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Noticeable Drivetrain Shake at Idle #1542134
12/01/13 03:05 AM
12/01/13 03:05 AM
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MuuMuu101 Offline OP
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So, my Dart has a noticeable drivetrain shake when the car idles. You can feel and hear it especially when sitting at a light. 2 months ago when my mechanics checked the compression on my 273, they said one cylinder was reading low compression (I believe around 50-60 psi). I've heard that could be a cause for the shake as technically the engine isn't completely balanced. What other causes could it be from? Bad engine mounts?

Again, this can only be felt at idle? Should I be particularly worried about it? I only drive the car about a 10 mile round trip once every 2-3 weeks or so.

Thanks for your help!

Re: Noticeable Drivetrain Shake at Idle [Re: MuuMuu101] #1542135
12/01/13 04:39 AM
12/01/13 04:39 AM
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Keizer, Oregon U.S.A.
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elmor353 Offline
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I had the same problem with the 440 in my truck. Didn't seem to notice when driving it, but at an idle, it shook pretty bad. Had a burnt exhaust valve and no compression in one cylinder. What were the rest of your cylinders running for compression? Normally you don't want to run more than 10 percent difference.

Re: Noticeable Drivetrain Shake at Idle [Re: MuuMuu101] #1542136
12/01/13 11:52 AM
12/01/13 11:52 AM
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Lincoln Nebraska
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RapidRobert Offline
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It ain't from that (low comp in 1cyl). There is something else going on that's affecting multiple cylinders. Get down there & do a quick visual to eliminate the mtr mounts. check rotor phasing, blast out the 2 carb mixture screw holes with brake kleen, check the plugs & wires. Spray for vac leaks. EDIT Is that a solid lifter 273? Not sure if the lash was way off if that would do it otherwise if so I'd think it would of showed up on the compression test. Maybe someone can chime in if that is a potential

Last edited by RapidRobert; 12/01/13 12:23 PM.

live every 24 hour block of time like it's your last day on earth
Re: Noticeable Drivetrain Shake at Idle [Re: MuuMuu101] #1542137
12/01/13 12:22 PM
12/01/13 12:22 PM
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chicagoland,usa
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buildanother Offline
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A weak cylinder will cause a "rock" or a "miss" type of idle which is different feel than a vibration. A poorly sealing valve will not be noticeable off of idle many times though. I had a dakota that set a misfire code while at idle and had only 70 psi in the cyl with a burnt valve.

Re: Noticeable Drivetrain Shake at Idle [Re: elmor353] #1542138
12/01/13 07:38 PM
12/01/13 07:38 PM
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SoCal
MuuMuu101 Offline OP
I got lucky at Woodward!
MuuMuu101  Offline OP
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Quote:

I had the same problem with the 440 in my truck. Didn't seem to notice when driving it, but at an idle, it shook pretty bad. Had a burnt exhaust valve and no compression in one cylinder. What were the rest of your cylinders running for compression? Normally you don't want to run more than 10 percent difference.




I believe he said the others were running somewhere around 120-130 psi. I'm not too sure. Honestly, I don't know too much about engines or how to troubleshoot them, but I'll be done with my next school quarter in 2 weeks and may have some time to fiddle around with it during my Christmas break.

Re: Noticeable Drivetrain Shake at Idle [Re: MuuMuu101] #1542139
12/01/13 07:54 PM
12/01/13 07:54 PM
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Kent, Wa
340SHORTY Offline
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maybe you have lumps in your gas..


I am truckless..
Re: Noticeable Drivetrain Shake at Idle [Re: MuuMuu101] #1542140
12/01/13 08:22 PM
12/01/13 08:22 PM
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JohnRR Offline
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What ignition system on the engine? This is not a drivetrain vibration if it is happening when stopped and at idle, this is an engine vibration.

Re: Noticeable Drivetrain Shake at Idle [Re: JohnRR] #1542141
12/01/13 09:32 PM
12/01/13 09:32 PM
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SoCal
MuuMuu101 Offline OP
I got lucky at Woodward!
MuuMuu101  Offline OP
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Quote:

What ignition system on the engine? This is not a drivetrain vibration if it is happening when stopped and at idle, this is an engine vibration.




It's electronic. Someone swapped out the standard points system.

Re: Noticeable Drivetrain Shake at Idle [Re: 340SHORTY] #1542142
12/01/13 09:33 PM
12/01/13 09:33 PM
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SoCal
MuuMuu101 Offline OP
I got lucky at Woodward!
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Quote:

maybe you have lumps in your gas..




What do you mean by this? I do fill it up with 91 octane (highest I can get over here).

Re: Noticeable Drivetrain Shake at Idle [Re: MuuMuu101] #1542143
12/01/13 10:07 PM
12/01/13 10:07 PM
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Lincoln Nebraska
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RapidRobert Offline
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I'd start on a few things & see if I could pin it to either fuel (carb/vac leak) or ign (plugs/wires/reluctor gap/rotor phasing)


live every 24 hour block of time like it's your last day on earth
Re: Noticeable Drivetrain Shake at Idle [Re: RapidRobert] #1542144
12/02/13 01:36 AM
12/02/13 01:36 AM
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Keizer, Oregon U.S.A.
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elmor353 Offline
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On the 440, it had zero compression in #3 cylinder. At an idle it would shake your teeth loose. Put on a fresh set of heads which made compression even in all cylinders and the shake went away.

