• To ALL forum users - As of late I have been getting quite a few private messages with questions about build ups here on the forum, or tech questions about your personal project. While I appreciate the interest, sending me a private message about these topics distracts from, and undermines the purpose of having a forum here. During the day I wear many hats as a small business owner-operator and I work tirelessly to provide the absolute best service possible to you, our valued customer. When I created this forum I rounded up some of the best minds I knew so that any tech question you might have could be asked and answered by either myself or one of my highly experienced moderators, this way the next time this same question is asked the answer can be easily found and utilized by the next IH enthusiast having the same question. This allows me the freedom to run the day to day operations of the business and minimize the impact to shipments and shop activities that these distractions can cause. It is of the up most importance for me to complete the daily tasks in order to best take care of you our customer, all the while providing you a forum to get the level advice and input you have come to expect and deserve from the premier IH shop in the country.

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    Jeff Ismail

Need Help Shaking out a Vibration


New member
Okay everyone, been having a vibration since my rebuild and I was wondering if you all could give me some general information so I can try and isolate/prevent myself from sinking more time and money in it.

1974 2wd 100 series with 345 and a Sniper 2300 efi bolted on, DUI dizzy. Originally 3 on the tree, but converted to T407 during this rebuild. Has the Dana 44 rear, FA5 front suspension and B&M shifter in the floor for the 727.

Tranny donor was a 71 1110 that had a 392 and the 727 in it. Had the trans rebuilt and a new TC with the kit (didn't do the rebuild of the tranny myself, had "a guy" do it for me). I did the installation myself which is most likely where the issue lies. Wanted to drop the 392 in, but the block wasn't cast for the side motor mounts for my suspension so I had to go back with the 345. Since the bell housings were the same, I just assumed all was the same but we all know what assume means.

Installed the crankshaft hub then the flex plate, made sure the TC was engaged on the shaft and bolted it all up nicely after the 6th attempt with the tranny dipping forward and me catching the TC. The only thing I had aligned during this was where the roll pin was on the hub and flex plate. Given the conversion that was being made, had a new driveshaft made and had it balanced as well on an axel-line machine.

Vibration occurs around 2300rpms in park or neutral and at highway speeds around 50 and 65. Can definitely tell its a "spinning" vibration and it feels like its right beside you in the cab.

My big questions are this. Is the flex plate for the 392 balanced differently than that of the 345, like is it balanced to counter the engine weight or is it just balanced to itself? Also, the TC came with the kit so is there a difference in the 727 IH build and I have the wrong TC (direction on the right one needed)? Given the vibration we are most likely going to just replace the TC either way to avoid damage.

Thanks in advance!


IH engines are externally balanced, so the ring gear is part of that balance equation. You could have the flex plate neutral balanced at a machine shop. When you're driving, have you tried shifting the trans neutral to let the engine rpms drop to see if that has any effect on the vibration at road speed?


New member
Thanks Scoutboy I forgot about that, I have shifted into neutral and the vibration goes away. So its definitely tied to the engine rpms. When I let off the gas in gear at highway speeds the vibration does get worse as it pitches forward before decelerating.

I'm going to slide the tranny back next week and get a look at it again using a lift this time. I have a feeling this is a simple problem that I'm overthinking, but I've been trying to isolate this for over a year now and most people in my area wont touch this thing because they know nothing about it.
Is the crank pulley/ dampener original? These are also externally balanced, cant remember if the pulley body is drilled for balance while attached to crank or not.


New member
The dampener is an original dampener but I cant say it's the original for this engine. I have 3 laying around and I remember one of the dampener separated from the pulley so I discarded it. Is there a difference between the 392 and 345 dampener or are they the same?


New member
Been doing some searching and reading and have found several mentions toward the TC for Chrysler's had a balancer installed to bring the engine assembly into balance. At this point I'm not sure which TC I have but when we get it off I will identify it, but can anybody point me towards the correct TC for this trans?


