67 RS Conv Vibration - Team Camaro Tech
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post #1 of 13 (permalink) Old Jan 20th, 00, 11:14 AM Thread Starter
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Guys, I have a shake in my car which occurs only at 65-70 mph. I have replaced every front end component except the idler arm (it was still good). I got rid of the drums and went to disks. I put in a new trans, I had the wheels ballanced on the car. I've had the wheels ballanced three different times at different places. I had the a-arms totally rebuilt, both top and bottom. As far as I can see there is nothing left and I still have the shake. Any ideas? I am wondering if this was a design flaw in the convertibles. Maybee it's the drive shaft but it seems to me if it was, it would shake all the time.
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post #2 of 13 (permalink) Old Jan 20th, 00, 11:43 AM
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Not real familiar with convertibles except that they are are supposed to have "cocktail shakers" in the corners to counteract torsional vibrations. What you have could very well be a driveshaft inbalance or the incorrect pinion angle. Did the car just start doing this or was it like this when you got it? I'd ck the rear trans mount and the u-joints first and look for any signs of missing driveshaft weights. Driveshaft balancing is fairly cheap if you need it done. I have had a bad experiance with aftermarket trans mounts that held the tailshaft up too high and caused this type of vibration. Sagging motor mounts could also cause this. Hope this helps-Dan in WV
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post #3 of 13 (permalink) Old Jan 20th, 00, 12:24 PM
 
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You didn`t mention alignment. Have you had it checked also?
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post #4 of 13 (permalink) Old Jan 20th, 00, 01:52 PM
 
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I had a similar issue with a truck. Turned out to be the rear outer wheel bearings giving side to side shimmy also about 60 to 70 mph.
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post #5 of 13 (permalink) Old Jan 21st, 00, 04:06 AM
 
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My $0.02
A bad u-joint will also cause vibrations at diffeerent speeds. A quick visual check can also verify that it is seated/installed properly.

------------------
67 Chevellle SS Conv
69 RS Camaro
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post #6 of 13 (permalink) Old Jan 21st, 00, 05:13 AM
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It sounds drive shaft related! Maybe give this a try to isolate the problem. Put the rear of the car up on jack stands (be safe!) engage the transmission and run the rpm up to where the vibration usually starts. If it doesn't vibrate, I would guess that the problem is in the suspension or body. Some part of the car that would only vibrate if the car was at speed. If it does vibrate, it is probably in the drive line as the body and suspension are at a standstill. Now, disconnect the driveshaft and run the rpm up. If no vibration, the problem is somewhere from the driveshaft to the back of the car(drive shaft balance, u-joints, rear end components,etc). If there is vibration, I would look from the tranny forward somewhere in the drivetrain (tranny mount, motor mount, bad harmonic balancer etc).
I had vibration once that was caused by the u-joints failing. The faster the car went, the worse the vibration got. Almost no vibration occured until over 40 miles an hour. I also gave myself the problem once by not getting the rear u-joint properly seated in the yoke! duh.
I hope this is helpful, as this will drive ya nuts!
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post #7 of 13 (permalink) Old Jan 21st, 00, 01:19 PM Thread Starter
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Everyone thanks you have given me some new ideas. I did forget to mention I had it alligned, bought new tires, and replaced all of the body and steering rubber with poly components, so I know it's not any of these. I haven't tried the drive shaft yet. I figured since the shake was only at 65 mph that it would not be related to the RPM since it doesn't shake at the same rpm at a lower mph. The rear wheel bearings sound like it might be a possibility. If I figure it out I'll post to help others.
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post #8 of 13 (permalink) Old Jan 22nd, 00, 04:21 PM Thread Starter
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Denver, I tried what you sugested, and no vibration while it was jacked up at any rpm. This leads me to believe it is in the suspension. I've had the front end totally rebuilt. Does antone have any experiences with this kind of a shake being caused from the rear suspension. I have already checked the rear wheel bearings and seem to be ok. Also the u-joints are ok. Can the rear spring set up cause something like this. Thanks again for any ideas.
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post #9 of 13 (permalink) Old Jan 22nd, 00, 05:37 PM
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Have you checked for runout on your rims? The tire can be perfectly dynamically balanced on a wheel balancing machine, but the relative wobble of the tread with respect to the vehicle (caused by a bent rim) may translate into vibration.

If you still have drums on the rear, you may want to balance them as well.

You could test the rim theory by swapping your wheels/tires temporarily with a friend's set and going for a test drive.

------------------
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LeMans Blue, formerly Grotto
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post #10 of 13 (permalink) Old Jan 23rd, 00, 11:18 AM
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When you had the rear of the car in the air, and ran it thru the gears to the speed it occurrs at, Did you have the car supported by the axle or the frame. If it was by the frame, your axle geometry would be different than it usually is on the ground. This could cause a pinion angle vibration to go away. Wheels and tires and brake drums are a possibility also. Good luck-Dan in WV
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post #11 of 13 (permalink) Old Jan 25th, 00, 05:35 PM
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Rick,

Check out: www.gsp9700.com

Go to "locate a gsp 9700" and plug in your zip code, and you will be able to find who has this machine in your area. This is a machine that will road test your wheel and tire assembly off of the vehicle to detect the amount of Road Force Variation in your assembly. Yes, the machine will also measure the runout of your rims radially and laterally. This is an awesome machine, and works wonders for those hidden vibration problems. Wheel balancing sometimes just isn't enough anymore.
If you have any specific questions, E-mail me at [email protected].

[This message has been edited by BelgianSS (edited 01-25-2000).]
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post #12 of 13 (permalink) Old Jan 26th, 00, 04:52 AM
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A vibration at that speed range sure sounds like a tire and/or wheel. Try to locate a spare set and swap them out. Worst case, find one (your spare?) and take turns swapping it and see if it makes a difference. On 2 occasions I have had new or fairly new tires that balanced well still shake. I spent a bunch of money changing other things before finally coming back to the tires. I switched mine with a friends and the shake disappeared. I ended up swapping out a new tire and never had another problem. This can be a particular problem with radials if a ply shifts or separates - although that doesn't happen much anymore.

------------------
Scott
'69 400SB, Richmond 5-speed
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post #13 of 13 (permalink) Old Jan 26th, 00, 06:11 AM Thread Starter
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Well everyone thanks for all the help. I tried the spare tire on all wheels and that wasn't it, but the good news is I did figure it out. I have air shocks due to the poor mono spring, when I let the air out of the shocks 50% of the vibration went away. So I forked over the money and installed 5 leaf springs with poly bushings and the problem went away. Never would have thought a weak spring could cause this but it did. The good side is, now that I have replaced the entire front end, installed disk brakes, new tires and new leaf springs the car rides really nice. Thanks again for all the advice.
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