Moparts
What went wrong? flex plate, converter, or tranny?
Posted By: 71nonRT340shaker
What went wrong? flex plate, converter, or tranny? - 08/13/13 02:16 AM
I have had a nasty vibration in my car since I got it running. I put about 200 miles on it 2 years ago, the tranny mount was shot so I put a new one in hoping the issue would go away, and it got 20 times worse. I haven't really driven it more than in and out of the garage when I want to work on a DD since. The car came from a guy who built it in 83, and parked it a few years later. I have no idea why it was parked he said his kids were born and that was that, maybe it had other issues so wasn't driven any longer? Beats me, it came with a Mallory dual point set up, but the dist. was gutted. I never heard it run before buying it 7 years ago.
The motor is smooth as can be at idle, it doesn't shake at all with your hand on the valve covers. Around 1500 - 1800RPM it starts to shake on the inside and its not comfortable to even sit in, it rattles your teeth. Here's the front of the flex-plate, and it appears the left ears on the stock plate (looking at from the front of the car) are bent. What does a flex plate failure look like? I have heard they crack, would that cause this issue? Obviously the plate is damaged but could it be the tranny/converter?
The motor is a 9-9-68 casting 340 with the early (thinner) dampener which I already swapped with another one I had, the converter doesn't have any weights welded onto the flat spots. I thought this was all correct maybe I'm wrong? It's a 727, and it vibrates in park, neutral, and all forward/reverse gears. Timing is set at 28 or 30 flat with no vacuum advance, electronic conversion Evan's harness and MP dist, orange box.
Thanks in advance, TC...
Posted By: stumpy
Re: What went wrong? flex plate, converter, or tranny? - 08/13/13 02:26 AM
Pull the trans because something is very wrong with that fles plate. I'm not sure if it could be installed backwards or not but it has to come apart.
Posted By: 71nonRT340shaker
Re: What went wrong? flex plate, converter, or tranny? - 08/13/13 02:33 AM
When I finally looked at it this evening I was happy to see the flex plate had visible issues. I don't know if it can be installed backwards but it would make perfect sense. All of the bolts in the plate appear to be intact and tight.
Posted By: stumpy
Re: What went wrong? flex plate, converter, or tranny? - 08/13/13 02:43 AM
You will want to check the converter snout fit into the crank area. When the converter is fit in the trans all the way it should be about 1" in from the edge of the case. With the trans bolted up you can push the converter flush to the flex plate. The flex plate should not bend to meet the converter pads. Also be sure to line the flex plate and converter bolt holes up and mark one ear on the flex plate and the corosponding pad on the converter they only fit one way. One hole and one pad are offset.
Posted By: Cab_Burge
Re: What went wrong? flex plate, converter, or tranny? - 08/13/13 04:46 AM
Posted By: 71nonRT340shaker
Re: What went wrong? flex plate, converter, or tranny? - 08/13/13 12:53 PM
Thanks for the quick replies. The plate is almost certainly on backwards, it all makes sense because the mounting holes only allow it to line up one way. I'm sure having the holes offset because the plate is on backwards causes the whole deal to be out of round and therefore vibrate. It's amazing the guy I got it from never changed it around?
I'm not doing anything crazy with the car just want a jump in and go cruiser, I'm most likely going to order the B&M 10230 and some new bolts. With any luck the flex plate was the weak link and it didn't rough up the crank or back of the block. Maybe I can even get to drive this thing before the weather breaks.
Posted By: Cab_Burge
Re: What went wrong? flex plate, converter, or tranny? - 08/13/13 05:49 PM
Quote:
Thanks for the quick replies. The plate is almost certainly on backwards, it all makes sense because the mounting holes only allow it to line up one way. I'm sure having the holes offset because the plate is on backwards causes the whole deal to be out of round and therefore vibrate. It's amazing the guy I got it from never changed it around?
I'm not doing anything crazy with the car just want a jump in and go cruiser, I'm most likely going to order the B&M 10230 and some new bolts. With any luck the flex plate was the weak link and it didn't rough up the crank or back of the block. Maybe I can even get to drive this thing before the weather breaks.
