Vibe Question for the Engineers
Melting Slicks
Joined: Feb 2017
Posts: 3,232
Likes: 1,232
From: PHX AZ
Sam, how are you determining that the vibe is coming from the engine (alone) vs driveshaft balance and or coupling and finally driveshafts.
You seem to be describing a 'one-per-rev' vibe....does this correlate to 4th gear at 1:1 ratio?
Is the vibe noticeable 'through the gears'?
Hal
You seem to be describing a 'one-per-rev' vibe....does this correlate to 4th gear at 1:1 ratio?
Is the vibe noticeable 'through the gears'?
Hal
Pro
Joined: Jan 2016
Posts: 502
Likes: 103
From: Reno Nevada
You have an internally balanced engine, do you have a flywheel and balancer designed for an internally balanced engine, or do you potentially have the wrong flywheel? Just a thought I had not seen in the above posts.
Is my vette stock?? HAHA
Joined: Oct 2015
Posts: 20,185
Likes: 9,321
From: Im not allowed to tell you
2020 C3 of the Year Finalist - Modified
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
2016 C3 of Year Finalist
Ahhh yes...that question. The car ran so poorly from various issues (carb, valves, alignment, vacuum leaks) when I got it, its hard to say. Rebuilt the carb, set the valves, ignition wires, cap, rotor, points, timing. How did it run? The one time I can remember (there may have been other drives but I simply don't recall them) it ran through the rev range smoothly. I even commented to my wife about it. Since then, well, new clutch/flywheel package, heads, balancer, drive shaft, half-shafts, rear trailing arms, alignment, engine mounts, trans mounts, cam, timing chain, exhaust system (stock). Could one of those altered how it runs? Sure.
You gave yourself the answer in this statement. It ran good then you changed all these things and it appeared. So start with these items and either change them out one at a time to the original piece you have or tighten them.each time you touch something you need to test to see if anything has changed
- If its static you can eliminate all the driveline parts as an issue. clutch forward would be the issue
- If its dynamic but doesnt change with the rpm shifts related to the cars speed, then its the driveline either. So if its at 3200 rpm but starts at say 30 mph but not at lower speeds at 3200 or whatever then its driveline.
- you can make sure the engine mounts are in correctly and tight as well as the trans mounts. Then take it for a drive.
- Exhaust systems can create a drone that you can feel, especially turbo style mufflers. It could be those if its static. Also the engine vibration can be felt through the frame if the exhaust is hitting the body or frame at any point. Check that and islolate and rub points and test drive it.
- if its dynamic you can take out the driveshaft and half shafts and check the U joints to see if they all pivot freely. one or more could be tight or bad. Did the driveshaft get put back in correctly? They are balanced to the yokes. I have never personally had a vibration issue related to a driveshaft imbalance but it can happen.If you happen to notice a loose u Joint fastener as you remove them, tighten it up and test drive it, a loose fastener can be the culprit
- heads, timing chain or cam...dont see how they could be an issue
- clutch and flywheel. If you can keep the car at 3200 and push in the clutch , it should change indicating a clutch issue. if not shift into neutral and release the clutch. If you maintain rpm and the car slowly coast down in speed but the vibration is constant it would be from the transmission forward. At this point if the vibration is there it would eliminate the clutch and could be the flywheel or the balancer. To test either they would have to be removed. In this case I would pull the motor and put it on an engine test stand.
- Once its on the test stand you can run it and see if the vibration is still there. If not its the car itself like a loose body mount or the engine/ transmission was hitting the body. You can also use a stethoscope to see if you can hear it neat either end of the engine
If you can manage to get underneath the car safely and have someone get the rpm up to 3200, use a stethoscope on the exhaust and then the transmission, the oil pan up to the front of the motor. The vibration should be audible
Last edited by Rescue Rogers; Mar 31, 2021 at 09:16 AM.
Melting Slicks
Joined: Dec 2009
Posts: 3,229
Likes: 656
From: Thunder Bay
If I have read this correctly, it started after you did all the work you listed. The only two items on the list that are likely to cause the vibration you are describing are the clutch/flywheel and the vibration damper. I would replace the original vibration damper and see if it goes away. If not, it's the clutch/flywheel.
