351c engine vibration

[wwhite72]

new post from new member. looking for Cleveland experts here. my 72 cleveland has a rhythmic vibration that i cannot track down. MSD says its likely the coil. Mechanic says it could be a failed Crane hydraulic lifter. here's what i have: 72 351c with edelbrock intake, CHI 2v heads, Crane gold race rockers, hydraulic roller cam custom grind by Crower, crane hydraulic retrofit lifters, alum water pump, MSD 6AL box with MSD distributor. The FMX was rebuilt twice due to a bad mechanic in NJ. 2800 stall converter, 3.50 gears in a tru-trac. i notice the rhythmic vibration before i changed the rear from a 2.75...as soon as i swapped to the 3.50 gears the vibration became more pronounced and faster. The drive shaft has been balanced. the front end is all new Moog and the alignment is new 1/8 in X 0 degree by 2.00 degrees. I have a new coil but havent installed because it has been cold. i installed a new electronic voltage regiulator and new 58 alternator. I am leaning toward the trani being the problem because the FMX is crap. MSD thinks the vibration is from the coil dropping at rpm higher than 3000, the mechanic thinks 1 or more crane hydraulic lifters could be bad...but that is the most expensive swap. any thoughts? please note i am not great with site posting, all new to me. thanks

 

[71STANG351C]

I had the same problem with my '72 Mach 1 years ago (exact same drivetrain). It was after I had the engine out for a rebuild and reinstalled that my car had those same symptoms...turned out to be the flywheel...the orientation was off when everything was bolted back in. After we separated the trans from the engine and realigned the flywheel and retorqued, it was gone. Might be something to consider??? Hope this helps...

 

[hyena429]

I had the same problem with my '72 Mach 1 years ago (exact same drivetrain). It was after I had the engine out for a rebuild and reinstalled that my car had those same symptoms...turned out to be the flywheel...the orientation was off when everything was bolted back in. After we separated the trans from the engine and realigned the flywheel and retorqued, it was gone. Might be something to consider??? Hope this helps...

+1 to that...My cousin had one allmost come unbolted...He thought his motor blew up...was the flywheel coming loose......And did you get new wheel barrings in that rear end too? I had some go out on mine few years ago...started a little tiny vibration and a growling kinda sound a bit ruff...so i had new ones pressed in...and fixed that issue.

 

[wwhite72]

i had the engine rebuild done by Joe at Danbury for the short block, so it came back with a factory balancer and flywheel and crank, all original stroke. i did have the top end and block installed in the car by another shop but cant think why they would have taken off the flywheel for the install? My mechanic verified the parts are factory an installed correctly. i guess it could be a source, but the guy is good and still thinks a lifter(s) is bad. I have heard that no hydraulic lifter is immune from failure and am looking at the new Lunati high RPM for the Cleveland. but at $750 a set it painful to think of the final install cost.


new wheel bearings in the rear? yeah, those are all new. kinda funny, i had to replace most of the rear components because one rear tire almost fell off when i drove it off the transport due to egged out bolt holes. figured the original owner hadnt done much mait after that. Had mismatched brake cylndrs...not uncommon in 71-73 rear brakes! new wheel bearings, caps, new carrier, new diff, new gears.

 

[marks73]

If it has a distinct rythm to it. Is it there in Park or neutral? Does it increase with the RPM's? I would think the lifters would be any easy enough look see just removing the valve covers and idling the engine. (will make a mess though) I'm actually leaning more toward the flywheel as well if yes to these questions.

 

[not2old]

I fixed one that had a cooling fan with a broken fan blade. Odd but true and easy to check.

Alan L

 

[don29163]

Harmonic Balancer outer ring slipped ?

 

[Jeff73Mach1]

Harmonic Balancer outer ring slipped ?

I was coming to post the same thing. Might double check that the drive shaft wasn't turned 180 degrees leaving the u joints out of phase also.

