Harmonic balancer question
Anyone ever had a balancer go bad? I’ve got a funny vibration in my conv (327/365) at about 2500 RPM. the vibration cycles (comes then goes…). The vibration is there when the car is stopped clutch in or out. Its also there when I’m going down the road. I was thinking either trans input shaft or balancer. What do you guts think??

Thanks.
Chuck

 

If it's like mine, a small vibration that only you really notice, I have the same thing at around 2000 rpm. It's been there for 15 years. During that time, the clutch, trans, heads and balancer have been changed with no effect. I suspect the motor and/or trans mounts but have not changed them. I figure that if it hasn't chucked any parts though the pan by now, its not a big problem.

 

I have seen it, but on the later models (70s). Never on a midyear.

 

The outside ring is known to "slip" on BB's and if it does on yours it will show up when you check your timing

Doug

 

I had a vibration problem on a 65 365hp once and I couldn't find the cause until the waterpump seized due to a bad bearing. New waterpump-no more vibration.

 

I have been watching these "vibration" threads with some interest. The cause is often never found or at least reported on in many cases if the vibration was indeed fixed.

There can be quite a number of causes. I've been waiting for someone to report he fixed his problem by removing the unknown brand of motor mounts and replacing them with genuine GM mounts and fixing his "vibration".

I haven't seen that yet but I believe it may be the root of some of these vibrations many seem to complain about.

 

I have been watching these "vibration" threads with some interest. The cause is often never found or at least reported on in many cases if the vibration was indeed fixed.

There can be quite a number of causes. I've been waiting for someone to report he fixed his problem by removing the unknown brand of motor mounts and replacing them with genuine GM mounts and fixing his "vibration".

I haven't seen that yet but I believe it may be the root of some of these vibrations many seem to complain about. These mounts aren't just merely blobs of rubber encased steel, they're tuned to the engine/chassis. At least the GM mounts are. The aftermarket, probably not.

 

Did the vibration just start or has it always been there ?? Have you stood over the motor and watched for something out of balance (water pump/fan, balancer etc....) or have you only been sitting in the car when it does it ?? Does the car have Air Conditioning ??? I had a Camaro years ago that had the compressor seize while I was going down the road which caused a major vibration. Since the A/C had it's own belt and was seperate from the water pump and alternator I just cut it off with my trusty knife. The vibration stopped but the ride home wasn't pleasant..... Maryland in the summertime..... in the afternoon....., and I was wearing a suit and tie !!!!

 

For what's it worth, I'll give you my experience.

Several years ago I developed a vibration around 2,000 to 2,500 rpm.
(350/370). Over time it got worse. Mainly showing up in the shifter under acceleration.
Balanced the flywheel/clutch and PP, with no change.

Last year I decided to change the harmonic balancer. (8")
The vibration was completely eliminated.

My theory......
-The vibration is coming from the combustion on each cyl. Each time
a cyl fires, it creates a "shock" on the crank. This rotational shock
is absorbed by the harmonic balancer.

- My harmonic balancer was the original '70. It looked perfect.

- I think that the rubber had turned very hard and was unable
to dampen the vibrations.

- It seems that the forged steel crank engines with high compression
are more prone to this problem.

A new balancer from GM is obsolete for the LT-1, however, the ZZ4
balancer has the exact same specifications, just has more degree lines.
I verified that the TDC mark was accurate.

I'm sure there are many sources of vibrations, however the harmonic balancer was mine.
Barry

 

I tend to disagree that motor mounts "eliminate" vibrations. The engine should NOT vibrate in the first place if everything is OK.

Now newer 4 + 6 cyl cars use special mounts but these motors vibrate much more due to the # of cylinders!

 

Have you ever driven a car that had the solid steel engine mounts in it like the drag racers use? A perfectly internally balanced engine will rattle the fillings out of your teeth.

My '63 has a vibration at the stated rpm in this thread. I found the engine had a bent fan blade. I fixed it and the vibration lessened but still there. Since it was a replacement engine by a previous owner I assumed the vibration was engine related. Fast forward a year. I built a new engine and installed it. New clutch, flywheel, pilot bearing, alternator and fan/fan clutch. The engine was balanced along with the clutch and flywheel. The engine configuration was changed from a 300 hp to a 360 hp. The vibration was still present.

Next, thinking the exhaust pipes were setting up some kind of resonant vibration, I changed out the '63 exhaust support at the transmission mount for the solid mounted '64. The vibration problem lessened but still there.

I didn't change the motor mounts when I changed the engine. I know they are not GM which the originals were US made. Most, if not all replacement now are made off shore or in Mexico.

There seems to be a disproportionate number of complaints about mid-year Corvette engines vibrating starting at around 2500 rpm than you see on other vehicle line discussion boards despite the fact the the common denominator is the engine and related accessories.

Maybe Corvette owners are picky. I don't know. I know engine vibrations are a pet peeve with me.

My '65 is smooth as silk at all rpm's. It still has the factory mounts. Go figure!

 

MikeM,

Are they fluid filled or must be a specific type of rubber? Where do you get factory replacement motor mounts? I was taught to always always replace those when the engine is out. Like throwout bearings, always replace them.

 

Mid-year Corvette mounts are not fluid filled unlike modern engine mounts in today's four cylinder cars.

Replacements can be had from Chevrolet that supposedly meet the requirements of the original design specifications. At least a short while back they were still available.

I sometimes wonder how much the solid mounted '63 body contributes to the vibrations felt in '63's also.

 

I am definetly going to keep that in mind. I had a 59' a few years ago (which I see is now at Pro-Team) that got a heck of a vibration after the engine was out. I couldn't find anything. Tried rotating the driveshaft even though I knew that it was an engine issue. Nothing.

Very interesting and thanks for the tip MikeM.

 

thanks for all the feedback guys.

I've already replaced the water pump and fan.

I'll keep u guys posted if i get it resolved.