BRIDGING WITH TWO CISCO ROUTERS AND T1

Hello,
I am having some trouble getting my two cisco routers to work via a T1 line. I need to setup bridging across the T1, but can’t seem to get the bridging function to work. Both IOS are 12.0 and and one routher is a 3640 with a T1 wic card the onthe is a 1720 router with a T1 wic card. I have the Two routers configured for the T1 line and one of the routers are providing the clock. Th CD lite comes on and the AL light goes of. Both Serial lines come up, but they won’t pass any trafic. Any suggestion would be great. Thanks
Jason