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Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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 TWSM7vrzLADbmYQaionwg5sDW3P6oaM5D3tdezXMm7z1T+B+twIDAQAB
MIC-Info: RSA-MD5,RSA,
 TIG17MiG4ktW5g6JnFzatNgXLsbfaLOvahddkrB/AIwSawn/o73OQEwaIdYvP0fo
 m+r2P/6FXTjJPw0nyFLGaA==

<SEC-DOCUMENT>0001127602-09-017977.txt : 20090825
<SEC-HEADER>0001127602-09-017977.hdr.sgml : 20090825
<ACCEPTANCE-DATETIME>20090825165755
ACCESSION NUMBER:		0001127602-09-017977
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20090821
FILED AS OF DATE:		20090825
DATE AS OF CHANGE:		20090825

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			TWIN DISC INC
		CENTRAL INDEX KEY:			0000100378
		STANDARD INDUSTRIAL CLASSIFICATION:	GENERAL INDUSTRIAL MACHINERY & EQUIPMENT [3560]
		IRS NUMBER:				390667110
		STATE OF INCORPORATION:			WI
		FISCAL YEAR END:			0608

	BUSINESS ADDRESS:	
		STREET 1:		1328 RACINE ST
		CITY:			RACINE
		STATE:			WI
		ZIP:			53403
		BUSINESS PHONE:		2626384000

	MAIL ADDRESS:	
		STREET 1:		1328 RACINE STREET
		CITY:			RACINE
		STATE:			WI
		ZIP:			53403

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	TWIN DISC CLUTCH CO
		DATE OF NAME CHANGE:	19770217

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			EPERJESY CHRISTOPHER J
		CENTRAL INDEX KEY:			0001225634

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-07635
		FILM NUMBER:		091034457

	MAIL ADDRESS:	
		STREET 1:		1328 RACINE STREET
		CITY:			RACINE
		STATE:			WI
		ZIP:			53403
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>form4.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2009-08-21</periodOfReport>

    <issuer>
        <issuerCik>0000100378</issuerCik>
        <issuerName>TWIN DISC INC</issuerName>
        <issuerTradingSymbol>TWIN</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001225634</rptOwnerCik>
            <rptOwnerName>EPERJESY CHRISTOPHER J</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>TWIN DISC, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>1328 RACINE ST.</rptOwnerStreet2>
            <rptOwnerCity>RACINE</rptOwnerCity>
            <rptOwnerState>WI</rptOwnerState>
            <rptOwnerZipCode>53403</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isOfficer>1</isOfficer>
            <officerTitle>CFO/VP Finance/Treasurer</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2009-08-21</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>3500</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>12.23</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>39563</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1351.4446</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>401(k)</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Includes Awards of Restricted Stock pursuant to Twin Disc, Incorporated 2004 Stock Incentive Plan.  2,500 shares will vest 100% July 24, 2011 and 12,180 shares will vest 100% August 3, 2012.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Christopher J. Eperjesy</signatureName>
        <signatureDate>2009-08-25</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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