Vibration

[Brad Thomas]

1970, 454, 4-spd.
I have been dealing with a vibration problem for over 5 years now. I have tried everything I can think of to remedy it...including waiting for the bad part to fall off. The vibration starts about 2800 rpm in 4th gear. I can't tell if it's there in other gears so I do not know if it's and rpm issue or mph issue. The vibration will rattle the shifter to the point it will shake your whole arm if you hold the shifter handle. You can feel it in the car itself, and also feel it in the gas and clutch peddle. The strange thing is, it's not always there. very rarely it will be gone completely. The norm is there. Once I get to 2800 rpm it is there. The strange part is the severity varies greatly. Sometimes it's there but tolerable, sometimes it is almost undrivable. The stranger part is that by pushing the clutch peddle in and releasing it a few times I can change the severity of it. If it's in the middle of being bad, popping the clutch peddle will make it much worse or much better. I have to keep doing it until it goes away...which is never completely, but about 90% better. I have run the car without drive belts, changed the engine and trans mounts, changed the clutch assembly, changed the entire transmission, changed carbs, played with timing and tuning, changed u-joints, changed wheels and tires. I do not believe it is in the engine because I can change the severity of the vibration which should eliminate a bad balancer ( checks good ) or unbalanced engine. I assume it's not trans related because the entire trans was replaced and flywheel resurfaced. My guess is that since popping the clutch changes it, I must be doing something to load or unload something in the chassis. I would think after all these years whatever is causing this would have broke by now. I'm at my wits end here and am thinking about watching a low milage original car vibrate down the side of a hill. lol. Please help !!

[Timothy B.]

Re: Vibration

Is there any vibration WHILE the clutch is pushed in? Vibration only exists while clutch is engaged? Does it do it in all gears? Is it more associated with a particular speed or RPM or both?

[Brad Thomas]

Re: Vibration

There seems to be no noticable vibration while clutch is pushed in. I can not tell if it is rpm or mph related. In 3rd gear 2800 rpm it does not seem to be there, but have not turned the engine to a high enough rpm to reach the same speed I would in 4th.

[Mike Cobine]

Re: Vibration

If it doesn't vibrate when the clutch is in, but does when it is engaged, then your clutch disc is borken or a spring from the hub is missing, throwing it out of balance.

Everything else is still moving at that speed even if coasting, so the vibration should still be there.

[Timothy B.]

Re: Vibration

I would suggest that you further troubleshoot the situation. You need to find out if the vibration is associated with the car going a particular speed regardless of what the engine is doing, or if it happens at any car speed but at a consistent engine condition. For example, same RPMs but different gears.

Something must be severely out of balance between the drivetrain (driveshaft and differential) and the engine/clutch assys. Do you know if you have the driveshaft in backwards or 180 out from where it should be relative to the differential input flange? There at one time were paint markings on the flange and the shaft indicating where they should be. That by itself should create a more constant vibration, but it is possible that a second balance issue elsewhere forward of the clutch could combine with the other to create these symptoms. As you depress and release the clutch, sometimes you get lucky and the clutch reengages at a point where the two balances issues cancel each other out. Other times that add and make things worse.

Perform some more troubleshooting and see what you find out. Also, check the orientation of the drive shaft. On may car, the paint spots are on the rear of the shaft and that is the same end with spot welded on weights. If you can't tell or the markings are all gone, try relocating the driveshaft rear u-joint 180 deg and see if that makes a difference.

[Timothy B.]

Re: Vibration

Mike is right, typically if it's rear drive train related it will be there regardless of the clutch being in or out. That said, you indicated you changed the clutch assys...and you say the vib changes and sometimes disappears with the clutch out. The only way I can see that would happen is if conditions similar to what I described in my first note exist.

[Verle R.]

Re: Vibration

Also check/replace the pilot bearing.

From your description I suspect the clutch disk/pilot bearing.

Verle

[Richard D.]

Re: Vibration

Brad:

In addition to what the other folks are advising (who know a hell of lot more than I do) I would also check your motor mounts.

Mine were bad when I first got my 68, and the car would vibrate like mad at a certain speed.

Once they were replaced, smooth as silk.

Just a suggestion,

Rich

[Richard D.]

Re: Vibration

Oops, reread your post and you already changed your mounts!

Sorry,

Rich

[Terry F.]

Re: Vibration

I vote for looking at the clutch disk and pilot bearing, based on your description. Terry

[Tracy C.]

I'd have the driveshaft balanced... in fact

because of the inconsistant symptoms, it almost sounds like something is loose inside the driveshaft (mud dobber nest or chunks of flaking rust) causing the varibility in the vibration.

good luck,
tc

[Brad Thomas]

Re: I'd have the driveshaft balanced... in fact

Clutch assembly has already been replaced...including a different transmission. No changes were made by doing this.

[Mike Cobine]

Re: I'd have the driveshaft balanced... in fact

When you replaced the clutch, did you pull the flywheel and have the pressure plate and flywheel balanced?

Almost any parts guy will tell you that you are nuts and it is totally unnecessary, but I have had a lot of holes drilled in so-called brand new "balanced" assemblies when they come back from the shop.

Having the vibration changing from a lot to less sounds like the disk is out of balance, since it does change position each time you engage, so it will add and subtract to any out of balance the pressure plate is each time you shift.

Four tests:

1. Rev the engine to the 2800 and up while sitting in neutral.

2. Rev the engine to the 2800 and up with the clutch pedal pushed in.

3. Drive the car, take it to 2800 RPM and up in gear.

4. Drive the car, take it to 2800 RPM and push in the clutch. Rev the engine above and below 2800.

Results:

If the vibration is there in #1, it is not driveline or suspension related, but contained to the engine and clutch assembly and transmission input shaft. If it is not there, then it is driveline or suspension related, including tires.

If the vibration is there in #2, it is engine/flywheel/pressure plate related but not disk. If it is there in #1 and not in #2, it is the disk.

If it is there in #3 but not in #1 or #2, then it is driveline or suspension, including tires.

If it is there in #4 but does not change as you rev the engine, then it is possibly the input shaft of the transmission or the pilot bushing.

By chance is this an engine from an automatic car or did you have the engine rebuilt? If so, there may not be a pilot bushing in the crank.

[Timothy B.]

Re: I'd have the driveshaft balanced... in fact

Brad,

I would drive the car to a speed that the vibration is constant, at that point I would slide the shifter (without pushing in the clutch) into neutral and shut the enging off, then you will know if the engine and clutch are suspect. If the car still vibrates, the problem is from the transmission back. Could this vibration be a wheel bearing or tire? Steer the car left and right to see if the vibration smoothes out as that will load and unload the wheel bearings and give a indication of condition.

[Mark Ring]

Re: I'd have the driveshaft balanced... in fact

I had a car that did this once. The vibration would come and go at speed and would shake the shifter and whole car pretty bad. The driveshaft was out of balance and it caused the rear bushing in the tranny tailshaft to wear out as well. Solution was a new balanced driveshaft/yoke and a replacement tailshaft bushing.

If it were my car I might run it up on stands without the driveshaft in place and run it up the gears to see if it goes away. Might get a little messy with the gear oil leakage and all but at least you would be able to rule out everything in front of the driveshaft. I would not run it very long, just long enough to verify the problem.

Just a thought.

-Mark.