency, arrangement, moratorium and other similar laws affecting creditors'
rights generally and to the application of general principles of equity.

        (c) No consent, approval or authorization of or declaration,
registration or filing with any governmental authority or any nongovernmental
person or entity, including, without limitation, any creditor or stockholder of
the Borrower or any Guarantor, is required on the part of the Borrower or any
Guarantor in connection with the execution, delivery and performance of this
Amendment or the New Notes or the transactions contemplated hereby or thereby
or as a condition to the legality, validity or enforceability of this
Amendment, the Credit Agreement as amended hereby or the New Notes.

        (d) No event has occurred and is continuing or will result from the
execution and delivery of this Amendment that constitutes an Event of Default
or Potential Event of Default.

        Section 6. REFERENCE TO AND EFFECT ON THE CREDIT AGREEMENT AND OTHER
LOAN DOCUMENTS.

        (a)  From and after the Amendment Effective Date, each reference in any
Loan Document to such Loan Document or any other Loan Document shall mean and
be a reference to the respective Loan Document as amended hereby.


                                     -6-


<PAGE>   7


        (b)  The Credit Agreement and all other Loan Documents, as amended
hereby, shall remain in full force and effect, and are hereby ratified and
confirmed.

        (c)  Except as expressly provided herein, the execution, delivery and
effectiveness of this Amendment shall not operate as a waiver of any right,
power or remedy of the Administrative Agent, the Lenders, the Swing Line Bank
or any Issuing Lender, nor constitute a waiver of any provision of the Credit
Agreement or any other Loan Document.

        Section 7. GOVERNING LAW.  This Amendment shall be governed by and
construed in accordance with the internal laws (as opposed to the conflict of
law provisions) of the State of Illinois.

        Section 8. HEADINGS.  Section headings in this Amendment are included
herein for convenience of reference only and shall not constitute a part of
this Amendment for any other purpose.

        Section 9. COUNTERPARTS.  This Amendment may be executed by one or
more of the parties to the Amendment on any number of separate counterparts and
all of said counterparts taken together shall be deemed to constitute one and
the same instrument.  Signature pages may be detached from multiple separate
counterparts and attached to a single counterpart so that all signature pages
are physically attached to the same document.

        IN WITNESS WHEREOF, this Amendment has been duly executed and delivered
on the date first above written.

                                   TRANSPORTATION MANUFACTURING        
                                    OPERATIONS, INC.                   
                                                                           
                                                                           
                                   By: /s/ Guillermo Kareh Aarun               
                                       -----------------------------
                                       Name:  Guillermo Kareh Aarun             
                                       Title: Chief Executive Corporate Officer
                                              and Secretary

                                   By: /s/ Rafael Gomez Flores
                                       -----------------------------
                                       Name:  Rafael Gomez Flores
                                       Title: Chairman of the Board 
                                              and President

                                                                           
                                   Guarantors:                         
                                                                           
                                   HAUSMAN BUS SALES, INC.             
                                                                           
                                   By: /s/ Guillermo Kareh Aarun               
                                       -----------------------------
                                       Name:  Guillermo Kareh Aarun             
                                       Title: Chief Executive Corporate Officer
                                              and Secretary

                                   By: /s/ Rafael Gomez Flores
                                       -----------------------------
                                       Name:  Rafael Gomez Flores
                                       Title: Chairman of the Board 
                                              and President




                                     -7-



<PAGE>   8


                                   MCI ACCEPTANCE CORP.                  
                                                                             
                                   By: /s/ Guillermo Kareh Aarun               
                                       -----------------------------           
                                       Name:  Guillermo Kareh Aarun             
                                       Title: Chief Executive Corporate Officer

                                   By: /s/ Rafael Gomez Flores
                                       -----------------------------
                                       Name:  Rafael Gomez Flores
                                       Title: President
                                                                             
                                                                             
                                   MOTOR COACH INDUSTRIES, INC.          
                                                                             
                                   By: /s/ Guillermo Kareh Aarun               
                                       -----------------------------           
                                       Name:  Guillermo Kareh Aarun             
                                       Title: Chief Executive Corporate Officer
                                              and Secretary

                                   By: /s/ Rafael Gomez Flores
                                       -----------------------------
                                       Name:  Rafael Gomez Flores
                                       Title: Chairman of the Board 
                                              and President
                                                                             
                                                                             
                                   MOTOR COACH INDUSTRIES-CHINA, INC.    
                                                                             
                                   By: /s/ Guillermo Kareh Aarun               
                                       -----------------------------           
                                       Name:  Guillermo Kareh Aarun             
                                       Title: Chief Executive Corporate Officer
                                              and Secretary

                                   By: /s/ Rafael Gomez Flores
                                       -----------------------------
                                       Name:  Rafael Gomez Flores
                                       Title: Chairman of the Board 
                                              and President
                                                                             
                                                                             
                                   TRANSIT BUS INTERNATIONAL, INC.       
                                                                             
                                   By: /s/ Guillermo Kareh Aarun               
                                       -----------------------------           
                                       Name:  Guillermo Kareh Aarun             
                                       Title: Chief Executive Corporate Officer
                                              and Secretary

                                   By: /s/ Rafael Gomez Flores
                                       -----------------------------
                                       Name:  Rafael Gomez Flores
                                       Title: Chairman of the Board 
                                              and President
                                                                             
                                                                             
                                   CUSTOM ASSETS CORP.                   
                                                                             
