high speed vibration - Team Camaro Tech
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post #1 of 33 (permalink) Old Mar 24th, 01, 06:16 AM Thread Starter
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69camaro w/3speed saginaw exhibits vibration at high speeds. the the vibration is so noticable that it seems to want to throw it out of third gear.(shifter knob really moving). The motor (rebuilt =20k miles)is very smooth (reving out of gear) Rear end guts replaced (3;55 posi). Uni joints on drive shaft also replaced = 10k miles ago. Car has vibrated since i've owned it = 3yrs. The only components not replaced are the tranny and drive shaft. Any sugestions or experience in this problem greatly appreciated.

THx JC
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post #2 of 33 (permalink) Old Mar 24th, 01, 07:06 AM
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Saginaws loose the front bearing alot. This sounds like what your problem is. Is this a different block bellhousing combination? the factory ones are usually pretty close but there is a possibality that they are not a match and the trans is out of alignment with the crankshaft.

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post #3 of 33 (permalink) Old Mar 24th, 01, 07:45 AM
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At high speeds the stock driveshaft will distort and cause a vibration like you are talking about. You may need to switch to a larger diameter or thicker wall driveshaft.

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post #4 of 33 (permalink) Old Mar 24th, 01, 08:58 AM Thread Starter
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yes, the original block, bell housing and tranny was used. the block was drilled to 125 over to accomidate std 350 pistons, and a 350 crank and harmonic balancer was installed approx 1.5yrs ago (was original 307) The car always had the problem, even w/ the 307 and 3:08 rear end, but is much more noticable w/ the 3:55 posi rear end.
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post #5 of 33 (permalink) Old Mar 24th, 01, 10:01 AM Thread Starter
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<BLOCKQUOTE>quote:</font><HR>Originally posted by joe clance:
the original block, bell housing and tranny was used. the block was drilled to .125" over to accomidate std 350 pistons, and a 350 crank and harmonic balancer was installed approx 1.5yrs ago (was original 307) The car always had the problem, even w/ the 307 and 3:08 rear end, but is much more noticable w/ the 3:55 posi rear end. <HR></BLOCKQUOTE>

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post #6 of 33 (permalink) Old Mar 24th, 01, 10:08 AM Thread Starter
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<BLOCKQUOTE>quote:</font><HR>Originally posted by big gear head:
At high speeds the stock driveshaft will distort and cause a vibration like you are talking about. You may need to switch to a larger diameter or thicker wall driveshaft.

<HR></BLOCKQUOTE>

Can it also be a balance issue w/ the drive shaft? how can diagnosis be made for bending or balance problem, or does it matter if it is the shaft itself (rebalance / replace). Is there a good drive shaft that won't GM the way to go.

again, thx for your reply
joe.c
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post #7 of 33 (permalink) Old Mar 24th, 01, 10:23 AM Thread Starter
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<BLOCKQUOTE>quote:</font><HR>Originally posted by oger:
Saginaws loose the front bearing alot. This sounds like what your problem is
<HR></BLOCKQUOTE>

would this not be notiable at low rpms? how about under a high load at low rpms? I'm compelled to believe it is either the tranny or drive shaft, however, a dianosis to eliminate one of them would be really cool. the car has done this since i've owned it, but after th rear end overhaul and 3:55 gear, it is very noticable (due to higher RPM's at tranny/driveshaft speed). Any suggeations appreciated.

thx
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post #8 of 33 (permalink) Old Mar 24th, 01, 01:50 PM
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What kind of speed? It is possible the factory balance weights have come off the drive shaft or it is a little bent. How is the trans rear bushing?

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post #9 of 33 (permalink) Old Mar 24th, 01, 06:15 PM
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When I was assymbling transmissions for Brewco Motorsports they ran a Jerrico with 3rd gear converted to overdrive at the road courses. The increased driveshaft speed caused a bad vibration that they could not find. After talking to some other teams someone asked them what diameter driveshaft they were using. Turns out they were still using the driveshaft for the non-overdrive trans and the increased driveshaft speed caused the shaft to flex which caused a bad vibration. Switching to a shaft 1/2" larger cured the problem. The stock driveshaft in your Camaro was not designed for high speeds.

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post #10 of 33 (permalink) Old Mar 25th, 01, 09:39 AM
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Have you checked the trans mount? Your symptoms are classic for either an out-of-round or out-of-balance prop shaft, or an internally-separated trans mount (which you can't see on the car); they're only about $8.00, and a failed one will amplify an out-of-balance prop shaft vibration. I'd also suspect you're getting some harmonics from the new crank and pistons if the entire rotating assembly wasn't re-balanced as a unit when it was rebuilt.

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post #11 of 33 (permalink) Old Mar 25th, 01, 12:28 PM Thread Starter
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<BLOCKQUOTE>quote:</font><HR>Originally posted by JohnZ:
Have you checked the trans mount? Your symptoms are classic for either an out-of-round or out-of-balance prop shaft, or an internally-separated trans mount I'd also suspect you're getting some harmonics from the new crank and pistons if the entire rotating assembly wasn't re-balanced as a unit when it was rebuilt.

<HR></BLOCKQUOTE>

What is a prop shaft? is the internal trans mount external to the trans,(replacable w/o tranny removal) the original 307 did the same thing.
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post #12 of 33 (permalink) Old Mar 27th, 01, 08:04 AM
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I had the same issue with my car. The motor was smooth and I have a new rear end/u-joints. I just replaced my tranny and now the vibration is gone. With the new tranny I had to get a new drive shaft. The old trans seemed fine (M21) I do not think it was the transmission. My bet is that the drive shaft was the problem. I got a drive shaft from Brookline Machine in Boston Ma for $150.00. This is all they do (Make Drive Shafts) if you need a place to get one. They ship.

My old shaft was rusted - I think now that this may thow it out of balance as it aged..

Jeff

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post #13 of 33 (permalink) Old Mar 27th, 01, 08:18 AM
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As previously suggested I would also check your transmission mount. Mine was bad. If all else fails get it up to 70MPH and shut the engine off with the car in neutral. This will eliminate some moving parts...
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post #14 of 33 (permalink) Old Mar 27th, 01, 09:21 AM
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Joe

Sounds like the driveshaft needs to be straightened and balanced. If the slip yoke was put back on 180 deg. off from it's original position when the u-joints were replaced, it will be out of balance. If the shaft is dented, or has been banged hard in any way... it's out of balance.

Typically, if the shaft is out of balance it will start to vibrate (and make a droning sound) somewhere around 50-60 mph and then get worse as speed increases to a point, and then get somewhat better at even higher speed.

A shop that does front-end and suspension work on large trucks usually also does driveshaft work. Some machine shops can also do the work. Good luck.

Mark
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post #15 of 33 (permalink) Old Mar 27th, 01, 09:26 AM
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Another good place for driveshaft work is a 4X4 offroad truck place. Since they work on raising the pickem'up trucks all the time they have to work on the shafts too! Kevin

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