My wipers are doing the same thing. They work ok when I get in the car and once I am driving for 20-30 minutes, they start to slow down, then they eventually lock up and stop. I went into a store and came out and they worked ok again, but then did the same thing about 20 minutes later and stopped working. Could it be a bad relay or a motor going bad??? I will try them without the arms on and see what happens.

It is possible that the nuts that attach your wiper arms are loose. This would cause them to slip on their shafts.

I doubt that the lock problem is related to the wiper problem. If it is, it might involve a bad power connection that reduces the voltage going to power these items. (A real long shot!)

Good luck with your new brick.
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96 855R, 95 855,854, 90 744 Ti - 340,000 Volvo miles put on 7 bricks

take the wipers off and then turn the motor on, and see if it moves freely. If it does then it's not electrical

You just might need to bend the wipers outward some.
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'88 240, '92 745, '98 v70 John, Tampa Bay