Is this a flywheel imbalance problem?

[Blue71]

Tuned everying up in the '74 w\ C-4 automatic the other day. Got rid of all the unnecessary vacuum lines and that helped a ton. It still has a decent vibration when you rev it up. The shake follows the RPM range. If in Neutral...you can rev it up say to 5000 RPM's and it shakes/ vibrates a little , but when it comes down to about 1200 RPM's it shakes/vibrated the entire Bronco, motor, lift gate tailgate and all pretty good until it settles down to about 800 RPM's and it smoothes out to where it is almost gone and idles smooth. I checked all the mounts(tranny,motor, etc too) You can feel it at highway speeds at a constant vibration. You can push the throttle to 1200-1500 RPM's and she shakes everything prttey good. It did this before the tranny was rebuilt, fly wheel resurfaced, and torque converter was rebuilt by a reputable local company. It shifts great and runs good to , just vibrates. Any ideas. Imbalanced flywheel? Wrong flywheel.....it has been replaced in the past I know this because it used to have a 300 flywheel when the guy sold it and it shook like crazy. A guy supposedly installed the corrct on for my C-4 even before the tranny rebuild.Torque converter imbalance? Sorry this is long.

Thanks Much,

Blue71

 

[70bucks]

Did your tranny rebuilder know you were having the vibration problem? There were two different weight flexplates 28oz. and 40? I would think any tranny guy worth his salt would have checked the weight of the flexplate if he knew you were having vibration problems. When I was sold the wrong balanced flywheel it was fine at idle and low RPM's and crazy at high RPM's. Pull off the access plate/dust cover and see if there are numbers on it. Mine is accessible so we could compare. If there aren't numbers on it measure length and width of the weight for comparison. Now the painful question. Do you know what year the block is? The newer blocks take the heavier balance. From what I uunderstand the only way to know what year your block is, is to pull the intake manifold and get the casting numbers. How about a bad harmonic balancer, an oil leak will shoot out the rubber in a hurry. Good luck.

 

[howiebilt]

The harmonic balancer could be the problem . If the wrong one is on there it will change everything . The flexplate must also be the right one as well as the torque converter .

It has been my experience that Bwoncohowie is our resident expert on all things dealing with the trannies and flexplate situations . If he doesn't find this post ... send him an e-mail

 

[broncnaz]

hope you didn't pay for your flex plate to get resurfaced if you did someone gypped you flex plates dont get resurfaced I would check the balancer also it has probably slipped

 

[Blue71]

Guess he didn't resurface the flex plate. I was thinkin flywheel when they did my clutch on the '71. Oops. I'll check the balancer. How can it be checked? Keep'em comming.

Thanks Much,

Blue71

 

[RogerCB]

First off, the damper timing ring only displays timing marks, if it slips, it only makes it hard to time the motor with a light, the pork chop, or balancer portion of the damper is keyed to the crank snout, and can't move. I would bring into question the flex plate , should be 28oz, or other recpriocating parts on the front, or back of the motor. ....I don't think it's "tune" related

You'll think I'm BS'n you, but my Bronco and I went "swimming"...deep enough to bury the crank pulley in mud. Ran fine immediately after we pulled it out, but the next day it vibrated better than my wifes favorite toy!.......turns out the mud settled overnight in the front crank pulley, and acted like a misplaced crank weight. Let us know what you find!

 

[Johnnyb]

If you haven't instsled a late model motor

You already know about the balance change in later model 302/5.0 motors. Therefore, I would guess the vibration is the result of the harmonic balancer. If the rubber wears out, it can rotate and cause imbalance.
Static time the motor. Put #1 at TDC (use compression tester to make sure you are on the compression stroke), then if TDC isn't TDC, get a new balancer.

 

[Unregistered]

balancer

I'm putting an explorer 5.0 in, if your looking for a new balancer RHP has a nice unit for around $75.00 with all the timing marks you could need.