I was seeing if anyone could help me figure out what is causing vibration/shaking coming from the rear. I will explain when it started happening to after replacing the rear brakes. I have a '13 g37x sedan 7AT. Also, I am 100% sure it is not a tire balancing issue and not an issue with proper/even torque on the lug nuts.

About a week ago, my car started shaking in the rear, the sound and vibration/shaking feels like hitting those ripples on the side of the highway, plus with the feel of being slowed down. I noticed it would slightly go away when I deaccelerate, not applying the brakes. Before I took my exit, the vibration did stop, but happened again after exiting and going 35mph. When I got home, I went to check the rear and when looking inside of the rear right rim to check the brakes, I smelt metal burning, like burning clutch.

On the next day, I drove and there was no shaking/vibration and no burning smell. However, during the next 2 days, I noticed that when I parked and set my parking brake, the issue came back and the smell came back. When I didn't use my parking brake at all on the 3rd day, there was no shaking/vibration, burning. To sum it up, whenever I used my parking brake, those issues would appear when driving, but go away after driving about 5-10 miles either on the highway or city.

On the 4th day, I decided to replace the rear brake pads and rotors since they did need to be replaced, also thought a warped rotor or worn pads would cause the problems I am having. When I inspected the brake pads, there was even wear on all the rear pads, which for me, rules out a sticking caliper. But, after I installed everything and drove to do the break in for the new pads, the vibration/shaking and burning smell came back, NOT the burning smell of new rotors/pads. On the 5th day, I didn't use my parking brake at all and the issues never appeared the whole day. Again, it only happens when I set the parking brake. Also, the smell and vibration/shaking is only coming from the rear right.

Right now, my only guess is having to do with the parking brake and/or the shoes possibly needs adjustment via star nut behind the rotor, which I did not think I had to do after I replaced the rear rotors cause the issues happened before I replaced the rear rotors or did anything to the rear brakes. I will be adjusting the parking brake after work, but I wanted to see if anyone had any other explanation why when I use my parking brake, the issues appear compared to when I do not use the parking brake. Could the parking brake shoes be rubbing or hitting the rotor while driving and loosen after a while? I did noticed today that when I set my parking break, a clicking noise coming from the rear can be heard and the car would roll back unless I push the parking brake pedal down all the way to the floor, sometimes it wont catch at all and the car would roll back with the sound of bad pads, but then stop (done in neutral). But again, this happened even before I replaced the rotors.

 

I've had similar experiences with vibration at highway speeds, but no burning smell. My rear rain guard was unsecured so I blamed that. Would be very interested if its its related to the parking brake. Mine seems to operate like yours, and needs to be pushed to the floor to work properly.

 

I should've mentioned that the problem with using the parking brake and feeling vibration for a mile or 2 started after I ran over a raccoon. He went under my passenger side tire and through the rear. So, I'm assuming his body pulled on the parking brake cable cause I noticed it was hanging a bit, but need to see pics/do research if it is supposed to be where it is right now or bracketed onto something.

Anyways, I couldn't work on problem cause my dumbass forgot to take out the lug nut key when I went to test drive after replacing the rear brakes. But last Friday, I noticed that my parking brake pedal became stiffer when I left work and it engaged with the pedal halfway in, but again, the problem still exists, only after using the parking brake. I am pretty sure I need to adjust the tension via the star nut where that whole is on the rear rotors. I'll be fixing it this week and will give an update.

 

Any update on this?

This problem came back a bit differently, its not the rear splashguard this time.
I thought it was due to a dragging rear caliper, so I did the BBK upgrade (needed all 4 brakes and rotors anyway). Got new PPS tires, mounted and road force balanced and an alignment.
Now braking is completely smooth, it drives arrow straight, but at 75MPH+ theres a shake (seemingly from the rear passenger side) that vibrates through to the mirror.
Regardless of RPM the shake is the same, it gives off a quiet low humming sound. No steering drift, no vibration in the wheel.

When I did the brakes I inspected the whole steering system. No play in anything, boots are not torn, no leaking shocks, everything is torqued to spec.
I'll climb under there Saturday and check the driveshaft linkage, rear diff bushings, trans bushings and engine mounts. Iirc theres a TSB on pre-2012s to free up the driveshaft linkage to correct this problem. Shouldn't affect mine, but will consider this if everything checks out.

 

Definitely a rear drivetrain or wheel/tire issue. If you're satisfied with the wheel balance, look at rear bearing first.

 

Have you check subframe and trans bushings

 

It's the brakes only if it vibrates when braking.

Otherwise, look closely at your tires. It may have some issue with one or both. Get it road-forced balanced and have the tire shop thoroughly inspect it. One of my tires had a bulge in it that wasn't detected until the tire was off the wheel!

 

Sorry guys that I havent replied, but did find the problem after finding my lug nut key. I dont recall if I mentioned it in my org post, but the issue I had started after a raccoon decided to run across the highway and ended up being ran over from the front right. After knowing the raccoon hit directly on the right side and under the tire, he did flew under the car, coming out from the right rear. The strangest thing is that there was no blood, body parts or even fur, but there was scratch marks under the right corner of my front bumper(seems he tried to hang on but the tire caught him. I will explain further about the incident and its relation to the issue I had.

So, I did replace my rear brake pads and rotors the evening I ran over the raccoon, not sure if i correctly mentioned that in my org post. The shaking occurred with no use of the brakes, not the tires at all(were only a few weeks old), and was not a wheel bearing, a drivetrain, bushings issue. It was actually the parking brake pads.

Going back to the raccoon incident, i think his body may have put enough force to somehow mess with the adjustment, like being caught up on the cable. I think I did ask in my post if the cable is supposed be be slightly hanging or bracketed to something, like the rear subframe since I did hear metal clinging towards the back when the raccoon incident happened. When I did my rear pads and rotors, I failed to notice why it was easy for me to remove and reinstall the right rotor, knowing that you have to loosen the parking brake up a little and/or adjust the "star nut" which is located through the hole on the center of the rotor.

After all that, the problem was indeed the right rear parking brake pads floating inside the rotor at certain speeds, which caused the shaking and the smell of burning clutch. This gave me the idea that the cable was most likely tug by the raccoon with enough force for it to mess with the adjustment on just that side. Since I couldnt figure it out for a couple weeks and driving with those pads warping from the friction, I did replaced the parking brake pads and rotor, the shaking is gone, and my parking brake pedal feels like it should.

I did read about similar issues, with other cars brands (especially a lot of bmw and Audi owners). Most of the issues I read on their forums were caused when some didn't know about the rear rotor only coming out by loosening the parking brake (models with that type of parking brake configuration) , they end up banging the hell out of the rotor to come out not knowing they are also messing up the placement of the parking brake pads, especially when reinstalling the rotor by using "gentle" taps on it and torquing down their lugs so that would push in to line up the rotor.

Thanks for the replies and suggestions, trust me, I thought it was a stuck caliper or a wheel bearing going bad that almost made me upset especially the G only being 3 years old and bought it when it was new. My 99 P11 never had issues like this, so I was a little cranky about a newer car having bearing or brake problems without an unknown source.