Need help with vibration!!

I don't know why you "assume" it's the engine

You have said twice that it DOES NOT VIBRATE in neutral with the car stopped. This indicates OTHER than the engine and clutch.

DETERMINE that first!!!!

Get it in gear, clutch in, parking brake engaged, and block the tires for safety. Rev the engine at different RPMs until you are satisfied...........one way or the other..........that it does or does NOT vibrate

If it does NOT vibrate, put the gearbox in neutral, and take your foot off the clutch. Repeat the test. take your time. Rev quickly, rev slowly, hold it at different RPMs until you are SURE what you are hearing and feeling.

If there IS vibration the very FIRST thing to check is the belt(s). With the engine cold, you can run it long enough with the belts "off" to determine if they are the problem, could even be something wrong A/C, water pump, alternator, PS pump, etc.

Unless the engine (it is not a motor, unless you've converted it to battery power) has something serious wrong such as bent valves, whatever, 3500 is NOTHING.

Hell my Dart---before I tore it down for paint---has 3.7's in the rear----CRUISES at 70 at about 3300!!!


Make sure your tach is accurate, though. You can "figure that" online with the various calculators. You need to know your tire size, your rear axle ratio, and whether the 4 speed is an OD or "regular" 4 speed. Use a GPS if possible, and get a good solid reading at about 60 mph VS RPM in "high" gear.

Then feed that into an online calcuator.