I just finished building up a road bike (early 90s steel). The last thing I did was changing out the cables and STI shifters. I had to adjust the derailleurs after that. The gears seem to shift nicely now, but to my great surprise I found that when I move the pedals backward (counter clockwise) there appears to be a lot of tension to put the rear wheel to spin backwards. The same cassette, chain and cranks were on the bike before and worked nicely. Any idea, where the problem could lie? Thanks!