Automatic Trans. Vibration in 3rd gear

[rcannon440]

I have a 1969 Dodge Charger that I just performed a transmission swap from a 727 to a 518 overdrive unit. Everything turned out well and works great except the fact that the car now has a bad vibration while in 3rd gear and goes away when in overdrive. I have replaced the flex plate torque converter, drive shaft and had the transmission rebuilt. I would like to know if there are any transmission guru's out there that can tell me if it sounds reasonable that the transmission could have something bent in it? THX

[MSRacing89]

If it happens through all rpm ranges in 3rd gear then I suspect something could be wrong with the trans. If it is in small window, then I would be looking driveshaft or driveshaft angles.

[rcannon440]

An update to this problem. I have since tried troubleshooting this problem by putting the car on jack stands and running it up. The vibration still exists, so I then removed the rear wheels and drums still have the vibration, I then removed the drive shaft and installed an extra yoke, still have the vibration with no drive line installed. I then unbolted the transmission from the cross member and jacked up the transmission off of the cross-member, vibration is now gone. I lower the transmission back down but do not bolt it up to the mount, vibration is back. To me it sounds like something with the transmission but what? It's not the torque converter it is new.

[cdr]

only in 3rd ? or is it rpm ?

[ACUDANUT]

Sorry mate, most of only use 4 speeds and 727's. Don't try to fix something that ain't broke.
If you want MPG, your in the wrong hobby.

[Back N Black]

 This seems like a common problem with the 518 overdrive unit. I have a friend with the same problem, he gave up and swaped back the 727.

[rcannon440]

It happens mainly in 3rd gear between 35 and 45 MPH.

[cdr]

It happens mainly in 3rd gear between 35 and 45 MPH.

well it would seem like a problem inside the trans ?

[rcannon440]

to Back n Black. Can you give me anymore details on what caused the vibration.

[RECHRGD]

It happens mainly in 3rd gear between 35 and 45 MPH.

Define "mainly".  If it's happening at the same rpm, but to a lesser degree in 1st and 2nd it would point back to a driveline problem.  I seems that you've eliminated that though. I feel you're pain......

[cdr]

take all your belts off & see if vibration changes.it wont hurt to run a short time with no water pump belt.

[Back N Black]

to Back n Black. Can you give me anymore details on what caused the vibration.

He is still trying to figure it out.

[Kern Dog]

Sorry mate, most of only use 4 speeds and 727's. Don't try to fix something that ain't broke.
If you want MPG, your in the wrong hobby.

A guy asks for help and you dish out this crap? If you're happy getting 10 mpg, thats your choice. SOME guys like to evolve from "knuckle dragger" status.
Do you still run drum brakes and bias ply tires? Still listen to AM radio exclusively?

[randy73]

at what speed did you set you converter to lockup?

sounds like a convertor or govenor issue, call PATC in La., I put a 95 46rh behind my 340 and PATC told me some come with govenors for diesels and that will cause issues.

[ACUDANUT]

Sorry mate, most of only use 4 speeds and 727's. Don't try to fix something that ain't broke.
If you want MPG, your in the wrong hobby.

A guy asks for help and you dish out this crap? If you're happy getting 10 mpg, thats your choice. SOME guys like to evolve from "knuckle dragger" status.
Do you still run drum brakes and bias ply tires? Still listen to AM radio exclusively?

Do you still watch porn in your mothers basement. ?

[Kern Dog]

Is that a question? People that use English should use proper punctuation. People that ask for advice don't need to be told that "This is how we did it back in  the 60s, no need to try to do any better. Thinking like that means that you never improve anything. If you live your life that way, so be it. The OP might just be a bit more adventurous than some people.

[JB400]

Sorry mate, most of only use 4 speeds and 727's. Don't try to fix something that ain't broke.
If you want MPG, your in the wrong hobby.

A guy asks for help and you dish out this crap? If you're happy getting 10 mpg, thats your choice. SOME guys like to evolve from "knuckle dragger" status.
Do you still run drum brakes and bias ply tires? Still listen to AM radio exclusively?

Do you still watch porn in your mothers basement.

You two need to take your slander to pm's.  Let's leave the thread to helping the op with his problem.
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Is this a big block car or a small block car?  If it's a big block car, it could be you didn't cut your bellhousing off square, or the bell housing is bent in some way, throwing things out of whack.   Might be something to check.

[moparsr2fast]

  Recheck the torque convertor bolts, flywheel bolts, and the bellhousing to block bolts. Sometimes it can be the simplest thing..

[rcannon440]

Well it sounds as though a simple request for help has stirred up some serious talk. I do appreciate all comments good or bad although I will say that installing an overdrive unit was my own decision regardless if someone else thinks it was foolish. I am very happy with the 14-15 MPG and cruising at 70MPH at 2300rpm's. To each his own I guess.

OK so enough of that. I am hear to gladly report that I have resolved the vibration problem!!!! It turned being something that I had looked at many times but never paid attention to it. As many of you know this project requires modifying or making a new cross member for the transmission to mount to and also a different rubber transmission mount. As it turns out the metal side of transmission mount was rubbing against the side of the new cross member making the rubber insulator totally ineffective. I drilled out the hole for the mount a little bigger and moved it over slightly and that was it. I still am not sure why the vibration was so bad in 3rd gear though.

Thanks for everyone's input. Sometimes it's the simplest things that cause the biggest problems.

[JB400]

Glad to hear you got it resolved

[cdr]

Well it sounds as though a simple request for help has stirred up some serious talk. I do appreciate all comments good or bad although I will say that installing an overdrive unit was my own decision regardless if someone else thinks it was foolish. I am very happy with the 14-15 MPG and cruising at 70MPH at 2300rpm's. To each his own I guess.

OK so enough of that. I am hear to gladly report that I have resolved the vibration problem!!!! It turned being something that I had looked at many times but never paid attention to it. As many of you know this project requires modifying or making a new cross member for the transmission to mount to and also a different rubber transmission mount. As it turns out the metal side of transmission mount was rubbing against the side of the new cross member making the rubber insulator totally ineffective. I drilled out the hole for the mount a little bigger and moved it over slightly and that was it. I still am not sure why the vibration was so bad in 3rd gear though.

Thanks for everyone's input. Sometimes it's the simplest things that cause the biggest problems.


now that IS good news !!!!!!!

[Kern Dog]

The vibration I was having in my Charger was also due to a point of contact like yours. My crossmember was touching the metal portion of the trans mount.
Glad you resolved it in your car!

[rcannon440]

The vibration I was having in my Charger was also due to a point of contact like yours. My crossmember was touching the metal portion of the trans mount.
Glad you resolved it in your car!

That is exactly what happened to mine! Same thing WOW

[John_Kunkel]

W. I still am not sure why the vibration was so bad in 3rd gear though.

That's the strange part, contact is contact...it shoulda vibrated in any gear.