Vibration

[jayem]

I have a vibration that comes on at about 65 mph and gets worse the higher the speed. It feels like a drive-line issue. The drive line and yoke have been ballanced twice, I've had the tires and wheels checked and ballanced twice, the 9 inch rear end has been completely rebuilt. Any ideas? engine off ballance? clutch off ballance? bf goodrich tires need shaved? help!

[Mr.Fixit]

If it is your engine or clutch, than vehicle speed is irrelevant, it will do it with the car sitting still if you bring up the RPM's. I bet the tires/wheels. If you can swap tires and wheels with a buddy, that is the best way to check. I have had this problem on customer's cars before, the tire shop says the tires are balanced perfectly, but swap them out for a different set and the problem follows the wheels/tires, not the car.

[Jim Werth]

I has the same thing except at a lower speed. Mine ended up being the transmission. It would start to shake and would go away in neutral or when I pushed in the clutch. Reving the engine made no difference. Found out the output shaft has a small shake. Drove it about a mile. Now it sounds like somebody put marbles in the transmission. Going to pick one up this afternoon. Jim

[Charlie]

Jayem,
Is the pinion of the 9-inch rear parallel to the engine axis? This is a common problem with 4-wheelers. I know you can't have that much phasing misalignment, but in a lightweight car maybe a little is all it takes.
Charlie

[B L & sons]

Like Mr Fixit if you know what your RPS,s are at 65 bring your motor to that with your car parked if the vibration is there maybe your harmonic damper has slipped.
Bill

[meangreeny]

Just a comment on a recent vibration issue a cobra colleague and I solved with unknown vibrations we had in our cars (noticable between 1800 and 2200 RPM). FYI - Our vibrations were more noticable when our cars were moving (i.e. a vibration in 5th gear at 2000 RPM was more noticable than than in 1st or just bringing up the revs at stand still).

We both have 351w engines, B&B Cobras and side pipes hard mounted to the car (i.e. bolts).

When we unbolted the pipes from our cars all vibrations went away. Our vibrations were from the pipes hard mounted to the cars. Our solution was to engineer a rubber washer mounting system where the pipes are mounted to the car. This solved most of the problem (90%) but my next step is to go to a custom muffler shop and engineer a mounting system that supports the pipes and allows for free movement at the same time.

[Rich]

Jay, I had the sidepipe vibration thing too. One side was just touching the frame next to the front wheel well. Pretty much the same fix as meangreeny. I cut up rubber pieces off a muffler hanger and used them for washers on the bolts that mount the sidepipes to the frame.

Rich

[jayem]

Thanks for all the help,I will isolate the side pipe from the frame.
The vibration happens between 1800 & 2000 RPM and is worse
in 5 gear. This might solve the problem. Jay

[BlueRooster]

If it doesnt, are you doing a dynamic balancing of the wheels? If you are afraid to put weights on the outside of your wheels you may never rid yourself of that vibration. I recently had all my wheels done and they all have weights on the outside. Now it runs smooth as silk.

Dane

[Jim Werth]

B+B does sell rubber mounts for the side pipes. Jim

[Bish Wheeler]

Jay,

I had to go to weights on the outside of the rear wheels to get rid of the vibration. Now as smooth as can be, I'll bet it's the wheels.

Bish

[Zderf]

Shaggey dog story Jay.. but it finally paid off. 4 years, now settled....

http://cobra.terraworld.net/forums/s...ight=Vibration

Yours Always,

Zderf