-----BEGIN PRIVACY-ENHANCED MESSAGE-----
Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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 TWSM7vrzLADbmYQaionwg5sDW3P6oaM5D3tdezXMm7z1T+B+twIDAQAB
MIC-Info: RSA-MD5,RSA,
 HlpgvWnpLuxOWcu1bNb5zrCIFL23/InZRCVLM+U21Pk1dT5v9WMrdYasZajlRBUy
 HBXq9allRtv/tAYCAXmK0w==

<SEC-DOCUMENT>0001048128-04-000005.txt : 20041222
<SEC-HEADER>0001048128-04-000005.hdr.sgml : 20041222
<ACCEPTANCE-DATETIME>20041222125329
ACCESSION NUMBER:		0001048128-04-000005
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20041221
FILED AS OF DATE:		20041222
DATE AS OF CHANGE:		20041222

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			SUN HYDRAULICS CORP
		CENTRAL INDEX KEY:			0001024795
		STANDARD INDUSTRIAL CLASSIFICATION:	MISCELLANEOUS FABRICATED METAL PRODUCTS [3490]
		IRS NUMBER:				592754337
		STATE OF INCORPORATION:			FL
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		1500 WEST UNIVERSITY PKWY
		CITY:			SARASOTA
		STATE:			FL
		ZIP:			34243
		BUSINESS PHONE:		9413621200

	MAIL ADDRESS:	
		STREET 1:		1500 WEST UNIVERSITY PKWY
		CITY:			SARASOTA
		STATE:			FL
		ZIP:			34243

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			KOSKI THOMAS L
		CENTRAL INDEX KEY:			0001234881

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-21835
		FILM NUMBER:		041219903

	BUSINESS ADDRESS:	
		STREET 1:		SUN HYDRAULICS CORP
		STREET 2:		1500 W UNIVERSITY PARKWAY
		CITY:			SARASOTA
		STATE:			FL
		ZIP:			34243
		BUSINESS PHONE:		9413621200

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			KOSKI ROBERT C
		CENTRAL INDEX KEY:			0001234880

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-21835
		FILM NUMBER:		041219904

	BUSINESS ADDRESS:	
		STREET 1:		SUN HYDRAULICS CORP
		STREET 2:		1500 W UNIVERSITY PARKWAY
		CITY:			SARASOTA
		STATE:			FL
		ZIP:			34243
		BUSINESS PHONE:		9413621200

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			KOSKI CHRISTINE L
		CENTRAL INDEX KEY:			0001234878

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-21835
		FILM NUMBER:		041219905

	BUSINESS ADDRESS:	
		STREET 1:		SUN HYDRAULICS CORP
		STREET 2:		1500 W UNIVERSITY PARKWAY
		CITY:			SARASOTA
		STATE:			FL
		ZIP:			34243
		BUSINESS PHONE:		9413621200

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			KOSKI BEVERLY
		CENTRAL INDEX KEY:			0001234877

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-21835
		FILM NUMBER:		041219906

	BUSINESS ADDRESS:	
		STREET 1:		SUN HYDRAULICS CORP
		STREET 2:		1500 W UNIVERSITY PARKWAY
		CITY:			SARASOTA
		STATE:			FL
		ZIP:			34243
		BUSINESS PHONE:		9413621200

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			KOSKI FAMILY LP
		CENTRAL INDEX KEY:			0001234879

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-21835
		FILM NUMBER:		041219907

	BUSINESS ADDRESS:	
		STREET 1:		SUN HYDRAULICS CORP
		STREET 2:		1500 W UNIVERSITY PARKWAY
		CITY:			SARASOTA
		STATE:			FL
		ZIP:			34243
		BUSINESS PHONE:		9413621200

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			KOSKI ROBERT E
		CENTRAL INDEX KEY:			0001048128

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-21835
		FILM NUMBER:		041219908

	MAIL ADDRESS:	
		STREET 1:		1500 WEST UNIVERSITY PARKWAY
		CITY:			SARASOTA
		STATE:			FL
		ZIP:			34243
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>primary_doc.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2004-12-21</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001024795</issuerCik>
        <issuerName>SUN HYDRAULICS CORP</issuerName>
        <issuerTradingSymbol>snhy</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001048128</rptOwnerCik>
            <rptOwnerName>KOSKI ROBERT E</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>1500 WEST UNIVERSITY PARKWAY</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>SARASOTA</rptOwnerCity>
            <rptOwnerState>FL</rptOwnerState>
            <rptOwnerZipCode>34243</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001234879</rptOwnerCik>
            <rptOwnerName>KOSKI FAMILY LP</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1></rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity></rptOwnerCity>
            <rptOwnerState></rptOwnerState>
            <rptOwnerZipCode></rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001234877</rptOwnerCik>
            <rptOwnerName>KOSKI BEVERLY</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1></rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity></rptOwnerCity>
            <rptOwnerState></rptOwnerState>
            <rptOwnerZipCode></rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001234878</rptOwnerCik>
            <rptOwnerName>KOSKI CHRISTINE L</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1></rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity></rptOwnerCity>
            <rptOwnerState></rptOwnerState>
            <rptOwnerZipCode></rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001234880</rptOwnerCik>
            <rptOwnerName>KOSKI ROBERT C</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1></rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity></rptOwnerCity>
            <rptOwnerState></rptOwnerState>
            <rptOwnerZipCode></rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001234881</rptOwnerCik>
            <rptOwnerName>KOSKI THOMAS L</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1></rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity></rptOwnerCity>
            <rptOwnerState></rptOwnerState>
            <rptOwnerZipCode></rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2004-12-21</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>1000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>15.95</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>2311337</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                    <footnoteId id="F1"/>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>64623</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                    <footnoteId id="F2"/>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>107162</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                    <footnoteId id="F3"/>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>141215</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                    <footnoteId id="F4"/>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Shares owned directly by Koski Family Limited Partnership.  Shares owned indirectly by Robert E. Koski, Beverly Koski, Christine L. Koski, Robert C. Koski and Thomas L. Koski, each of whom is a general partner of the partnership or the controlling person of a corporate general partner of the partnership.</footnote>
        <footnote id="F2">Shares owned directly and solely by Christine L. Koski.</footnote>
        <footnote id="F3">Shares owned directly by Robert E. Koski and indirectly by Beverly Koski, Robert E. Koski spouse.</footnote>
        <footnote id="F4">Shares owned directly by Beverly Koski and indirectly by Robert E. Koski, Beverly Koski spouse.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Gregory C. Yadley, as Attorney-in-Fact for Robert E. Koski, Beverly Koski, Koski Family Limited Partnership, Christine L. Koski, Robert C. Koski and Thomas L. Koski</signatureName>
        <signatureDate>2004-12-22</signatureDate>
    </ownerSignature>
</ownershipDocument>

</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
-----END PRIVACY-ENHANCED MESSAGE-----