w1ctc

I have this vibration problem. It starts about 2k and is no longer noticeable by 2500. I have changed the harmonic balancer and run the engine without the belt on to eliminate the fan, water pump and alternator. I first noticed this after putting on a double pumper carb and ran it hard a few times. It does it clutch in or out, stationary or moving. It does not appear to be a miss since I can give heavy throttle at low speed in 4th without any feel of skipping. The clutch is new last year and the flywheel was resurfaced then. I can feel the vibration in the seat but it is not noticeable with my hand on the motor. I can find no exhaust pipe problems that would cause this. This is a 327 with a mild hydraulic cam, Edelbrock heads, and an old C3B intake. Other than the vibration it runs great with the DP. Could a sloppy timing chain cause this?

richbopp

I'd check the vacuum advance. Might be sticking/sluggish and then jumps in at 2.5K.

mymaur

Check all the u-joints. Be sure they are all tight and in the proper place. If the problem started after you installed your clutch and resurfaced the flywheel it is likely a balance issue.

2 cents

Shurshot

I am having a somewhat similar problem

I just adjusted both my DP accelerator pumps by the book and got a noticeable seat of the pants increase in performance. However I have picked up a vibration that I did not notice before. I feel it everywhere and more so through my hand if I push on the shifter. Not sure of the exact starting point for it but I notice it just riding around and that normally runs from 2000 to 4500

I have gone over the entire car and everything is tight as can be, The only thing I noticed wrong is that my clutch arm is destroying my floor pan.......... maybe some experimenting with the arm position or length might change that but it only contacted when shifting and at this point has made enough room for itself

So I am back to the carb that is only pulling 5 pounds at 1000 idle .... drops to zero if I try to ease away without a short rev but is happy by 1500 without a load on it.

So all new gaskets for the carb as soon as I locate a secondary 4.5 power valve and then I will put it back on and try again.

Don't know what else to do

Doug

Plasticman

Since it occurs stationary and moving, you have not eliminated the clutch disc (missing section of friction material is always a possibility). Try running with the clutch pedal down, and the Vette stationary, and in a gear (to stop the clutch disc from rotating).

You have eliminated the accessory driven items (fan, pump, alternator), and replaced the balancer. So the root cause must be "internal' to the engine (if not the clutch). However, as we know, a V8 engine always has some vibration (hence the need for rubber motor mounts, etc.).

If you cannot feel it on the engine, and only in the seat, obviously the seat is the cause. Just kidding.

The fact that you are feeling it in the seat says that it is severe enough to be transmitted that distance (at that rpm/freq.). I would also look hard at the motor mounts and trans mount to see if the rubber is old and hardened. If the mounts are in good shape, then look for any potential place where the engine and exhaust system has "grounded" (understand you have looked there, but it may be grounding with slight engine movement).

I don't have an answer to why it began with the installation of the new Holley, since the engine appears to be running properly (other than maybe something breaking off while "testing" the engine after the install).

Good luck,
Plasticman

Double-E

Have you checked engine and trans mounts?

wmf62

i think the installation of the carb is just a coincidence, and not a cause. there is a very good chance you have thrown a portion of the clutch disc lining from 'running it hard'; i have had a portion of the lining come off the last 2 discs i have had. this will create a vibration at low rpms that will go away at higher (at least it did for me...)



Bill

Shurshot

Well I certainly hope my disc (or w1ctc's disc) has not found a way to start to come apart. With the TKO 600 everything has to come out to do any clutch work.

Mine is a 12 inch setup with a 5 finger disc that is suppose to be good for a lot more than what I am putting out and unless necessary I am not going to think in that direction....... hate being sick to my stomach.

I am hoping it is the one thing I have not checked and that is the header bolts....... my tubes make direct contact with the frame right below the door joint and at the end of the collector. That was another penalty from having the heads angle milled with an 4 inch exhaust system that was already using all the planned room for it. If there is problem there and with the trans cross member being nearby that could contribute to what I am feeling. Had I thought all that out while under the car the other day I would have checked it out then. I was kinda focussed on mounts and shafts at that time.

I am going to be on it most of tomorrow so I can play this weekend with a "sporty" Roush mustang in the neighborhood that does a rev/ short burn when he sees me

Doug

w1ctc

Thanks for the sugestions. I did think about the motor mounts and as an experiment, I put a floor jack under the engine and jacked it up enought to take the load off the front mounts. It had no effect. The clutch feels fine but I'll take a look and see if its anything like yours Bill.
I did unbolt the the pipes from the trans mount brackets and again, no joy. If it was the carb or the vacuum advance it would vibrate differently at the same rpm with a load than no load (throttle opening would be different) I think I'll try messing with the trans mount next. It will really bother me to put it up for the winter without a solution.

Doug, 5" is real low unless you have a big cam. You might have a vacuum leak (I'm sure already thought of that but it maybe hidden on the buttom side of the intake) Must be hard to get it moving from a standstill like that.
Bob

Nzzz

I would say motor mounts.

65Tuxedo

I had this problem. Went through several possible diagnostics. It was the pilot bushing. Am on the third one. This time with new trans, so I don't expect further issue.

Good luck.

wmf62

when my clutch disc became 'unbalanced'; it wallowed out the pilot bushing, allowing the input shaft to flop a bit.
Bit

67L36Driver

With your low 5" manifold vacume at idle I'd bet you stuck or bent an intake valve. Broken valve spring is another possibility. Weak cylinders will smooth out at higher rpm.

Do a compression check.

Shurshot

Hi Bob

Thank you for your reply

I can understand you not wanting to put it away for the winter thinking something is not ready for the spring. However reading everything that you are checking says you will find it....... you are very thorough.

Between what you have done and the suggestions of others this has been a very informative thread

Yes my cam is fairly large but I did pick up a couple of pounds at idle today. I had opened a closed port on the base plate but the hose connection I had put in for the PCV/vaccum line was not sitting right for the angle of the hose pressing against the metering block. Between that and some other changes it really smoothed out....... seems to be making more power too

However I will not know if the vibration is totally gone until I take it for decent ride.

Doug

65vettetpimod

maybe try putting the other carb. back on to eliminate a problem
with the new double pumper,just a quick suggestion.

w1ctc

I never would think that a carb. could cause vibration but.... ya never know. The funny thing is that I started to get the same vibration from my lawn tractor today. Seem some of the internal engine parts wanted out and escaped through a hole in the block along with the oil.