I've now got 1,000 miles on the car after my LS swap and I'm staring to get some vibrations settling in. At first I thought it was driveline issues but I'm now thinking not. Here is what has happened so far:

- after 300 miles I had my exhaust modified due to drone issues. They modified the magnaflow setup so that I had no body contact and this clearly made a difference.
- around 400 miles I started noticing a vibration under deceleration. I thought maybe I had some driveline angle issues but on further inspection, it did it at a stand-still under throttle. I then thought maybe clutch, but it's as smooth as can be
- at 500 miles I got the engine dyno'd. Their were some signs that as the engine torqued under full throttle, one header primary was intermittently hitting my sterring shaft causing a knock sensor issue. This was very minor.
- now since the weathers been so nice in Houston, most of my miles are with the t-tops off and the windows down. I notice nothing at that point because of wind noise
- this weekend I put the tops back on and that's when I really noticed it again, and it seems worse

So, I feel vibration in the shifter. I feel engine vibration just sitting still. If I rev it, it increases. When I got out of the car after driving for 45 minutes, I could feel my body having the after effects of vibration (as if I was vibrating).

So I need advise for all of the obvious and not so obvious things to check.

Car mods:
LS3 480 hot cam
Keisler rs500
Rebuilt rear diff (Tracdog)
New driveshaft
All new u joints (spicer)
Flaming River rack
ARH headers
Van Steel front coil overs
Rear mono spring with QA1's adjustable
New C7 seats (I noticed it more when I installed these. They are bolted to the floorboard with no tracks)
Magnaflow SS dual exhaust (2 1/2")

Thoughts????

 

What clutch?
Mike

 

Not really sure it should be a LS problem - just as likely to happen if you replaced everything and something is off with SBC stuff. No vibration in mine, in fact it is way smoother now than when I had the big cammed small block - and I have solid engine mounts. Assuming nothing is rubbing or it is not harmonics from the exhaust - If it happens sitting still, then your drive shaft is eliminated. Something internal to the engine, trans, or clutch. The clutch operating smoothly does not eliminate it being out of balance. Didn't you put in a used engine and trans? You are sure nothing is wrong with them? When everything is taken apart and put back together it is easy for something to maybe not be tight or a fastener to back off. Not much help I know, good luck.

 

Everything is new. GM crate motor.

I'm not sure what clutch I got. Keisler spec'd it for my engine and transmission. They also provided the new flywheel as the crate motor is setup for an auto out of the box.

Motor mounts are the red poly energy suspension brand.

 

Flywheel, clutch, pressure plate?
frequency? harmonics/oscillations?

 

What's on the front of the motor? Pulley's all nicely aligned?

Vibration all the time at all RPM's, or just a harmonic?

iPod's and iPhone's have a couple of vibration apps if you can find a way to mount them solidly.

 

I would first off make sure all belt driven items are tight and the belt is tight. After that drive the car and when you feel the vibration depress the clutch to free wheel the drive line. Is it still there free wheeling ? I would go so far as getting to 45mph depressing clutch and shutting the motor off and coasting in Neutral.

 

Start simple... Pull the accessory belts and see if the vibration is still there.

Rev the engine a few times and then press the clutch and rev it again , is it still there.

Since it happens wether moving or not that takes out the driveshaft and rear. Removing the accessory belt takes out accessories and water pump.

Silver sport transmission took over Keisler I believe you might be able to contact them and describe your issue could be tranny or clutch issue.

 

Well I took the car to the my local corvette mechanic and he diagnosted........

That I'm Imagining It All

He told me that I have normal vibration with an LS3 Hot Cammed Motor with Headers.....I have nothing to worry about.

The suggestion that he did have is to swap the poly motor mounts out for solid. He said this would reduce the vibration that I feel. He also thought since my tranny mount was solid, I could be seeing amplified vibrations.

any thoughts?

 

Interesting he said he wants to use solids on the motor to reduce vibrations but said the solid trans mount maybe enhancing vibration. Curious to see what works out. I am running poly motor mounts also. I think I have a rubber trans mount if I remember correctly. Again. No real road miles yet. Swapping out the clutch MC right now.

 

I am running solid engine mounts, and a stock C3 rubber trans mount. I didn't do it for vibration, and I don't know if it helps or not. My idea was to not be completely rigid and the trans would have a small amount of play. The engine then could add a little stiffness to the front of the frame and I wouldn't have to worry about the engine mounts. I ran the same way when I had the SBC in my 74, (in several other cars as well) and it always worked well for me. Would it help your vibration? - I have no idea.

 

It was interesting that there was more vibration level in the drivers's seat (from the pedal) than there was from just feeling the top of the intake. As I rev the motor you can feel it in your foot, but not on top of the motor.

Go figure... Like he said, I'm very paranoid. It's like it should be. I'm chasing something that's not there.

 

If everything is OK, and you still don't like the vibration, you might try dampening the floor pan. You said you felt it through the new seats, maybe the floor is vibrating from the exhaust harmonics. Something similar to Dynamat may help dampen everything. This will be one of my future projects.

 

I wouldn't do the solid engine mounts, you will feel EVERYTHING then. Stick with the poly mounts.

Did you have the flywheel/clutch/pressure plate balanced? If it's doing it when sitting in the driveway and just revving it, it's definitely engine related..(not internally necessarily). As mentioned try pulling the accessory belt and see if the vibes change.