How can I tell which motor mount is bad?

[LeakySeals]

Hi,
2000 corolla CE 150k.

After a process of elimination with the engine (plugs, coils, vacuum lines, TB/iac/maf cleaning, etc) it would appear that the sudden rough idle at a stoplight may actually be vibration from a failed motor or transmission mount.

Questions:

Can a motor mount suddenly fail?

if so...

How can I tell which mount has failed? Symptoms are reverse and neutral perfect, drive real bad, park, less bad.

 

[JHZR2]

Good question - would be helpful to know how to tell for engines in both orientations.

 

[Radman]

Yes, motor mounts can fail. Many are silicone filled and simply wear out. In college my girlfriend had a Ford Tempo that used to eat the upper mounts. The Nissan Sentra that I have is known for the Tranny mount failing.

Rough Idle isn't the same as excessive mechanical play. If you can't figure it out get a free inspection.

 

[Mark72]

I own a 1995 Lumina and I keep this car meticulously maintained. For the last year my car had rough idle when I would come to a stop and then smooth right out. It finally got worse and that freaking dash was rattling apart proactively. I took it in, they replaced the lower motor mount. Mine is a hydraulic filled mount…engine runs smooth as glass now. Yep, I bet you money that’s what it is…it’s not the engine running rough, it’s the vibration resonating through the framework. Let me know

 

[Chris142]

Powerbrake it and see where the engine moves the most.broken mount will be obvious.

 

[LeakySeals]

I revved the engine with foot on brake in drive. The engine twists toward the crash-wall, away from radiator. Would that indicate the problem is the rear mounts that get pressure on them? Nothing visibly wrong, can't hear anything, just a vibration that rattles the interior horribly

 

[Mark72]

Originally Posted By: LeakySeals
I revved the engine with foot on brake in drive. The engine twists toward the crash-wall, away from radiator. Would that indicate the problem is the rear mounts that get pressure on them? Nothing visibly wrong, can't hear anything, just a vibration that rattles the interior horribly


I own a 1995 Lumina and I keep this car meticulously maintained. For the last year my car had rough idle when I would come to a stop and then smooth right out. It finally got worse and that freaking dash was rattling apart proactively. I took it in, they replaced the lower motor mount. Mine is a hydraulic filled mount…engine runs smooth as glass now. Yep, I bet you money that’s what it is…it’s not the engine running rough, it’s the vibration resonating through the framework. Let me know.

 

[Mark72]

read my above post...my car rattled like an old dump truck until I replaced my motor mount.

 

[Chris142]

Originally Posted By: LeakySeals
I revved the engine with foot on brake in drive. The engine twists toward the crash-wall, away from radiator. Would that indicate the problem is the rear mounts that get pressure on them? Nothing visibly wrong, can't hear anything, just a vibration that rattles the interior horribly
Now do it in reverse and see what it does.

 

[LeakySeals]

Originally Posted By: Mark72
read my above post...my car rattled like an old dump truck until I replaced my motor mount.


Yes I saw that, thank you. Looking at the parts, a 2000 corolla CE auto/4 spd o/d has 4 motor mounts all different and a transmission mount. I'm trying to figure out which mount it is, replace it myself. Symptoms are reverse and neutral perfect, drive real bad, park, less bad.

 

[Mark72]

Originally Posted By: LeakySeals
Originally Posted By: Mark72
read my above post...my car rattled like an old dump truck until I replaced my motor mount.


Yes I saw that, thank you. Looking at the parts, a 2000 corolla CE auto/4 spd o/d has 4 motor mounts all different and a transmission mount. I'm trying to figure out which mount it is, replace it myself. Symptoms are reverse and neutral perfect, drive real bad, park, less bad.


I'm sure my GM engine is much different than your mounts are set up. The only mount that was bad was the one right under the engine that is filled with hydraulic fluid

 

[LeakySeals]

Question to anyone who has replaced a motor mount. Did your oil pan gasket leak after replacing the mount?

Procedure calls for engine support via hydraulic jack and a load dissipating board that the oil pan. My concern is compression of the oil pan gasket, causing a leak.

 

[LeakySeals]

Another question to those that have replaced a mount: Should I replace the mount(s) that get downward force as the engine revs in drive? Drive is where the bad vibration occurs

 

[Smoky14]

Originally Posted By: LeakySeals
Question to anyone who has replaced a motor mount. Did your oil pan gasket leak after replacing the mount?

Procedure calls for engine support via hydraulic jack and a load dissipating board that the oil pan. My concern is compression of the oil pan gasket, causing a leak.

In a word NO. Not much chance of that being the cause. Replacement of most timing belts require the engine to be held or slightly lifted by jacking the motor and I've never had one leak.
Smoky