I've been experiencing a bad vibration at around 60-70mph on my truck ever since I bought it. I have been blaming the tires (dunlops) that came with it. However, after reading several posts here, I wondered if it could be a driveshaft issue.

I decided to undo the driveshaft from the transfer case to see if the companion flange nut might possibly be loose. It wasn't. In order for me to get the driveshaft down, I had to unscrew the bolts holding up the center support bearing. When I bolted the driveshaft back up, I tried to bolt the center support bearing back exactly as it was. But, when I looked down the driveshaft it just didn't look straight. So, I loosened the bolts and put the driveshaft as straight as possible by looking down the driveshaft length and then retightened the support.

To my amazement, my truck is now almost vibration free. In my bumbling, I have almost fixed my problem. I can live with it now, but it could be just a little better.

Should I take it somewhere to have it balanced? Should I consider going with a one-piece drivehsaft?

 

if all of the u-joints are good, you could get it balanced, but i doubt that it is out of balance much if you have all of the factory weights on it and its not dented, it sounds like more of a center support problem, and you cant go to a one piece because of how long it is, my reg cab has a one piece, but im also a little over a foot shorter than you, the reason that you cant have such a long driveshaft is that at high driveline speeds, the center of the shaft will want to "whip" out, causing it to bend itself and tear up the undercarrage of your truck

 

We replaced the 2 piece shaft on our 85 PU with a 1 piece. The center bearing destroyed itself. Have had no problems since. I don't know if it is possible to do on your setup.

 

The first Xtracabs had an odd vibration problem that was fixed at the time by installing a one piece driveshaft. (They eventually figured out that the angles caused by the center bearing mount were wrong and changed that, but a lot were retrofitted to one-piece shafts and that fixed it.) There are mid-range trucks out there with 12 foot driveshafts, the length isn't really a problem... Sounds like you might have a steady bearing problem or a bent driveshaft, as Superjoe said, assuming your U-joints are good.

 

I drove my truck today and it seems that the vibration has increased again. Perhaps it is my imagination, but I am pretty sure it was much less yesterday when I dropped and reattached the driveshaft. I know it was. Maybe the trouble is in the support bearing.

I read somewhere about swapping to a one-piece. It is my understanding that the shaft must be bigger and therefore the brackets that hold up the support bearing must be removed to accomodate the larger driveshaft, which would make it hard to revert back to the original driveshaft. If I knew that would fix my problem though, I would do it.

I still think some of my vibration is coming from the tires, I just can't tell how much at the moment. All the vibration that I have is in the steering wheel. It seems that if it was only the driveshaft, I would feel it elsewhere.

Thanks for the replies.

By the way, I have thought about dropping my rear driveshaft and driving in 4-hi to see if the vibration goes away. Can I, and would there be any problem with that?

 

I completely removed the rear driveshaft and ran it in 4 Hi. It still has a shake at about 60mph. So, I guess it isn't the driveshaft.

I'm tired of troubeshooting. My gut says it is the tires. Looks like I need to buy a new set to be sure though.

 

Put the truck on jackstands and observe the wheels at speed. Make sure you get both wheels going btw, and not just one. Have you ever had these tires balanced? You can also check for out of round on the jackstands. Do the basic checks for mud packed in the wheels as well btw, particularly the backside of the wheels where they frequently aren't cleaned.

 

I haven't technically done that yet, but last week I had a co-worker follow me in another vehicle. He noted that 3 out of 4 of my tires had a noticeable shimmy. He was able to drive alongside and I switched lanes so he could get a good look.

I need to do like you said and put it on jack stands to see if I can detect anything. The tires are clean-no mud or dirt.

I have even had them lug balanced on a Hunter machine. Once I found this site and read about the Hunter, I decided to give it a try in desperation. I didn't really know about the road force values until after I had it done. But, the shop that balanced them last marked my tires with a grease pencil on the inside. Each one has a number. The numbers are 44, 26, 16, and 6(?). It is my understanding that a road force number of about 16 and above is bad. So, if that is the case, I have 3 crappy tires. The shop owner didn't elaborate, but only said I might need to get new tires to fix my problem. These tires are almost new. The previous owner put them on before he sold it to me. He might have gotten rejects put on there for all I know. One has since went bad, and I have had it replaced at Goodyear. As a matter of fact, I think it is the one with the 44 number on it! They said it was an alignment issue. I don't really believe them.

Like I said earlier, they are Dunlops and many here have had issues with them. I have recently bought some alloy wheels of off eBay to replace my steel wheels. As much as I hate to spend the money, I think I am going to buy another set. I am considering Michelin LTX/ATs at the moment. It's not as aggressive as the Dunlops on it now, but at this point I don't care. I don't do heavy duty mudding anyway. My coworker had them on his Tacoma and he got many miles out of them.

The truck is very tight. Like new even. At this point, I just believe it is the tires.