transmission vibration

[vsj100]

Mine is a 68 Coronet/Superbee with a 440 and torqueflight 727. Under acceleration there is a vibration or flutter that starts at 20 mph or so. When I put it in neutral it goes away. I pulled the driveshaft and checked the U joints. They were ok. I have considered a trans rebuild but am looking for opinions on the vibration before doing that. I suppose it could be a mismatched harmonic balancer but I have not seen a Dodge with that before. Thank you all as always!

 

[khryslerkid]

Has the transmission been recently installed?

 

[azmoparboy]

Now I usually don’t throw my 2 cents worth in, but I would first check your drive line angles. You can down load an app. From Tremec toolbox. It cost nothing, goes on your smart phone. Also the tail of the transmission from left and right needs to be straight back to the rear axel. All of those cost nothing and you can eliminate them. I do wish you luck because chasing vibrations really sucks. I think many of us here with these old cars have had our share of them.

 

[WileERobby]

Have you checked your mounts ?

 

[matthon]

mounts

Pulled my hair out for months, on this forum.
Brand new engine mounts were bad, couldn't tell by looking at them.
Put the original crusty hard mounts back in, no issues in years.

 

[Darter6]

A little more info is needed. Tell us more about your car.
New to you ? Resent rebuild engine/suspension ? What type of engine mounts,poly or rubber ?

 

[Ron H]

Driveshaft balance?

 

[vsj100]

Has the transmission been recently installed?

no. The car is new to me. Bought it in July '23

 

[PurpleBeeper]

Torque converter?

 

[QuickBpBp]

Drive shaft could have good joints BUT it maybe out of balance itself. I had this similar experience recently on my 2017 Ram 2500. Turns out a poorly welded washer that balanced it had rusted and pushed itself off. All that was left was a small part of the weld. Thankfully it was still under the extended warranty and they put a brand new driveshaft in it. Problem solved.

 

[vsj100]

These ideas are all great. I have a transmission jack to push up against the motor mounts. There is a driveline shop close by.
I'll do the free stuff first. Thanks!

 

[Fran Blacker]

Check tailshaft bushing by pushing front yoke up and down. Had a bad one didn't rattle until 3000 3200 rpm.

 

[vsj100]

Yes y

Torque converter?

You get the prize. The current TC has no weights. The TF727 was behind a 383 before and when the 440 was installed the TC was not switched. Tomorrow I will change the flex plate out. Hopefully that solves it.

 

[PurpleBeeper]

Yes y

You get the prize. The current TC has no weights. The TF727 was behind a 383 before and when the 440 was installed the TC was not switched. Tomorrow I will change the flex plate out. Hopefully that solves it.

Well, all 383’s will be neutral balanced & a forged crankshaft 440 with small rods (‘66-‘69) will be neutral balanced also. However, “big rod” 440’s (‘70-‘73) and cast crank 440’s (‘74-‘78) will be externally balanced

 

[vsj100]

I installed one of those plates - see the picture - it cured the vibration.
Thanks for all of the tips!