Resto Mod 1973 Barracuda round 2

Author Topic: Resto Mod 1973 Barracuda round 2  (Read 24953 times)

Offline 70chall440

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Re: Resto Mod 1973 Barracuda round 2
« Reply #255 on: June 29, 2018 - 11:09:08 pm »
if your harmonic balancer is externally balanced and you have a 360, then you are good, but you need an externally balanced TC as well.

If you have a 340 and a harmonic balancer that is externally balanced, then it is wrong.
Current Mopar
70 Challenger RT 440-6, 73 Cuda (under const)
05 Durango, 99 Dakota, 01 Ram 4x4, 14 2500 4X4, 10 PCP Challenger RT, 01 Viper GTS ACR, 52 B3B w/330 Desoto Hemi, 70 Hemi RR, 61 Jeep FC170
Past Mopars
9 x Challengers. AAR Cuda, 4 RR, 2 GTX, 4 Chargers, etc... (too many to list)




Offline redo1973

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Re: Resto Mod 1973 Barracuda round 2
« Reply #256 on: July 21, 2018 - 08:12:32 am »
Time for an update. It's been a month but I expected that.  We tried to figure out the issue sooner but my son the auto technician had his wedding and honeymoon so that delayed things. We have since done the following and once again some lessons learned.  I had a noticeable wobble in one wheel as the flange was bent but not the main cause of the vibration.  I've since replaced both axles with Mosers.  We sent the drive shaft out for evaluation.  Low and behold, it was bent, needed balancing and the slip yoke was pinching the U-Joint! :faint: I now regret not simply buying one but this is now like new.  All I can think of is that this car was in an accident.  There was clear damage on the rear driver side quarter when I bought the car but the extent of the damage looked like sheet metal.  Based on these recent discoveries, I'm now thinking was hit diagonally in the rear and caught the wheel as well.  We've run the car on stands and the pulsating vibration is gone.  There is still a vibration but one that is more related to "normal" mechanical/rotating that I feel is more familiar to the car I had in the 80's.  We'll do another shake down ride this weekend.

Offline redo1973

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Re: Resto Mod 1973 Barracuda round 2
« Reply #257 on: July 21, 2018 - 08:26:17 am »
BTW - I double checked my motor balancing.  My 340 motor is a February 1972 casting 2780930.  Per my research, Mopar switched to cast cranks for 1972/1973 which are typically not internally balanced.  I have a crank # 3462387 that fits the time-frame of casting per the charts on MyMopar.  I also confirmed through pictures I took during assembly that have a cast crank.  I installed an externally balanced Harmonic Balancer and Torque converter.  The motor does not shake at idle or higher RPM's although there is vibration through to the steering wheel.  I associate this level of vibration to be the rotating parts sending vibration through the stiffness I added to the K-Frame and urethane motor mounts.  Although I researched the balancing topic during the engine build, if I do a restoration again  :roflsmiley: , I'll pay more attention to this.  If not balance internally, would probably have elected a balanced flex plate over the converter and probably avoid the urethane mounts.  It appears that there are more part options for internally balanced motors.

Online djw383

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Re: Resto Mod 1973 Barracuda round 2
« Reply #258 on: July 21, 2018 - 08:27:10 am »
How about the tires? Flat spots?

Offline 70chall440

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Re: Resto Mod 1973 Barracuda round 2
« Reply #259 on: July 21, 2018 - 12:17:41 pm »
An internally balanced engine requires a neutrally balanced harmonic dampener and TQ, these are sometimes called non-balanced or unbalanced. That said, if you had the wrong components on the engine, you would get a vibration relatively early in the RPM climb and it would get progressively worse.

Flat spots in the tires will be consistent and exhibit vibration early on and get more pronounced with an increase in speed.

So let's break this down, if you are getting a vibration through the steering wheel at idle, then it has to be a result of engine vibration transmitted through the K frame. That said, you are probably correct in that what you feel is normal. The steering column is rigidly mounted into the dash frame and any vibration in the car can be felt generally. So long as the vibration isnt horrible or violent you are probably good.
Current Mopar
70 Challenger RT 440-6, 73 Cuda (under const)
05 Durango, 99 Dakota, 01 Ram 4x4, 14 2500 4X4, 10 PCP Challenger RT, 01 Viper GTS ACR, 52 B3B w/330 Desoto Hemi, 70 Hemi RR, 61 Jeep FC170
Past Mopars
9 x Challengers. AAR Cuda, 4 RR, 2 GTX, 4 Chargers, etc... (too many to list)