                                   By: /s/ Guillermo Kareh Aarun               
                                       -----------------------------           
                                       Name:  Guillermo Kareh Aarun             
                                       Title: Chief Executive Corporate Officer
                                              and Secretary

                                   By: /s/ Rafael Gomez Flores
                                       -----------------------------
                                       Name:  Rafael Gomez Flores
                                       Title: Chairman of the Board 
                                              and President
                                                                             
                                                                             
                                   TRANSPORT TECHNOLOGY CORPORATION      
                                                                             
                                   By: /s/ Guillermo Kareh Aarun               
                                       -----------------------------           
                                       Name:  Guillermo Kareh Aarun             
                                       Title: Chief Executive Corporate Officer
                                              and Secretary

                                   By: /s/ Rafael Gomez Flores
                                       -----------------------------
                                       Name:  Rafael Gomez Flores
                                       Title: Chairman of the Board 
                                              and President





                                     -8-


<PAGE>   9


                                   UNIVERSAL COACH PARTS, INC.           
                                                                             
                                   By: /s/ Guillermo Kareh Aarun               
                                       -----------------------------           
                                       Name:  Guillermo Kareh Aarun             
                                       Title: Chief Executive Corporate Officer
                                              and Secretary

                                   By: /s/ Rafael Gomez Flores
                                       -----------------------------
                                       Name:  Rafael Gomez Flores
                                       Title: Chairman of the Board 
                                              and President
                                                                             
                                   Lenders:                              
                                                                             
                                   THE BANK OF NEW YORK                  
                                                                             
                                   By: /s/ John R. Ciulla
                                       -----------------------------           
                                       Name:  John R. Ciulla
                                       Title: Associate Vice President
                                                                             
                                                                             
                                   KEYBANK NATIONAL ASSOCIATION          
                                                                             
                                   By: /s/ Marianne Mell
                                       -----------------------------           
                                       Name:  Marianne Mell
                                       Title: Vice President
                                                                             
                                                                             
                                   COMERICA BANK                         
                                                                             
                                   By: /s/ Richard C. Northrup III
                                       -----------------------------           
                                       Name:  Richard C. Northrup III
                                       Title: Associate Vice President
                                                                             
                                                                             
                                   HUNTINGTON NATIONAL BANK              
                                                                             
                                   By: /s/ Thomas G. Myers
                                       -----------------------------           
                                       Name:  Thomas G. Myers
                                       Title: Vice President
                                                                             
                                                                             
                                   BANK OF HAWAII                        
                                                                             
                                   By: /s/ Donna R. Parker
                                       -----------------------------           
                                       Name:  Donna R. Parker
                                       Title: Vice President




                                     -9-



<PAGE>   10


                                       NATIONSBANK, N.A.                    
                                                                            
                                       By:  /s/ Valerie C. Mills           
                                           --------------------------------
                                            Name: Valerie C. Mills         
                                            Title: Sr. Vice President      
                                                                            
                                                                            
                                       THE SANWA BANK, LIMITED, CHICAGO     
                                       BRANCH                               
                                                                            
                                       By:  /s/ Tomomi Omura
                                           --------------------------------
                                            Name: Tomomi Omura
                                            Title: Assistant General Manager
                                                                            
                                                                            
                                       THE SUMITOMO BANK, LIMITED           
                                                                            
                                       By:  /s/ S.M. Kanunski
                                           --------------------------------
                                            Name: S.M. Kanunski
                                            Title: Vice President       
                                                                            
                                       By:  /s/ H.W. Redding
                                           -------------------------------- 
                                            Name: H.W. Redding
                                            Title: Vice President and Manager
                                                                            

Commitment:                            THE FIRST NATIONAL BANK OF CHICAGO,
-----------                                 Individually as a Lender, the
$20,000,000                                 Swing Line Bank and an Issuing 
                                            Lender, and as Administrative Agent

                                       By:  /s/ Gary Gage
                                           --------------------------------
                                            Name: Gary Gage
                                            Title: Sr. Vice President      


                                       NBD BANK, Individually as an exiting 
                                            Lender, Swing Line Bank and Issuing
                                            Lender, and as the resigning 
                                            Administrative Agent

                                       By:  /s/ Gary Gage
                                           --------------------------------
                                            Name: Gary Gage
                                            Title: Sr. Vice President      



                                    -10-


<PAGE>   11




                                   SCHEDULE I
                                       TO
                                AMENDMENT NO. 2
                                       TO
                                CREDIT AGREEMENT
                            DATED SEPTEMBER 30, 1996

                           EXISTING LETTERS OF CREDIT



<TABLE>
<CAPTION>
                  Letter of                 Expiration
        Issuer    Credit No.   Face Amount    Date          Beneficiary
        ------    ----------   -----------  ----------      -----------
        <S>        <C>         <C>          <C>         <C>
                                         
        NBD Bank   S149309     $  400,000    11/21/97    OLD REP INS. CO.
                                         
        NBD Bank   S149310     $  280,000    11/21/97    TRANSAMERICA INS. CO.

        NBD Bank   S149311     $2,000,000    11/21/97    CONT CASUALTY CO.

        NBD Bank   S149307     $1,000,000    11/21/97    WORKERS COMP ADM
                                                          SUNWEST BANK

        NBD Bank   S149848     $1,000,000    5/6/98      AETNA CASUALTY
</TABLE>












                                     -11-