I have a different MY but the rear subframe is similar. Not sure what you mean by front bushings, there's a carrier arm under the diff and 2 bushings near the top. Inserts in the top bushing make some difference but not much. Carrier arm bushings or inserts make a huge difference. Also subframe bushings/inserts nearly remove the clunking on 1-2.

Whatever slop is left after that is from the front end. Had a friend ride along in front and rear seat with stethoscope to floor while I tried to make the jerking more noticeable. It sounded like most of the noise was up front so maybe engine mounts are the answer. You can also get aluminium driveshaft carrier bushings, not sure if they actually help anything.

 

Harder bushings anywhere in the driveline, suspension, or engine mounting will return more feedback to the user. I personally can't see how this would make a major impact.

Pitch stop mount, motor and transmission mounts. That'll make a difference. You'll eliminate most of the movement and the minor amount the diff can move will probably be not noticable. It's been ages since I was under mine but I don't recall much if any movement there compared to everything forward.

 

Thanks for the replies fellas.

@silver_scooby I was using the FSM terminology. The brace/mount we're talking about sits in front of the two that go on top.

Anyway, good to hear changing the carrier mount bushings help. I assume you did yours? Did you press out OEM or replace the entire mount with aftermarket? Gotta love and admire you and your buddies using a stethoscope to track noise haha. If only I can convince a friend to sit inside my engine bay so I can pinpoint the source of some false knock

Yes I'd say engine mounts or trans mount maybe. The latter is pretty flabby from the factory, and I heard the engine mounts on 02-07 WRX/STi and 08+ STi tear in half horizontally and split. Track guys even split Group N's like that. Saw the driveshaft bearings, and agree, don't see how that'd help anything. Also heard stock ones can be a PITA to remove.

@XJman True, the trifecta definitely needs to be on equal footing, so to speak. Don't want it to be a buzzy noise fest since I daily mine, so plan is to go Group N all around. Just dreading the engine mounts, but some recent reading indicates it's not too bad if using the right tools.

You can see in this video the amount of movement in that area. I can see how stiffer bushings there would help:

 

If not a friend, maybe a niece/nephew?

I didn't replace the bushings, just whiteline inserts on the carrier arm. For the top bushings on diff, MY21 has some bracing welded to the subframe so inserts don't work out of the box, had to cut and use only the top half of inserts and washers. If inserts don't work your arm bushings might be shot, mine were actually pretty stiff and the only problem was the voids.

Trans mount is cheap, easy and makes a small difference, although I didn't change the subframe bushings so maybe that's the issue. Pitch stop again makes a difference but I don't like the idea of putting the stiffest mount on the firewall so I put a group n there. Given your car's age, buy insulators for the pipes before you remove your intercooler, those things will probably tear.

The engine mounts look like a bitch to replace based on videos and I personally wouldn't even try them without a lift. Let us know how the car feels if u replace the engine mounts. I want to change those but group N doesn't work for FA20, have to get aftermaket urethane mounts which might be too much for a daily.

 

Haha he's just over a year old so perfect size

Wait is the carrier insert the one that goes only on the driver side bushing with the voids? Because the bushings are different, and the passenger side is solid.

Agree I didn't like the idea of a stiff ass pitch mount attached to the already sketchy firewalls on these cars. I put a Group N one too which I forgot to mention, although based on my squeeze test it felt exactly the same as the stock piece. According to some reading I did apparently they're the same part. So who knows until I actually measure the durometer, which I may look into doing.

What did you mean by insulators for the pipes? Maybe specific to 15+. Are you referring to the TMIC to TB Hose? Already replaced that with a Perrin. Stock was in terrible shape and definitely leaking.

They do make Group N Engine Mounts for 15+ WRX! From my research they use the same mount as the BRZ, so the STi versions for them (ST41022AS000 and ST41022AS010) will work. FastWRX seems to think so too.

 

Perfect age too, 6 month old niece likes boxer and rotary engine noises so I'm going to flood her play area with cars.

Yes carrier insert is only on one side and that made the biggest improvement for me. Bushing rubber felt stiffer than group n trans mount, just needed to fill the holes.

Manual calls them insulators, basically two little pieces of gasket material tube. They go between pipes and seal the inlet & outlet of intercooler.

Thanks for the part numbers on group n, this is good news. Now i just have to work up the courage to tackle that job.

 

That's awesome. There's something about the UELH on Subarus that kids like. My buddy's kid says he "likes the way it makes him feel". My nephew instantly knocks out in my car. Definitely going to be Subros

Wow surprised an insert made that big of a difference. And we're talking about the rocking back and forth at low speeds right?

Oh ok, thanks for the reference. Older cars use a weirder version on both ends of the factory hose on the outlet that are bound to leak, and they do, and an o-ring type gasket on the turbo.

