351c engine vibration

[MotoArts]

Engine or trans mounts? (Had a engine mount rubber go bad and do this long ago).

Rear axle U-bolts and/or center pins (changing pinion angle)?

Hard to diagnose without seeing or hearing it.

 

[MeZapU]

Is the vibe there with the engine revved in neutral or only when driving under load?

Years ago when I went from 2.76's to 3.50's I had a much more minor vibe happen. After about 3-4 weeks after the swap my harmonic balancer came apart. Replaced it with a streetdamper and have been running it for about 15 years now.

 

[wwhite72]

can i swap in any harmonic balancer made for the 351c ? doesnt the rotating assembly have to balanced together?

 

[turtle5353]

can i swap in any harmonic balancer made for the 351c ? doesnt the rotating assembly have to balanced together?

Im pretty sure you can swap any balancer for a Cleveland. I had one come apart once and just used a spare I had in the garage, and it worked fine. If you need one let me know. I think I have 2 in the garage somewhere. Definitely have one from my last motor.

 

[wwhite72]

the mechanic confirms the Ford balancer is good, and the flywheel is correct. MSD thinks the coil is causing higher rpm misfire so im planning ti install the new epoxy coil i have this weekend. the mechanic also thinks one of the Crane hydraulic retro fit roller lifters could have failed. Crane says they never fail. the vibration becomes more of a banging above 60mph so im trying the cheaper route first. If it is a lifter that will be expensive. Lunati just introduced a high rpm hydraulic roller for the 351c....around $750 a set though.

 

[TommyK]

Maybe a cracked flexplate or a loose torque converter.

This is what I would be looking at. Also, as has been suggested, pull the flexplate inspection cover off the bottom of the bellhousing and make sure the drain plug is aligned with the hole. Even if it is, if it has ever been installed and tighten without it being aligned with the hole, there is a good chance the flexplate is bent.

I hate to suggest this but a bad wrist pin can act like this as well.

 

[droptop73]

the mechanic also thinks one of the Crane hydraulic retro fit roller lifters could have failed. Crane says they never fail.

Can I call BS on this one!

Although I doubt that is the issue based on the description of the noise.

 

[wwhite72]

follow up; it was the coil. for some reason the coil was failing as the rpm climbed. would idle smooth as silk, nice power off idle. when i got to around 45-50 it would start missing in a rhythmic way and only get worse. By 70 mph it was causing a thumping you could feel and hear as the cyl's were dropping. not good at all. swapped in a new MSD coil and like a new engine again. i installed the epoxy MSD to deal with the factory location. MSD warns against the horizontal mounting Ford used on the 351C. Though the oem Ford coils seemed to last a long time. Maybe it was due to the lower voltage the original coil used? I do think i should put in an additional ground strap since the only one i see is the battery cable tab that grounds to the inner fender wall on the regulator bolt. I saw that the 1970 Boss 302 used a vertical coil mount on the front of the drivers side head, and without any AC on my car i could probably adapt that install location as well. but it runs great again so i'll just leave it until the next time.

 

[TommyK]

follow up; it was the coil. for some reason the coil was failing as the rpm climbed. would idle smooth as silk, nice power off idle. when i got to around 45-50 it would start missing in a rhythmic way and only get worse. By 70 mph it was causing a thumping you could feel and hear as the cyl's were dropping. not good at all. swapped in a new MSD coil and like a new engine again. i installed the epoxy MSD to deal with the factory location. MSD warns against the horizontal mounting Ford used on the 351C. Though the oem Ford coils seemed to last a long time. Maybe it was due to the lower voltage the original coil used? I do think i should put in an additional ground strap since the only one i see is the battery cable tab that grounds to the inner fender wall on the regulator bolt. I saw that the 1970 Boss 302 used a vertical coil mount on the front of the drivers side head, and without any AC on my car i could probably adapt that install location as well. but it runs great again so i'll just leave it until the next time.

Thanks for posting the resolution. It may help someone down the line.