Hey everyone it's been awhile, I have a 67 Camaro 350ci 400TH 3:55 possi the issue is a harmonic vibration. Everything I've read that are potentail causes of my issue have been done some even done twice. Here is what I have under load the vibration resinates from the front to the rear and back again on revolutions. I had the rear rebuilt twice checked out fine, The tranny twice checked out fine, new drive shaft, new flywheel, new torque converter B&M 2000 stall, front end completely rebuilt, Checked phasing 88 degress on tranny tailshft and 88 degrees on pinion, new wheels and tires balance out perfect, alignment straight as an arrow. Idle is at times tough to get right the motor is basically stock 300hp no lobby cam. I have not replaced the harmonic balancer yet or the motor mounts. The vibration is at all speeds but not noticable at a stop indle. I have also noticed it doesn't show up until the car is up to temp 185 degrees. 103 mph down the highway did not notice the vibration car was smooth. I'm about to go insane if I do not find this issue, please someone help me with this thing.

Thank you

Does it still do it at highway speeds if you kick it into neutral?

No I did that has well if I travel down the highway at speed and throw it in Nuetral it will go away when I bring the RPMs up it will return which should indicate a driveline issue I would think. The same with it in my driveway if I bring up the RPMs in my driveway I get the same harmonic vibration. I did go to my local machine shop and they suggested that an after market crank may have been placed in the car but not balanced. I appreciate any help with this I'm at a lose with a bunch of money spent and still have this issue. I am willing to either purchase a crate motor but then again me not being certain I must hesitate before I spend the money on this new motor. The tranny and the rear housing are dead on even to the ground at 88 degrees each the driveshaft has not been balance but I had it built from a race shop that does a ton of driveshafts a day and it is true with a dial indicator. This simply has me at a lose and again I appreciate any ounce of help in resolving this again thank you

Sounds like you have eliminated everything except the engine. If it does it in your driveway in neutral then you have an engine balance problem. Before tearing the engine down and having it balanced install a new quality damper. If yours is old chances are that could be the cause. Also if the flex plate was replaced it may need balancing. I would replace the damper first and if that doesn't solve the problem then have the flex plate checked. Worst case you may have to disassemble the block and have the rotating assembly re-balanced.

Good luck.

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If you can get it to do it in your driveway, more likely it's an engine rpm vibration, not a driveline vibration , your talking sitting still with the wheels on the ground right?
Is the exhaust grounding out against the frame anywhere?

How about trying a "fluiddampner"? Never used one but it might help take up any off balance on the front of the crank.

Have you tried pulling all the belts and then spinning it up quickly? (don't let it get hot!)

I agree, if it does it in park on spinning it up on the freeway, it's got to be engine.


Mark

I hate to admit it but I'm almost convinced it is the motor. The motor only has about 3000 miles on it and was in the camaro when I purchased it and because the guy I got it from swore it wasnt the motor, I know I'm stupid I went and delt with everything else. But you guys I think you are correct the machine shop I deal with said the same thing balance internally caused by an after market crank that was put in the motor and possibly not balanced. So I want to thank you guys for all the in put on this I thought that I might have missed something or something was over looked you know how it is when you continue to look for these things you find your self so frustrated it blinds you to my current position insanity. So any suggestions on crate motors I'm thinking 350ci 425hp actually I just need the long block I can use all my bolt on gear it's new haha, Thank you guys for all the help on this on I truely appreciate it. The only thing is all the paint and body is new and during disassembly never pulled the motor "because its new" this swap should be fun. I better call my body shop in the event a touchup is needed. thank you all once again and I will let you know how it turns out.

You could always try it with belts off for a few seconds and see if it does it then as well....in case the fan or other accessory could be the culprit...Or even remove the bolts for the torque converter to be sure there as well.

I agree. It would be a shame to change the engine to find the same vibration with all the same accessories hooked up.
I lost a fan blade before and you wouldn't believe how the whole truck shook.

Great suggestions and something I didn't even concider. I will run the car up to temps because that is when it is most prevelent and then pull the belts to see if the vibration is there. I appreciate the suggestion and will do this in the morning today I have to go out of town I will let you know what I find again thank you for the input.

Yes the wheels are on the ground and I did check the exhaust and its not touching the frame or floor boards. Intresting you mention this though because my E-brake cable does lay accross the exhaust, hmmmmm do you think, maybe how would that cause a harmonic vibration though. Anyway thank you for the advise appreciate it very much.

If your fan is not a clutch fan then your vibration should still be there if your engine is hot or cold. Some SBC are internally balanced and some are externally balanced. The flex plates are different for these engines. Before I started just replacing parts and spending a ton of money, I would use a process of elimination. Since you have already eliminated the drive train. Your problem has to be from the torque converter forward. Start with the easy stuff already suggested at the front of the engine. If that doesn't work, drop your flywheel dust cover and shift the torque converter on the flex plate to the next bolt hole. If there's still no change, then drop the tranny, remove the torque converter, support the rear of the engine with a floor jack and run the engine. If the problem is still there then you will have eliminated all but the basic engine. Time for a balance at that point.

There is no need to remove trans....... Simply remove the dust cover and then the 3 torque converter/flexplate bolts and slide torque converter back then run engine.

I'd do a cylinder balance test. If it gets worse when it's hot there may be an ignition or valve train issue.
Balance doesn't change because of engine temp, except with a clutch fan. ( as previously stated by Ford SR.)

Later, mikey

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