R17, CR51, and 746 (no letters) are some numbers that will get you headed in the right direction. Searching parts websites using your vehicle data for this torque converter will be nearly fruitless. What you're looking for is a non-lock up converter for a Torqueflite A727 (TF8) with low stall in the '72-'75 model year range having a 12" diameter and 24 input splines. The flexplate bolt pattern is also a determining factor. AMC vehicles of similar vintage with V8 engine and A727 trans used exactly the same converter as IH, so that's another useful hint. Installing a re-man converter is generally considered part and parcel of any thorough auto trans overhaul. Not doing so is a sketchy practice. The one you have is likely correct for the application, but could probably stand to be refurbished or replaced. Taking it to a reputable auto trans shop would likely verify if it is the correct one or not and might open avenues for proper replacement.

Robert Kenney

Super Moderator
Just some of my insight on external balancing and the converter. I don't think you would never use the TC to balance an externally balanced engine. The balancer would simply wobble around as it spun on the flex plate.

In order to see if the 392 and other SV v8's used the same weighting on the front and rear crank appendages, you would need to look up part numbers across the 4 displacements.


New member
Alright folks, been a long road and I still don't have any answers on my vibration. I believe I have ruled out as much as possible now, so here is what I have done.

Put a new TC on her, no change in vibration.

Put on jack stands and ran it, vibration was there at same RPM range, 1800 to 2k. Drive shaft had no wobble. Pulled the axel shafts and diff cover, replaced axle shaft bearings and seals, pinion bearing and seals, serviced the carrier. Got some lash, but all in all still works good.

Pulled the drive shaft out and ran it, vibration still present at the same RPM ranges. Put on a new dampner (the newer design without the rubber isolater), vibration still there.

So, just pulled the tranny and confirmed the flex plate and hub were installed correctly with the roll pin, and yes they were. Ran the engine without TC and trans, vibration is gone. Did note there is only one way the TC bolts up due to the bolt pattern.

So now I'm left to the trans causing the vibration, but I'm as dumb as they come to transmissions so is this even an possibility? Once again, any advice here is welcome. Thanks!


How about posting photos of the parts you are using to attach the TC and the flex plate???

There is a spacer on the front side of the flex plate....AND there is a Reinforcement Ring on the aft side of the flex plate, installed prior to installing the TC.

Do you have BOTH installed?


New member
I'll take some pics and post, but yes I have both the hub and reinforcement ring installed.

I buried it in the last post, but with the TC amd trans out there is no vibration, all gone.

So I'm wondering (don't really trust the work the trans guy did for other reasons) could it be something on the input shaft of the trans causing this since the vibration is present even in park or gear. Or would it be more likely bad luck with TC number 2?
Do you have the alignment hollow dowels installed on the engine? There are supposed to be 2 alignment hollow dowels that fit in the engine, they align the bellhousing. Same size pins that the heads use for alignment.
The flex plate needs to be clocked correctly on the crank flange. There is a roll pin that locates how the flywheel or flex plate indexes to the flange. Many times, someone taps that roll pin out and installs it in the wrong position. This is a particular problem after a flywheel has been resurfaced at the machine shop. I've seen it more than a couple times where they tap it back in the wrong hole.
You should see some scarring on the flexplate from the lock washers on all the holes but one. That hole never had a bolt. Just the alignment pin. If it has a bolt now, and your pin is in one of the scarred up positions, that's your problem. Fly wheels and flexplates carry balance weight like the balancer on the snout of the crank. Clock it wrong, and it'll feel like a paint shaker.


New member
Anyone know the relation to Flexplate weight to Harmonic Balancer on the 345 with 727 auto? i have read (dont know if its true) that Flexplate weight should align with Harmonic Balancer weight???
Anyone know the relation to Flexplate weight to Harmonic Balancer on the 345 with 727 auto? i have read (dont know if its true) that Flexplate weight should align with Harmonic Balancer weight???
There is supposed to be a pin in the flex plate or flywheel that aligns it.