I have been experiencing a problem at high speeds of my car "humming". I dont really know how other to explain it. The car is smooth (no vibration), but it just "hums". Since it is speed sensitive, it would lead me to believe the problem was in the driveshaft, rear end, or wheels. The rear end *shouldnt* be the issue as I just had that completely rebuilt with brand new axles and bearing (did the same thing before the rebuild), the driveshaft *should* be perfectly balanced, and the wheels have never had the problem before.....no wheel weights have fallen off. Even though there is no "vibration", a humming noise is a harmonic frequency that has to be initiated by a very small form of vibration to the best of my knowledge.

Setup:

Strange 12 bolt (fresh rebuild)
Denny's nitrous ready driveshaft (supposed to be high speed balanced)

The humming starts at about 100mph and slightly increases the faster the car is traveling. I took it up to ~155mph the other night and it was not crazy loud, but none the less present.

Has anyone ever experienced this?
Thanks, Jason

 

Stock motors will do 150?!

My LS1 driveshaft is quieter than my stock shaft was (I never had vibe problems until after a hard launch at the track). Basically, the time before the stock shaft was "messed up" it was still louder than the LS1 shaft. If you have an LS1 shaft in your stash I'd try that first.

Any possibility that it could be tire noise?

Thinking out loud...
Ryan

 

Thanks man I appreciate the reply.

Its definatly not tire noise tho....its driveline or a wheel balance issue I am pretty sure. ??

Jason

 

Jason,

Did you use a Ratec solid sleeve when you rebuilt your 12 bolt? If so, check the runout of your driveshaft back at the pinion yoke. I had a Ratec sleeve that was machined out of parallel once and it threw the pinion yoke off-center when the pinion nut was bound down. Took me a year to find it! Back to crush sleeves for me.

Steve

 

Thanks for the input Steve I will ask the guy who just freshened my rear end up.

Where these the same symptoms you were having?
Thanks again
Jason

 

I had serious driveshaft vibe problems from about 55 MPH on up. This was with 4:10 gears. I was using a Denny Nitrous Ready DS and sent it back to him multiple times to have it checked and rebalanced. I have found that once you rule out a bad drive shaft, you need to take a good look at what's going on at each end. I've had problems on both ends. On the rear, The Ratec sleeve was machined out of parallel. This shifted the pinion yoke U joint saddles off center by about .040 TIR or .020 Off Center. This can be checked in the car with a dial indicator on the end U-joint bearing caps. After I changed out the Ratec sleeve my TIR went to .005 TIR or .0025 off center. On the transmission end, I found that I had a worn and oblonged tailshaft bushing. With the yoke splines being pretty darned loose, the yoke was allowed to wobble at high speeds and set up all kinds of crazy harmonics. The T56 tailshaft bushing is not very long so it doesn't guide and stabilize the yoke very well even in the best of circumstances. I redid my T56 with a Viper output shaft. The Viper bushing is a larger diameter and most importantly, it's almost 1.5 times as long as the stock GM T56 bushing. This arrangement stabilizes the trans yoke far better then the OEM design. Less wobble = happier driveshaft. Besides all of that, A heavy steel DS will probably not behave too well at 150 MPH. I'd check whats going on at each end, then borrow an aluminum DS and test that out also.


Hope I helped

Steve