Cisco 2610 not routing

[escchr]

I have just taken over the network infrastructure where I work and my cisco skills are not the best. I am trying to put in a Cisco 2610 router and have configured for the most part but I am get weird results. This is my setup

Router A
e0/0 ip is 172.16.1.254 connects to main site
s0/0 ip is 192.168.254.20 connects to a dsu over the serial line of this router to another dsu on Router B

Router B(the one I am having the problem with)
e0/0 ip is 172.16.26.254 connects to network at branch office
s0/0 ip is 192.168.254.18 connnects to a dsu over the serial line to router A

The problem I am having is when I am consoled into Router B I can ping over the dsu to Router A to both interfaces. From the local network 172.16.26.0/24 I can ping both interfaces of Router B, but I cannot ping anything past that. I know it is a routing issue but I cant for the life of me figure it out.
I have setup just one route on Router B
ip route 0.0.0.0 0.0.0.0 s0/0
I would think this would work for the 26 network but it is not. Keep in mind I am no expert here so I know it is something stupid that I am missing. What could be causing this?

 

[vipergg]

You put a default route on router B. How does it know how to get back if you don't have a route on router A also pointing back. You need a route on "A" pointing to anything you need to get to on router "B" also.You could also implement dynamic routing protocols like EIGRP or OSPF to eliminate this worry .

 

[escchr]

Forgot to mention that Router B is replacing an existing router that Router A already had routes for.