Failed motor and/ or transmission mounts that showed no external signs of their failure

[GON]

18 months ago I rebuilt a 2005 Lexus GX470 that was in a front end collision that deployed the driver's airbag. I have driven the GX470 for about a year with zero issues, except if coming to a abrupt stop, a substantial thud goes through the vehicle, and the engine stalls, but usually will not die. About one second later, everything goes back to normal.

Initial research suggested the issue may be driveshaft related, a lubrication issue. I discounted the driveshaft, as that didn't explain the engine stall. Someone posted that a motor mount/ trans mount could cause this issue, and the reason for the stall was a loss of vacuum if the engine moved. A visual inspection of the mounts showed no issue, and "revving" the engine with the brake applied and vehicle in drive showed little movement of the engine.

I replaced the two engine and one transmission mount. With the old mounts out of the vehicle, I inspected the mounts and found nothing I could identified as broke, tired, or weakened in the mounts. I installed the new mounts, and now after abruptly braking, the car has zero issues that were happening with the original mounts.

I am surprised the mount(s) are bad, yet a visual inspection both in the vehicle and out of the vehicle show no issues.

 

[Graham Piccinini]

Good to know, thanks for sharing!
My sister's 2009 Hyundai Genesis 4.6L developed a slight vibration. Very faint, but always there. I told her right away it's the mounts.
She took it to a trusted and well respected shop and they said mounts are good.
Since then we replaced some sensors, EVAP components, oxygen sensors, all with OEM parts. Improvement was there, but there was no complete elimination of the vibrations.
I was busy, so she reached out to another trusted mechanic. He agreed that mounts are good, but his expensive scanner didn't reveal any issues otherwise. He replaced the transmission mounts per request, and suddenly vibration is cut by 60%. I bet the remaining 40% is in the motor mounts. Unfortunately those require dropping the subframe with the engine, and then lifting the subframe off of it, or somehow dropping the engine even lower than already disconnected subframe... Strange design on that V8.
We'll replace them eventually, because my sister still loves that car all these years later, despite some issues along the way. But this was/is also a case of very good looking mounts, that are actually bad.

 

[Jdeere562]

Strange stuff happens. I once bought a brand new 1990 Oldsmobile Cutlass. Drove it about 200 miles, before taking it on vacation in Branson, MO. Mainly a test run before the long trip. All seemed fine.

Got about to our resort and we rolled down the windows. Heard a clicking sound from the RH front wheel. Thought the vacation was ruined and would need to find a dealer there to repair it under warranty.

Got to the resort, jacked it up to check the bearings and brakes. All seemed normal, so I put it back together and went for a test drive. Noise was gone. Put the hub cap back on and the noise was back. Visual inspection looked fine. Finished the vacation and took it back home to the dealer. Said I needed a new hub cap under warranty. They looked at me strange and thought I was crazy. Had their tech check it out. Grabbed a hub cap off another car and the clicking was gone. Never heard of that before.

 

[The Critic]

If the old mounts are placed next to the new ones, you may find them to be collapsed.

 

[CKN]

Strange stuff happens. I once bought a brand new 1990 Oldsmobile Cutlass. Drove it about 200 miles, before taking it on vacation in Branson, MO. Mainly a test run before the long trip. All seemed fine.

Got about to our resort and we rolled down the windows. Heard a clicking sound from the RH front wheel. Thought the vacation was ruined and would need to find a dealer there to repair it under warranty.

Got to the resort, jacked it up to check the bearings and brakes. All seemed normal, so I put it back together and went for a test drive. Noise was gone. Put the hub cap back on and the noise was back. Visual inspection looked fine. Finished the vacation and took it back home to the dealer. Said I needed a new hub cap under warranty. They looked at me strange and thought I was crazy. Had their tech check it out. Grabbed a hub cap off another car and the clicking was gone. Never heard of that before.

The vehicle in question was involved in a front end collision. It would not be unusual for things ( motor mounts) to be tweaked even a little- even though such damage could be seed by the human eye. If you followed the original thread- it was moderate damage-IMHO. It was in the junkyard and declared a total loss.

 

[SC Maintenance]

I have thought about replacing my xterra mounts due to age and miles given lots of people seem to have issues with them. Yet I have no sign of any problem? Your post makes me even more confused.

 

[SwampSurvivor]

The hydraulic engine mount in my Focus was bad. I didn't really see anything wrong with it but the vibrations were awful.

 

[clinebarger]

Loss of vacuum?

 

[GON]

Loss of vacuum?

This is the thread that suggested a vacuum induced issue caused by failed motor mounts.

Engine try to stall when sudden Brake applied and accelerated. - ClubLexus - Lexus Forum Discussion

GX - 1st Gen (2004-2009) - Engine try to stall when sudden Brake applied and accelerated. - 2009 Lexus GX470 - 1,05000 miles - Engine try to stall when sudden Braking applied, and as soon as the engine is accelerated I feel a Big Knock, it doesn't happen on a normal Braking situation, only on...

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