Yea no prob. Looked into using them on mine since I like the circular design like my stock ones but that stand off/spacer on the bracket will cause issues. It seems integrated so can't be easily removed. Anyway, I say go for it man! The more videos I've watched the easier it seems. Just as long as you have the right tools, mainly for those rear bolts.

 

Inserts were surprisingly effective. Rocking goes away above 5mph, below that it reduces but doesn't go away. Subframe bushing inserts are pretty effective as well while you are down there. Apart from voids, there are gaps on stock bushings that allow the subframe to move up & down. Yup I think I will go for it now that group n is an option, by tools I assume you mean 6 point sockets & u-joints?

 

At least for my bugeye, the rear diff bushings were the most impactful modification I had installed. It completely transforms the car.

 

This is interesting to me.

There would be so much more slop moving forward in the drivetrain that it wouldn't make sense. Was there something that I missed when under there that would make the movement in the diff housing that impactful?

 

Thank you.

 

Good to know, I'll get some flex heads before trying this. How do you torque the bolts if sockets won't fit?

Lol, had a few too many during install did we?
The passenger side trim piece above radiator will hold beers. You can also hang a cupholder with u-bracket off the large bolt for master cylinder brace.

The carrier arm doesn't come off directly. You have to remove two nuts on the bottom and a u-bolt type hanger along with the bolt that goes thru bushing. Also something's weird about the diff. You would expect the top bushings to hold the diff in place but mine dropped down when the carrier arm was removed and had to be supported. Maybe the top bushings go into a bracket that just braces against the diff?

 

You don't lol. You torque the other one and try to replicate the best you can by feel. My buddy gets surprisingly close, and he hates me torquing everything to spec

You know funny thing is I don't drink, which makes it that much weirder! I seriously can't remember. No way I'd throw out extra bushings. Maybe they were missing? Will hopefully get under there tomorrow and check.

Yes I'm confident on the carrier and how it mounts. The top two definitely go in the diff but at the very back end of it, so I can see how it'd still droop down.

 

Yay yay, I hate tightening by feel. I always end up worrying about the slightest noise for weeks after. I'll see if I can borrow an open end torque wrench. Maybe with a flex head attachment it will fit.

The insert is too big to throw out by mistake. If the picture in your post is recent, it's probably not installed. The flat disc on insert has larger diameter than bushing.

 

Yea I'd want to torque it too. I've gotten creative with a crows foot for the knock sensor. Not sure that'll work for this though.

That's not my car, just a pic I pulled off Google for reference. Yea definitely not by mistake. I was thinking intentionally but, why? Thankfully I can confirm visually. Maybe don't even need ramps. Stick my phone under there with video recording.

 

Phone's enuf. In the stock pic u can c the bushing on left side. If insert is installed u will see the flat part extend well past that, almost covering the entire flat aluminum area around bushing.

This is a long shot but if you threw them out intentionally, it could have been fitment issues. The bushing inserts are too thick and you have to force the arm back in or force the bracket to open very slightly to get the arm in. Another issue is that stock bushings are not perfectly formed. There are random thin strands of rubber inside the voids that prevent the inserts going in. You have to clean up the voids with a blade or key before the inserts will go in.

 

Sooo....yea

Don't do drugs kids. They come back to haunt you

 

Lol guess the inserts were installed and didn't help you enough then. Let us know if anything else makes a big difference.

 

Lol yea idk how much more replacing the bushings or the whole mount will improve things. I think I have to focus on engine and trans mounts next.

 

I see, and I take it you didn't do the install?

 

Me and my buddy did. The kit comes with bushings for 3 locations; the two top mounts and then this one. For the life of me I couldn't remember putting it in but apparently we did lol.

 

Ha! That's pretty funny.

 

Sorry about bumping an old thread but I have an update, at least for 15+. The diff & cross-member inserts have a break in period. They eliminated rear end clunk initially but ~2months/4k miles later the clunk is back, it has just shifted from 1-2 to the 3-4 upshift for some reason. Still an improvement over stock bushings.

 

No worries, this info may help someone in the future. This is a metal on metal kind of audible clunk, or more of a feel?

Maybe the inserts soften the stock rubber bushings even further by effectively putting more stress or pressure on them? Have to admit, initially the difference was noticeable, but later less so. Or maybe I just got used to it.

 

i hope it's not driveshaft lol. Top bushing is my guess. The lower inserts were probably stiff enough to stop that movement initially. Once they softened a bit the top now makes noise. There's also a different clunk that sounds like metal on metal. That went away completely with subframe bushing inserts.

That's some nice weather, it was 45 in the morning and 85 in the afternoon last week.