Vibration - repost - Team Camaro Tech
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post #1 of 30 (permalink) Old Jan 21st, 01, 01:03 PM Thread Starter
Al
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Al McKenzie
 
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The file for this topic got messed up and I'm reposting what is available from a backup.
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Topic: Vibration
Joe G

Posts: 11
From: Benicia CA
Registered: Jan 2001
posted 01-21-2001 01:30 AM
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I have a 69 with a 396/TH400-355 posi installed. I don't have any info on the engine modifications, but it has headers, holley 750 doublepumper and from it's idle and throttle response seems to have a fairly agressive cam. The problem is a vibration that is RPM related. There is a heavy resonant vibration, at about 2500-3000 RPM. I had a new driveshaft built, but that was not the issue. It has 3" series 40 Flowmasters to which I have added a crossover pipe and have extended the exhaust over the axle to exit properly at the rear. I did this to quiet it down. The vibration does not appear to be exhaust related. I have read in magazines that vibrations can be caused by having the wrong harmonic balancer. How would one tell if the balancer is right or wrong? Could the torque converter or flex plate cause this? The engine and transmission run very well. I do not know if the engine was balanced when built; it was set up for drag racing.

oneforu

Posts: 16
From: petal,ms usa
Registered: Jan 2001
posted 01-21-2001 07:27 AM
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is noise coming from front or back? does it sound like maybe a mount or bearing loose.
you may want to check the flywheel (make sure bolts are tight) also check tourque converter bolts for tightness
[This message has been edited by oneforu (edited 01-21-2001).]

[This message has been edited by oneforu (edited 01-21-2001).]


William
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Registered: May 2000
posted 01-21-2001 10:26 AM
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One common bb mod is to change to 7/16" rod bolts. They are obviously heavier and require engine re-balancing. This is why there are 2 steel 427 cranks; one for 3/8", one for 7/16". The factory never used 7/16" bolts in a 396.
Check out the easy stuff first; wrong/broken motor mount, loose bolts, etc. If the motor has the big bolts look for signs the crank had metal added.


Joe G

Posts: 11
From: Benicia CA
Registered: Jan 2001
posted 01-21-2001 11:09 AM
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Thanks for the tips. The vibration seems to be coming from the front, although it's hard to tell. I feel it more than hear it.
The motor mounts are tight. I'll check the flywheel bolts out.
Thanks. It's been a while (20+ yrs) since I was into hotrods!

orangeone

Posts: 8
From: Des moines IA USA
Registered: Jan 2001
posted 01-21-2001 11:46 AM
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I had a vibration with a small block/auto trans car.
My engine was balanced and very fresh so I ruled that out, then I had my drive shaft balanced but made no difference. I even changed rear ends. My car still felt like there was a giant bull frog under the car somewhere.
It turns out that the fly wheel was bent.
when I unhooked the fly wheel from the torque convertor you could see it wobble back and forth a quarter inch.
changed the fly wheel and the vibration was gone. hope this helps.

orangeone

Posts: 8
From: Des moines IA USA
Registered: Jan 2001
posted 01-21-2001 11:47 AM
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I had a vibration with a small block/auto trans car.
My engine was balanced and very fresh so I ruled that out, then I had my drive shaft balanced but made no difference. I even changed rear ends. My car still felt like there was a giant bull frog under the car somewhere.
It turns out that the fly wheel was bent.
when I unhooked the fly wheel from the torque convertor you could see it wobble back and forth a quarter inch.
changed the fly wheel and the vibration was gone. hope this helps.

Joe G

Posts: 11
From: Benicia CA
Registered: Jan 2001
posted 01-21-2001 12:22 PM
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Thanks. I'll try unbolting the torque converter. Can I just slide it back without removing the transmission? It looks like I can but don't want to break anything while experimenting. Can I run the engine with it slid back to check runout/vibration levels?

orangeone

Posts: 8
From: Des moines IA USA
Registered: Jan 2001
posted 01-21-2001 01:12 PM
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You should have plenty of clearance with the torque converter pushed back.
With the engine running you will be able to
tell if the vibration is driveline or engine by having the two separated.
It taught me a lesson, dont change u-joints or balance your driveshaft before trying this first!
with only three bolts on the torque convertor it is quick and easy.
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post #2 of 30 (permalink) Old Jan 21st, 01, 06:49 PM
 
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I had a similar vibration in my 79 and I did the U-joints, still there then decided to put a new cam in and when I saw 1" + slack in the timing chain I about [email protected]#t. Well that got rid of 80% of the vibration and then I replaced the output shaft bushing in the nose cone of the TH350 and wella no more Vibration! . Crab the driveline yoke at the trans and move it, if you feel more than .008 of play then its time for a new bushing. The bushing and seal come in a kit for $8.00 and it took me an hour to remove and replace everything, easy fix, hope this helps.

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post #3 of 30 (permalink) Old Jan 21st, 01, 06:59 PM
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I checked the output shaft for play when I had the driveshaft out. It was tight.
Thanks
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post #4 of 30 (permalink) Old Jan 21st, 01, 07:48 PM
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If you are looking at the flywheel, make sure you have the right one. The 396 and 427 were internally ballanced, while the 454 and 502 are externally ballanced. If you have a 396, there should be no large weights on the flywheel. I have heard of people adding heavy metal to a 454 crank and making it an internally ballanced engine, but never the other way around.

