Guys/Gals Ive got a 1993 D350 dually club cab with the Getrag. Its got roughly 250ish thousand miles and a vibration between 42-50 miles per hour. I am pretty sure it is in the drive train because it will do it in 4th, 5th and even neutral. The vibration is most noticable on deceleration or coasting. I have replaced all 3 U joints, cleaned/degreased both drive shafts, replaced the carrier bearing, the tranny mount, all 4 rear tires, made sure the wheels were all centered properly etc. The rear yoke coming out of the tranny was loose, I tightened the big nut the best I could. Im out of ideas. The vibration is not teeth rattling but more of a shudder. I have considered pinion angle due to old wore sagging leaf springs, but figured it would have to be sagging REAL bad to cause an issue. I have searched and searched Im out of Ideas. Suggestions?

 

Sounds like wheel balance issues, Are the fronts balanced?...Mark

 

I have not personally balanced the front wheels since I have had the truck. Pretty sure it is not the front wheels/tires. I'm pretty sure I would be able to feel that in the steering wheel. Do you agree?

 

did you loose a weight off the drive shaft?

 

I have to say that you would not necessarily feel it in the wheel. I subscribe to the most likely theory. These symptoms, vibration at only certain speeds, are very commonly caused by wheel balance issues. I would start there...Mark

 

x2 on what Mark said.

 

Well then next stop front wheel balance. More to come. Thanks for the help.......But first let me throw this at you, I was suspecting pinion angle as I said above. I loaded my 600ish pound Harley in the bed tonight and viola the vib is gone. What do you think now?

 

I would still start at tire balance and go from there. The weight on the back changes many dynamics, including the load on the tires. Rarely does a vibration come and go so consistently if it is part of the drive train, like a thrown weight off the shaft. Start simple and easy to fix and go from there...Mark

 

When mine did that, it was mainly from power to coast it would vibrate like crazy...turned out the big nut on the yoke was loose on the front of the rear driveshaft (back of TC...or tranny if you're 2wd).

 

I would find an impact gun and put on the rear of the TC nut and see if it tightens up any.

 

I don't think his truck is a 4x4 does a 2wd getrag have a slide in yolk like a 2wd auto?

 

Yes standard slip yolk...could be a worn interior tailshaft bushing?

 

I have the same symptoms so I am going to replace the tailshaft bushing. Ill post my findings.

 

the 2wd getrag has a FIXED yoke.

It is easy to check the pinion angle. I'd take an hour and pull the shaft to take some readings with a protractor. The output of the getrag and the rear axle pinion yoke faces should be parallel.