I wouldn't , and don't, use the B&M flexplates now do to some guys having issues with them vibrating(the externally balanced ones) and the converter bolt holes not lining up correctly 
I would either buy a new one, if you need and want a SFI spec. one for racing, or go to a tranny shop or junk yard and buy a good used one 
I have a dozen or more of all three sizes( 11 and 12 inch bolt patterns, small and big converter bolt sizes) and types(6 and 8 bolt crank flanges) hanging on the wall, to bad your not closer 
Posted By: 71nonRT340shaker
Re: What went wrong? flex plate, converter, or tranny? - 08/13/13 06:07 PM
I wasn't aware of the B&M having issues, I put one between the 72 or 3 340 and 904 in my Dart project that I haven't touched in 7 years. Obviously never started it but I thought that was the way to go at the time. I will look into another brand, I figured if i'm going through the trouble to yank the tranny in my garage I should put a new one in and get one that's SFI approved. I may very well have a used one laying around that I can put in as well. Thanks again for the heads up.
I'm going to start taking it apart this evening, I'm hoping I don't break any bolts and create a mess especially with the headers.
Posted By: John_Kunkel
Re: What went wrong? flex plate, converter, or tranny? - 08/13/13 08:51 PM
You can't put a flexplate on backwards for several reasons.
Posted By: MoparforLife
Re: What went wrong? flex plate, converter, or tranny? - 08/13/13 08:59 PM
Quote:
You can't put a flexplate on backwards for several reasons.
I agree with you John. Virtually impossible to do to put on a flexplate wrong. The bolts would not line up on either the crankshaft or the converter.
Posted By: therocks
Re: What went wrong? flex plate, converter, or tranny? - 08/13/13 09:03 PM
Man that had to make a ton of noise from the looks of it.Oh and to the people that say you cant put a flex on backwards.Guess again.Had a guy at the shop that did on the Mittsy 2.6.He didnt think anything was wrong with all the bolts not lining up.But he put it in and had the motor all bolted together.It was a lot of work but he did it.After all these years I still wonder how.Rocky
Posted By: 71nonRT340shaker
Re: What went wrong? flex plate, converter, or tranny? - 08/13/13 10:00 PM
I'll have more pics as time allows to drop the tranny. If it can't go backwards I don't know what I will find. And not to say it didn't make a boat load of noise back in 83, but it makes zero noise minus a slight resonating vibration around 1800 or 2k that goes away just above that. The inspection cover is loose and I figure causing that sound. It just shakes like crazy, no rattles, bangs, grinding etc.
Posted By: MoparforLife
Re: What went wrong? flex plate, converter, or tranny? - 08/13/13 10:03 PM
Quote:
Man that had to make a ton of noise from the looks of it.Oh and to the people that say you cant put a flex on backwards.Guess again.Had a guy at the shop that did on the Mittsy 2.6.He didnt think anything was wrong with all the bolts not lining up.But he put it in and had the motor all bolted together.It was a lot of work but he did it.After all these years I still wonder how.Rocky
You cannot do it on a big or small block. Bolt hols are offset on both the crank and the converter.
Posted By: John_Kunkel
Re: What went wrong? flex plate, converter, or tranny? - 08/13/13 10:42 PM
Not only are the bolt holes offset but the flexplate is dished toward the motor, if you could get it on backwards the converter would be shoved back into the pump and the starter likely wouldn't fit.
Posted By: stumpy
Re: What went wrong? flex plate, converter, or tranny? - 08/13/13 11:00 PM
How about some pics as you tear it apart. Front of the converter when you drop the trans and a pic of the flex plate before and after you remove it.
Posted By: MoparforLife
Re: What went wrong? flex plate, converter, or tranny? - 08/13/13 11:05 PM
Quote:
Not only are the bolt holes offset but the flexplate is dished toward the motor, if you could get it on backwards the converter would be shoved back into the pump and the starter likely wouldn't fit.
Yep - many things that say you can't do it!!!
Posted By: forphorty
Re: What went wrong? flex plate, converter, or tranny? - 08/13/13 11:49 PM
One thing you might consider when you change the flexplate is to get some converter bolts with a thinner head. The bolt head in the pic looks pretty thick and they can get very close to the block.
Posted By: OldMoparMan
Re: What went wrong? flex plate, converter, or tranny? - 08/13/13 11:52 PM
The thing that bothers me is the location of the swipe mark on the flex plate. If I'm thinking correctly the only thing that protrudes off the back of the block in that area is the camshaft plug. With what you described I would have to say the plate is deflecting as the rpm's go up from a very worn fit or broken flex plate.
I've seen this happen on electric motors with plastic fan that don't rub turning by hand but hit the endbell or cover when running at full speed.
