<?xml version="1.0"?>

<ownershipDocument>

    <documentType>4</documentType>

    <periodOfReport>2003-05-27</periodOfReport>


    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000764039</issuerCik>
        <issuerName>TECHDYNE INC</issuerName>
        <issuerTradingSymbol>TCDN</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001030318</rptOwnerCik>
            <rptOwnerName>PARDON BARRY</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>  </rptOwnerStreet1>
            <rptOwnerStreet2>  </rptOwnerStreet2>
            <rptOwnerCity>  </rptOwnerCity>
            <rptOwnerState>  </rptOwnerState>
            <rptOwnerZipCode>  </rptOwnerZipCode>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>President</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeSecurity>
        <securityTitle>
            <value>Common Stock, $.01 par value</value>
        </securityTitle>
        <transactionDate>
            <value>2003-05-27</value>
        </transactionDate>
        <transactionCoding>
            <transactionFormType>4</transactionFormType>
            <transactionCode>J</transactionCode>
            <equitySwapInvolved>0</equitySwapInvolved>
            <footnoteId id="F1"/>
        </transactionCoding>
        <transactionTimeliness>
            <value></value>
        </transactionTimeliness>
        <transactionAmounts>
            <transactionShares>
                <value>31400</value>
            </transactionShares>
            <transactionValue>
                <value>1.88</value>
            </transactionValue>
            <transactionAcquiredDisposedCode>
                <value>D</value>
            </transactionAcquiredDisposedCode>
        </transactionAmounts>
        <postTransactionAmounts>
            <sharesOwnedFollowingTransaction>
                <value>62133</value>
            </sharesOwnedFollowingTransaction>
        </postTransactionAmounts>
        <ownershipNature>
            <directOrIndirectOwnership>
                <value>D</value>
            </directOrIndirectOwnership>
        </ownershipNature>
    </nonDerivativeSecurity>

    <footnotes>
        <footnote id="F1">On 2/25/00, Mr. Pardon acquired 40,000 shares by exercise through par value payment of $400 and issuance of a $69,800 three-year non-recourse promissory note with the shares being held in escrow until the promissory note was satisfied.  Mr. Pardon is hereby surrendering 31,400 shares to the Issuer in exchange for cancellation of the promissory note.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/  Barry James Pardon</signatureName>
        <signatureDate>2003-05-29</signatureDate>
    </ownerSignature>

</ownershipDocument>