In contrast, if a 454 lost the weight (they are only tacked on) off it's flywheel, it might cause a vibration too.

Keith
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post #5 of 30 (permalink) Old Jan 22nd, 01, 05:30 PM
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Should there be weights on the flexplate? I'm not sure how one tells if it is the correct flexplate.
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post #6 of 30 (permalink) Old Jan 22nd, 01, 07:16 PM
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yes on a 454/502 there are. a nice piece on metal welded on to it.
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post #7 of 30 (permalink) Old Feb 13th, 01, 12:13 AM
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More info on the vibration.
The engine itself is smooth. I hold my hand on it at 2800-3200 rpm and can't feel anything abnormal. (Car on stands, running engine in gear) But I can feel it in the body a bit. It is inside where I can feel it the most. In the wheel, in the seat, etc. But I can put my hand on the driveshaft tunnel and not feel anything!? Can't feel it on the console either.
It is a dull reverberation/resonant vibration. Almost like a flat-spotted wheel bearing feels. But it feels the same whether in gear or in neutral so it's not the drive train/axle.
Wonder if the body/frame are amplifying vibration from the engine that I can't detect by feel?
Strange. Any advice is welcome.
Thanks, Joe

------------------
69 SS396 Clone, B&M TH400, 3.55 12 Bolt Posi, Blue w/White Z28 Stripes, Chrome Rally Wheels
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[This message has been edited by Joe G (edited 02-13-2001).]

[This message has been edited by Joe G (edited 02-14-2001).]
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post #8 of 30 (permalink) Old Feb 13th, 01, 11:56 PM
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I unbolted the torque converter today and ran it (on stands) to see if anything changed in the vibration. It didn't. At least it's only the engine!
I then compared it to my 454 truck engine vibration (in nuetral at 3000 rpm). I felt the truck engine valve cover. It runs a tad smoother than the Camaro, but not much. Maybe the 396 is just a little out of balance with the cam and the body is amplifying it (a lot)?
Still pretty strange and disconcerting at 65 mph.
Suggestions on what to check next?
Thanks
Joe

------------------
69 SS396 Clone, B&M TH400, 3.55 12 Bolt Posi, Blue w/White Z28 Stripes, Chrome Rally Wheels
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post #9 of 30 (permalink) Old Feb 14th, 01, 03:26 AM
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You don't have solid motor amd subframe mounts do you? You will get some vibration with these.

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69 rallye green X77 Z/28,1967 SS 396 Conv. 1974 c-10 454 swb
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post #10 of 30 (permalink) Old Feb 14th, 01, 07:06 AM
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The motor mounts look new and are the rubber is very hard, but they are still rubber. The body bushings are also new looking and very hard; polybushings, maybe? They feel more plastic than rubber.
I am thinking of putting ploy bushings in the front end; if these are poly bushings and aggravate vibration, I'm not sure that's the way I want to go.
Thanks for the advice.
I sure am learning a lot here!
Joe

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69 SS396 Clone, B&M TH400, 3.55 12 Bolt Posi, Blue w/White Z28 Stripes, Chrome Rally Wheels
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[This message has been edited by Joe G (edited 02-14-2001).]
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post #11 of 30 (permalink) Old Feb 14th, 01, 07:28 AM
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It is easy to check the dampner if it is smooth on the inside {engine side} it is correct if there is a 1/2in raised area about 1/4 of the way around it is for a 454 or 502 and it will definately cause a vibration.

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post #12 of 30 (permalink) Old Feb 14th, 01, 01:17 PM
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Joe,
i had a problem very simular to what your describing... turned out to be a broken valve spring... was only slightly working do to the damper spring, boy was i lucky it didn't drop.


worth a shot to check it out.

------------------
My '68 Camaro
Doug G.
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post #13 of 30 (permalink) Old Feb 14th, 01, 11:46 PM
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Doug, how did you find the spring? Was it obvious when you pulled the valve covers? I've had mine off trying to determine valve lift with a dial indicator (didn't work) and kinda felt around the rocker arms. I did not see anything obvious. When I cranked the engine over, all the lifters seems to move equally.
I'll check again if I know what to look for.

I also felt around the inside of the harmonic balancer; it feels smooth. No grooves or raised areas. I guess it's OK??

Thanks for all the advice here!
Joe


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post #14 of 30 (permalink) Old Feb 15th, 01, 03:11 AM
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When you drive at the rpm range where the vibration happens , do you feel it in the seat or steering wheel? If you put the car in neutral, does it do away. Checking on jack stands isn't always the same as real conditions. If you feel vibration in the seat, it's probably from the back of the car, etc.
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post #15 of 30 (permalink) Old Feb 15th, 01, 03:00 PM
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this won't work due to your cross over tube... but when i started the car up i noticed a sucking sound from the tail pipe... i held my hand over the left , then right pipes and felt it suck back . i pulled all the rockers and could see it plain as day... coils looked "stacked" at full close on the valve.

good luck.

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