Been sniffing out a driveline vibration for the past several weeks. The u-joints felt tight but there was play either in the rear one or the pinon bearing was bad as there was plenty of play back there. With 177k miles the u-joint was suspect. After pulling the driveshaft, lo and behold! It was neither. The pinon shaft nut was loose allowing the flange to wobble around and vibrate. This is the original setup, never been worked on. The original torque setting is around 250-300 ft lbs. How this ever came loose is beyond me. Tightened it back up and voila', no more bad vibes! (How to get the rear driveshaft bolts off is a whole separate subject)

 

At what speed did you get the vibrations? I get a very consistent humm between 50-55mph. I am not sure if it is the driveline or if the tires are the cause. Are my symptoms similar to what you experienced? If not, any ideas?

Thanks.

 

[font size="1" color="#FF0000"]LAST EDITED ON 24-Apr-01 AT 05:04 PM (EST)[/font][p]Mine would occur once around 50-55 and again more pronounced at 70-75mph, shaking everything to the point I thought the transfer case was the problem. It was just transfered vibration. I also have a "body drum" at exactly 45mph, consistent over any type pavement. Mine is a 91 AWD, extended. This is transmitted road noise and I haven't found any cure. (Although I can't remember this happening when we first owned the van) You can distinquish between this and driveline vibration by selecting a lower gear and running the speedometer to the same speed where the noise occurs. If yours still drums at 50-55 is it probably road noise. If it happens at another speed it is likely driveline as the lower gear causes the driveline components to turn at a higher speed thus the noise would appear at a different interval. If you suspect driveline I would be glad to help you sort it out as there are several possible causes. Hope this helps!

 

I appreciate the feedback. I will try the different gear thing tonight. If it doesn't pan out to be road noise I'll get back to you. Thanks.

 

Transmission gear selection will not affect the rate the driveshaft and axles turn at a given speed. If the drive shaft is turning at 2000 rpm at 50mph in third gear, that same drive shaft is going to be turning at 2000 rpm at 50 mph in overdrive.
The engine speed/input shafts will be different for different gears selected, but not the final drive or axles.

 

Good point. So how could you check this then?

 

Mea culpa! I checked my reference (a trouble shooting guide) and that is their recommended method. It sounded reasonable to me at the time, but your post makes sense when you stop and reason it out. The driveshaft and axles are a fixed ratio. Can't believe everything you read. Sorry for the misinformation.

 

I'm not a rearend mechanic, but I did learn a few things from some of them. There is a brass crush sleeve that gets "squished"(hi-tech term) when the rearend is first put together. Technically, the crush sleeve should be replaced when being retorqued, for the correct preload on the pinion. I know,I know, I wouldn't either! Just be on the lookout for excessive rearend noises down the road. Who knows, you may get lucky and have got it at the right spot. At this point, its a waiting game. You might even pull it off again and put some blue locktite on it,then retorque it.

Driveline vibrations can sometimes be diagnosed by traveling above the speed at which the vibration or "drone" sound is heard, then let off the gas and coast down past the problem speed. If the problem is changed or goes away completely, its driveline. If it doesn't change at all....its in the tires or something. Thats what the instructors at Ford Motor Company taught me years ago when I first started this crap. For those hard ones, there are some Hi-Tech tools out there,like a "REED TACHOMETER". You write down the readings,then go down the graph and it'll tell you if its driveline or what. They were $500 about 5 years ago.