I bought a new chain for my bike. I didn't have the old one. I went online and found Shelden Browns website. It says to wrap the new chain around the largest sprockets front and rear without routing throught the derailluers. I did this and the chain is to short. How do they account for different length rear derailluer cages anyway. Mine is a 8 speed XT medium cage. Can I piece the chain back together? Or do I have to buy a new one?
Thanks to all that respond..........

Did you remember to add the two half-links of chain (1") as suggested at that website? The length of the derailleur cage doesn't really matter since the idea is to just have the chain long enough to reach when the cage is pulled all the way forward. Yes it is possible to piece the chain together again, but the procedure depends on the type of chain (narrow Shimano chains require special pins) and whether or not you pushed the pin completely out when you shortened the chain.

You forgot one important step -- after wrapping the chain around big ring/big cog, you ADD one link, which is 3 rollers long. Or, about an inch of chain.

That WILL work for you if you do it right -- it's worked for me for the last decade.