Broken Motor Mounts

[donjetman]

Did the driver side on my Avalanche this weekend. I'm convinced that 99% of GMT900s on the road are out there with destroyed mounts.

It's on my list of things to do.

 

[alpha_omega]

edit: deleting doubled reply post

 

[alpha_omega]

I suspect at least one of my engine mounts has failed. I can feel it clunking from a dead stop with anything more than mild-moderate acceleration.

Also..... I'm getting a thud when 1st starting out for the day during the 2-3 shift. Even with almost no throttle the shift is harsh. I don't think the two are related, other than maybe the hard shift causing the mount to fail faster than normal.

What is the the part # for the H3 mounts, and why is the H3 mount better? (curious)

Have you checked and/or changed the other fluids (including the trans filter)? It might be the culprit if you’re having shift issues. Better to catch it now.

 

[SNES Avalanche]

Serious question. I replaced the driver mount and not the passenger mount.

Is it possible that my slightly rough idle when in drive is because with one good and one bad mount the truck is now vibrating more?

 

[iamdub]

Serious question. I replaced the driver mount and not the passenger mount.

Is it possible that my slightly rough idle when in drive is because with one good and one bad mount the truck is now vibrating more?

The cause of the vibrations aren't worse due to the mount combination. You're now feeling the vibes that were already there more since you now have a firmer mount. Replacing the passenger side might make the vibes a little more pronounced. These things commonly have what feels like an intermittent miss at idle. It's possible that the lower RPM and additional load while in gear exaggerates it. But it's also possible that you have a small problem (dirty injector(s), weak fuel supply, dirty MAF, carbonized chamber(s), etc.).

 

[SNES Avalanche]

The cause of the vibrations aren't worse due to the mount combination. You're now feeling the vibes that were already there more since you now have a firmer mount. Replacing the passenger side might make the vibes a little more pronounced. These things commonly have what feels like an intermittent miss at idle. It's possible that the lower RPM and additional load while in gear exaggerates it. But it's also possible that you have a small problem (dirty injector(s), weak fuel supply, dirty MAF, carbonized chamber(s), etc.).

...This makes a ton of sense Thank You!

Going to make a separate post on everything I've tried so far to hopefully get to the bottom of this one. The engine only had 25k miles / isn't throwing codes so it's worth the elbow grease.

 

[stapleto]

So I just returned from my mechanic after a routine oil change and he shows me I have a cracked drivers side motor mount!!!! WTF... I mean seriously GM? You would think they would install a strong enough motor mount for what people use these SUV's for. My mechanic ony works with GMC and Chevy's and he said he is noticing this often.

Has anyone else experienced this problem?

Oh and cause where it is located, not the cheapest of repairs either..

Yep, I replaced the drivers motor mount also! Why GM continues to sell unreliable parts like motor mounts which can be very dangerous in very expensive vehicle's?

 

[SNES Avalanche]

Finished the passenger mount yesterday. I've done a lot of jobs on cars and the angles on this one are comical.

Turns out my starter posts were rusted out, so it turned in to quite an adventure when it broke in my hands on reinstallation.

 

[iamdub]

Finished the passenger mount yesterday. I've done a lot of jobs on cars and the angles on this one are comical.

Turns out my starter posts were rusted out, so it turned in to quite an adventure when it broke in my hands on reinstallation.

You were fortunate to discover this now rather than the connection fail while out on the road somewhere.

You got used to the vibes at idle yet? They're pretty easy to ignore unless you do a lot of idling. Even then, just tell yourself they're a good thing cuz they mean your engine is still securely mounted and you won't be doing that job again for 200K miles or more.

 

[SNES Avalanche]

You were fortunate to discover this now rather than the connection fail while out on the road somewhere.

You got used to the vibes at idle yet? They're pretty easy to ignore unless you do a lot of idling. Even then, just tell yourself they're a good thing cuz they mean your engine is still securely mounted and you won't be doing that job again for 200K miles or more.

Haha not yet.

I’m used to our normal vibes but these ones seem to be getting a little worse as time goes on. The upside is that all the things I’ve done on the truck have definitely improved the overall “feel”.

 

[iamdub]

Haha not yet.

I’m used to our normal vibes but these ones seem to be getting a little worse as time goes on. The upside is that all the things I’ve done on the truck have definitely improved the overall “feel”.

You might actually have a problem that's progressing or it's the typical vibes and you're just more in tune since we tend to do that after every mod.

 

[SNES Avalanche]

You might actually have a problem that's progressing or it's the typical vibes and you're just more in tune since we tend to do that after every mod.

Keeping an eye out! I can say it has gotten worse since I originally noticed it when it was once every 4-5 seconds. Now we're in a pretty constant state of stumble / occasionally it feels like it's sputtering if I put it in gear before it's fully warmed up. Also, the truck seems less able to hold idle correctly as it fluctuates more.

I rechecked all of the vacuum lines last night and they're solid but it's time to give it a smoke test. Also going to take another pass at my O2 sensors / Coil packs.

Truck still isn't seeing any "misfires" when I'm monitoring via the OBD2 reader.

 

[iamdub]

Keeping an eye out! I can say it has gotten worse since I originally noticed it when it was once every 4-5 seconds. Now we're in a pretty constant state of stumble / occasionally it feels like it's sputtering if I put it in gear before it's fully warmed up. Also, the truck seems less able to hold idle correctly as it fluctuates more.

I rechecked all of the vacuum lines last night and they're solid but it's time to give it a smoke test. Also going to take another pass at my O2 sensors / Coil packs.

Truck still isn't seeing any "misfires" when I'm monitoring via the OBD2 reader.

Cleaned the MAF? Double checked the intake couplers? Air filter not clogged?

 

[SNES Avalanche]

Cleaned the MAF? Double checked the intake couplers? Air filter not clogged?

Yep all completed.

 

[iamdub]

Yep all completed.

Have access to a scanner that will at least show live data? You might wanna stay ahead of this in case it's something critical developing.

If you decide to dive in, start a thread so we can follow you and help more easily.

 

[Meccanoble]

Yep, I replaced the drivers motor mount also! Why GM continues to sell unreliable parts like motor mounts which can be very dangerous in very expensive vehicle's?

I havent checked in for a little while but my Hummer mounts are still working like a charm, no issues. Hopefully everyone is moving towards these and not another tahoe mount.

 

[donjetman]

I'm gonna install: 2 Hummer H3 mounts, tranny mount, and both front differential carrier mounts w/bushings soon. Wish me luck. The engine mounts look like a PIA.

 

[gooffeyguy]

The heat shields make them a PIA

 

[bill1013]

I'm at 115K and I just changed both of mine out. They were the hydraulic type and the right one was leaking, so I changed both. Funny thing was that after the change out the slight vibration I used to get when braking went away. Go figure.

 

[EvergreenZ71]

So glad I found this thread!

So my 2009 Tahoe 6.2L has had the initial acceleration thunk for a week or so and had an appointment for the transmission shop to take a look when it experienced a dashboard Christmas light show (service stabilitrack, service traction control, ABS light) when I accelerated onto the freeway, but no apparent loss of function. I’m pretty sure this thread diagnosed my problem so I’m ordering parts.

But that isn’t my question.

I’m thinking it may also be time on my 2010 suburban 2500. Did a search around those keywords but nothing. Anyone know if the same design flaw & fix is pertinent to the 3/4 ton SUVs?