Should I do a drain and refill or a drain and refill then flush of transmission fluid

1998 GMC JIMMY
125,708 MILES • 6 CYL • AUTOMATIC
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ROYCAR71
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I am near my interval to replace my transmission fluid in both of my vehicles(GMC Jimmy 98 and Ford Expedition 97). My question is should I do a drain and refill and replace filter or drain and refill replace filter than Flush new transmission through cooler lines?
Jun 25, 2012 at 2:01 AM
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ASEMASTER6371
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flush first is my recommendation.

Roy
Jun 25, 2012 at 2:03 AM
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ROYCAR71
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Disconnect cooler supply line and pour new transmission fluid in. Put pan underneath cooler line and turn on engine. Transmission fluid flows in pan as I continue to add new transmission fluid and old transmission fluid comes out of cooler supply line until new transmission fluid shows coming out stop engine. Then I should drop transmission pan and change filter and gasket and loose some new transmission fluid just poured in to flush out old fluid. Then top off to required level. Is this how it is done? Thanks.


P.S. both vehicles have over 100,000 miles and never had flush done.
Jun 25, 2012 at 2:18 AM
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ASEMASTER6371
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no. you need the actual machine that circulates the fluids. when you do it this way, you starve the main shaft of lube with an open cooler line.

Roy
Jun 25, 2012 at 2:39 AM