Correct vibration damper for 71 base 350
Thread Starter
Le Mans Master
Joined: Mar 2001
Posts: 6,640
Likes: 287
From: Ann Arbor Michigan
Correct vibration damper for 71 base 350
Unfortunatly I purched the wrong vibration damper for my base 71' 350. The one I bought and installed was for all 72-82 350's. The one I needed fits only 68-71 base 350's. What's the difference in the 2? When I compare the old one I took off to the new (incorrect) one, they look identical. The reason I'm asking is that I have an engine vibration at any RPM over 2500. Note that it vibrates standing still so it's not in the drive line. Can the damper cause this?
Thread Starter
Le Mans Master
Joined: Mar 2001
Posts: 6,640
Likes: 287
From: Ann Arbor Michigan
Re: Correct vibration damper for 71 base 350 (73Ken73)
I was afraid you were going to say that. I changed the cam as well, but just with a mild Edlbrock job that they reccomended. Can the cam cause the vibration? The engine idles well and has plenty of poop. Now I'm confused.
Melting Slicks
Joined: Oct 2001
Posts: 2,065
Likes: 1,395
From: Halifax, Nova Scotia, Canada
Re: Correct vibration damper for 71 base 350 (Duke94)
I don't know much about a small block 400. I know it's externally balanced.
Is it achieved by the flywheel and the balancer ??? I don't know.
If the balancer is part of the crank balance on a 400, Any chance you got a 400 balancer installed ?
Is it achieved by the flywheel and the balancer ??? I don't know.
If the balancer is part of the crank balance on a 400, Any chance you got a 400 balancer installed ?
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
Re: Correct vibration damper for 71 base 350 (Duke94)
Base 71 350 used a balancer with od approx 6 3/4". 400 balancer is 8" od and the outer ring has "a chunk missing out of it" so it is clearly counterweighted for external balance 400. I agree, if they look the same & the timing mark is in proper spot then they should be the same. Other 350's used a 8" balancer but it doesn't have "a chunk missing out of it" at outer ring.
Where'd you get balancer ... manufacturer ... p/n? I have some x-ref books ... maybe I can look up your p/n.
Yes the balancer can be source of vibration. Also, if you have a manual trans, there could be loose flywheel/pressure plate bolts ... or possibly a spring or other small part ma've been thrown out of assembly ... causing imbalance. If you have auto trans, there could be loose flexplate/convertor bolts ... or possibly a crack in the flexplate.
The following is little more than a guess ... maybe the length (not diam) is slightly different (maybe 1/4") as I think about 70-71-72 there may've been some changes in pulley spacings. Also, I think about 68 there was a change in timing mark(tdc)-to-crank key index.
Where'd you get balancer ... manufacturer ... p/n? I have some x-ref books ... maybe I can look up your p/n.
Yes the balancer can be source of vibration. Also, if you have a manual trans, there could be loose flywheel/pressure plate bolts ... or possibly a spring or other small part ma've been thrown out of assembly ... causing imbalance. If you have auto trans, there could be loose flexplate/convertor bolts ... or possibly a crack in the flexplate.
The following is little more than a guess ... maybe the length (not diam) is slightly different (maybe 1/4") as I think about 70-71-72 there may've been some changes in pulley spacings. Also, I think about 68 there was a change in timing mark(tdc)-to-crank key index.
Thread Starter
Le Mans Master
Joined: Mar 2001
Posts: 6,640
Likes: 287
From: Ann Arbor Michigan
Re: Update on Correct vibration damper for 71 base 350 (jackson)
Thanks for all the replys I have a 4 speed. I just installed the old vibration damper= no improvement. I have also disconnected PS pump, alternator and removed the fan and clutch likewise no help. Also checked all motor mounts and bolts=OK (and new). I'm beginning to think it's something in the clutch, but I didn't touch it during resto. It almost seems like initially it doesn't vibrate, then after accelerating to 3500 RPM and take foot off the gas it starts vibrating then continues until RPM is below 2000. I did replace all the clutch pedal anti rattle and return springs, which were missing when I got the car. I'm wondering if it is the throwout bearing. I don't know how many miles it has on it (car shows 22K, but it has WAY more than that). What do you think?
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
Re: Update on Correct vibration damper for 71 base 350 (Duke94)
Thanks for all the replys I have a 4 speed. I just installed the old vibration damper= no improvement. I have also disconnected PS pump, alternator and removed the fan and clutch likewise no help. Also checked all motor mounts and bolts=OK (and new). I'm beginning to think it's something in the clutch, but I didn't touch it during resto. It almost seems like initially it doesn't vibrate, then after accelerating to 3500 RPM and take foot off the gas it starts vibrating then continues until RPM is below 2000. I did replace all the clutch pedal anti rattle and return springs, which were missing when I got the car. I'm wondering if it is the throwout bearing. I don't know how many miles it has on it (car shows 22K, but it has WAY more than that). What do you think?
The clutch friction disk itself has springs in it... that is what I refer to as parts thrown from assembly. Here's a link to a recent failure like I suggest to investigate. http://forums.corvetteforum.com/zerothread?id=409540
If (that is IF) you pull the clutch pak ... don't skimp ... if it looks like it's old stuff ... and you're gonna keep car ... change it all (pilot bearing, throw out bearing , clutch disc, pressure plate) ... if there's any question if flywheel is bad, have an expert determine if flywheel also needs to be surface grinded (machined). Ya don't wanna do this job (clutch pak R&R) but once.
[Modified by jackson, 3:35 PM 10/13/2002]
Thread Starter
Le Mans Master
Joined: Mar 2001
Posts: 6,640
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From: Ann Arbor Michigan
Re: Update on Correct vibration damper for 71 base 350 (jackson)
jackson,
If I take the inspection cover off the front of the bell housing, will I see the broken springs (if there are any) or is the flywheel in the way?
If I take the inspection cover off the front of the bell housing, will I see the broken springs (if there are any) or is the flywheel in the way?
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Racer
Joined: Apr 2001
Posts: 395
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From: Shoreline WA
Re: Correct vibration damper for 71 base 350 (Duke94)
Around 70 Chevy made a change to the timing marks on the damper. If you use a newer damper with the older timing tab, your timing will be off. You may need to change your timing tab to a later one for correct timing.
This is noted in David Vizard's "How to rebuild your Small-Block CHEVY"
Mike
This is noted in David Vizard's "How to rebuild your Small-Block CHEVY"
Mike
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
Re: Update on Correct vibration damper for 71 base 350 (Duke94)
jackson,
If I take the inspection cover off the front of the bell housing, will I see the broken springs (if there are any) or is the flywheel in the way?
If I take the inspection cover off the front of the bell housing, will I see the broken springs (if there are any) or is the flywheel in the way?
Yes, maybe ... If pieces are small enough to have left the clutch pak ... but still too large to have found an exit from bellhousing (ie clutch fork hole). Note: springs etc may have broken up/ground up. Alas, you cannot see the spring portion of clutch friction disk without pulling the clutch pak apart. I know, news not so good. BTW, when/if those springs do come out ... the clutch usually becomes more "grabby" ... those springs serve as a kinda shock absorber/dampener.
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
Re: Correct vibration damper for 71 base 350 (SLine78)
Around 70 Chevy made a change to the timing marks on the damper. If you use a newer damper with the older timing tab, your timing will be off. You may need to change your timing tab to a later one for correct timing.
This is noted in David Vizard's "How to rebuild your Small-Block CHEVY"
Mike
This is noted in David Vizard's "How to rebuild your Small-Block CHEVY"
Mike
