I finally finished my winter projects, which included a new ACT HD clutch and FMIC install. My car now vibrates a LOT, especially when engine braking. It is not speed related, but seems to be RPM related. It sounds normal at idle, but if I let off the gas above 3500 it vibrates the whole car.

I had my flywheel resurfaced at Napa, so it shouldn't be out of balance. I can't find anything making contact that would cause these vibrations.

Any ideas? I have to drive 4 hours back to school a week from today.

 

are the flywheel bolts still all tight/torqued? If they backed out even the slightest it would vibrate pretty bad

 

I torqued them to spec and double checked them, I really hope I don't have to pull the tranny again.

 

sounds like drive shaft related, i had a ford truck with a bad u joint that vibrated in a similar way.

 

That would be speed related though since the driveshaft rotation directly depends on the speed of the car and not the rotation of the engine.

Maybe something is up with the clutch? Either that or the flywheel.

 

Yeah it's not dependant on speed so I ruled out the driveshaft right away. I don't know what I could've messed up with the clutch/flywheel.

 

looks like your pullin the tranny again man.. hope you have someone to help ya

 

Maybe a bad clutch disk or the flywheel got screwed up by Napa?

 

It's an ACT HD clutch from FM, so I doubt that's an issue. Resurfacing the flywheel shouldn't change the balance at all, should it? Is there any way I could have installed the flywheel off center or something?

 

Since your project only included clutch/flywheel and FMIC, i have to assume that it is the clutch/flywheel that is the problem. I replaced a clutch/ resurfaced flywheel about 6 months ago and the damn thing started rattling really badly, getting worse. It seemed to be rpm dependant as well and I was able to limp it home 3 miles. When I opened it up, several of the bolts had come loose. Now I use Loctite and torque to spec + 10 ft/lbs

 

My dad and I are planning on dropping the tranny tomorrow, we'll see what we find. I did use loctite on mine.

 

I may have found the problem! My downpipe was very close to the frame by the motor mount. I was able to pull it by hand to make it hit, and that would explain why the noise/vibration got so much louder under engine braking. We were able to secure it higher and it barely moves at all now.

I started and ran the car with no unusual noises, but don't want to drive it in our unplowed 6" of snow, especially if it's going to break down. The roads should be clear and dry tomorrow, so I'll find out if we really fixed it or not. Wish me luck, guys.

 

Your DP NEEDS to have flex in the system. I made the mistake of welding a bracket and bolting it to the transmission (like the OEM mount).

Two days on the track and I was left with a big hole where the bracket used to be.

As long as you secure it loosely and don't physically alter it's position with constant force you should be ok.

 

Stiffer motor/tranny mounts will help keep the DP from making contact as often, specially when engine braking, if that ever becomes an option for you.
All depends on how close your DP is to everything though, what did you mount it to and what did you use to do it?

 

It's still able to move on its own, but it no longer hits anything when it does so. I would've gotten the Mazdaspeed motor mounts before doing this project, but the whole college student/no job thing stopped me.

 

ok good...I just don't want others to make the same stupid mistakes I did.