Question about vibration

[47heaven]

Trying to analyze what could be causing a vibration when I accelerate, but when I let off the gas it stops as it's coasting. Is this a sign tghat I'm due for a tune up or one of the cylinders is not firing? Don't know where to begin? Any ideas?

[55 Fargo]

Darren, maybe some more details might help.

Is this case while the engine is both cold and warmed up, what speeds does this happen, how is your gas mileage, is the engine starting okay, does it run well at idle, what about when you rev it up in neutral with no load.

You can test for a cyl not firing easily, by disconnecting a plug wire at a time.

When was the last time your engine was tuned up?

[P-12 Tommy]

Any noise with the vibration? It wouldn't hurt to check the u-joints on the driveshaft.

Tom

[55 Fargo]

Any noise with the vibration? It wouldn't hurt to check the u-joints on the driveshaft.

Tom

I concur

[47heaven]

No, no noise with the vibration. The driveshaft is a modern one that was installed four years ago.

Idle is kind of rough when first started, but gets a little better when it's warmer. The vibration occurs whether it's cold or warm...only when the accelerator is pushed, and also at all speeds. Gas miliage was 17-19 mpg. Not sure what it is now. The engine hasn't been tuned since it was rebuilt...four years ago. I am running an electronic ignition in the car.

[Vazlov1949]

Motor Mount?

[47heaven]

Motor Mount?

Motor mounts were replaced four years ago.

[desoto1939]

The issue might be a worn vibration dampener. This would consit of the lower pully on the front of the engine that has the timing mark. These have a ruber encased pully and they breakdown over the years. This happened to me after having a new clutch and Pressure plate. Changed the Dampener and the engine smoothed out completely. this was on my 39 Desoto big 6 engine

Rich Hartung

desoto1939@aol.com

[greg g]

Is the vibration accompanied by a misfire? Could be something as simple as a spark plug wire not seated properly in the distributor or on the plug, which would show up under load when a weak of missing spark would be noticed, and then smooth out when less power is being called for. With the car at idle open the hood in the dark and look for any leaking sparkes. As a weak spark and missfire might not be noticed at cruise. Is your dizzy cap in good condition?

[Tom Skinner]

Dear 47Heaven,

Your problem is solved. Its your Throttle Spring vibrating on the Metal Spark Plug Tubes. Take your Spring Off and re-install Presto no more noise.

I just did the same thing when I removed my wires and Painted everything up and re-installed my Sring backwards it made the same noise.

Check that and lets hope thats all it is.

Tom

[47heaven]

Dear 47Heaven,

Your problem is solved. Its your Throttle Spring vibrating on the Metal Spark Plug Tubes. Take your Spring Off and re-install Presto no more noise.

I just did the same thing when I removed my wires and Painted everything up and re-installed my Sring backwards it made the same noise.

Check that and lets hope thats all it is.

Tom

So what you are saying, Tom, is that the throttle spring touching the wire loom is causing the vibration? It's not a matter of noise. I don't quite understand what you mean. It's vibration from the engine that is felt through out the car when I accelerate, not noise.

[Tom Skinner]

47Heaven,

My bad, I thought maybe it was a spring vibration noise, not vibration throughout the whole car.

Tom

[james49ply]

My thoughts on the vibration you are having could be in the drive train, u-joint, or differential. worn or loose pinion bearings will cause this, as well as a bad u joint. also check your engine-trans mounts, if they are worn or soft, they could case metal to metal contact and cause vibration. all of the above may not be heard as sound, but felt throughout the car.

[greg g]

Is the crankshaft pulley running true at idle or is it woblbing??? If your engine has the harmonic balancer style and it not running true it could be delaminating and sending the vibration through the engine mounts.

[adam_knox]

Not to hijack this thread or anything but I'm having the same issue with the 94 Jeep Wrangler. Accelerate and I get a back massage from the seat vibrating, let off the gas and the noise almost disappears. If I'm on the freeway doing 50 it rattles, throw it into neutral and rev the engine no noise. So by that account the good guess is U-Joint? I could see that being an issue since the car is jacked up with those huge tires and original rear-end. Problem is that its really cold out at the moment and no garage to work on. Are U-Joints hard and time consuming to put in? Can it wait till it at least mid-Feb when we get a day in the upper 40's or am I likely to find the drive shaft dragging on the concrete if I keep driving it?

[Niel Hoback]

Just my opinion, but for me, vibration on acceleration but not on cruise or decel, is usually caused by a cylinder miss, maybe from weak or no spark. Maybe even low compression.

[dezeldoc]

Thing is he feeling a miss or a vibration? two totally different animals. i am leaning towards drive line also, check all nuts and bolts and make sure they are tight. not all the motors have the rubber balancers some are just a pulley. when you drive it try and push the clutch in and step on the gas and see if it does it or not. just because you replaced it 4 years ago does not mean it can't be bad.

[47heaven]

Okay....it seems I have a good list now of what look for, thanks to all your guyses imput so far.

The motor mounts and drive shaft were replaced four years ago when the engine was rebuilt.

First thing I'm going to do is check the sparkplugs, wires and make sure the electronic ignition is set right. As mentioned, it could be missing too. Basically, I should just give it a tune up and see if that solves it. If not, then I know that I nned to go to the other steps.

Yesterday, I noticed that when I accelerate I still have the vibration, but when I let off the gas and coasted, the vibration was stronger. Now, I'm confused. This only happens on the surface streets. When I'm on the freeway at faster speeds, I don't get the vibration when I let off the gas. So this weekend I will be going down the checklist and see what I can find. Anymore, ideas will be appreciated.

[greg g]

one more possibility, is your parking brake fully releasing???

[47heaven]

one more possibility, is your parking brake fully releasing???

As far as I know it is, Greg. In fact, the cable has a little slack in it.

[greg g]

even with the cable loose it still might be hanging up a bit. Might be worth the crawl under for a looksee.

[Oldguy48]

Just a shot in the dark, but years ago I had a Pilothouse, and the flywheel bolts somehow loosened. Mke a lot of vibration and noise. Tightened the bolts, and the problem went away.