Sure could use some tech help ! I am building a 62 Plymouth Savoy , using a 400 motor and 727 trans from a 78 Cordoba donor. Motor has been rebuilt , trans rebuilt, original torq converter rebuilt. Problem : at aprox 2000 rpm there is a definite out of balance vibration , seems to fade away at higher rpms and lower rpms. I have looked at the front balancer , its the original, heavy on one side and it reading true to TDC at # 1 and I don't suspect it has slipped. I know the flex plate will only bolt on in one position and I have tried to reposition the weight on the converter but the flex plate is drilled to only allow one possible location. Some thing I did notice was when the front balancers heavy side is rotated straight up the torq. converter weight is at the bottom. Any good advice will be greatly appreciated !
Rebuilt as in new gaskets and a paint job or rebuilt as in new pistons an overbore and etc. Are we sure that the rod caps didn't get changed around and that everything is in its proper location? Did you run the engine before and was it smooth through the RPM range? Are we sure that the converter is the same converter and has the proper balance weight for the engine? Or did the rebuilder just give you a different converter and tell you it is the same one? What did the converter rebuild consist of did that cut the welds out and replace the vanes or just change the oil and clean it or????? Lots of questions here I know sorry.
I would assume that the 78 Cordoba had a 400? The convertor has to go with the type motor not the Trans, as far as the weight goes, but I'm sure you know that.
============= For twisted V8s the end counterweights are at 180 to each other. The external counterwieghts are pretty much an extension of the end counterweights so are positioned similarly. Fancy German V8 http://www.kenrockwell.com/bmw/images/m3-2007/crank-781.jpg More mundane unloved small block Olds. https://encrypted-tbn2.gstatic.com/...aGY4lE6CmP07Dar-eos8_woRONgP3jXreRqWU_AJtocck Even Ford flatheads with 3 mains http://www.prewarcar.com/images/caradvert/11111a_resized.jpg
Bored to .030 , one cyl was sleeved , had small freeze crack, bored back to .030, .010/.010 on crank , speed pro Hyp. flat top pistons , new cam , valves,lifters,springs , everything new except for block and crank ! Motor runs great and tranny pulls hard and shifts firm. The converter was out for rebuild (by reputable Austin trans shop) so I don't know what was required internally . Stall testing converter was good. Im to the point of despair and am considering tack welding more weight to existing weight, if it gets worse Ill start grinding some off.
34 toddster , yes , its all from same donor car, 400 for sure, externally balanced. Converter is weighted. And weight positioning by factory offset holes at crank and at Tconverter. So they make it to where you cant screw up. (supposedly)
Squirrel , The piston weight was close enough for a street motor , but I do know the "feel" of 8 pistons out of balance, this vibration is not the same and from underneath the car (running at 1800 to 2000 rpm she shakes right at the bell housing visually in time to a mark spray painted on converter.
Hence my questions. How much more do you suppose a .030 piston weighs. All rotating assemblies have a spot in the RPM range where harmonics will lay the vibration game. On a properly balance engine it is normally not as noticeable as on an engine that is not. A factory balance is nominal at best and when you start changing things sometimes you get lucky and the changes enhance the balance and sometimes the changes do not enhance the balance they do just the opposite. I am going to go out on a limb here and say that the 2000 RPM range is where this engine normally gets hit by harmonic vibration and when the heavier pistons were thrown into the mix it made it more noticeable. Of course I could be wrong I have been wrong almost once before.
How big is the weight on the converter? Is it about 1.1" wide and 3.5" long? or 1.8" wide, and 3.5"long?
You are correct in all respects and you know the feel of out of balance pistons im sure. This isn't a harmonic type of vibration , its more like a lump lump lump . Im not going to go back into the engine. so maybe I can add or subtract to improve drivability. Ill post results . Thanks for replying.!
squirrel, Now we are on to something ! I did not know there were different size weights ! Ill measure mine and see what I have. Could the difference be for the older Tconverters that had a drain plug ? Hmmm. gotta go now thanks!
Also could be the difference between external balance 440 and 400. That is why I asked of you got the same converter back or if they gave you a different one. Yep just checked B&M shows a different part number for the 400 and the 440 external balance motors.
Good luck. See that '55 Dodge to the left. That is still running the original 270 Hemi which has been bored 30 over, new pistons, new cam, new "Hot Heads" Special made harmonic balancer. Engine has been balanced with all the new parts. Seeing that the engine was internally balanced I needed a zero balance torque converter. Mopar utilized two different balance operations back that . They had an internal balance engine that need no external weights to help in balance. The other route they went was to balance to engine using the weights on the torque converter. So I have a balanced engine, a new torque converter with zero balance and all this is backed up by a '95 Dodge pickup 518A over drive trans. Oh and I also have the most annoying vibrations you an imagine. Mine comes in about 1200 RPM. I have had that unit out of the car twice. Had some very good mechanics from the area check it with me. We have tried adding weight to the flywheel or take some weight off. If you've seen some of the later Mopar flywheels they look like Godzilla took a hunk out of them. So like I said "GOOD LUCK". I've been driving this Dodge a lot with this problem. Made four trips to Salina KS. For me that's a 2000 mile round trip. Drove it 70, 75 MPH all day long on the trip. (16) hours.) I almost wish something would break then I would know where the problem was. But so far all is well. I will keep watching this post to see if any special answer comes up that hasn't already been discussed.
There ya go. I sent an external balance converter to get reworked (stall changed) back in the '90s. The company had them exchange but if I was willing to give them a week turnaround I could get the same one back and the rep said that he would wait the extra week so I did.
...I have references that show six different weight configurations; 20, 25, 50, 60, 100 and 120 grams. The 78-400 could have been equipped with a lock-up converter; was this so equipped and also part of the rebuild? One repair option is to use a B&M flexplate and a 'zero' balance converter. .
I cant see how a zero balance converter will ever work on a cast crank engine. I possibly missed that bulletin.
It is also possible that someone rebuilt the 400 and used a steel crank. He then used the cast crank balancer (out of ignorance) and the cast crank converter was used! That would be a problem. So then is it a cast or steel crank?
In a 36 year old engine many changes could have happened. I used to tinker with torqueflite transmissions and found many modifications.
All b and rb engines balance with different balancers and flexplates depending on whether it has a cast or steel crank. The Chrysler yellow book shows a pic of a counterweighted balancer and flexplate with a weight on either side of the convertor drain plug. All 400's are b series but there are 2 different cast cranks depending on whether it was a 2 or 4 barrel engine. Unless someone installed a forged crank from an early 383 you should be correct on the balancer. The question is which flexplate is correct?
Did you ever find the source of the imbalance? Has the crank balancer been replaced. I know, I know, but unless the trans shop mixed your converter with another one..that's all I got. I got a great deal once on a 68 Barracuda big block car cos the guy put a cast crank 400 in with a standard 1968 flywheel, and that was a bad feeling. But I sold the 400 and put a 383I had sitting around,steel crank .030 badger/trw cast pistons. The car was happy, I was happy but then the motor blew a head gasket..anyway, good luck I also have a 62 Plymouth with a 383 HP out of a 64 Plymouth Runs sweet. Got pics of your 62?
The Jalopy Journal
