Motor mount failure?

gmc
yukon

#1

My truck has the 6.2 liter engine. My mechanic tells me that one of the motor mounts is starting to fail. Is there a way I can confirm this? There is a Very slight clunk when I move the vehicle from a dead stop. Is this a clue???

I really don’t know.


#2

Open the hood.

Start the engine.

Set the parking brake.

Firmly step on the brake pedal with your left foot.

While someone watches the engine standing at the side of the vehicle, place the transmission in drive, slightly step on the accelerator and release it.

If the motor mount is failing, the engine will twist too far.

Now do the same thing in reverse.

Tester


#3

If you don’t trust the mechanic to tell you the truth or you think they are incompetent, why are you still using them?

@Tester is right about how you tell a failing mount unless it is a fluid filled mount which some of the later versions of these trucks have. Those show by leaking coolant and greater vibration although they don’t always let the engine move too far.

Either way, I’d suggest you need to find a trustworthy mechanic.


#4

Yes, second opinion.


#5

It could definitely be the motor or transmission mount. If you had access to the same make/model and could do a side by side comparison of the experiment above, if the motor mount was the problem you’d probably be able to notice the difference in the amount of engine twisting motion. But without something to compare against, and no experience doing this, you might not be able to tell yourself. Mechanics will often put the truck on a lift and use pry bars to see how much the mounts yield to their prying force, that’s another way to test them. If you shop did that, and they have plenty of experience, if they tell you the mount is the problem it probably is.

fyi Other things can cause clunks when taking off from a start. One very common reason is a drive shaft u-joint has failed. Or if your drive shaft is a two-part version with splines, if the splines aren’t properly lubed it can make a clunk when starting and often when stopping (in gear). Testing for failed u-joints is pretty easy, and lubing the splines is easy to do also. So you might ask your shop to try that first.