Bad Vibes

I own a 99 Silverado 5.3L Extended Cab 8' box 4X4 with 89k miles. About two weeks ago, I noticed that the entire truck began to vibrate only on deacceleration at 6-7 MPH. It seems to be more pronounced when I've been driving for a while. It will do it even when I'm coasting without breaking, it will do it when it's in Neutral coasting, it will do it with or without the 4wd engaged. I tried shutting off the engine while the vibes happen and the problem stops. The vibrations are only at that speed and there are no noticeable performance problems with the engine or transmission shifting. The best way I can describe it is that it feels like I have cupped tires at that speed.
I took it to the dealer since it's still under warranty. They repaired other known problems like a leaky transfer case seal and said that the tires where out of round causing the vibration. Seeing that I had 40k on those tires, I thought it could be possible. The very next day I spent $500+ for new tires and balancing and still had the very same problem. I took it back to the dealer and complained. 5 hours after I dropped it off, they called and said they didn't notice the problem. Naturally since the truck was not driven for a great distance, the problem was not as pronounced. The service manager and I drove the truck a short distance and the problem was slight. He did notice a little vibration and took it back into the shop and grabbed a road test computer that monitored any error codes or backfires while it was driving. It found none. He didn't think it was a problem and attributed it to a "lean bump" caused by seasonal gas. If I had a dime for every time I heard that I'd be a rich man. I forced him to write on the service report that the problem was noticed and is being monitored. Mainly because the extended warranty will expire in 4 months or 11k miles. By the way, 30 gals of 93 octane gas and the problem is still there. I consider myself a little more knowledgable then the average Bubba when it comes to auto mechanics, having rebuilt several engines over the years. If I had to guess, I feel it's something in the transmission/drivetrain area. Any suggestions would be appreciated.

Thanks,

Bubba K

I have the EXACT same problem with my 99 2WD 1500, ext cab short bed. I have 92K on it, and first noticed around 80-85K. I haven't done any research on the problem, but I've been thinking that it has something to do with the torque converter lockup. Like you, I'm more knowledgeable than the average bubba, but I'm no tranny man. Can anyone provide some insight into how the lock-up actually works?


Tom

What about a universal joint being bad. I know on my old '75 K10 when the uni's were going, I'd get a noisey vibration while gassing it at higher speeds, and then when I'd let off, because the drive shaft would shift off-center, it would really vibrate the truck.

I've noticed in my '02 Silverado 2500 HD, a similar vibration and noise is occuring above 70 mph. I'm thinking the uni's might be going again. I've got just over 49,000 miles on it, but I beat the b@!!$ off this truck on the beach. I've yanked numerous guys out of the sand that don't know how to air down, and I think it's starting to take it's toll (too bad most of them have been my own friends calling me in the middle of the night). I heard a click in the front end at the end of the season last year, and now this. But I'm taking it in for a tranny/diff/transfer case fluid change in a month or so, and I'll have them look at it.

Since I've bought it new, I've had 4 u-joints replaced. The usual symptom I've had is that they start to squeal like a stuck pig. It's possible I might have another bad one but I think if it where shifting the driveshaft, it would be vibrating at various other speeds.

Since I've bought it new, I've had 4 u-joints replaced. The usual symptom I've had is that they start to squeal like a stuck pig. It's possible I might have another bad one but I think if it where shifting the driveshaft, it would be vibrating at various other speeds.

When you replaced the ujoints did you replace them with off the shelf joints not made for the aluminum shafts? If you replace them with off the shelf joints, they will acctually corrode the aluminum yokes, and it will cause a problem. The Ujoints you need are coated on the ujoint caps to prevent this. You might also want to look at balljoints, driveshaft balance, if you have a two piece shaft, take a look at the carrier bearing (in the center of the two peice) and make sure it still is in good shape. If you replace the joints, did you put the shaft back together exactly how you took it apart? and believe it or not, with bad joints, the shaft will appear to be fine at certain speeds and not others due to the harmonics of the shaft when spinning. I used to work at a driveline shop, and delt with customer's all the time that had issues with vibrations.

Just my :2cents:

James

Since it's still under warranty, the dealer performed all the work. There's no telling how they did it. Some things can't be assumed. It was probably 30k miles ago when the last one was replaced. When it vibrates, I have shut off the ignition while in drive and the vibes immediately stop. Doesn't the shaft still spin at that point? Although I suppose there's no load on the driveshaft at a coast. However, it is a 2 piece shaft and I'll have to crawl under there myself and take a look see.

BubbaK

I suppose it could be a U-joint or something with the driveshaft, but it happens at very low speeds - like 4-7MPH. Mine actually "shudders" and rattles the dash. Not severe, but noticeable....and it doesn't always do it either. The "shudder" starts softly and gets stronger before it abruptly stops. It just doesn't seem to be a U-joint in my case, but it's worth a look. :)


Tom

How about a bad motor mount? Since you turn the engine off and it stops vibrating, this could be the culprit.

I think NUCLEUS.ONE has a good point!
you might want to add the tranny mount as well.

When you shut down your engine while the drive train is turning, you increase loads. This might be enough to put you outside of the vibration frequency?

Update...
I had a trip to make last Friday and jumped on the interstate. I thought she was going to finally let loose. In addition to the increased low speed vibrations there was a new growl at 50 that sounded nasty. I completed my trip and on the way back everything was fine. No vibes or growls. I suspect the ujoints are shifting. Can the ujoints and carrier bearing be visually inspected for play and rust or does it need to be disassenbled? Also I'm assuming the truck needs to be completely off the ground and trans. in neutral?

BubbaK

I crawled under the truck last night and the u-joints look in good shape. I did not take them apart, but they had no play in any axis or rust. It was difficult to tell if there was play in the carrier bearing since it is enclosed in a flexible rubber housing or if the play came from the slip yoke right next to it. The rubber around the bearing did have some cracks in it.

I crawled under the truck last night and the u-joints look in good shape. I did not take them apart, but they had no play in any axis or rust. It was difficult to tell if there was play in the carrier bearing since it is enclosed in a flexible rubber housing or if the play came from the slip yoke right next to it. The rubber around the bearing did have some cracks in it.

I had the exact same problems....it is your u-joints. The original oem were sealed units, but the grease leaks out and they go. Mine started out as a minor vibration at certain speeds. Dealership couldn't figure it out until things were really bad, almost lost my drive shaft by the time it was figured out. Needless to say I don't go to that dealership any more. :screwy: Replaced front and rear joints with new spec'd GM u joints (they now have a grease nipple) and all is well. Suggest you don't wait. Mine appeared fine and the next time they were looked at they were ready to fall out. Hope this helps

I had a bad vibration at speed and it made bad noises up front. I jacked up the truck and shook the driver side wheel. The wheel bearing was gone. You might want to check out the wheel bearing. My truck had 107,000 miles on it when it went out. It only seemed to do it at acceleration at first, but then it got worse. The only downfall is that you can't just replace the wheel bearing. You have to buy the whole piece, which includes the hub and the lug bolts. It cost me $156 and this was dealer cost. Just check it out to be sure.

Eventually, the vibrations returned at all speeds above 20mph on acceleration. I just replaced the front ujoint and all is well now. I should get at least another 20K miles before the next one goes again. It seems as though it's been that way since I bought it new. Thanks for all the input.

same problem with mine at 75,000. it was the u-joints, they look okay outside, no play, but inside they seize rusted shut. with the truck on jacks, and it in gear, load the tranny using the brakes while observing the driveshaft turn, it will probably look slightly bent as the seized joint won't allow it to pivot.