Vibration at 75mph. 1997 Tahoe- Not the tires or wheels

[coorlt]

1997 Tahoe, 2 dr. Vibrating bad at about 75mph. Feels just like a tire out of balance but it is not tires. Had them trued and balanced and even tried another set off of another truck. I replaced pitman arm and idler arm then had front end aligned by a reputabled front end man. It is not in the tires or wheels. I replaced both U-joints on the drive shaft and still have not fixed the problem. One mechanic told me it could be the harmonic balancer but the rubber looks good to me. Others have told me it could be in the rear end. I hunting for help here. Anyone ever had this problem? The only other thing spinning at 75mph. is the engine, transmission, and rearend, and the driveshaft. I guess it could be a bent or twisted drive shaft but wanted to see if I could get any feedback on this site before I had the shaft put on the lathe. Let me know if anyone has had these kind of drivetrain problemss on there 97 tahoe.
Thanks Wayne

[GMMerlin]

Originally Posted by coorlt

1997 Tahoe, 2 dr. Vibrating bad at about 75mph. Feels just like a tire out of balance but it is not tires. Had them trued and balanced and even tried another set off of another truck. I replaced pitman arm and idler arm then had front end aligned by a reputabled front end man. It is not in the tires or wheels. I replaced both U-joints on the drive shaft and still have not fixed the problem. One mechanic told me it could be the harmonic balancer but the rubber looks good to me. Others have told me it could be in the rear end. I hunting for help here. Anyone ever had this problem? The only other thing spinning at 75mph. is the engine, transmission, and rearend, and the driveshaft. I guess it could be a bent or twisted drive shaft but wanted to see if I could get any feedback on this site before I had the shaft put on the lathe. Let me know if anyone has had these kind of drivetrain problemss on there 97 tahoe.
Thanks Wayne

The best thing to do is get hold of a EVA (electronic vibration anaylizer) and record the vibration frequency..this way you can determine if this is a 1st,2nd or 3rd order vibration.
Does this vibration start at 75 or gets worse at 75?

[coorlt]

Thanks for the reply Merlin.
The vibration starts at about 70mph, Then you have to accelarate to about 80 then let it come back to 75 before the real vibration starts happening. Don't know if that rings a bell or not.
I'm about 400 bucks into this vibration and hoping I can figure out what it is. I'm not familiar with a EVC. Actually I've never heard of one but I will ask around. This is not a big city so I'm sure it's not available local. We do have a dealership (Chev.) I'll ask them.
I'm not in to part replacing either, but the parts I replaced needed repacing anyway.
I'm a firm believer in finding the problem and fixing it, But now I'm down to either of these items:
1. Bent or twisted drive shaft.
2. Rearend somehow out of alighnment
3. Transfer Case?
4. Transmission (But the torque converter should shutter at other speeds, right?)
5. Harmonic balancer.......Looks good to me......Don't look like it's separating
What else is spinning?????????
Please explain about 1st 2nd and 3rd vibration
Thanks a ton....Wayne

[010175]

Did you check you front disks? Does it vibrate when the truck in neutral? Just thinking. Dave

[Ucantcme57]

I had bad vibration at 75 it got worse as you went up.. You couldn't get to 80 without feeling like the car was going to snap. Rear U joint was fine, turn out was the front one, You could have a misbalanced driveshaft, I have to rotate and balance my tires every 3k or they do that, I had to tighten my yoke in the rear when i replaced the u-joints. Replaced with greaseable ones, grease every 3k. May have belt seperation...? Did a weight fly off the driveshaft?