Re: Noticeable Drivetrain Shake at Idle [Re: MuuMuu101] #1542145
12/02/13 02:34 AM
12/02/13 02:34 AM
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JohnRR Offline
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Quote:

Quote:

maybe you have lumps in your gas..




What do you mean by this? I do fill it up with 91 octane (highest I can get over here).




Why are you wasting money running 91 in that engine ?

Re: Noticeable Drivetrain Shake at Idle [Re: JohnRR] #1542146
12/02/13 02:52 AM
12/02/13 02:52 AM
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Posts: 12,375
SoCal
MuuMuu101 Offline OP
I got lucky at Woodward!
MuuMuu101  Offline OP
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Posts: 12,375
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Quote:

Quote:

Quote:

maybe you have lumps in your gas..




What do you mean by this? I do fill it up with 91 octane (highest I can get over here).




Why are you wasting money running 91 in that engine ?




I wasn't sure what the recommended octane was. Most people I heard run 91. I just didn't want to develop an engine knock. What do you recommend?

Re: Noticeable Drivetrain Shake at Idle [Re: MuuMuu101] #1542147
12/03/13 02:32 AM
12/03/13 02:32 AM
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JohnRR Offline
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What's the rated compression ratio ?

Edit ... mymopar.com says rated at 8.8 so it's closer to 8.0 , you should be able to run it on 87 ...

Re: Noticeable Drivetrain Shake at Idle [Re: RapidRobert] #1542148
12/03/13 11:42 AM
12/03/13 11:42 AM
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Dcuda69 Offline
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It's got a dead hole!! I bet it shakes

Re: Noticeable Drivetrain Shake at Idle [Re: Dcuda69] #1542149
12/03/13 12:02 PM
12/03/13 12:02 PM
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CT
GTX MATT Offline
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I worked on a buddies 383 last year that had a dead cylinder from a burnt valve, it idled rougher than it should have but it didn't shake violently.

Is it worse in gear, even if you bring the revs up to the same as idle in park? Sounds like a busted motor or tranny mount to me.


Now I need to pin those needles, got to feel that heat
Hear my motor screamin while I'm tearin up the street
Re: Noticeable Drivetrain Shake at Idle [Re: JohnRR] #1542150
12/03/13 01:53 PM
12/03/13 01:53 PM
Joined: Dec 2010
Posts: 12,375
SoCal
MuuMuu101 Offline OP
I got lucky at Woodward!
MuuMuu101  Offline OP
I got lucky at Woodward!

Joined: Dec 2010
Posts: 12,375
SoCal
Quote:

What's the rated compression ratio ?

Edit ... mymopar.com says rated at 8.8 so it's closer to 8.0 , you should be able to run it on 87 ...





Thanks!

Re: Noticeable Drivetrain Shake at Idle [Re: GTX MATT] #1542151
12/03/13 01:55 PM
12/03/13 01:55 PM
Joined: Dec 2010
Posts: 12,375
SoCal
MuuMuu101 Offline OP
I got lucky at Woodward!
MuuMuu101  Offline OP
I got lucky at Woodward!

Joined: Dec 2010
Posts: 12,375
SoCal
Quote:

I worked on a buddies 383 last year that had a dead cylinder from a burnt valve, it idled rougher than it should have but it didn't shake violently.

Is it worse in gear, even if you bring the revs up to the same as idle in park? Sounds like a busted motor or tranny mount to me.




It's no better or worse whether it's sitting in Park in the garage or in Drive at a red light. I'm not sure if my center console is bolted down completely, but once it starts going, you can hear and see it rattle and vibrate. It also doesn't seem to happen all the time while driving (either that or I'm not noticing it).

Re: Noticeable Drivetrain Shake at Idle [Re: MuuMuu101] #1542152
12/03/13 02:12 PM
12/03/13 02:12 PM
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Grand Prairie,Texas
stumpy Offline
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Easy test is to ground a test light and poke it into each each plug wire cap, one at a time, at the distributor cap. The plug wire that doesn't change the idle is the bad cylinder. Then you can see if it's the wire, the plug or compression causing the miss.

Re: Noticeable Drivetrain Shake at Idle [Re: stumpy] #1542153
12/03/13 03:59 PM
12/03/13 03:59 PM
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dogdays Offline
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The answer is simple, you have a bad cylinder. Your mechanic told you. One man's "rock or shake" is another man's vibration.

If you remember which hole was bad, pull the spark plug wire on it and see if it makes any difference in the engine's behavior. I bet it gets slightly worse, but doesn't change a lot.

Whatever you do, don't go making a lot of changes all at once. This is a simple problem with an expensive solution. You probably need a different engine or at least a valve job on your existing heads.
If it is a valve, you can sometimes tell by pulling the coil wire and turning the engine. Listen for a hiss every other revolution. If it comes through the carb it's an intake valve. But dollars to doughnuts it's an exhaust valve and the hiss will be heard at the exhaust.

If this is the case, I'd suggest looking for a mid-80s Fifth Avenue for heads or complete 318.

Also, unless your 273 came with a factory four-barrel carb there's no reason to put in 91 octane fuel.

Keep us posted. There's more collective brainpower on this board than in most garages.

R.

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