Back after long break and vibrating.........

Long story short on the 70 I had a driveshaft cut and balanced for the 9" rear end. The rear end was something I just picked up along the way and seems to be in good shape. Anyways I'm getting a good bit of vibration that seems to be rpm related.
The shop I had cut the driveshaft was suppose to balance it as well..... but who knows.
Is there any tricks to isolating a vibration or anywhere besides the driveshaft to look for causes????

Any help is appreciated. Car info is mostly in my signature but I can fill in the blanks if need be.

Thanks guys!!

 

how old are the tires and has it been sitting long?

 

Was the vibration not there prior to the driveshaft and differential installation? I'm assuming these two components were installed at the same time.

You write the vibration is RPM related, you therefore should get the vibration at that given RPM in each gear. Is that the case? If not, your vibration is MPH related.

 

Yes no vibration before that i can recall. However it went through an entire overhaul and sat for about a year so i could be recalling tjat wrong.
Yes rpm related. Vibrates in each gear around same rpm.

 

Tires are 5 years old probably. Sat for about a year

 

If the vibration occurs at the same RPM in each gear then your issue is engine or transmission related, not tire, driveshaft or differential.

What happens with the transmission in neutral and you bring the engine RPMs up to the specified rate, do you feel the vibration while sitting in the car?

 

Agreed... Driveshaft or rearend will viberate at a set vehicle speed reguardless of RPM..

 

Would a torque comverter cause this?
Thinking about it now when i put engine and trans together it took me forever to get the converter to engage with the trans pump and lock in right. Converter looked to be slightly not perfectly round on the trans side where it slips over and engages the oil pump of the trans.

 

I will try this but that 347 is rocking and rolling might be hard to tell if its vibrating lol

 

Absolutely, the convertor may have been damaged during installation. Even a torque convertor that is manufactured by a company not having tight tolerances in their build specifications can cause vibrations. That is why quality driveline components are important.

Do you have the correct flex-plate for your engine?

 

Yeah flex plate is for roller motor.
I will pull the converter and swap in a spare and see if vibration goes away

 

Most 347 are balanced for 28 0z front balancer and flexplate, which were used on pre 1981 engines... The late 5.0 stuff is 50 oz... Unless you have a oddball 347, that 5.0 flexplate is likely part of your problem...

 

Yeah balancer and flexplate are both for a roller engine.

 

Krazy i just sww what you were saying. That same engine ran in a foxbody with the same trans and no vibration before we had the engine freshened up.
The more i think about it the more likely its the converter. It had a different converter in it before and we swapped to this one for the maverick

 

In that case you should have the correct balance parts... There are early 28 oz balancers & flexplates for the late engines(have those parts for 331 going in my T-Bird). After 1981 it makes no difference if they are roller or not, cranks were changed(cheapened) in 1982 & roller motors were yet to see light of day...