So...i know a little bit more now, but the problem is still here...What i know so far and what was tested:

Problem: ENGINE is not shaking in neutral or maybe is shaking so little, that you can't really notice. Whan you apply gas it shakes. SHaking than translates to the whole car and steering wheel. The more gas you give, the more it shakes (when the car is standing still, so the car is not a problem).
We have disconnected the fan and shaking is the same so it must be the engine.

I have a Mustang Coupe, 302 engine, 3 speed manual trans., 1965.

- Crankshaft : 2M A
- Engine block: C8OE 6015 A
- Balancer (old one, it was replaced with a new one now): C5AE 6316 A2
- C6ZE-6380-A is my flywheel number

What has been tested or replaced:

- Spark plugs are ok, wires are ok too
- Engine mounts are ok
- Balancer was replaced with a new one for 302 and shaking is the same.

Help!

 

are all cylinders firing? did you check to see if you have the plug wires correct. did you check the firing order?

 

Since you say the engine mounts are ok....aka....they aren't ripped (which is hard to tell by visual inspection when they are still on car) have you inspected the trans mount?

 

Check the timing. My car did that a couple of weeks ago, at any speed, it felt like the whole front suspension was going to come off of the front of the car. I advanced it a little, and it went away. My timing was set at 16 degrees BTC.
It helped me. What is your timing set at?

 

what year car was the motor from? do you have the correct balance flywheel? if its a pre 86 motor you need a 28oz balance if its 86 or newer you need a 50oz ... i had this same problem with mine

 

this is incorrect...the balance changed in 82

 

81... we where both wrong...my apologies. anyways as i said i put a 91 302 in my 67 mustang and just to get it going i used a 28oz balance flexplate and the problem was exactly as you described. it looks like your crank is the 28oz imbalance. but i was shipped two incorrect flexplates before i received the proper one. one was a 28oz 157tooth and the other was a 50oz 164 tooth when i ordered a 50oz 157, i guess im trying to say double check your flywheel with the part number

 

My flywheel number is C6ZE 6380 A, so it has a 28oz weight and fits my 302 engine which is from year 68.

 

I had a "shaking" problem a couple of years ago. It turned out to be my motor mount. Mine would only shake when I put the car in reverse, driving forward was fine. My guess it depends on which mount is bad.

I looked, pryed, etc., but could NEVER see a "break" or "tear" in the mount. I finally bought a new set (and upgraded to the Ron Morris adjustables) and the problem went away like turning a light switch.

If you have another set of mounts, or can get your hands on a set, swap them both out.

It may not be the problem....but it sounds very similar to the situation I had, only in reverse.

Good luck!

 

Do a compression check on all cylinders and let us know if they are all within 10 - 15 psi.

We can only assume that your clutch assembly is not off in any way.