Knock / Vibrate @ high speed...

[Z Holladay]

Hi folks, new to the board. 08, 4.6L, 2WD ST Limited. K & N CAI, Gibson exhaust system, SCT tuner, 87 octane. No other modifications. Getting moderate knock / vibration after acceleration onto freeway above 60 / 65mph. Lasts for a minute or 2 then goes away. Otherwise runs great!



Can't tell if it's motor or drive train. Looking for any ideas / suggestions to isolate problem. Any help is much appreciated...

 

[Vic Sorlie]

How many miles on this Trac? Is it an engine knock or metal-on-metal? I'd look at the driveshaft. Not that easy for a DIYer to diagnose though.

 

[Richard L]

Hard to diagnose this without hearing it, but the clue might be in the Gibson Exhaust system. Look underneath the vehicle to insure that all the exhaust hangars are in place and that there is plenty of clearance around the pipes and muffler. Also examine anyplace where the exhaust runs close to the body, frame or suspension parts, looking for any rub marks that would indicate that the exhaust might be bumping.



Years ago, I had a problem with my 1965 GTO making a knocking noise in the rear. It sounded like the driveshaft was bumping on the tunnel when accelerating. Once I got to cruising speed, the noise and vibration stopped. It turned out that the oval shaped muffler was twisted and too close to the floor pan. The normal flexing of the exhaust while accelerating was causing the muffler to vibrate against the floor. Simply loosening the clamps and twisting the muffler to move it away from the floor eliminated the problem.



...Rich

 

[carl boger]

I just had similar situation. Mine turned out to a small aluminum bracket from the CAI system and my filter dropped and was vibrating against the fender. Just saying. Let us know what it turns out to be.

 

[EddieS'04]

As Rich said about the exhaust system. The exhaust tubing tends to expand in lentgh when hot. At curves and bends.

When cold you may see good clearance. When hot not so. Just fYI, had it happen to me.

 

[marlon giese]

more details needed to really do more than take potshots...