Odd Vibration.

[Bebop Man]

Over the last few months, my Bronco ('86, 5.0 EFI) has developed an odd vibration. It starts around 800 RPM, builds up til about 1700 RPM, and fades away by the time I'm past 2500 RPM. It is engine speed related, as I can duplicate the same thing just standing still. The tranny lever just vibrates and wobbles back and forth like a massager. The motor doesn't seem to shift or move in the bay, so I don't think it's a motor mount.

Is something getting ready to explode internally? Any ideas?

 

[Krafty]

sounds like balancer or flex plate

 

[Bebop Man]

sounds like balancer or flex plate

Any way to check it with out dropping the transmission or pulling the engine?

 

[Krafty]

with the engine running and vibrating open the hood and have a good look at your crank pulley, if it is wobleing alot and you have an external balancer behind it then it would be worth removing the crank pulley and balancer and inspecting it. if it is bad you should see physical damage to it.

Note:you will need a puller to remove the balancer.

I had a 302 that had a bad balancer witch shattered and took out my timing cover, chain and gears. $800 later I found out with the 2nd balancer going out I had a bad bottom end.

a way to check the flex plate (this isn't perfect cause you don't get to see much) is remove your starter and trans dust cover, with a johnson bar on the crank nut turn it over and examine the flex plate from underneath with a flashlight.

it is best to rotate the engine the way it normally spins while running, Clockwise if looking at it from the front of the vehicle.

 

[Bebop Man]

Isn't the flex plate only on Bronco's with an automatic transmission? Or do manual's have them too?

 

[Krafty]

sorry didn't see that you had manual, and you are correct only automatics have flexplates, but Manuals do have a flywheel that serves the same purpose for starting but I believe that the flywheel is much beefier and don't know if that would be a problem area or not for this sort of thing.

the check is the same either way to check without removing trans or engine.

 

[Bebop Man]

I watched the fan and pulley, and saw the nose wobbling. Further examination showed the seal for the bearing on the fan clutch had come loose, and the shaft was no longer centered in the clutch, making the whole thing rotate eccentrically. One new fan clutch later, and the vibration is all gone.

Thanks for the help, Krafty!

 

[Krafty]

no problem glad I could help.

 

[Seabronc]

Thanks for reporting back, it may help someone in the future.

Good luck,

>-

 

[Bebop Man]

Help,

I just purchased a 1996 ford bronco and the motor has a vibration at idle.I cant seem to find a harmonic balencer anywhere for it......bronco has an 302/5.0.

If any1 has 1 or any info please e-mail me at

[email protected]

thanks,

Derek

Do you mean where to buy one? Or where to find it on the engine? For sale, i found them both at LMCTruck.com and Jeff's Bronco Graveyard. If you mean where is it... In the front of the engine, below the fan pulley. It's the pulley with the timing marks.