Chevrolet Repair: Truck shakes, rattles and rolls., chevy c10, seat of your pants

Question
Hey guys; I have a 86 Chevy C10 with a 305, auto trans and no A/C. My truck shakes pretty bad from 65-70MPH, but rides smooth at higher and lower speeds. Any ideas what could be the culprit, or what I could do to help narrow it down?

Answer
HI SHAUN, THE FIRST THING THAT COMES TO ME ON THIS TYPE PROBLEM IS TIRE BALANCE OR BENT WHEEL. IF YOU FEEL THE SHAKE IN THE STEERING AT THESE SPEEDS I WOULD CK THE TIRE BALANCE AND MAKE SURE ALL THE FRONT END SUSPENSION IS ALL TIGHT..BEING THAT THE SHAKE STOPS OR LESSONS AFTER 70 MPH IS USUALLY TIRE BALANCE..IF YOU FEEL THE SHAKE IN THE REAR OF TRUCK LIKE IN THE SEAT OF YOUR PANTS THIS AGIAN SOUNDS TO ME LIKE TIRE BALANCE..IF THE SHAKE WERE UNDER ACCELERATION ONLY AND WHILE YOU COAST IT SMOOTHS OUT THIS WOULD BE FROM THE DRIVELINE,SUCH AS BAD OR LOCKING UP U- JOINTS IN THE DRIVESHAFT..THIS SHOULD NARROW IT DOWN FOR YOU I WOULD THINK..IF NOT GET BACK TO ME AND WE WILL CHAT MORE.. GOOD LUCK,,,TOM...