Vibration at Idle after Motor Mount swap

Mathoran

Original poster
Member
May 3, 2012
54
So I was getting a vibration at idle when in gear sometimes, usually when the engine was cold. After reading a bunch of threads I decided to change the motor mounts. I bought them from Gmpartsdirect so unless they are counterfeit I assume they are GM ones. The old mounts have 95k miles on them and the passenger one was compressed a good bit.

I put them on and now the vibration is worse and is always present even in neutral/park(not as bad as in gear). Its worse in drive than in reverse. It feels like what people describe happens when they put on aftermarket motor mounts. Its a steady vibration that i can mostly feel on the floor. I noticed the top of the motor mounts have some minor adjustability, but I tried them in every position and same vibration. I even loosened the exhaust and tranny mount to make sure they weren't under stress.

If I leave the top nuts of the mounts loose i dont get the vibration (if i recall correctly). Removing the belt = no change in the vibration. No codes at all. All I can think of to try is buying a new set of mounts at the dealer and trying them out. If its not the mounts then my only other thought would be something with the tranny like flexplate/TC out of balance. I have also been trying to track down a high speed vibration issue but I don't know if it could be related. At 75-80 mph theres a little bit of vibration that I can mostly see because the objects in the rear view mirror become fuzzy while i can see them fine in the side mirrors. And yes the rear view mirror is tight.

2005 GMC Envoy with 95k miles. Nothing has ever been done to the tranny. I'm doing a filter/pan drain soon. Car runs great otherwise.

Any ideas?

Thanks
 

gmcman

Member
Dec 12, 2011
4,656
You stated the vibration was at idle when cold, what RPM was the vibration at? Generally the non OEM mounts have trouble damping vibrations at the 600 RPM idle which is 10Hz. If you are getting vibrations when cold and the RPM's are near 1K then there is other issues.

Generally bad mounts will be smooth at 700 RPM or above but right at or near 600 is where the GM mounts shine.

Does the vibration go away in Neutral or Park, or just in Drive or Reverse?
 

Mathoran

Original poster
Member
May 3, 2012
54
KNBlazer said:
clean throttle body,
change spark plugs,
check cpas...
Throttle Body cleaned the day after I put the mounts on.
Spark plugs changed 20k miles ago
CPAS untouched but doesnt have oil in the plug if that matters.

The Vibration is there at stock idle 600 rpm. It does not go away when in neutral or park, but it less noticeable. I have not tried power braking it to see if it goes away at higher RPM. will try tomorrow. While driving though it goes away so I think its just at idle.
 

KNBlazer

Member
Feb 8, 2012
811
I have a rough idle feeling that changed from all the time to now only in drive at a stop after replacing my CPAS with a GM replacement... the leftover vibration, I take are bad mounts...

on the spark plugs, you go with AcDelco?
 

IllogicTC

Member
Dec 30, 2013
3,452
Are you certain the mounts were installed correctly and to the proper torque values as appropriate?

I and a few others have made purchases from GMPD before and it's always been a direct replacement, no Dorman or other garbage. I understand that it's actually a side business of a dealership, and the prices are offered low because a.) they can get parts at less than MSRP in the first place and b.) they use only standard shipping and use a few other tricks (mine came in a Suave box rather than a fancy USPS flat rate or something) to make some money off the sale.
 

Mathoran

Original poster
Member
May 3, 2012
54
yes I used the correct ac/delco spark plugs. I've considered the CPAS. might pick one up this weekend but Its never thrown a code and most threads ive read it didnt solve their problem unless it was actually full of oil or throwing a code.

I'm pretty sure the mounts were installed correctly. I torqued them to spec. not really anything else that can go wrong. the bottom pin is alligned etc.

The mounts seem to be GM. I didnt pay a ton of attention to the packaging but they were in clear plastic bags and the GM part number is in raised lettering on the rubber part. Look just like original.
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
When I had bad mounts from years of banging the engine on them when I hit the frame on rocks, I retuned my idle using EFILive from 600 to 725 for a few weeks until I could get them changed.

When it's the rotational resonance that's clearly related to the mass of the driveline (the reason it's worse in DRIVE than NEUTRAL), you should be able to see it the most on the intake manifold. On mine, the manifold oscillated (at 10 Hz) almost 3/8". Enough that if you touched a screwdriver to it, you could hear the 10 Hz very clearly.
 

