Vibration in 6th gear. Thoughts?

[SEJohnson]

I've noticed a vibration in 6th gear on the highway in my '02 HO CTD. If I am gradually accelerating, the vibration begins at 72 mph, and continues on up through 80 mph (I haven't been up much higher). But if I am on the pedal, the vibration will begin as soon as I hit 6th at around 55 mph or so. The vibration feels like it's coming from the rear half the truck (I can't feel much of it in the steering wheel, but a little shake is there). Around town at lower speeds and in 1st-5th it drives smooth. I haven't heard any noises coming from the drivetrain either. Has anyone experienced this same symptom? Or have thoughts on the source? Maybe a wearing u-joint? The tires are freshly mounted and balanced, and the truck was aligned last week. If engine RPM at these speeds would help, I can go check and reply. Thanks!!

[Mopar1973Man]

Most likely is a bad u-joint... I would pull the driveshaft out completely and inspect each joint closely. It's nearly impossible to inspect a u-joint with the driveshaft installed in the truck...

[Wild and Free]

If its a long box be sure to check the driveshaft hanger bearing or carrier bearing as some call it. Also check the slip yokes for excessive play as that will cause bad vibes as it will easily explained "Jump rope" If you understand. Check t-case to tranny bolts and mounts and make sure they are still there and tight. And like you were on the way to do Check them u-joints. These are just some of what I have seen on these rigs.

[SEJohnson]

It's a short box truck. Is there a way to get the driveshaft out without removing the u-joints from the shaft via hammer/socket? Is there a slip yoke on the output of the transfer case? I'm familiar with the 'on-driveshaft' slips. I haven't gotten a repair manual for it yet so I can't immediately refer to that (I'm looking for one right now though). Thanks. SJ

[Wild and Free]

Just remove the U straps that hold the ujoint to the axle yoke to remove the drive shaft from the vehicle. the front shaft has a bolt on flange yoke at the t-case with 4 bolts. The rear shaft just slips onto the output shaft of the t-case. The CV joint at the t-case end of the front driveshaft can cause vibes also when it goes bad. Most do not know they are greaseable with a grease needle. Not all are though, some are factory sealed. I think 2nd gens are factory sealed but 3rd gens are greasable again. I have a custom built front drive shaft for pulling and had a greasable cv joint installed.

[SEJohnson]

Ok, sure enough...not hard to pull that out. So I have it out now, and I'm going to press out the U-joints with sockets and a vise. What should I be looking for in a worn u-joint? When I replaced one on my Toyota, it was fried (i.e. the bearing were dust), so I have little experience with slightly worn joints. The needle bearings and caps on the joint ears that were in the axle yoke look pretty good, and I don't feel any slop in those two. Thanks again. SJ

[Wild and Free]

Roll them and see if they feel smooth or if they feel ratchety or bumpy "Knurled" is the term for this if not smooth then they are shot. I wouldn't press them out if they are not bad.

[Mopar1973Man]

:bang: Well I'm in the same boat... As I left for Lewiston yesterday I got a weird vibration as well... Got about 8 miles from home and pulled over and checked... sure enough the front driveshaft was sloppy... :cry2: So I turned around and loaded up in Mom's truck (96 Gasser) and hauled for Lewiston... So I'm in the same boat...

[SEJohnson]

I got the rear u-joint out of the shaft and cleaned up the pins. I noticed some vertical scoring on one pin (which looked like marks from the needle bearings, but this may have happened when I was hammering out the u-joint (turns out our vise isn't big enough to get sockets and the yoke in the jaws, so I reverted to hammering)). On the same pin, it looked like some of the steel had been chipped off - the surface of the pin looked rough and slightly pitted. I put all the caps back on the joint and checked for play. I found three of the four caps had very slight lateral play in them, but could this be due to void created when I removed some of the grease during clean up? Or should there be no noticeable play EVER? Do you folks think I should check the forward u-joint now as well? Or replace the rear joint and install the drive shaft to see if the vibration was fixed? Thanks for the help. SJ

[Wild and Free]

I would check the front, from your description its not the cause of a vibe. You generally won't notice slightly worn joint as a bad vibe until they are near total failure. You don't need to remove the joints from the shaft though, save the time and money and just go by feel. By the way are you pinion seals leaking? If the pinion bearings are starting to fail it will cause vibes also.

