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Discussion Starter #1
Took the camaro for a test drive yesterday for first time. Rebuilt 406, m20, new 12 bolt 373. first second and third had very bad vibration, 4th was better but still had shake. felt like it was directly under the tunnel. the motor idles very smooth and has no vibration at higher rpms. I used the 350 flywheel 11inch, and the 400 counter weight plate,. I think its in the trans, the input shaft did have some wear on it, just thought id take a chance on it. My question is, i have a m21 to try in it, should in be concerned about the vibration coming from the flywheel clutch area? i did have the flywheel resurfaced would that caused the shake, also my clutch dosnt engage till the very top of the pedal, i need to back it off some, but could that do it, after engagement? Any input would be appreciated. thanks
 

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He used a 400 balance weight,which allows you to use a 350 flywheel.He has a stick,and 400 flywheels arent that common.BTW,400's and 350{2 piece rear seal} use the same tooth count and starter.Since you claim the vibration is related to engine speed and not vehicle speed,I am thinking that it is still in the clutch or engine.The 400 weight you have isnt always the way to go,you might have wanted to have the crank balanced with that weight.I am thinking maybe the pilot bushing is missing or incorrect and the imput shaft of the trans is wobbling and bringing the clutch disc with it.Good luck.
 

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the motor idles very smooth and has no vibration at higher rpms.
If you have no vibration reving the engine with the car sitting still and the clutch pushed in and the trans. in gear the engine and flywheel are not the problem.Then try it with the clutch released and the trans. in neutral if it vibrates then it's the clutch or trans.If it only does it when driving it could be trans. or driveshaft.
 

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Isolate it as much as possible by trying to duplicate it sitting, moving, no driveline, etc. It could be several things.
Does it vibrate while sitting? If it's only while driving it could be a simple as pinion angle causing driveline vibration.
 

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Discussion Starter #8
installed new pilot bushing with trans. there is no vibration with the car in idle with the clutch in, or in neutral. when i start to engage the clutch the vibration starts. Bought the engine from a friend so it was complete didnt have a chance. the input shaft looks to have excessive play in it, installed the other one tonight, test drive tommorrow if weather allows.
 

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when i start to engage the clutch the vibration starts.
Chris,

I think maybe you are describing the problem wrong. It sounds to me like you have clutch "chatter" which is more like a "shake" than a vibration, which is usually rpm related.

Once the clutch is totally engaged is the shake still there ? I guess it could be the trans but you might also want to look at motor mounts and trans mount. If they are worn out they can let a lot of vibration come through to the body.

Also, the 400 "balance plates" are not always perfect. The ones I have seen stated that they were to be used to get the balance close and the crankshaft still needed to be finish balanced.

Persoanlly, I dont like the idea of a plate bolted between the flywheel and the back of the crankshaft. I would get the correct 400 flywheel or find a good machine shop that does balancing and have them "unbalance" your 350 flywheel to work with the 400. Its a simple job if you have any kind of modern balancing equipment.
 

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Discussion Starter #10
Bill, i guess it is more like a shake, ordered a 400 flywheel today, when i drove it today a large amount of it was gone, but its still there. also on an unrelated matter, when i accelerate near shift point, it has a popping sound, nothing ive heard before, dosnt it in each gear. Is it lack of fuel? im running a 600 holley, could it be denonation? thanks
 

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My 406 is internally balanced, and I had my flywheel balanced along with my pressure plate. When I had the flywheel and pressure plate on my 350, I had some vibration come through the shifter and it got progressively worse as the rpms increased. After I had it balanced and put on the 406, the problem completely disappeared. Since you have an externally balanced engine, I wonder if the same process can be applied to fix the problem.

BillK mentioned something about unbalancing the flywheel. I assume this means removing a certain about of material from it by drilling holes in the flywheel were the clutch disc does not go?

When does it pop? On the 1-2 shift? The float level in the carb might not be high enough. It is also possible that your running out of fuel on the fuel pump side. What size fuel line do you have from the tank to the pump, and from the pump to the carb?
 

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Discussion Starter #12
3/8 line, it does feel like im running out of fuel. i was worried about the 600 being too small. as far as the flywheel. the 400 new is 140.00, i have a friend that has one that has been drillled. probably go with new one, third times the charm pulling that trans.
 

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3/8 line, it does feel like im running out of fuel. i was worried about the 600 being too small. as far as the flywheel. the 400 new is 140.00, i have a friend that has one that has been drillled. probably go with new one, third times the charm pulling that trans.
what kind of fuel pump do you have? I have a 110 gph holley pump on my motor, and it gets plenty of fuel. :D

It gets old pulling the trans in and out. I know all about that. Another thing, have you checked bellhousing alignment? If it is off it can also cause the vibration. This can be checked with a dial indicator or an alignment tool that browell bellhousing makes.
 

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Someone mention when you have the trans out of the car have you started the engine to see if there is any vibration? If so, could be the wrong harmonic dampener. If that was changed during the rebuild could cause a good shake.

Does it vibrate when you coast in gear at higher speeds or only in gear running down the road? Could be Pinon like other said or trans mount coming apart?

Did you check the condition of the u-joints?

Just thoughts. Good luck with it.
 

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Did you use a 350 or 400 Harmonic Balance wheel? They are different too for internally or externally ballanced. For my 400 internally balanced Scat crank assembly I had to replace both HBW and flex plate with new ones for a 350 - per the machine shop that balanced the motor.
 

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BillK mentioned something about unbalancing the flywheel. I assume this means removing a certain about of material from it by drilling holes in the flywheel were the clutch disc does not go?

?
Andy,
You can drill it enough on the back side (engine side) around the edge to make it match the factory 400 unbalance.
 

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Andy,
You can drill it enough on the back side (engine side) around the edge to make it match the factory 400 unbalance.
Thanks for the clarification.:thumbsup: I learn something new everyday. Mine was drilled to remove material as well, but I didn't know if the process was the same or not for the 400 flywheel. Now I know. :yes:
 

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Discussion Starter #18
bought a new flywheel today for it, it is a factory 400, it has been drilled, and has the weight bar in it. trans mount is new, when i pulled in the driveway yesterday i coasted and it still vibrated. i really think its the flywheel, if its not ill move on to the driveshaft and rear. i wasnt comfortable with the flywheel weight anyway, and since im heavy a muncie ill use the other flywheel and convert the other 69. my fuel pump is stock, swapped it out with a 700 cfm, should clear things up. also my harmonic balancer is the original stock. thanks for all the input guys. if anyone needs a muncie install let me know, i can do with my eyes closed at this point. thanks
 

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Discussion Starter #19
swapped the flywheel, solved the issue, smoothed completely out. still have the popping but thinks thats timing, could it be valve lash?
 

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Id recommened any new 400/406 build to be internally balanced.
I built my 406 and spent the extra cheddar on internally balancing the crank so i could use the lighter weight dampner and tci flywheel,
plus helps th elife of these engines ecs. with some longer rods like these 6" rods they'll run real good.
 
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