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vibration at idle
https://slantsix.org/forum/viewtopic.php?t=58084		 Page 1 of 1
Author:  '67 Dart 270 [ Fri Jul 17, 2015 9:16 am ]
Post subject:  vibration at idle
My newly rebuilt slant runs great, lots of power, responsive, etc. No issues there...engine idles smoothly, when not in gear you can set a glass of water on it and it barely shows vibration in the water. No vibration while driving.

but, I have vibration when in gear at idle with the brakes engaged, like at stoplights. It's not the flex plate, I'm almost certain it's the new motor mounts/tranny mount combo. Mine is a '67 but when doing the engine swap, I changed to 73-76 type K frame, spool mounts. I used factory type mounts (not poly).

Any tips with spool mounts? I simply torqued them down after I dropped (lowered carefully) the engine in. Can they be torqued too tightly or is there any adjustment there? Do these "wear in" over time; I ask this because the vibration seems to be less than when I first test drove it (I've only put about 400 miles on the engine so far), but still its annoying enough. My old '67 mount system had no vibration at all.

Are soft poly mounts better to avoid vibration? I heard they are actually worse for vibration issues, that's why I went with stock mounts.

Thanks all, for any tips on this.

Brian
Author:  emsvitil [ Fri Jul 17, 2015 2:49 pm ]
Post subject: 
If you have power brakes, I'd say it's the vacuum booster leaking.........

That would mess up the mixture on the #6 cylinder.
Author:  '67 Dart 270 [ Fri Jul 17, 2015 5:35 pm ]
Post subject:  no power brakes...
No, I have regular old manual brakes...must be stiffer rubber in those mounts, either tranny, engine or both...

brian
Author:  wjajr [ Mon Jul 20, 2015 7:01 am ]
Post subject: 
Quote:
must be stiffer rubber in those mounts, either tranny, engine or both...
Could be mounts are transmitting harmonic vibrations causing a resonance where nodes of motion combine to make larger movement at the rpm engine is turning at idle in gear. Try moving idle rpm up or down a little and see if vibration changes.

One more thought, are all mounts, transmission & engine, formed from same material. Could be having softer transmission mount may upset frequency cancelation. Or vibration is causing something attached to engine to vibrate.

I once had a Crown Vic, which factory attached an arm with a cylindrical weight cantilevered bolted to "Y" pipe which I suspect canceled out some resonance developed in exhaust system from rotating mass of engine and or transmission.
Author:  SlantSixDan [ Mon Jul 20, 2015 10:15 am ]
Post subject: 
WJA has a good point about harmonics and such. There's a cast iron vibration-damping weight bolted to the underside of the transmission tailhousing on a variety of cars originally equipped with engine mounts like yours (though I don't know what year the tailhousing started coming drilled and tapped to accept it—one source says 1972). You might check with Pat "Torqueflite Patty" Blais.
Author:  Reed [ Mon Jul 20, 2015 10:25 am ]
Post subject: 
I have about three of those cast iron transmission damper weights I have salvaged over the years. The problem is the rubber inserts for the bolts have all melted away from transmission fluid leaks. Anybody know of a source for new rubber inserts?
Author:  Louise76 [ Tue Jul 21, 2015 10:43 pm ]
Post subject: 
Maybe not your problem, but... On 9-11-2001 we bought a /6 Scamp that had a "growl" at idle, out and in gear (A-904). Finally couldn't trust it, so changed the engine and new mounts- still growls. Changed the trans out and installed that vibration dampener- still growls. Inspected the exhaust, did some experimental anti-vibration steps- still growls. Inspected K-frame bolts, body & frame welds, anything that might vibrate and cause the growl- no help. The growling noise is throughout the body, not just something rattling. When stopped, driving, neutral and in gear at low rpm. Disappears on the highway. Never found it, so we just live with it, as it has not escalated nor decreased. :?
Author:  sixinthehead [ Wed Jul 22, 2015 3:47 am ]
Post subject: 
You might be able to narrow it down with judicious use of a stethoscope (long screwdriver) to be sure where to start.

Pay special attention to the exhaust - the new mounts may position the engine differently than before, putting extra stress on a hanger or ?

Especially since the noise has seemed to diminish somewhat, it sounds like the interference is 'self-clearancing' :lol: .
Author:  '67 Dart 270 [ Fri Jul 24, 2015 7:25 am ]
Post subject:  thanks all
Yes, it has diminished, and I did check the exhaust system to make sure it was hanging loose so to speak. I think maybe the mounts and such need to work in a bit, I've only put 500 miles on the engine so far. If it persists though, I might look into that vibration dampener idea.

brian
Author:  wjajr [ Fri Jul 24, 2015 9:16 am ]
Post subject: 
Quote:
If it persists though, I might look into that vibration dampener idea.
I think you misinterpreted my vibration dampener example. All I was trying to get across is things located away from engine can pick up a harmonic, resonate at one or several hertz in a section or part divorced from an engine, and to look at anything hung to undercarriage, or even body parts making noise.

Adapting an exhaust damper from anything but the same model and year car would be a crap shoot, and I don't think would work. After rereading your initial post I see that 1967 chassis has been outfitted with later model parts of slightly different design. I would start with the non 1967 parts as a contributor to problem. If later K Member is one that utilizes rubber mounting biscuits make sure its mounting bolts haven't bottomed out before snugging member up tightly to front sub frame.

I have a 1967 convertible and the only time it made a clunking noise as if a main bearing was knocking at low rpm when in reverse with brake on turned out to be worn out engine mounts allowing intermittent header contact with power steering gear. New mounts and some shim stock lifted engine enough to clear steering gear. Other noises have developed after wrenching on the old girl, and were easily found, and abated.
Author:  SlantSixDan [ Fri Jul 24, 2015 3:37 pm ]
Post subject:  Re: thanks all
Quote:
I think maybe the mounts and such need to work in a bit
Mounts do not "work in" ("break in", "seat in", etc).
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