Need help

[teamradrz1]

I just installed a newly shortened and balanced driveshaft for my 71 K5 Blazer has 3/4 ton axles and he put a 3/4 ton yoke on the driveshaft to match the pumpkin yoke. Looks perfect but I drove the truck home with the original shaft that was too short and everything was OK put the new shaft on and drove down the street fine but as soon as I hit the brakes softley was only going like 20MPH I heard and felt a Vibration sounded like my nobby tires hitting the fender. doesn't do it taking off or traveling down the road but when I use the brakes it's there pretty consistantly. I'll call the shop Monday but wanted to hear any ideas?