340 converter

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9moes

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I have a 340 with a 904 behind it .i had the trans rebuilt not long ago by a good trans man. the only problem is now the car has a viberation. at first i thought it might be the universals or the drive shaft. (the trans had to be rebuilt because my younger brother shifited it in reverse at full throttle ( lock out did'nt work)at about 70mph).After knoting his head i took the car to the shop .Ialso put a new converter in it . the trans man said he had to weld a weight that came off the old converter to the new one .which i watch him do. then i left . When i came back to get the car i notice the virbration right a way.Trans man was'nt there when i picked it up .can some one tell me how i can check to see if the weight was put back in the right spot .i'm almost sure it's nothing to do with the drive line or universals because i fee it when i crank the car and sit there. the guy is a good trans man.Maybe he bolted it in wrong holes when he put it back on. ANY help on what could be wrong would really help.thanks
 
What year of 340?? The later ones were "externally" balanced and had a weight on the front by the timing cover. Also take car for a drive, shift to neutral and as you are coasting let off the gas(so the engine is at idle) if the vibe continues I would suspect something other than drivetrain..but its weird how this just started...
 
THANKS guys for the replys. before this happened ,when you cranked the car it was smooth( still had lope from cam ect..) but it was smooth. When i first cranked it after the trans build , it was rough feeling, how do i say it it felt like it wasn't ballanced just sitting there,not in gear or any thing .Just wondering if its got some to do with the weight on the converter or could the flex plate have got bent during the shift in to reverse while peged in drive. i'm almost sure its a 70 year motor think its got a mp crank in it but will check tomorrow. it feels like its out of balance some how. if the converter bolts in only one way could the weight been welded on the wrong side. Is there some way to check this .weight lines up with certain postion of crank or what.you dont even have to put it in gear to feel this . thats why i feel sure its not in the drive line. Maybe more sugestion on what to check, thanks Also when i drove the car after the reverse stunt it didn't have this feel just wouldn't change gears.thats why the trans rebuild.
 
9moes said:
THANKS guys for the replys. before this happened ,when you cranked the car it was smooth( still had lope from cam ect..) but it was smooth. When i first cranked it after the trans build , it was rough feeling, how do i say it it felt like it wasn't ballanced just sitting there,not in gear or any thing .Just wondering if its got some to do with the weight on the converter or could the flex plate have got bent during the shift in to reverse while peged in drive. i'm almost sure its a 70 year motor think its got a mp crank in it but will check tomorrow. it feels like its out of balance some how. if the converter bolts in only one way could the weight been welded on the wrong side. Is there some way to check this .weight lines up with certain postion of crank or what.you dont even have to put it in gear to feel this . thats why i feel sure its not in the drive line. Maybe more sugestion on what to check, thanks Also when i drove the car after the reverse stunt it didn't have this feel just wouldn't change gears.thats why the trans rebuild.
Click to expand...

weight on converter ????

340 with steel crank has no weight on converter.....

340 with cast crank takes it own special weighted flexplate or weighted converter...a 360 weighted converter can not be used with a cast crank 340 nor a steel crank 340...

need to verify what you have
 
flexplate has a off setted lug so the weight is positioned in the right spot...also the flex plate will only bolt on to the crank one way
 
Did you get the problem fixed, because I have the same problem with my car and checking to see whats wrong with my car thanks
 
70aarcuda I checked the motor its a 69 model with a mopar preformance cast crank don't know about flex plate but i watched the guy grind a weight off the old converter and spot weld it back on the new one .i had drove the car right after the mishap there was no viberation then ,trans just wouldn't change gears.after trans was built and installed i noticed it right when i cranked the car up. could the converters been built different in side so the weight was different than the old one .i'm confused as why i have a vibration now or should i say fills like something is hanging on one side of my motor as it turns .help me if you can thanks.
 
Thanks 70aarcuda ,I did'nt know there could be a combination of weights on the converter.(weight on front face of converter for balancing the engine,weight on out side of converter to balance the converter) I think some where in the rebuild processs the weights for the engine got left off or some thing. All i know right now about the engine is its a 69 340.mp cast crank,x heads,nasty cam,904.Maybe mopar performance can help on engine balance or even the converter .Just know i can not run it like it is. cudalady this might be the same problem you have .Going to keep asking ,looking, hunting till i find out how to fix it.
 
You have a cast crank....Externally Balanced.
My money is the weight was either not welded back on the converter,or it was put on the wrong place. The weighted converter is a thing of the past. Most people are using a neutral balanced converter (no weights) and using a externally balanced flexplate,along with a externally balanced harmonic balancer.
Cope Racing Transmissions has a 340/904 externally balanced flexplate. $85.00
Team that up with the correct harmonic balancer and neutral balanced converter,and your rolling. Unfortunately the trans has to come out.
 
At risk of sounding clueless and going out on a limb.... Is it a vibration or a miss-fire? Dad always popped the distributer out of a small block in smaller mopars when dropping the trans...just to make sure the cap didn't get f'd up if the engine rocked back too far against the firewall.... just sayin............
 
Seems as though a cast 340 crank may be a late 72 or 73 which are externally balanced.Check your balancer on the front of the motor see if it say anything.If they put a new convertor in and used one for a 69 340 it may be an internal balanced convertor and you may have an external balanced engine.He may have welded the balancer on 180 degrees around.
My 340 block had no crank and was going in a 318 car so I bought a 318 cast crank for a 70 dart and used the convertor and balancer off the 318.When looking for a crank nearly all the places I checked listed the cast 340 crank as a 318 crank also which are internally balanced.So checking the balancer ont the front will help alot.
 
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