It will be interesting to see the pics of the damage
Posted By: 71nonRT340shaker
Re: What went wrong? flex plate, converter, or tranny? - 08/14/13 12:50 AM
I'm going to call this bad news because the flex plate doesn't appear to be nearly as bad as the pics show. As it was already said the flexplate is installed correctly and everything looks ok. I got the header and starter off to get this far after work today. First is the inspection cover...
Posted By: 71nonRT340shaker
Re: What went wrong? flex plate, converter, or tranny? - 08/14/13 12:50 AM
Flex plate with basically the rust rubbed off.
Posted By: 71nonRT340shaker
Re: What went wrong? flex plate, converter, or tranny? - 08/14/13 12:54 AM
Here's the converter its fairly small in diameter compared to some I've seen may or may not be the correct one? Also the flat you can see in the pic is where the weights would be, and this motor shouldn't have any on the converter, correct? Thanks again for helping me out...
Posted By: Cab_Burge
Re: What went wrong? flex plate, converter, or tranny? - 08/14/13 04:09 AM
Quote:
Here's the converter its fairly small in diameter compared to some I've seen may or may not be the correct one? Also the flat you can see in the pic is where the weights would be, and this motor shouldn't have any on the converter, correct? Thanks again for helping me out...
That is a after market race converter, not a stock one 
I think I see a washer under one of the converter mounting bolts, take it out and leave it out 
It looks like your working on a SB motor, yes? Next thing is to figure out if the motor was a externally balanced cast iron crankshaft motor originally or not What crankshaft dampener is on it now? Post a picture of the front of the motor with the pulleys and dampener so we can see them from the front
Posted By: stumpy
Re: What went wrong? flex plate, converter, or tranny? - 08/14/13 04:24 AM
I looks like a crankshaft bolt head or something is against the converter in the second photo and that shouldn't be. And you still need to figure out why the flex plate ears are bent.
Posted By: buildanother
Re: What went wrong? flex plate, converter, or tranny? - 08/14/13 06:04 AM
You wouldn't be the first one to experience flexplate to insp cover carnage. Everything else looks pretty much normal.
Posted By: MoparforLife
Re: What went wrong? flex plate, converter, or tranny? - 08/14/13 09:34 AM
Bolt head looks pretty thick, funny it didn't hit on the block webbing. Also on the dusct cover. There are a couple of variations with the converter mounting screw groove in a different location depending on the converter used.
Posted By: BB65Barracuda
Re: What went wrong? flex plate, converter, or tranny? - 08/14/13 10:54 AM
I think I see a washer under one of the converter mounting bolts, take it out and leave it out!
Cabs right, looks like wrong bolts and the washers aren't helping.
That's obviously what is tearing up the inspection plate.
Posted By: 71nonRT340shaker
Re: What went wrong? flex plate, converter, or tranny? - 08/14/13 12:24 PM
Quote:
It looks like your working on a SB motor, yes? Next thing is to figure out if the motor was a externally balanced cast iron crankshaft motor originally or not What crankshaft dampener is on it now? Post a picture of the front of the motor with the pulleys and dampener so we can see them from the front
Cab this is from earlier in my post I can get a pic this evening if needed but:
The motor is a 9-9-68 casting 340 with the early (thinner) dampener which I already swapped with another one I had of a 70 motor, the converter doesn't have any weights welded onto the flat spots on the motor side. I thought this was all correct maybe I'm wrong? It's a 727, and it vibrates in park, neutral, and all forward/reverse gears. Timing is set at 28 or 30 flat with no vacuum advance, electronic conversion Evan's harness and MP dist, orange box.
Thanks again for all of the great feedback, I'm happy to hear the washers and what not don't look ok. I'm well on my way to getting the tranny out, and it should be out by the weekend. It's not the ideal setup by any means the car is on jack stands and I'm laying on the garage floor. Makes sense it's not the stock converter the car doesn't engage like a newer daily driver when you put it in drive, and the neighbors love when I pull it in the garage at 10pm.
Posted By: poboyengineering
Re: What went wrong? flex plate, converter, or tranny? - 08/14/13 01:09 PM
Quote:
Flex plate with basically the rust rubbed off.
doesn't it look like the bolts holding the flexplate to the crank are hitting the converter? that would keep the converter too far away from the crank, and then the installer just pulled the ears down with the bolts, distorting the flexplate? just my
Posted By: 71nonRT340shaker
Re: What went wrong? flex plate, converter, or tranny? - 08/14/13 01:40 PM
Quote:
the installer just pulled the ears down with the bolts, distorting the flexplate? just my
I have my fingers crossed that's exactly what went wrong. With any luck a new plate, and 10 bolts and I'm good to go.
