I have a 1994 LT1 6spd. I don't know if this is normal or not, but once I get up to around 3500-4000 rpms and definately 5000 rpms, I notice some vibration in the accelerator pedal and the steering wheel, and also comes with a slight loss of power it seems like, or maybe i'm just imagining things. My last car was a 4 cylinder 1990 Celica, and I've never driven a v8 before, so I don't know if this vibration is normal or not. I'm not sure whats wrong, if anything's wrong... any help is appreciated. Sorry for the newbie questions...I just got the car and haven't had too much time to research and learn about it yet. There needs to be a "Newbie Alert" gremlin just for me, i'll put it in my sig...heh. :cheers:

 

First thing I'd check is wheel balance.

 

:iagree:

And since you just bought it, get the alignment checked also.

 

Indeed wheel balance check along with a 4-wheel alignment would be good insurance, especially if the tires are in good shape.

 

If this happens at speed then maybe wheel balance. An alignment wouldnt make your wheel shake unless its very very bad.

A few things i would check would be the balancer hub. The very bottom hub that the belt goes around. Try and stick your hand down there and feel if the rubber ring is wobbly/loose or cracked. Ive witnessed that a few times. You could also try running the car and just look at all the pulleys to see if they are still round.

second does your a/c still blow cold? some bad compressors will cause a vibration at high rpms because the clutches fail. I know cuz ive had the problem.

Try and find out if your flywheel has been machined. The manual says the flywheel Should NOT be cut even when replacing the clutch. The surface of the flywheel is not flat but conical and a machine job will destroy it. Also the cutting fluid that is used will very quickly destroy the rubber and materials between the dual mass flywheel. If this is the problem you will need a new flywheel. Gm sells them for big bucks but im sure you can find an uncut one somewhere. I got an uncut used one for $100 from a forum member who uograded his LT4 to a aluminum single mass.

Good luck and keep us posted.
:cheers:

 

Wheel balance :seeya

 

I've got a 94 6-spd, too, and I am fighting this exact same problem. First thing you need to do is isolate the vibration. If it is rpm dependant with the clutch engaged, it could be a number of things. You need to be sure it is at a
specific RPM range, not a specific SPEED range.

If it is rpm related (as mine is), try sitting in the driveway with the car running and depress the clutch pedal. Now SLOWLY bring the rpms up into the range that you think the vibration is present, all the time keeping the clutch in. When you bring the engine back down to idle, again, do it SLOWLY. This keeps all of the violent dynamics off of the engine internals (some have different theories about whether or not revving an engine with no load is bad, but if you do it the way I described here, you should be ok).

Now, is the vibration still there? Then it is isolated to the engine, and you don't have to worry about wheels, driveshaft, transmission, clutch, ujoints, differential, or anything else in the driveline.

Now, if it's isolated to the engine, one thing you can try to eliminate a bad accessory pulley or bearings as the culprit is to perform the previous test with the serpentine belt removed. Don't worry, the LT1 waterpump is not belt driven, so your engine won't overheat. Just don't run it too long or you'll drain your battery. Few minutes should be fine. If the vibration goes away, it could be caused by a worn serpentine belt, or a bad pulley or bearings on the AC or alternator.

If the vibration is still there (as mine is), then it's either the harmonic balancer, the flywheel, or a high rpm ignition miss. From what I've been told, high rpm misses on LT1s can feel like a vibration.

Let us know what you find. I'm going to be taking my balancer off next to inspect it. It looks ok at first glance, but it's really hard to get a good look at it when it's on the engine.

 

I went through the exact same diagnostics. Changed the balancer, no change. Ultimately, it was the dual mass flywheel, which I replaced, and added no weights, accepting the balance as it came from the factory. My car is a Rippie modded engine. In any event, this got 98 percent of the vibration out (used to come in at 3400, out at 4000, back in at 5400, out at 6000.) Good luck.

 

Did you have your engine internally balanced? If so, using the stock dual mass would definitely cause vibration, as they are usually weighted to balance the LT1.
I thought about the flywheel, but the car only has 40k miles, and I just can't see the flywheel going bad in that time. I'm the second owner, and to my knowledge the flywheel has never been re-surfaced.
The car only started the vibration in the last 6 months. As far as what I've changed on the car, plugs and wires and exhaust are the only things. That's what makes me suspect it might be a miss, because that's something that has definitely changed since I bought the car two years ago.

 

Id say opti spark especially if you say its losing power.

 

I too have had the same problem. I became curious when my timing mark did not line up. I found a spun harmonic balancer. changed it, all is good.

 

If that's all you've done, then it does sound like something other than the dual mass. Maybe grapknutz it right, optispark. In my case, I had other issues since the engine was not stock. Take care.

 

The optispark was replaced under warranty by the original owner. The water pump was leaking and they replaced the opti to be safe. I bought the car at 19k miles, and all of that was replaced at 13-14k. Currently, the water pump is leak free.
What I suspect to be the problem, if the balancer looks to be in good condition, is that I accidentally got some anti-seize on one or some of the spark plugs' electrodes. I've been told you might as well throw the plug away if that happens. If the balancer looks ok, I'll pull the plugs. I'll probably just buy some cheap NGK copper plugs and put them in to see if the miss goes away. That's a relatively cheap test. Cheaper than an opti or new wires, anyway.