I'm curious if anyone has ever had this problem or might know what causes it... at about 1700 rpms, no matter what gear, even neutral, it gets a rough vibration through the whole car.. only this RPM though. Think its exhaust? or internal engine maybe? Thanks

 

I believe SBC's have a harmonic that ocurs somewhere between ~2,000 - 3,000 RPM. This is why they have a harmonic balancer fitted to the front of the crankshaft, to absorb or reduce these vibrations. My LT-1 didn't vibrate at all until I put a piggyback UD pulley on it. Now it vibrates a little between 2,200 and 2,400 RPM, but it's not enough to concern me. The 357 in my 85 Firebird did the same thing. There's a good possibility that the rubber in your harmonic balancer may have deteriorated and allowed it to slip. Other than that I really don't know too much about it. I wonder how bad it would vibrate without a harmonic balancer? Probably pretty bad. Hopefully someone else can chime in and shed some more light on this.

 

Maybe your tranny mount is bad, and that's the only rpm you notice it at. I dunno though.

 

Sounds like an unbalanced driveshaft to me. LT1 stock driveshafts are notorious for this.

There was a service bulletin about it.

Dan

 

driveshaft with the car in neutral?...

 

Sorry, didn't see that part. Must be the beer. Ignore my previous post.

Dan

 

Yeah im with you. Check your mounts.

 

All mounts are good... even have the same vibration if i just keep then clutch pedal to the floor and rev it to 1700-2000.. its a rough vibration in there.. im not sure if its serious but... was only curious, thanks for the responses...

Beer does wonders also