Weinmann center pull vainqueur 750 brake grab

I am rebuilding an early 80's Peugeot with Weinmann center pull brakes. I switched the wheels from 27 to 900c. When I apply the rear brakes, the bike starts to slow, then the brake pads grab suddenly and the tire skids. The pads are aligned correctly on the rim. The wheel is brand new, so I don't think there is any residue or buildup on it. I have tried centering the pads and adjusting them within a few mm of the rim. I also have done the front toe in adjustment. Any suggestions?

I cannot get any photos to upload. Here are the links:

https://ep1.pinkbike.org/p5pb30220437/p5pb30220437.jpg

https://ep1.pinkbike.org/p5pb30220436/p5pb30220436.jpg