Rear windows are usually tempered glass which is more tolerant of stress. Windsheilds are much more tricky to remove safely. Many years ago, I successfully changed front and rear glass in a '68 Opel Kadett and my '61 Ponton 180b, however, much more recently, I tried to save a windsheild from an '86 BMW 535i that was headed for the junkyard. Despite cutting off all the external portion of the gasket, the glass was also glued in place with some type of sealant, so when I attempted to push it free it cracked!

Happy Motoring, Mark

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DrDKW