KNBlazer

Member
Feb 8, 2012
811
Only thing I can think of is determining which side is the culprit, and checking the bracket for damage and or lose bolts.... Not sure if a transmission mount would cause this as well....
 

Mathoran

Original poster
Member
May 3, 2012
54
I'll take another close look at everything again this weekend and I'm also gonna go ahead and change the transmission mount just in case.

I sat in it again today and its hard to describe. Vibration might not have been the best word for it. The car isnt shaking or anything. It's mostly like a drone that I can feel in my ears more than anything. The motor doesnt really move much at all. Once I drop it into gear the sound/drone builds up for a second to its max then just stays constant.

Thanks for the help I'll update again this weekend if I find anything.
 

BRomanJr

Member
Dec 9, 2011
371
Mathoran said:
I'll take another close look at everything again this weekend and I'm also gonna go ahead and change the transmission mount just in case.

I sat in it again today and its hard to describe. Vibration might not have been the best word for it. The car isnt shaking or anything. It's mostly like a drone that I can feel in my ears more than anything. The motor doesnt really move much at all. Once I drop it into gear the sound/drone builds up for a second to its max then just stays constant.

Thanks for the help I'll update again this weekend if I find anything.
You could also eliminate accessory drive problems by removing the Serpentine belt and run it for a couple minutes, see if anything changes.

If the "vibration" is gone, check all of the accesories for rough or noisy bearings. Could even be the fan clutch. Try this to narrow it down.

Also check Power steering fluid, dark? low?.

Welcome and Good Luck.
 

Mathoran

Original poster
Member
May 3, 2012
54
BRomanJr said:
You could also eliminate accessory drive problems by removing the Serpentine belt and run it for a couple minutes, see if anything changes.

If the "vibration" is gone, check all of the accesories for rough or noisy bearings. Could even be the fan clutch. Try this to narrow it down.

Also check Power steering fluid, dark? low?.

Welcome and Good Luck.

I mentioned in the original post that I ran it without the belt and no change so its not that. I actually had to replace my power steering cooler last week cause it sprang a leak. Fluid is topped off.
 

BRomanJr

Member
Dec 9, 2011
371
Mathoran said:
I mentioned in the original post that I ran it without the belt and no change so its not that. I actually had to replace my power steering cooler last week cause it sprang a leak. Fluid is topped off.
Missed that.
 

Mathoran

Original poster
Member
May 3, 2012
54
Just a minor update. I did some driving and once the car drives for a while and is warmed up it goes away completely. I replaced the tranny mount today and it seemed to be gone, but the truck wasn't stone cold either. Need to do some more testing to be sure.

When I put the truck in gear with the ebrake on and looked underneath the exhaust was vibrating a lot. After the tranny mount it seems to be less but ill keep an eye on that too. I followed the whole exhaust and its not close to anything'. Hopefully something with the tranny mount was bad and/or binding up transmitting the vibration from the exhaust. truck has always had an intermittent rattle from underneath when in gear and at low rpm which got worse with the new mounts. Cat doesn't make noise when I hit it.
 

Mathoran

Original poster
Member
May 3, 2012
54
Wanted to update this. What I thought was a vibration turns out was just the exhaust drone/resonance at idle. My original muffler was just replaced because something was loose inside making the rattling noise at idle. Put in a Walker quiet flow ss muffler and the rattle is gone, but now I notice the drone/resonance a little more. Everyone I have sit in the car to show them the resonance looks at me like I'm nuts so for now I'll just let it be. If the a/c is on 2 or higher or the radio is on I can't hear it at all. Thinking of doing a pcmofnc tune soon and maybe raising the idle some as the resonance is worst at lower rpm.

As for my high speed vibration issue I just had my ujoints replaced with spicers and my driveshaft balanced and the vibration is gone. The rear joint was sticking in a certain spot and the driveshaft was a little out of balance.
 

Sparky

Member
Dec 4, 2011
12,927
That's partially why I put an OEM muffler on mine when the original was shot. I had heard some reports of some resonance and I didn't like it.
 

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