BSeery

We took the 1980 out for a long cruise today, and noticed a vibration that has me concerned.

At about 2500 RPM I get a vibration that shakes the car pretty good. It does not mater what gear I am in so it's not driveline related. It will happen at 50 MPH in 3rd or 80 MPH in 4th.
I feel that it is coming from the motor, but what would cause this. It's a stock ZZ4 crate engine with that is 4 years old but less than 10K miles on it.

Any ideas or suggestions?

cosmicvette

Is it an auto or manual?

A friend installed a V6 in a hotrod he was making and had this really annoying vibration that was dependant on engine rpm, it turned out to be a faulty torque converter.

Another idea, and please pardon my ignorance but is the ZZ4 crate motor externally or internally balanced? How is the harmonic balancer?

cosmicvette

Twin_Turbo

Check the balancer the flexplate and the converter.

bobs77vet

fan clutch.......check this out....

mrvette

Brian, you had another thread of some length about the 2004?? install?? wonder if you drive shaft angle is correct, may check the pinion snubber also....GENE

Eddie 70

This was a problem with mine when I first installed the rebuilt motor. I wound up taking out the clutch fan and installing an electric.

BSeery

It is a 700R4 transmission. No fan clutch because I have converted to electric fans.
It wouldn't be the drive shaft or pinion snubber as it happens at different speeds but at the same engine RPM. Driveshaft would happen at the same speed but at different engine RPM depending on gear.
Torque converter is new - less than 2K miles on it.

How can I check a balancer?

rihwoods

First watch it for "wobbling".(I would also check the crank pulley too.)

Make sure if/when you pull it that the druff key is OK and that the cranks keyway is not beat up.

Tom Johnson

Mine was a busted driver side motor mount.

camaroneil

i would definately check the motor mounts,
had this happen to me before,
natt

isosceles

does it do the same thing sitting in the driveway out of gear?

would a bad balancer produce the same results if revved in neutral?

MotorHead

If it's auto wouldn't you get the same vibration in neutral at that RPM ?

I am having the same problem as you only mine is 5 speed and it is just a slight vibration mainly in the shifter at about 2500RPM not too bad but enought to let me know something is not perfect.

Both of us can rule out anything after the tranny from the driveshaft back because it happens in every gear at the same RPM and is not dependant on speed of the car.

Now mine does not vibrate in neutral with the clutch engaged so this tells me the motor is OK which makes sense because I did not have the vibration before installing new transmission, so I am baffled too.

Motor mounts is interesting though, I never really thought about that I might go to the poly mounts

rihwoods

I'd do a visual check at idle,no matter what,looking at all pulleys.Vibration levels can vary. I had one that showed up at 70MPH and it turned out to be my worn clutch assembly.But in this case.....???

ESU

It's not a tire out of balance is it?

BSeery

Nope - it's engine RPM related and not MPH related. I can have it happen in 3rd gear at 50 MPH or 4th gear at 80 MPH.

I will have to have someone rev it up for me while I check under the hood.

MIKER

Did this vibration develop suddenly or has it always had some vibration at ~2500 rpm?
While parked, put the car in neutral and slowly rev it up to the point where you feel vibration. This will eliminate all sources other than the engine, engine accessories, and torque converter.

You can unbolt the torque converter from the flex-plate and slide it away from the engine. Rev the engine to see if the vibration is still present.

Perhaps you have one cylinder that is misfiring under load!?!

Good luck and keep us posted.

78vettman

I have the same problem out of my 78 vette. My vibration starts at ~3500 RPM and eases up at ~4500 RPM in every gear no matter the speed. I have a 4 speed manual trans.