Hello car nuts. I have a 94 Z28 LT4 355. Hope someone can help me with a vibration issue. Running a 3:73 gear with 3 1/2 aluminum drive shaft. While driving at about 60-65 I start getting a vibration, once I back off the throttle it intensifies significantly. If I get back into throttle it settles down but still there. Now here's the funny part, if I barely tap brake petal it goes away and soon as I get back to throttle it comes right back. I have asked many people and nobody has been able to help. I went to Shane Burgess from Thunder Racing and he has no answers. So I thought maybe someone here might have an idea.

 

Did you replace the U-joints on the aluminum driveshaft when it was installed? If not, you probably have some play in one of the U-joints. I had the same issue with junkyard LS1 driveshaft, put in new heavy duty U-joints and vibration was gone...I'd replace both if you don't know the mileage they have.

 

Speaking from experience, an aluminum drive shaft = vibration issues.

Have the unit straightened and balanced.

(FYI = I have my 3" aluminum drive shaft straightened and balanced about every 2 years.)

Having said that, as "Ahritchie" stated, new u-joints could be required as well.

If it's not the ds, then in addition to having the wheels balanced, shaving the tires (to make them perfectly round) could help as well.

 

Is there a way to "test" to see if driveshaft is the problem?

 

Does it "clunk" when put in gear? Grab one side of the joint and fondle around the other side and look for play or stick a big screwdriver in it and try levering it...there should not be any play obviously.

 

There is no play and it does not clunk. I'm going to put it on jack stands and try having someone put it in gear and feel the tail shaft for a vibration.

 

Usually if there is a bent/unbalanced driveshaft issue the vibration will be constant once a certain speed is reached regardless if the car is accelerating or decelerating, or if there is slack in the drivetrain. It's possible the backlash in the diff. could be out of whack. Not sure if it would be u-joints. Usually those make noise under acceleration.

 

Could be your rear end has given out, pull the cover and inspect.

 

I checked the rear. New Richmond 3:73 gears. No noise coming from rear end/housing.

 

I had the same problem in my 95 Z28 after I put 4.10 gears in it . No body new what it was and then one day we put it on the lift and I noticed it had a very slight wobble in the passenger side tire after we found out it wasn't the tire or rim it was the axle . It was just barely noticeable replaced it and it stopped . The axle was bent from hard take offs, soon after I replaced the other one . Make sure there heavy duty and if you haven't already put a heavy duty transmission mont in . I hope this helps

 

Ok, I will have to look into that. Makes sense with how it goes away soon as I put just a touch of pressure on the brake. Thanks.