Drivetrain vibration? Something else?

[Argyll]

I have a 1993 Cheyenne W/T 1500 2WD, longbed, 5spd manual tranny, with 180K miles. I'm the original owner. The fuel pump went bad last week so I had to take it to a local service shop to have it replaced.

 

After getting it back, it now has a slight vibration that seems to be coming from the drivetrain somewhere that only occurs between 50 and 65 mph roughly. When travelling at 55mph is where it seems the worst. It's a feeling like if you drove on a ridged warning track in the emergency lane of a highway, a fast frequency low tone buzz type of vibration that can be felt throughout the truck. If I push in the clutch and take it out of gear while travelling at 55-60mph, the vibration stays constant, so I don't think it's in the transmission, but not sure.

 

So I call the service place and ask them if they loosened or removed anything besides the fuel tank. They said yes, they did drop the driveshaft in order to get to the tank more easily. So I immediately thought, maybe they put the shaft back in 180 degrees out. I myself loosened and rotated the driveshaft 180 degrees at the rear differential yoke (I did not remove it from the tranny end). This made no difference, vibration is still there.

 

I thought maybe a tire or wheel might be out of balance, so this morning I had all 4 tires rotated and balanced. But vibration is still there. I can't find what it causing this for the life of me. Is it possible the U-joints of the drive shaft got bent somehow when the fuel pump initially went out? Because the truck was sputtering and jerking before I could limp it off the highway to a safe parking spot.

 

Any ideas on what else I should check would be greatly appreciated. Thanks.

[asilverblazer]

I would have the drive shaft and U-Joints checked to make sure it is straight and balanced. It could have been damaged, though I doubt it by the jerking, or the shop could have dropped it or somehow knocked one of the balance weights off or tweaked it somehow.

[Bish]

I would have the drive shaft and U-Joints checked to make sure it is straight and balanced. It could have been damaged, though I doubt it by the jerking, or the shop could have dropped it or somehow knocked one of the balance weights off or tweaked it somehow.

 

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Ditto. I had a similar vibration and decided to have it checked at a driveshaft and rear end place. Sure enough, not only was it out of balance but it was slightly bent. $60 later and it is smooth as silk. I do not recall dropping it and I never had a shop pull it. I'm not sure what caused it but it was a cheap enough fix.

[the blur]

20 years ago I worked at a shop, and the owner put a lifted truck on the lift, and the lift hit the drive shaft. the driveshaft did get a slight ding in it, and sure enough the guy came back bitching.....

 

the owner denied any wrong doing, and the guy didn't know enough to look at the drive shaft....

[Argyll]

Thanks for all the replies . Because the place I took it to for the fuel pump replacement said they dropped the shaft to do the work, I can only think that it has to be the shaft that's out of whack now. I can't visibly see anything else wrong. This truck rode like a cadillac before, and now it has this vibration, so I can't imagine what else it could be.

 

It's hard to believe these driveshafts are that sensitive. I know that they're gonna say that all they did was loose it from the rear and lower it out of the way to do the tank work, and that there's no way they could have bent anything. But I have no idea if they might have let it slip and it fell and hit the ground, or pulled on the U-joint at the transmission or anything like that. I guess I'll at least take it back and ask them if they'll check it. Maybe they have a balancer at their shop. The svc. manager did tell me to bring it back in and they'll have a look.

 

Anyway, thanks for the comments and advice. This is a great forum btw. Thanks to all that participate and make it possible.

[redvett]

The shop screwed it up let them figure out what they did.

[Argyll]

Following up with the findings here. I found the problem myself. I took my truck to my Father's to replace the rear axle seals last weekend. After that, we took another look at the driveshaft. He noticed immediately that one of the clips on the rear universal joint was missing from the driveshaft. I didn't even notice that before.

 

Without both clips, it's possible for the shaft to be off-center when put back in. So obviously when they replaced my fuel pump they must have somehow knocked that clip off, and the shaft wasn't remounted perfectly centered. My dad and I just rebolted the shaft making sure that the yoke saddle was flush with the one clip that did remain. After doing this, no more vibration whatsoever. Ride is smooth as silk again, what a relief. I didn't yet tell the shop about this. I'll mention it to them the next time I'm there though.

[Frozen001]

Following up with the findings here.  I found the problem myself.  I took my truck to my Father's to replace the rear axle seals last weekend.  After that, we took another look at the driveshaft.  He noticed immediately that one of the clips on the rear universal joint was missing from the driveshaft.  I didn't even notice that before.

 

Without both clips, it's possible for the shaft to be off-center when put back in.  So obviously when they replaced my fuel pump they must have somehow knocked that clip off, and the shaft wasn't remounted perfectly centered.  My dad and I just rebolted the shaft making sure that the yoke saddle was flush with the one clip that did remain.  After doing this, no more vibration whatsoever.  Ride is smooth as silk again, what a relief.  I didn't yet tell the shop about this.  I'll mention it to them the next time I'm there though.

 

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Get yourself a clip or it will move on you again....