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Another vibration question/chevy 350

4K views 7 replies 4 participants last post by  jipjip 
#1 ·
cj7
350 chevy/sm465/np205tc
3 inch lift
33's
All drive shafts and tires have been balanced I am running CV Joint.
new wheels

My problem is 60 to 70 mph. At this speed my rpms are about 2500. I did notice when I rev the engine to about 2500 rpms in neutral I feel a vibration coming from the engine. I thought maybe with the clutch engaged running 60 to 70 mph at this rpm the fly wheel could be out of balance making the vibration more evident at speed. Any suggetions. On the 350 is there any thing else that would cause the vibration? Can the fly wheel be removed without pulling the motor. Thanks for any suggestions.
 
#2 ·
Flywheel can't be removed without separating the engine from the tranny.. so one of them has to come out. I'd pull the tranny myself. I stick an engine hoist in from the door and drop a chain thru the tranny cover hole to raise/lower the tranny. I know that SM465 is pretty heavy. Since you can reproduce the vibration by just revving the motor up to 2500 RPM, I'd assume it's something in the engine balance. Maybe a flywheel for a 400 was used on the 350 by mistake? The 400s are externally balanced while the 350 is internally balanced. Likewise.. maybe the wrong harmonic balancer? Take a peek at the engine to bellhousing bolts too and make sure they're tight. Loose bellhousing bolts can cause an engine vibration. Just a check on the driveshaft situation to be safe.. the rear axle pinion is pointed at the transfer case output right? Since you're using a CV shaft it the pinion snout should be pointed at the rear yoke. If not, you'll get a vibration at speed (but that shouldn't affect revving the engine in neutral).. just some ideas..
 
#3 ·
When I bought the fly wheel I did not have it balanced. Should it already be balanced from when I bought it new? Dropping the tranny should be much easier than pulling the engine. That is a good Idea about the bellhousing bolts. I will check those for sure. Is there anything else that could be out of balance in the engine? I do have a good pinion angle. The angle is almost dead on to the tc.

when the clutch is engaged at speed would this make the vibration more prevelant?

thanks
 
#4 ·
Your flywheel should have been balanced. They are normally a bolt on and go type of a thing. Possibility exists that you got a defective one but like its been suggested, you should start with the balance of the motor.

On the issue of harmonic balancers, did you throw on an old one? It's usually an ok practice but I was just wondering. If it is a used on, I would check for any signs of seperation of the balancer. Also, The 400 chevy balancer is larger, if I remember correctly, than the 350. If a 400 balancer was used, I could see a vibration issue being possible.
 
#6 ·
Easy to do, pull the old one and press on the new one. They make a tool that screws into the crank snout and then cinches the balancer on. Don't try to run it down with the retaining bolt or it will strip the threads. Also, it's not recommended that you beat it on with a hammer... although that's usually how I get them on. Is this a newly rebuilt engine? Did it have vibes before? What's been changed recently?
 
#7 ·
This is my 2nd long block from Jasper. The first one thru a rod after about 2000 miles. Yes this is a used balancer that I pulled from a older 350. The engine prior did have a vibration but, it did not bother me. Now since I notice it at 65 mph I need to find and fix it. Everyone seems to think it is the tires. But I am going to change it and see what happens.

thanks
 
#8 ·
also a good place to look is your engine and trans mount. if these are worn in any way (or even polyurethane), they can transfer normal engine vibration frequencies into the frame of the truck causing it to vibrate at a set rpm.
do you have used mounts on anything, are the mounts stressed?.
i would start there. it doesnt cost anything to look ;)
 
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