[Mopar1973Man]

Make sure you clean up the holes in the yokes so you not fighting to beat the new joints in... Use a light sandpaper and remove the rust and junk from the holes. But don't over do it... Once assembled it should be a nice smooth action in all angles. It shouldn't be stiff, tight or rough feeling... I'll most likely have a write up after I do my fronts...

[Wild and Free]

One other thing I need to ask is what "Frequency" is the vibe? Slow and heavy like a tire out of balance or high speed vibe like driveline 3-3k rpm range? Does it change with engine rpm or road speed or both? Another check is to jack stand it at all 4 corners and run it up to speed with the tires off the ground and isolate it from front to back. Or just jack stand the back and chock the front to prevent rolling. and run it in gear with tires off the ground.

Edited January 10, 2010 by Wild and Free

[SEJohnson]

There's no play nor grinding nor noise coming from the front joint. It feels pretty good. I'll leave that one alone for now. The pinion is not leaking any fluid and I checked it for play, laterally in all directions and with the length of the vehicle. It was solid in every direction. When turning it there was slight gap between the gear teeth engaging in the rearend...but this is normal, correct? I'm heading for the install of the rear joint and I'll post back one I get a test drive in. SJ

[SEJohnson]

I can't really say if it's at a higher or lower freq (haven't had enough driving vibration experience to say), but it's definitely a couple thousand RPM. It increases with engine speed and road speed, pretty linearly too. I haven't been able to 'push through it' like some vibrations I've had in other cars...but then again I haven't explicitly tried to do this. I had four new tires mounted and balanced (by the shop our family has been taking all of our cars to for over ten years) two weeks ago. Alignment done too. :confused:

[Wild and Free]

When you test drive get it up to vibe speed and then mexican over drive it, Put it in neutral and coast at the vibe speed and let engine go to idle speed step clutch in and out while coasting just experiment and see if it is still there without the engine harmonics factoing into it and see if it just the same or how it changes it. Also can remove the front driveshaft and drive it that way just to eliminate it as a culprit. Its all about isolating it at this point. I have on more occasions than not had new tires be the worst culprits of vibes. I have a set now I have been fighting for a few thousand miles and numerous rebalances and they are just out of round a bit. Got a warranty replacement set and got the same issue 2 of them are out of round. so I drove them to round them out and its getting better now to get them rebalanced again.

Edited January 10, 2010 by Wild and Free

[SEJohnson]

So the vibration was still there at the same speeds after the rear u-joint install. I hadn't read the post about the front drive shaft until after my drive, so I will be trying that tomorrow morning - checking it for play, removing it, and going out for a test. I'll report with the results. At 80 mph I shifted into neutral to coast, and the vibration was still present until speed reduced to the 72 mph (that I mentioned earlier) at which point the vibration went away. All symptoms were the same as before, so I'm going to say that as was mentioned, it seems as though the rear shaft is not the problem. 70 mph in 6th sat about 1970 rpm, just FYI. Thanks for the note on the tires. I hadn't heard about problems such as that before. SJ

[Wild and Free]

My current set do the exact same thing smooth as glass until about 70 then vibe comes on until 75ish and then smooths out again. Out of balance drive shafts will do the same thing also.

[SEJohnson]

FOUND IT!!....and fixed it! This morning I crawled under the truck and checked the front u-joint for slop with the shaft still installed. I saw one cap that was loose when I torqued the shaft by hand. So I removed the shaft and the u-joint and sure enough, one of the points of the joint was fried...no needles or grease to be seen. The double cardan joint at the rear of the shaft felt tight, so I left that alone, but I replaced the front joint (that mounts to the yoke on the axle) and reinstalled the shaft. I went for a drive before this though, without the shaft installed. The truck ran smooth right up to 85mph, where I decided to cut it since I'd seen three highway patrolmen within a two mile stretch of road. So I came home, installed the shaft, greased up, and went back for a drive. No vibrations this time! Same as without the shaft. I'm happy. Thanks for all the help, really. I tried greasing the middle joint in that double cardan with a grease needle...but not sure I did it right. No grease came out of it though when I pumped a few squeezes into it. Thanks again!! :thumbsup:Sam

[Wild and Free]

Glad to hear you got it figured out...........:biggrin:

[ipolute]

I also had a vibration, so the I took it to my tire place and had them rotate the tires a check the balance of them, sure enough one was out of balance. It fixed the problem.