Rear subframe bushing inserts vs steeda bushing supports

[sloopy]

I'm getting ready to address the excessive rear subframe movement to improve the handling and feeling of the car. I don't have any issues with wheel hop. I'm going to use the steeda subframe alignment kit (pn 555-4438) and I'm trying to decide between the polyurethane bushing inserts (pn 555-4045) and the bushing supports (pn 555-4437). I'm not understanding how installing the bushing supports would result in "no increase in NVH at all". If that's true, then I see zero downsides to the supports and it becomes the obvious choice (I'm not concerned about the difference in price). Why does the rear subframe need isolation when the front does not? Is it mainly to provide more isolation of the differential? I'm also considering the differential bushing inserts. My car has the factory exhaust and I don't want to introduce any significant amount of NVH. Especially any sort of low-pitched resonance. However, I do find some subtle gear noise while accelerating or decelerating to be pleasant. This is mainly from my experience with a tremec t5z, but a constant noticeable whine while cruising would probably get annoying.

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[SheepDog]

I'm also considering the differential bushing inserts.

Skip this part if you do not want any additional NVH.

Why does the rear subframe need isolation when the front does not? Is it mainly to provide more isolation of the differential?

Yes. The rear diff is responsible for almost all of the noise and vibration. The front is already isolated from the Engine via the engine mounts.

Do the braces if you really want to lock down the rear subframe
Steeda 555 5754 Mustang Coupe Rear IRS Subframe Support Braces (15-26)

 

[Oakley]

Skip this part if you do not want any additional NVH.


Yes. The rear diff is responsible for almost all of the noise and vibration. The front is already isolated from the Engine via the engine mounts.

Do the braces if you really want to lock down the rear subframe
Steeda 555 5754 Mustang Coupe Rear IRS Subframe Support Braces (15-26)

if you just do the rear inserts on the diff the only added noise is you can hear when you change gears in parking lots.

 

[SheepDog]

if you just do the rear inserts on the diff the only added noise is you can hear when you change gears in parking lots.

Not on my car. I did just the rears (red) and I can hear and feel the vibration going down the highway. However, I already did all the other things that would transfer this vibration straight into the cabin, so maybe if you Only did the inserts, it wouldn't be as noticeable.

 

[Oakley]

I have the keltec set with big bertha bolts. car is totally fine for long trips.

 

[sloopy]

Skip this part if you do not want any additional NVH.

Some amount of increased NVH is acceptable. I'd like to avoid increased road noise. Subtle gear noise only during acceleration and deceleration is acceptable, could even be pleasant for me. However, any significant increase in low-frequency resonance is not acceptable for me.

Yes. The rear diff is responsible for almost all of the noise and vibration. The front is already isolated from the Engine via the engine mounts.

But the rear is already isolated from the differential via its mounts. I'm guessing the combination of subframe and differential bushing inserts would still provide good isolation. As would just doing the subframe supports and no differential bushing inserts. But perhaps the subframe supports combined with the differential bushing inserts would introduce a significant amount of NVH. This is just my thinking.

 

[sloopy]

To be clear, when I'm talking about the subframe supports, I'm talking about these:

 

[MiamiGT350]

The subframe inserts will have minor NVH. I haven't done the work, but I have heard the differential bushings will be more NVH. I would start with just the subframe kit.

 

[sloopy]

Fair enough. But my main question is whether I should get the polyurethane subframe bushing inserts or the solid supports.

 

[RacerPaul]

Hi Sloppy, that's a good question. The manufacturers of the solid billet inserts recommend them for track and racing applications. I have the black polyurethane inserts on the subframe and differential mounts. I haven't noticed any additional NVH, but I have 90 percent hearing loss in one ear and 50 percent loss in the other, so the point may be moot. I have not noticed any additional NVH through the seat or steering.

 

[RacerPaul]

Sorry Sloopy, I hate that darn autocorrect!

 

[sloopy]

No worries :^)

Steeda says their aluminum rear subframe supports do not add any NVH. However, when combined with the diff bushing inserts (I'd go with the softer 80a reds), there may be a significant amount of NVH increase. I'd like to get some idea of what I'm in for with only this combination of aluminum supports and red diff bushing inserts. If it seems like too much, I'll do the subframe bushing inserts instead of the aluminum supports. If it's mostly just clunks and some gear noise on accel and decel, then that's great (maybe even welcomed and will make the car feel more racecar). If it makes the chassis resonate like a subwoofer, it's getting removed as quickly as possible.

 

[sloopy]

I guess it may be worth tagging @tj@steeda (enjoy your weekend first though).

 

[K4fxd]

I've got the solid supports and there is no noticeable increase in noise. The rear is firmer and the sound of bumps is sharper but not unlike any performance car. No harmonics, no resonances......

 

[sloopy]

That's awesome. Do you also have differential bushing inserts?

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