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Discussion Starter #1
New my 2013 3.8 but getting that lovely 2nd gear lockout that seems to have cursed this car.

Already have an Engine Leash & Transmission Mount on the way, the question now is

Because my current Diff mount seems to be shot (OEM, 90k anyways)....

Should I go with just a regular
OEM replacement, a Solid Aluminum Replacement, or Install a second mount?

Heres the research I've gathered so far
Regular OEM replacement
-Seems to wear out rather quickly

Aluminum Replacement
- Warnings about it cracking the brace, or damaging the diff (baddd!!!)

Install a Second OEM replacement
- Supposedly how the car was originally designed, but causes vibrations???

Anyone got any light to shed on this?
Thank you :D
 

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I'd rather do it myself
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There are two in the front of the rear subframe too. I put in another OE rear mount but you have to drill out the hole. It's been there three years or so with no issues but I'm not hard on the car. It does make a good difference.
 

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That 4th diff mount would definitely be recommended for nearly all cases. I shredded the single rear mount once (still under warranty when it happened thank god). The NVH from one should likely be negligible. The Genesis Sedans have nearly exactly the same rear subframe but they have the 4th diff mount, so clearly the NVH from the 4th diff mount isn't too bad for a luxury sedan.

Also get the diff bolt upgrade kit from 3P8 Performance. Those bolts are stronger and are almost necessary for higher power applications. Like I said before, I shredded one of the OEM bolts, so stronger ones are recommended.

Lastly, solid aluminum mounts are a risky route. They'll provided the most response and mount strength among the other options, but it provides no cushion for the diff mount bolts and provides a likely chance that you can just sheer a bolt off when launching the car. Poly mounts would be recommended if you're not comfortable with that chance.
 

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Big power increase without NVH needs the following:
Harshness of stability should flow from the front back, and wane slightly. What that means is the most substantial increase in non-flexion is at the main motor mounts. (Your engine leash is not worth a crap).
-So new OEM style engine mounts filled with 75 D urethane are perfect
- The trans mount is an experiment based on your power increase, and encountered NVH. I made two or three castings with differing compositions. For the 8ATs I found this to be 65A durometer urethane was perfect. The "D"s had too much NVH. A's differ from Ds in they are more rubbery (firm but absorb NVH). Ds are more plastic like, more rigid, but transfer NVH.
-The oem diff bushings are not bad, they just need the fourth. There is no vibration. Solid bushings are asking for trouble.
-3.8s forged diff bolts are quite good. They give greater bite and increased shoulder area as well.

Add the above and 3.8s rigid collars and bushing shims and your car will be a slot car. Awesome.

**Im pushing 600 whp, and my stuff is solid as a rock, smooth as well.
 

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Discussion Starter #5
There are two in the front of the rear subframe too. I put in another OE rear mount but you have to drill out the hole. It's been there three years or so with no issues but I'm not hard on the car. It does make a good difference.
Thank you !
This seems like the most cost effective option as I'm not planning to go big on power in the immediate future. You haven't noticed any negatives to the addition of that 4th mount?

For the installation, its just drilling the proper slot, then installing like any other?
:D

That 4th diff mount would definitely be recommended for nearly all cases. I shredded the single rear mount once (still under warranty when it happened thank god). The NVH from one should likely be negligible. The Genesis Sedans have nearly exactly the same rear subframe but they have the 4th diff mount, so clearly the NVH from the 4th diff mount isn't too bad for a luxury sedan.

Also get the diff bolt upgrade kit from 3P8 Performance. Those bolts are stronger and are almost necessary for higher power applications. Like I said before, I shredded one of the OEM bolts, so stronger ones are recommended.

Lastly, solid aluminum mounts are a risky route. They'll provided the most response and mount strength among the other options, but it provides no cushion for the diff mount bolts and provides a likely chance that you can just sheer a bolt off when launching the car. Poly mounts would be recommended if you're not comfortable with that chance.
Interesting how they never put that 4th mount in, seems like they cut corners on it, or had one bad test and weren't willing to risk it. The more I research the more I'm turned away from these solid mounts, especially since I'm planning on tightening up everything else.
Thank you!

Big power increase without NVH needs the following:
Harshness of stability should flow from the front back, and wane slightly. What that means is the most substantial increase in non-flexion is at the main motor mounts. (Your engine leash is not worth a crap).
-So new OEM style engine mounts filled with 75 D urethane are perfect
- The trans mount is an experiment based on your power increase, and encountered NVH. I made two or three castings with differing compositions. For the 8ATs I found this to be 65A durometer urethane was perfect. The "D"s had too much NVH. A's differ from Ds in they are more rubbery (firm but absorb NVH). Ds are more plastic like, more rigid, but transfer NVH.
-The oem diff bushings are not bad, they just need the fourth. There is no vibration. Solid bushings are asking for trouble.
-3.8s forged diff bolts are quite good. They give greater bite and increased shoulder area as well.

Add the above and 3.8s rigid collars and bushing shims and your car will be a slot car. Awesome.

**Im pushing 600 whp, and my stuff is solid as a rock, smooth as well.
This was extremely useful ! ! ! I've saved your comment to come back later when I'm ready to go for bigger power. The only thing stopping me from going with a FI kit right now is SMOG compliance. (California)

Thinking of pumping a 50 working up to a 100 wet shot through it, but hesitant to risk the engine on it.

Do you believe that the OEM mounts can handle this sort of power?

Its driven rather harshly, but the spray only being used rarely.
 

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I'd rather do it myself
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I did a write up of how I did it. Doing it in the drive way with a hand drill. Hard steel but it worked out good as the steel kind of mushroomed out when cutting. This reinforces the thickness of the subframe and gives the mount more surface area for contact instead of just the thickness of the steel.

Really a good improvement and still in great shape.

 

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Discussion Starter #7
I did a write up of how I did it. Doing it in the drive way with a hand drill. Hard steel but it worked out good as the steel kind of mushroomed out when cutting. This reinforces the thickness of the subframe and gives the mount more surface area for contact instead of just the thickness of the steel.

Really a good improvement and still in great shape.

Thank you! Bookmarked that thread for when I go at it. :D
 
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