90 Engine vibration
Thread Starter
6th Gear
Joined: Jul 2013
Posts: 6
Likes: 0
From: Kelowna
90 Engine vibration
I have a 1990 L98 convertible with 84,000 mi that I have owned for 10 years.
Last year the car developed a vibration at about 3500RPM which rattled the reverse ring so bad I thought it was going to come off.
The clutch began to slip and the release bearing got noisy so I replaced clutch, pressure plate, release bearing, and pilot bearing. The dual mass flywheel was in good shape, smooth, no defects, so was buffed up and clutch replaced.
The vibration continues and seems to come from the engine.
The vibration occurs at 3500 rpm in any gear, out of gear , stopped, in neutral, clutch in or out.
Harmonic balancer? motor mount?
Any help would be greatly appreciated!
Last year the car developed a vibration at about 3500RPM which rattled the reverse ring so bad I thought it was going to come off.
The clutch began to slip and the release bearing got noisy so I replaced clutch, pressure plate, release bearing, and pilot bearing. The dual mass flywheel was in good shape, smooth, no defects, so was buffed up and clutch replaced.
The vibration continues and seems to come from the engine.
The vibration occurs at 3500 rpm in any gear, out of gear , stopped, in neutral, clutch in or out.
Harmonic balancer? motor mount?
Any help would be greatly appreciated!
Melting Slicks
Joined: Aug 1999
Posts: 2,240
Likes: 42
From: Baltimore, MD USA
If you manually operate the throttle body linkage and rev the engine can you see
the engine vibrate or move.
You could also remove the serpentine belt and see if the vibration goes away. Could be one of the accessory brackets is cracked, bad tensioner, AC compressor pulley, alternator bearing etc...
The water pump wont be operating so don't do this test on a hot engine
For a balancer problem, disconnect the Brown wire going to the distributor so the computer can't advance the timing . Use a timing light and verify the timing is 6 degrees BTDC. If the timing is off it could indicate the balancer is separating.
the engine vibrate or move.
You could also remove the serpentine belt and see if the vibration goes away. Could be one of the accessory brackets is cracked, bad tensioner, AC compressor pulley, alternator bearing etc...
The water pump wont be operating so don't do this test on a hot engine
For a balancer problem, disconnect the Brown wire going to the distributor so the computer can't advance the timing . Use a timing light and verify the timing is 6 degrees BTDC. If the timing is off it could indicate the balancer is separating.
Last edited by Hooked on Vettes; Jun 3, 2014 at 04:33 PM.
Safety Car
Joined: Apr 2011
Posts: 3,660
Likes: 22
balancers DO slip and come apart !
I had one actually separate and I got a strange vibration out of nowhere and was baffled....
also, when I shut it down, I would hear this dinging noise for 10 seconds AFTER shutdown....metallic and ongoing even after the engine stopped turning. I FINALLY got under the hood and had someone else shut it off....and spotted the outer ring of the balancer spinning on the inner hub !
if you can see ANY dry-rot or rubber edges cracking around the edge of the balancer ring....go find a new one...its on borrowed time.
I had one actually separate and I got a strange vibration out of nowhere and was baffled....
also, when I shut it down, I would hear this dinging noise for 10 seconds AFTER shutdown....metallic and ongoing even after the engine stopped turning. I FINALLY got under the hood and had someone else shut it off....and spotted the outer ring of the balancer spinning on the inner hub !
if you can see ANY dry-rot or rubber edges cracking around the edge of the balancer ring....go find a new one...its on borrowed time.
Thread Starter
6th Gear
Joined: Jul 2013
Posts: 6
Likes: 0
From: Kelowna
Thanks for all the help!
Not having a lot of time I had a quick look last night and discovered a nut missing on an A/C brace.
I installed a new nut and then discovered that the vibration goes away when the A/C is switched off but comes back when I turn on the A/C.
I will check out the A/C pump.
Thanks again
Not having a lot of time I had a quick look last night and discovered a nut missing on an A/C brace.
I installed a new nut and then discovered that the vibration goes away when the A/C is switched off but comes back when I turn on the A/C.
I will check out the A/C pump.
Thanks again
Safety Car
Joined: Apr 2011
Posts: 3,660
Likes: 22
Get a light and L:OO:K <----- real close at the a/c bracket ! Those crack real easy behind the compressor and below where the tensioner is....
Ya gotta have ALL the nuts/bolts in the a/c bracket AND the braces! especially the braces. Some have 2, others have only one to the ex manifold.
Fortunately they make new brackets now....they ain;t real cheap but they can be had.
Ya gotta have ALL the nuts/bolts in the a/c bracket AND the braces! especially the braces. Some have 2, others have only one to the ex manifold.
Fortunately they make new brackets now....they ain;t real cheap but they can be had.
