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Got a 73 Fastback with C6 and 351 Cleveland few months ago. The engine has a severe vibration. The seller said it was the driveline. He had no other information. I bought it knowing I had a problem. The vibration is in the engine or transmission. The vibration is present when the transmission is in neutral and Starts to get real bad above 1000 RPM. The vibration is the same as if you put an external balanced flywheel on an internal balanced engine. After several months of research I started to work. I approached the problem like somebody had put the wrong crank in the engine. The engine has a twenty eight ounce imbalance harmonic balancer and a twenty eight ounce imbalance flex plate. I made a weight identical to the one on the flexplate and tacked it on the flex palte opposite the factory weight on the flex plate. Vibration was worse. Then I cut the weight in half and welded it on either side of the flexplate weight. Vibration was worse. I have a new harmonic balancer to put on. Now I am going to try and slide the torque convertor back and run the engine like that. Are there any precautions to take witht the torque convertor to keep it away from the flexplate? Any other ideas to try?
Vibrates in neutral and gets sever as RPMs are increased.
Vibrates worse with weight welded opposite stock weight.
Vibrates worse with extra weight welded on either side of stock weight.
Any help would be greatly appreciated. Dying to drive the car to a Saturday Night Rod gathering.
Thanks for reading and for any advice. BBFan
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Since it sounds like you have the trans out, see if you can push or pull the crank. If it moves, it's the thrust bearing. Had the same exact issue and I thought it was my fly wheel. I took the trans out and the went to take the fly wheel off. i notice that when I put some pressure on the fly wheel with the impact gun, the whole crank moved about a 1/4" . The I notice that I could push or pull the the whole crank in and out of the engine which = time for a new engine.
Have you tried to start the engine with the trans off and torque converter off? You'll need an old bell housing or use the one you have on your trans. That would help write off anything in the trans or torque converter.
ok i see you have a balancer you claim is 28ounces...how is the rubber ring sandwiched between the inner and outer layers? they are know to dry rot and then the outer ring slips and everything really gets out of balance..honestly id buy a new stock balancers and see if its fixes your problem...also take a pic of your current balancer and post i here
The new Balancer has the holes in the outer ring close to the timing marks. The balancer on the car has the holes much further away. Physically in other ways the balancers are very similar. The thickness of the outer ring is the same on both units. From what I can tell the 50 ounce imbalance has a different thickness outer ring. I am going to change the balancer tomorrow. Thanks
BTW the imblalance term and the imbalance weights have posed a question. What determines the position and size of the weights on the flywheel/flexplate? I always thought that each engine had to have the parts weighed.
Installed new 28 ounce imbalance harmonic balancer. No change in vibration. The engine is in the car with the transmission attached. I want to move torque convertor back and run the engine. I have found different ideas on being able to run the engine with the torque convertor slid back. Are there any special precautions to running the engine with the torque convertor disconnected from the flex plate and slid back?
you are not gonna be able to slide the converter back far enough to run the engine..the only way i see running the engine without a converter is if you have a C4 trans you could unbolt the bell housing and bolt it and the starter up..have you made sure the fly wheel you are running is 28 ounce?
Are you sure you have the right balancer? Was the engine rebuilt with a non stock balance factor? The crank, flex/fly and balancer all have to be the same "balance."
And FYI, the weight of the imbalance factor isn't the actual weight of the weights....it's the total force generated by the weights at a certain measurement factor. It's determined by the engineers, so for our purposes we just need to know that they all need it match.
Also, don't **** with balance stuff....it's vastly more complex than 99.9% of people realize, and balance failures causes crankshafts to explode; though typically only at higher rpm.
The weight on the flex plate on my flex plate has the same physical dimensions of the weight on a known 28 ounce imbalance flex plate. Additionally my flex plate does not have the slot cut into it opposite the imbalance weight. The 50 ounce plates I have looked up have that material cut out opposite the imbalance weight so the actual 50 ounce imbalance weight can be smaller by the amount of the cut out material.
Since rmodel65 says the toque converter cannot be unbolted and be slid back far enough to run the engine then the next step is to pull the engine. Then I can check the crank like stagnatic says. Plus have the torgue converter checked. The crank seems to be a candidate for causing the problem also. I have read that a 50 ounce crank is interchangeable with a 28 ounce crank and that may be the problem. Does anybody know how to tell the diffference between the 50 0unce and 28 ounce cranks ?
Just put the new 28 ounce balancer on last night. Flex plate and balancer are definitely 28 ounce units.
Do you know what is the position of the flexplate imbalance weight in relation to TDC. I know the flexplates and flywheels are made so they can be installed in only one position but this may have been altered. Thanks for your time and information.
Little Trivia info: I have two friends back in Ohio that bought two cars new in 1969. They still own the cars and don't drive them. One is a 1969 Mustang Fastback with 13,000 original miles original owner. This car had a mild front end collision in 69 and was parked and not moved since then. The other is a 69 Camaro with 45,000 original miles original owner. . It has been sitting in a barn for the last 35 years.
Have you checked the basics first, i.e. motor mounts? Loose or jacked up motor mounts/tranny mount will have similar vibration....
Would hate to see the OP tear everything apart only to find out it's a simple motormount. Remember, the seller said he thinks it's a driveline vibration...no other details provided.
Tried everything. Lifted motor with jack and tested mounts, same with transmission mounts. Vibration is definite and at raised RPMs. The weight on the flexplate is 180 degrees out of sync with the weight on the harmonic balancer. Is that the correct orientation. I have been searching and can't find a direct reference to where the weights are in relation to each other.
Are the weights on the balancer and flex plate in the same clocked index position ?
Starting to remove transmission. Unbolted torque converter and it easily rotated. For some reason the alignment dowels were removed. Rotated engine by hand more than one full revolution. No interference so I started the engine. Ran the engine up and down operating RPMs. No vibration. I suspect misalignment, probably damaged flex plate and damaged torque convertor, maybe damaged input shafts and bad bearings. Thanks for all the time, consideration and sharing of expertise. Thanks.
Have to put off removing the transmission until after Memorial Day. Any ideas why there are no pins to align the torque converter to the flex plate? Must have been some problem for them to do that. When I tried to move the troque converter away from the flex palte there was almost no preceivable movement back into the transmission. If there had been pins it would have been impossible to rotate the torque converter independent of the flex plate.
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