Could be the FMX, but the one I had was behind a 302 in a coupe and it was as good at 160K as my toyota was the day I bought it at 60K

 

[fordismyboss]

I had the same problem with my '72 Mach 1 years ago (exact same drivetrain). It was after I had the engine out for a rebuild and reinstalled that my car had those same symptoms...turned out to be the flywheel...the orientation was off when everything was bolted back in. After we separated the trans from the engine and realigned the flywheel and retorqued, it was gone. Might be something to consider??? Hope this helps...

Just happened to read this post; right in the middle of putting the car back together. I did not know flywheels had polarity. Is there a key or alignment notch/hole? On my Boss 351, I simply bolted up the flywheel, thinking it was balanced, and torqued it. I can easily remove it now and do it right!!! Obviously I'm new to this. Thank you for any help you can provide.

 

[RacerX]

The flywheel bolts are spaced so that they only go on one way. If you are one bolt hole off you cannot get all of the bolts to go in.

 

[fordismyboss]

The flywheel bolts are spaced so that they only go on one way. If you are one bolt hole off you cannot get all of the bolts to go in.

A fool proof design. I got lucky....but I'm going to remove it now and confirm the correct alignment. Thank you! RC

 

[TommyK]

Can you describe a little bit more about the nature of the vibration? Does it do it in Neutral sitting still as well or just while driving?

 

[T-Tom]

I don't remember about the spacing of the bolts (too long ago since mine was apart) or recall anything about your engine being balanced but when the balancing is done my machinist either uses a paint pen or a punch on the flywheel, pressure plate, and the crank for alignment purposes.

Good luck.

 

[Chris Womack]

The flywheel bolts are spaced so that they only go on one way. If you are one bolt hole off you cannot get all of the bolts to go in.

Ha ha, On my C4 I managed to bolt my flywheel/torque converter wrong. There is a hole in the flywheel to allow access to the torque converters drain plug -- I blocked it by mistake. It would engage with the starter fine -- so felt good at first -- but would hear funny noise when accelerating engine. Since the flywheel wasn't true (because torque converter drain plug was pushing against flywheel) one of the weights was making contact.

I backed off the transmission, and got torque converter and flywheel to bolt up the right way -- and it has been fine ever since. (The lessons you learn when you are young.)

This is easy to check, with the car securely raised: remove the two bolts that secure the flywheel inspection plate and turn the engine with a socket on harmonic ballancer (front of engine). On the C4 there are four bolts mounting torque converter to flywheel. If you see five bolts without seeing the drain plug (looks like an oil drain plug -- but smaller) then you have blocked it.

 

[wwhite72]

All good suggestions. I will be getting the car out soon for the spring and will have a list to go through. One thing i recall from the last drive was that it was smooth as silk up to around 45mph, then would pulse/vibrate right around 50 and get worse as speed increased. If i was cruising at 50 mph and put it to the floor the vibration would immediately become a hard banging and woudl stop as soon as i took my foot off the pedal despite the higher mph. That's why i am leaning toward the ignition as the source. If coasting down a steep grade it glides very smoothly at 60-70

 

[turtle5353]

A bad universal joint could cause that vibration since it goes away coasting and only appears at 50mph and up under acceleration

 

[wwhite72]

I had the shaft balanced and new ujoints installed when i swapped the rear diff/gears. I do wonder about the relationship between the angles of the trans and the rear. A few discussions on the correct geometry are around: the factory perches put the rear at 1 degree down. The front is also down, but because the converts need the stiffening plates under the rear seats the factory used taller engine mounts to give the shaft minimum clearance. I have always wondered if that could be a source of harmonic vibration? But, the joints are new. Also, that wouldnt account for the big increase in the vibration i get under load, but before the mph increases much. I can induce the thumping at low mph by stomping on the pedal. Almost like im dropping a cyl or 2.

 

[Jeff73Mach1]

u joints are cheap and easy (like my preferred dates) Always a good starting point. Even a newer U joint can be damaged in installation and can fail quickly.

Have you dropped the pan on your FMX to check for metal particles? It could be a damaged planatary gear.

 

[droptop73]

Maybe a cracked flexplate or a loose torque converter.