I have a 1979 F150 4WD pickup. It has a bad vibration at around 20 to
25 mph. The whole truck vibrates and rattles. The vibration stops if I shift into neutral, so that rules out the tires. I looked at the universal joints and they are fine. I finally took the truck to a mechanic, and he checked the same things I did (tires and univ. joints). He said he can not isolate the problem either. His only suggestion is a bent driveshaft. He said the only way to be sure is to take the driveshaft to a special shop that works on them, and have them test it. But, he said that there is no such place closer than 100 miles away, and the cost to travel there, plus the testing would probably cost more than getting another driveshaft from a junk yard. But he said it's a gamble if another driveshaft will solve the problem.Does anyone have any ideas? I am at a real loss on this one, and the mechanic said he is not sure too.....
Is there any way to check the driveshaft myself, if I remove it?
What else could cause this problem?
Like I said, it only vibrates badly at the 20 to 25 mph speed, and of course that is the speed limit in the local rural towns.
All advice appreciated !