Offline redo1973

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Re: Resto Mod 1973 Barracuda round 2
« Reply #260 on: July 21, 2018 - 09:06:42 pm »
Thanks Mike.   I put on some miles today and although there is a vibration, its most noticeable when I put it under load, like climbing a hill yet the car accelerates fine.  I would not consider this a "violent" vibration but annoying noise.  There is more like a drone from the exhaust.  To be honest, I don't remember what is "normal" and acceptable for these cars especially with the 2.5 inch exhaust and dynomax turbo mufflers.  Especially, since today's technology is so quiet and smooth.  The steering wheel shakes pretty good but settles in gear and with RPM.  My son is back tomorrow so we'll keep tracking but it is driveable. I'll let you know what we find out.

I've not heard of flat spots on radial tires.  How do I check that or are your referring to the biased tires?

Offline 70chall440

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Re: Resto Mod 1973 Barracuda round 2
« Reply #261 on: July 21, 2018 - 09:26:18 pm »
Yes radials get flat spots, the tires on my Viper are horrible about it. Takes a little driving for them to kind of even out.

Based on what you are saying in reference to the vibration under load, I would suggest you take a really hard look at your exhaust and where it runs. Are you running any type of torque strap on the engine. The vibration at idle and then under load has me thinking you have a bad or weak motor mount and it is being transmitted through the car, additionally when you are under load it is causing the engine to pull the exhaust up and hit something solid which can feel like a vibration. Just for fun, rig up a simple chain on the drivers side, bolt one end to the engine and the other to the frame. You want it to be tight. then drive it again and see.
Current Mopar
70 Challenger RT 440-6, 73 Cuda (under const)
05 Durango, 99 Dakota, 01 Ram 4x4, 14 2500 4X4, 10 PCP Challenger RT, 01 Viper GTS ACR, 52 B3B w/330 Desoto Hemi, 70 Hemi RR, 61 Jeep FC170
Past Mopars
9 x Challengers. AAR Cuda, 4 RR, 2 GTX, 4 Chargers, etc... (too many to list)

Offline redo1973

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Re: Resto Mod 1973 Barracuda round 2
« Reply #262 on: July 22, 2018 - 10:07:08 am »
I think that you are onto something.  I have the two brackets, probably 1/8 thick angle style that I've not determined how they mount.  I was thinking it to be some bracing between motor and transmission but haven't figured it out. I also have new motor mounts but will check tightness.  Sounds like today's task.  It's raining here on the east coast so I guess no yard chores today and I'll have to stay inside  :woohoo:

Offline 70chall440

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Re: Resto Mod 1973 Barracuda round 2
« Reply #263 on: July 22, 2018 - 11:21:34 am »
Post a pic of the brackets, they sound like the original trans to motor support brackets (kind of twisted, about 6-8" long)? Those brackets were usually tossed the first time the engine or trans came out of the car. Not saying they aren't useful but I've never run them on a modified car and have never seen any on a race car; in other words those brackets are not a contributing factor to your vibration.

Give the torque strap deal a try and see if that makes a difference.
Current Mopar
70 Challenger RT 440-6, 73 Cuda (under const)
05 Durango, 99 Dakota, 01 Ram 4x4, 14 2500 4X4, 10 PCP Challenger RT, 01 Viper GTS ACR, 52 B3B w/330 Desoto Hemi, 70 Hemi RR, 61 Jeep FC170
Past Mopars
9 x Challengers. AAR Cuda, 4 RR, 2 GTX, 4 Chargers, etc... (too many to list)

Offline redo1973

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Re: Resto Mod 1973 Barracuda round 2
« Reply #264 on: August 05, 2018 - 09:15:02 pm »
I don't know where time goes.  Here is a picture of those brackets.  As for the vibration, it seems to have minimized to a motor vibration that changes with RPM and then the exhaust drone.  We'll probably change over to rubber motor mounts over the winter.   

Offline 70chall440

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Re: Resto Mod 1973 Barracuda round 2
« Reply #265 on: August 06, 2018 - 12:10:55 am »
Yes, those brackets were used to connect the engine to the trans at one time.
Current Mopar
70 Challenger RT 440-6, 73 Cuda (under const)
05 Durango, 99 Dakota, 01 Ram 4x4, 14 2500 4X4, 10 PCP Challenger RT, 01 Viper GTS ACR, 52 B3B w/330 Desoto Hemi, 70 Hemi RR, 61 Jeep FC170
Past Mopars
9 x Challengers. AAR Cuda, 4 RR, 2 GTX, 4 Chargers, etc... (too many to list)