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Ask GM Tech (Cam) Your Own Question
GM Tech (Cam)
GM Tech (Cam), Chevy Technician
Category: Chevy
Satisfied Customers: 29534
Experience:  GM Grand Master Technician 2007. 14 years experience.
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I have a little problem that I need to try and pin point.

Customer Question

I have a little problem that I need to try and pin point.
When I throw 5th gear, usually i cruise at around 2500 rpms, and thats approx 65mph. Once i push her and get to like 3500 rpms, i get a vibration which seems to be coming between myself in the driver seat and the rear, soo i'm assuming the driveshaft. But this only happens when i start to push her in 5th, and starts around 3500 rpms.
Any idea of what this could be?
Here are some parts I am working with:
Edelbrock #77639 Dome Victor Jr. Heads
Scorpion Roller Rockers 1.5 Ratio
SRP Pistons # ***** 138089 Flat Top Forged
Comp Roller Cam Kit # ***** Serial #: VS4869-12
Ferrea Comp Series #F6116-8 Intake Valves 2.080”
Ferrea Comp Series #F6104-8 Exhaust Valves 1.600”
March Pulley System
Edelbrock #1812 AVS 800 Thunder Carb (manual choke) ** should have been electric.
Professional Products #52031 Intake Manifold Single Plane Operating Range 3000 to 7500 RPM
SCAT 4340 Crankshaft
Moser 9” Ford Rear with TRAC-LOC POSI--28 Spline Pinion, 1350 Pinion Yoke-Steel
Gears: 3.90
Wilwood Disc Brakes All Around
RAM Clutch
Tremec TKO-600 5 speed Tranny with upgraded bearings
UMI Performance Suspension : Subframe Connectors, Sway Bar, Control Arms, Panhard Bar, Tubular Front Steering Brace(aka Wonderbar), Hotchkis Springs, KYB AGX Adjustable Struts, Crossmember, Tunnel Mounted Torque Arm
Submitted: 2 years ago.
Category: Chevy
Expert:  GM Tech (Cam) replied 2 years ago.

Hi there, I am CAm. Sorry to hear about this issue, vibrations can be VERY difficult to narrow down. Let me ask a couple questions first. I am guessing no matter what it will not make the vibration in 4th or any other gear at 3500 RPM?

When the vibration happens, does it stop the moment you release the throttle or does it need to slow down to stop?

Thinking about the frequency of the vibration, does it feel like running over the rumble strips on the highway sides or is it faster or slower?

Customer: replied 2 years ago.
It occurs mainly once im around 65mph, soo it can occur in 4th but mainly evident once in 5th and i push it and mph hits 70+ mph. I should say its occuring when the mph is say 70mph and up. Picture yourself in the driver seat of a third gen camaro, just over your shoulder that hump in the backseat floor is where it seems to be coming from and its and its a steady vibration sound, doesnt sound bumpy as the way the strips on the highway. I can tell u that lets say im up to 80mph and its vibrating, if i come off the pedal and it slows down, the sound gets less and less and is not there at all by lets say 60mph
Expert:  GM Tech (Cam) replied 2 years ago.
OK so it does not sound like that, but is the frequency of it the same as that or similar?
IF so then I would be looking at possible drive shaft balance, runout, u-joint bad, that sort of thing. What I would do is lift the car and SAFELY secure it on jack stands on all 4 corners. Then start it and idle it in gear. Watch for the driveshaft to be bouncing or moving. If you see it move up and down, check the u-joints. They must be smooth and not loose. Look also for signs of a weight that may have fallen off. Also consider your tires. Did you just put different tires on? Did you have them balanced recently, throw a wheel weight, that sort of thing.
We need to work through these first to narrow this down without throwing parts and money needlessly at it.