I have a similar problem with a different set of circumstances. Been looking around but I can't seem to find the answer that I need.
History: 1970 Mach 1 with an implanted '72 351CJ that came out of a Cougar. This car had the factory small stall converter behind a C-6 tranny.
I have a top loader 4 speed bolted to it now onto a flywheel purchased at the Ford dealership a while back (for a 1970 351 C) and I am using a 11" Ram Clutch street strip plate and disc (awesome). I was having some vibration issues but nothing that bad. Slight vibartion at about 2,500 rpm range (worse above about 100 mph) . Running a 3.70 rear gear.
All '72 351CJ motor came with a "special" fatter harmonic balancer (similar to a 351 Boss - not sure if they are the same part number or not) which differ from the regular 351C motors.
Project: I have yanked the top-loader in favor of a T-5 from a '90 LX 5.0. Modified the T-5 bell housing with the block adapter and went to work. Found out that the bell housing was too small for my 11" clutch/flywheel combo and I don't wanna change that so I modified the top loader bell housing with an aftermarket adapter plate. Had the drive shaft cut down an inch and a half and rebalanced. Fit perfectly. Installation went smoothly and everything bolted right in nice and easy. Before you knew it I was ready for a test drive.
I am having the same 1,800 to 2,500 rpm vibration (real bad case of the whoop whoops) as described above. It will vibrate with the clutch shoved in at a dead stop but not nearly as bad. Cruising down the road and throwing it up into neutral makes the vibration go away.
I have since yanked everything back out and it all looks correct.
Here are my questions: Can I use a 351C harmonic balancer on this motor or even an aftermarket unit or do I need to have the stock "fatter" one rebuilt?
Can I have the flywheel (and clutch assembly) re-balanced off of the motor or are the Cleveland engines balanced internally?
I'm kinda stuck with this beautiful black Mach 1 up on jack stands and I really don't want to put it all back together just to pull it apart again. Any advice would be much appreciated. Thanks!
If the vibration only happens when you're driving the car, it's not the engine, it's the driveline or tires. If it does it in neutral, then it's the engine.
As long as the balance weight is the same, you can use whatever 351C balancer you want. 28oz is the stock balance weight.
I'm using the 351C flywheel (for a '70 model) that I used with the toploader so I am (pretty) sure that it is balanced to 28. I bought the flywheel in 1990 and it sat on the shelf in a box for years before I installed it.
Thanks for the info on the balancer. Looks like a 351C Fluid damper is in my future maybe.
Funny thing is it didn't vibrate nearly that bad (except at real high rpms) until I put the T-5 in it. Maybe the steeper gearing of the T-5 first gear brought the "sweet spot" rpm range down the scale a bit. Everything from the front of the T-5 is the same as it always was before the tranny swap (except for the new t-bearing). I had replaced the old brass pilot bushing with a 5.0 style roller bearing type years ago so I even left it alone too. I mic'ed the ends of the input shafts of each tarnsmission and they are the exact same size in diameter.
I am getting the vibration when I rev up the motor in neutral, just not nearly as bad as when I drive it (then again I'm not holding the revs at 2K while sitting still either...just the usual throtle goose).
Then I guess it would safe to have my flywheel and clutch assembly rebalanced then?