Please help with a problem I'm having with my '66 Mustang 200-6 engine / torque convertor vibrating. Originally, the car came with a 200-6 cyliner engine and a 3-speed standard shift. When I rebuilt the car, I put in a rebuilt C4 automatic transmission from another car, but, still using the same engine less the pilot bearing. Of course, I had to put in the flex plate on the end of the crankshaft, too. Now, the engine has a LOT of vibration to it while idling and at any speed. It doesn't jump around like a tire out of balance hops, but keeps a steady, heavy hum and vibration in the driveline that rattles things in the dash and all over the car. If you take the transmission out of gear to coast, the vibration is still dependent on the engine speed. If you cut the engine off while coasting, the vibration goes away. What's going on here? Is an engine that was in a standard shift car balanced differently than one in an automatic transmission car? Is it a MUST to use an engine from an automatic car and not mix like I did? Could the rebuilt DACCO convertor be bad or out of balance right out of the box? Let me say that the transmission works exactly correctly, no slippage or such, but I know it can't last long vibrating like it is. Also, I put a brand new harmonic balancer on the engine, absolutely no change in the vibration. Help!!!!

 

Engine/transmission mounts?

My 45 year old truck does that vibration/rattling thing too...

 

Thanks for the quick reply! All mounts, engine and trans, were replaced during the rebuild with new ones.

 

I was serious about the engine mounts part, but I was sort of making a joke, particularly about the "old vehicle" part...

 

I've heard this question asked before...many times.

What torque converter and flex plate did you use?

On 1965/70 Mustangs/Falcons/Comets & 1970/77 Mavericks/Comets with 200 engines and C4's, the flex plate is just that...a flat plate (C3DZ-6375-B), the teeth are on the torque converter.

There's also a required flexplate re-enforcing plate (CODE-6A366-A): 3 5/8" O/D / 23/64" I/D / 5/64" thick / (6) 29/64" mounting holes.

The usual reason for vibrations: Did you line the transmission up to the engine correctly by using the two dowel pins (3/8" X 9/16") on the rear of the block?

Failure to do so, will cause horrid vibrations and tear the center out of the flex plate...in no time.