C3.....Driveline vibration

[Mike R.]

Hi

I have a 1971 LT1 that has a vibration in it that starts around 2500 RPM to 3200 Rpm at 3400 its gone and the car is smooth.
Anyone have any ideas
Thanks
Mike

[Joe L.]

Re: C3.....Driveline vibration

Mike-----

The first thing that I'd check is the driveshaft. Remove it, install new u-joints, and have the ASSEMBLY balanced by a competent driveline shop. If that doesn't fix the problem, then I'd say clutch/flywheel imbalance.

[Eugene B.]

Re: C3.....Driveline vibration

Mike,
Joe has given you good advice. Before you spend a lot of money, you might consider disconnecting the drive shaft, rotating it 180 degrees, reconnecting the U-joints, and going for a test drive.

It might be a cheap solution to your vibration problem. I would rotate the shaft 180 at the rear end connection (not the transmission). You should also check that the factory weight that was welded on the drive shaft is in place at the rear end of the drive shaft. Perhaps someone has knocked it off or swapped ends with the shaft by installing it backwards.

In the old days, I've heard of folks installing a worm-type hose clamp on the drive shaft to achieve balance.

Good luck and good Corvetting.

Regards,
Gene

[Robert E.]

Re: C3.....Driveline vibration

Mike, your question is the exactly the same I posted a couple of weeks ago about my '71 LT-1. How long has it been doing it? I have the exact same vibration from about 2700 RPM thru to 3300 RPM. Does yours vibrate at a stand still or only while moving? Mine does both. The kind of responses I received where clutch, unbalanced drive shaft, defective harmonic balancer, etc. I just brought mine to a local Corvette shop here in Toronto and I'm still waiting for the news. I'm praying it's not an internal engine problem!!! Good luck to both of us.

Robert #41801

[Duke W.]

Re: C3.....Driveline vibration

Drive line vibration is speed senstive. If the vibration occurs in a given engine RPM band in any gear,then it is engine related.

Duke

[Mike M.]

Re: C3.....Driveline vibration

Mike,
First, does the vibration occur with the car stopped and the trans in neutral as you rev it through the 2500 to 3200 rpm range.
If so, then it is engine. If not then drive train.
To assure, take the car out, get it up to the speed where the vibration occurs and put it into neutral. Does the vibration continue, stop, get less, etc.
If the vibrations continue, it is drivetrain, if not, engine.
I once bought a '79 L-82, four speed car cheap because it had a vibration the dealer could not find. Replaced everything from tires, half shafts, driveshafts, rebuilt TX, flywheel, clutch, pp and vibration dampener. Was about to put in a new shortblock when the owner said enough and sold me the car.
I lucked out and found the problem quickly. And it was a vibration that only came on between certain rpms. What was it? The fan clutch was incorrectly machined at the factory. It must have been cocked in the jug during machining.
Anyway, it neutated (spelling?) around the shaft. Replace the clutch and the problem went away.

Mike

[Robert E.]

Re: C3.....Driveline vibration

Duke, I respect your response based on others I've read from you, but, how is it that Mike and I have the very same vibration between the same RPM range and have it be an engine related problem? I guess it could very well be, but what a coincidence.

Robert #41801

[Duke W.]

Re: C3.....Driveline vibration

You missed the point. The thread title is "driveline vibration", yet the question relates to a RPM related vibration.

Neither I nor anyone else can read minds. The question remains for the original poster: Is the vibration purely related to engine revs regardless of vehicle speed, or is is really a "driveline vibration" that would be related to engine speed - say 2700 in top gear?

Duke

[Mike M.]

Re: C3.....Driveline vibration

Correct spelling of the type of motion the fan clutch was moving through is:
"Nutation" or the motion of the plate in a wobble plate pump. Was hard to find because the fan clutch bearings were fine, no play. It was only after staring at the fan for awhile (with the engine running)that I noticed what seemed to be excessive "run-out" at the tips of the fan blades. Got a newspaper, rolled it up and jammed it into the fan (with the engine running) to stop the fan. Soon as I did the vibration ceased.

[Mike McKown]

Over this broad RPM range

the fan clutch is suspect as is the likelyhood of a fan blade bent in a fore/aft direction. That will do the same thing. You can use the method Mike M used or take another approach and take the fan belt off then rev the engine to the problem rpm.

If the car just started vibrating one day, all of a sudden, with some accompanying noise I would suspect you lost some of the facing off the clutch disc but you would probably notice the clutch not holding as well.

Internal engine vibrations tend to be a heavy vibration whereas driveshaft vibrations are lighter and more of a buzz.

[Robert E.]

Re: C3.....Driveline vibration

You're absolutely right. Mike needs to elaborate with regards to the symptoms.

Robert #41801

[John H.]

Re: C3.....Driveline vibration

Guys, you all have been very informative. I enjoyed all the suggestions, and will keep this in mind regarding my noise problem that makes a noticeable
clunk sound when clutch is let out. 72 all original with recent rebuilt clutch.
I didn't notice any noise before rebuild. however car has all old driveline
and suspension.
By the way, I'm the owner who started with a overflow plastic bottle that
backed up my radiator pressure and two years later when core was finally fixed
correctly, my car caught on fire in the shop and I'm still trying to sue the
shop for negligence. Get references, battery disconnect, halotron fire
exstinghuser. My story is to long to repeat everything in this tread. Big John

[Mike R.]

Re: C3.....Driveline vibration

First I'd like to thank everyone for all the good info.
After reading your responses I went out and drove the car to find out some more info.
at 3000 rpm with the car standing still it doesn't seem to have the vibration.
at 3000 rpm in first gear it is barely notice able. it seems to get worst as you go thru the gears. (i.e. its more noticeable in 2nd and more in 3rd and still more in 4th gear).
what does everybody think?
thanks again
Mike

[Craig S.]

Re: C3.....Driveline vibration

Mike - it sure sounds like a driveline related vibration, especially since it gets worse as the rpm of the driveshaft increases in each respective gear, and there is none at a dead stop just revving the engine.....Craig

[Duke W.]

Re: C3.....Driveline vibration

Yes, I does sound driveline related. You need to get the car up in the air and do a thorough inspection beginning with the engine/trans mounts. Then methodically inspect everything from the transmission yoke and front U-joint to the wheels/tires. Wiggle/shake every connection and look for play. Check all fasterner torques. Also check the axle mounts and look for misalignment of the transmission/axle.

Such driveline vibrations can be tough to isolate.

Duke