Help with diagnosing driveline noise?

[Defender67]

Purchased a 67 Camaro as a new project. Previous owner(s) installed a 12 bolt rear with 4.10s, built th400 with zz4 350. The rear suspension has ladder bars. Entire setup is about 10 years old, but only has 14k miles on it. Rear rubber is BFG DRs. Aside from that, I have no other information about what was installed or how. (it is a project car after all).

I can best describe the noise as a low-pitch hum that increases in volume with speed. It doesn't really become noticeable until about 40+ mph. I actually thought it was just the engine/exhaust until I was coasting down a hill at about 65mph and i shifted into nuetral, as the rpms dropped to idle... I noticed a majority of what I thought was engine noise was still there, presumably from the rear end.

I don't have regular access to a lift but would like to hear any ideas so I know where to start looking when I do get the car up.



My first thought is u-joints going bad. Any possibility the ladderbars are putting pressure on the wheel bearings? (the sound is similar to a wheel bearing, but I don't think it is that as I cannot hear it most of the time).

Any advice would be appreciated. Thanks!

[High Miler]

Hello,
Greg from Inland Empire Drive Line here.
Click on our logo in the list to the right. Then select "Power Train Set Up Guide". Once there click on "Trouble Shooting". You will find a list of suggestions arranged from most likely to least likely to solve your problem. From what you describe I'd guess the U-bolts are too tight. Let us know how this works for you.
Greg

[CamaroAJ]

or the drive shaft needs rebalanced.

gear noise will change with load most of the time. a pinion bearing can also make this noise. you can pull the drive shaft and turn the pinion by hand and see how it feels, if its smooth than i would check else where but if it feels even slightly rough then you could have a bearing going out.

[DarkoNova]

Does the noise get louder/quieter when you turn? Wheel bearing noise will change when you turn because you increase/decrease the load on the bearings when you turn. If the noise doesn't change when turning, then it's something with the driveline.

[High Miler]

DarkoNova brings up a good point.
GM Corporate axles use the axle shaft itself for the inner race of the wheel bearing. When the axle surface wears the noise will be just as you describe. To check, slide the axle out and look at the running surface. If it shows wear replace both axles and wheel bearings.
Greg

[Defender67]

Sounds like I have several things to check.

I would not be able to tell if the noise gets louder or quieter when turning. I can only hear it 40+ mph, any turns hard enough to detect a change in the noise would probably be met with undesirable results. =) I can't detect the noise at lower speeds.

I could not get it on a lift this weekend to turn the pinion by hand, I'll add that to the list. I'll also replace the U-joints for good measure. Fortunately it is only noise and does not have any accompanying abnormal vibration.

If these don't solve the issue, I'll pull the axles and check them out. Thanks guys. If I find a solution in the next coming weeks (depending when I can get the lift), I will post the solution (hopefully!).