The stock automatic FC has developed (out of the blue) a vibration. It starts at around 10MPH (it actually feels like a low frequency), and it progresively gets worse at around 40MPH.

If the car is coasting, the low frequency\vibration disapears; but as soon as there is load, the problem comes back up. Things that I've noticed is that are:

1 - If the car is under load, and I lift the gas pedal; and suddenly apply it, there is a quick\low "thump" sound that appears to be coming from the rear of the car.

2 - When setting the tranny to R or D, there is the same quick\low "thump" sound.

I lifted the car, and attempted to move the driveshaft from side to side, up and down; the driveshaft was rock solid. While under the car, I checked the diff mount, and it looks good.

Any ideas?

 

Things to look for:

- Driveshaft u-joins
- Loose front engine bolt or flywheel nut
- Broken engine mounts

The front diff mount won't cause a vibration; just a thug whenever you throttle hard and torque the rear-end up.

What was changed just prior to this symptom starting?

B

 

I have this same problem. I read somewhere it is the driveshaft U-joints that are going bad which causes vibrations to get worse during acceleration.

And OEM U-joints aren't replaceable

 

Thanks for the help!

Nothing was changed on the car, and its 100% stock (except for the now missing heat shileds). Turns out that it was the tranny mount (the cross memeber one)


I don't want to jinx myself, but I fixed the issue by replacing the tranny cross memeber mount, and both rubber blocks mounts at the tranny.

BTW - Mazdatrix sells a driveshaft with replaceable u-joints:
http://www.mazdatrix.com/g9.htm

 

What exactly was wrong with the tranny cross member?

Please tell me so I can check if I have the same issue.

 

The bushing was crack\borken on one of its side. Also, Mazdatrix claims the following:

The transmission is actually held up and in place by the "Y" blocks listed below. The crossmember is more obviously bad because it's bushing actually breaks, while the "Y" blocks rarely break, they just sag, causing the bushing in the crossmember to break out. If you replace the crossmember, but not the blocks, your new crossmember will soon fail. The bushing in the center of the crossmember is not designed to carry any weight.

So if yours is broken, consider replacing the Y blocks too; I did, just in case.

 

i have the same problem

 

Me too except it starts at 40 mph and get really bad @ 60.. I've replaced engine and trans. Would the front diff mount be the issue??

 

No. Check the driveshaft u-joints first. That would be my guess. Then move from there to other mounts. As mentioned earlier in the thread, a broken front diff mount doesn't really cause a vibration, just a thud when the car starts moving.

 

I've had problems with this and it was my driveshaft u-joints. I had to take the driveshaft out and check it to notice my front u-joint was sticking.

 

Well I've run out of mounts to replace only thing left is drive shaft

 

^ people have told you to check u-joints first...

 

the diff mount can put additional stress on the u-joints. sounds to me like the front diff mount went on vacation and the u-joints took a later flight.

if the mount was at fault he did at least cure the root of the issue first so cut him a break. even if it was just luck.

 

Also check that the parts of your rear subframe are all tight.. also some of the adjustment bars back there get worn and loose.. they are fixed pieces.. so have fun with that.. could always go grannies 8.8 setup and replace the irs so you'd never have problems again.. but then you have to do some thinking with that one.. Either way good luck.

 

Oh yes I do understand its that the drive shaft can only be the thing left that's causing it because originally like just a few days ago I went and bought all the mounts and trans mounts.. Installed it. Even though it got a bit better it still vibrates. But thanks I ended up ordering one off of Mazdatrix. Oh well at least i'll have semi newish drive train lol

 

+1.

B

 

is the vibration present when revving the engine in park or neutral ? a torque converter going bad can make vibrations