Posted By: Challenger 1
Re: What went wrong? flex plate, converter, or tranny? - 08/14/13 01:51 PM
Quote:
Quote:
the installer just pulled the ears down with the bolts, distorting the flexplate? just my
I have my fingers crossed that's exactly what went wrong. With any luck a new plate, and 10 bolts and I'm good to go.
How would a distorted flex plate cause a vibration?
Posted By: Dodgem
Re: What went wrong? flex plate, converter, or tranny? - 08/14/13 02:00 PM
I once had trouble with a 318 we but in a truck ended up the front pass motor mount was installed on the ears wrong. causing motor and tranny to be missaligned a bit always had to force it a bit to get trany in cross over right. One i fixed it vibration was gone?? On a 340 is there not some shiming to do with certain mounts to make sure it is in right!
Posted By: 71nonRT340shaker
Re: What went wrong? flex plate, converter, or tranny? - 08/14/13 02:24 PM
Quote:
How would a distorted fex plate cause a vibration?
If I'm understanding this correctly:
If the crank bolts are hitting the converter and they tightened the first flex plate bolt all the way initially, you would have to draw the plate to the converter with other 3 bolts (after the first one is tight the plate would be putting force on the heads of the other 3 bolts, or pulling away from the converter) which would bend the ears and create a spring like tension VS the plate laying flat against the converter as it should be and the bolts simply holding the 2 together.
Posted By: dogdays
Re: What went wrong? flex plate, converter, or tranny? - 08/14/13 05:08 PM
There's an assumption that the OP is making that doesn't sound right to me.
On stock converters that have weights, like for a 340 cast crank or 360, the weights are welded to the OD of the converter shell. But the OP has mentioned twice now that the weights would be welded to the flat area above the mounting bolt.
Is this common?
I am not that familiar with aftermarket converters and want to know.
R.
Posted By: 62maxwgn
Re: What went wrong? flex plate, converter, or tranny? - 08/14/13 05:37 PM
Remember,there are two different size bolt holes in the flex plate depending on the application,if you have a converter that uses small bolts and a plate with big holes,it will never be centered!!
Posted By: OldMoparMan
Re: What went wrong? flex plate, converter, or tranny? - 08/15/13 12:58 AM
There is something to what challenger1 said about the vibration even if the flex plate is bent from bolt pressure if it's centered it shouldn't cause vibration.
Because you stated that the engine runs smooth at idle that would tend to eliminate any part of the rotating assembly parts being off center or heavy to one side. If the vibration increases with the engine rpm's then something has to be deflecting and possible rubbing
I run a high speed balancing machine for electric motors and it doesn't matter if it's turning 400 or 2000 rpm's the out of balance amount doesn't change the only way to change it is to add or remove weight
Posted By: 71nonRT340shaker
Re: What went wrong? flex plate, converter, or tranny? - 08/15/13 04:11 AM
I didn't get much from ripping the trans out aside from the back of my head being soaked with transmission fluid and anti-freeze. The flex plate bolts were not very tight, none of the holes were rounded out or threads smoothed. Otherwise I don't see any damage. I also didn't take the converter out but I can't feel any weights on the back side of it either.
I'm going to order a new flex plate and bolts while it's apart, as well as motor mounts simply because they say made in Korea. I was hoping there would be a sign of something but I guess you don't know until you look. If it still shakes when it goes back together I guess I'll have to drop the pan to check the crank, and or put a new converter in it.
On a lighter note I can drop a 727 myself in a lot less time than I thought it'd take.
Posted By: 71nonRT340shaker
Re: What went wrong? flex plate, converter, or tranny? - 08/15/13 04:12 AM
converter
Posted By: Cab_Burge
Re: What went wrong? flex plate, converter, or tranny? - 08/15/13 04:42 AM
Posted By: BB65Barracuda
Re: What went wrong? flex plate, converter, or tranny? - 08/15/13 11:15 AM
Quote:
You might want to send that converter out to a good shop like ATI or Turbo Action and have them run it on thier converter dyno to see if it is out of balance or hurt internally
Much cheaper than a new unit and you will be certain to have a good piece when you get it back.
Posted By: 71nonRT340shaker
Re: What went wrong? flex plate, converter, or tranny? - 08/15/13 01:07 PM
Any idea on the cost and a ball park turn around? I need to have it back together before the weather goes south.
