Bought a '77 280Z unmodified with original 5-speed transmission, got the original L28 limping along briefly (3 cylinders were missfiring), then pulled all combustion components and converted the car to electric (NetGain Hyper9, 5x Tesla modules). Now there is significant*vibration at higher RPM (starts by*3000), which I assumed meant flywheel was not balanced well (I had the flywheel alone lightened slightly and balanced earlier). So I took the full flywheel and pressure plate assembly back to the local shop to re-balance.
Got my flywheel-pressure plate assembly back from the shop this week. They said it was very imbalanced, 12g off. So much so, there wasn't enough material to remove from one side of the pressure plate, they had to weld on a bit to the other side. Here's what that looked like:
They also marked pressure plate and flywheel with paint to make sure I reasemble it in the proper orientation. Here's the one picture I took at that step of the process (from the 'gram):
You can see the orange paint tick in the bottom right.
Problem is, the thing still vibrates just as much at higher RPM as before!
There is also an audible click/tick or something at low RPM.
Here are two videos showing what it sounds like with the transmission attached, revving up to 5000+. Camera is pointed at the shifter to see it bounce around because the tach isn't working presently.
First, with the transmission in neutral:
Same thing but holding the clutch pedal in all the way:
Separated motor from transmission, left flywheel assembly attached. Clicking is gone, and I did not get any of the vibration from before, I think. It is difficult to judge, it’s certainly still makes (some different) noise at high RPM but when exposed like this the assembly moves a lot of air too.
Here is a low-speed video:
And one going up to ~5000 RPM:
This suggests the issue is in my transmission right? I am trying to remember the behavior when I first got the car running (poorly) on the original engine. I don't remember the loud vibration, but it's possible it was simply drowned out by the engine before. I do remember it felt like a lot of heat coming up from the transmission through the shifter hole in the body, but I wasn't sure if this was a transmission issue or just excess engine/exhaust heat seeping in b/c of a lack of insulation.
I’m not sure how to diagnose from here. Any suggestions of further testing to isolate the issue?
I posted this on a Z forum as well, but those folks have no experience with EV conversions so they're unfamiliar with what things should sound like absent an ICE, figured I'd post here too.