Posted By: Yellow Fever
Re: What went wrong? flex plate, converter, or tranny? - 08/15/13 02:53 PM
Where in PA are you? Go to Pat's Convertors, they will check it out.
Pat's Converters Inc
101 Swarthmore Ave
Folsom, PA 19033
(610) 237-6900
Posted By: 71nonRT340shaker
Re: What went wrong? flex plate, converter, or tranny? - 08/15/13 03:14 PM
I'm a stone's throw from State College, just about 8 miles east.
Posted By: Yellow Fever
Re: What went wrong? flex plate, converter, or tranny? - 08/15/13 03:27 PM
That's a drive then, they are by me in SE PA, just south of Philthy!
Posted By: 71nonRT340shaker
Re: What went wrong? flex plate, converter, or tranny? - 08/15/13 03:40 PM
I'll figure something out, I was beat last night but I'm not giving up on the project yet and my DS motor mount is really spongy I can pry up on it between the k-frame and the ear that's bolted through it making everything move and twist. I'm curious to see if possibly the bottom of that bracket is rattling off the k-frame shaking the whole car when it's under a load. I'm stumped and will just take care of those few things and see if it magically goes away.
Posted By: 68_661charger
Re: What went wrong? flex plate, converter, or tranny? - 08/15/13 04:00 PM
The lack of a good drivers side mount will make noise when driving under a load but not necessarily when in park. I agree the convert bolts are too big and the stall on that convertor probably makes it a bear to drive??. Worst case is the crank is walking forward as the RPMs increase causing contact.
Posted By: 71nonRT340shaker
Re: What went wrong? flex plate, converter, or tranny? - 08/15/13 04:08 PM
I didn't do a ton of driving before putting the trans mount in last year but it was friendly on the street, made lots of noise, left hard from lights, shifted into 3rd around 60 - 65.
There's a steep road near my house we crossed over before the trans mount and it shook the worst it ever did while climbing the mtn. Beats me, new parts will be ordered what I get paid next week and with any luck it will settle a bit.
Posted By: Challenger 1
Re: What went wrong? flex plate, converter, or tranny? - 08/15/13 04:13 PM
Take a screwdriver and check the crank end play, do it between the flex plate/crank flange and block and then damper and timing cover.
Posted By: OldMoparMan
Re: What went wrong? flex plate, converter, or tranny? - 08/15/13 08:40 PM
You might want to run the engine now and see if there is any vibration there. The more things eliminated the less you have to think about.
Posted By: Supercuda
Re: What went wrong? flex plate, converter, or tranny? - 08/15/13 08:45 PM
Quote:
You might want to run the engine now and see if there is any vibration there. The more things eliminated the less you have to think about.
Not gonna be able to use a starter now.
Posted By: Cab_Burge
Re: What went wrong? flex plate, converter, or tranny? - 08/16/13 04:56 AM
Quote:
Quote:
You might want to run the engine now and see if there is any vibration there. The more things eliminated the less you have to think about.
Not gonna be able to use a starter now.
Unless you have nuetral balanced stick flywheel and bellhousing to match the size of the flywheel I do 
OP, I hope you find the problem Let us know what you do find
Posted By: 71nonRT340shaker
Re: What went wrong? flex plate, converter, or tranny? - 08/16/13 01:11 PM
Will do I talked to John at ATI racing yesterday. I'm going to send out the converter which btw doesn't have any weights on the outside of it. I'm planning to order a new flex plate/bolts, shumacher motor mounts and with any luck it will be good to go.
Posted By: MO_PA
Re: What went wrong? flex plate, converter, or tranny? - 08/16/13 01:35 PM
Are the alignment dowels in the block? I don't see them in the pics.
Posted By: 62maxwgn
Re: What went wrong? flex plate, converter, or tranny? - 08/16/13 01:35 PM
Quote:
Will do I talked to John at ATI racing yesterday. I'm going to send out the converter which btw doesn't have any weights on the outside of it. I'm planning to order a new flex plate/bolts, shumacher motor mounts and with any luck it will be good to go.
If you put that thing back in Bill's basement you won't have to worry about it !! 
Posted By: 71nonRT340shaker
Re: What went wrong? flex plate, converter, or tranny? - 08/16/13 01:49 PM
Quote:
If you put that thing back in Bill's basement you won't have to worry about it !!
Haha this is my 70 'cuda that came out of the Snow Shoe area, the challenger is a 4 speed car...
