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Discussion Starter #1 (Edited)
Whiteline Rear Differential Mount Bushings (KCA398)
Install and Impressions

Whiteline has released a new part of the 08; the KCA 398 rear diff bushings for the 08. These bushings are inserts that slide into the original bushings to help increase the stiffness. They are very easy to install taking roughly 30-45 minutes from raising the car to lowering it back down.

To start, here are the locations where the bushings will be going. This first picture is of the rear diff mounts located directly behind the rear diff. In this picture you can see the top slots that the bushings will slide into.

This image shows the location where the second set of bushings will go. The insert bushings will be going into the left bushing in this picture as it is the one with voids. The right bushing is solid.

Here is a close up of the mount on the left side. You can just make out the voids in the bushing where the inserts will fit.

Removal:
There are two nuts on the underside of the mount that must be removed.

Next, remove the two nuts and bolts on either side of mount. They both have 17mm hex heads.


A picture of the nut and bolt that is removed.

The mount removed. You can see that the left bushing has voids whereas the right is solid.

You can see how the insert bushing first into the mount. There are two different bushings, so make sure the right bushing goes in the right spot…..although it would be basically impossible to get them wrong. 

Bushing fitted into the mount.

Due to the inconsistency with the stock bushing manufacturing, the insert bushings may not full seat into the mount. They can be easily trimmed to fit with a razor or scissors.


Bushings fitted into mount.


Now it’s time to reinstall the mount. You may have to “massage” the mount into place with a dead blow hammer.



Turning attention to the rearward mounts. Begin by removing the two nuts on the end of the studs protruding from the rear diff. If the entire stud begins to come out of the rear diff, that is ok, but make sure you support the rear diff with a jack at that point. These nuts are 17mm hex head as well.


Once the nuts/studs are removed, apply grease to the insert portion of the bushing and the stock bushings in the subframe to easy installation.

Begin to slide the bushings into position making sure you have the correct slot in the correct hole. The bushings may be a bit difficult to slide in. Use a jack to raise and lower the rear diff as you push the bushings into place. A large pry bar can be used as well (lightly) to help push the bushings into place.

The bushings only need to be inserted into the stock bushings enough to begin threading the nuts/studs. Using the supplied washers behind the nuts will act as a press when tightening to push the bushings into place.

The rearward bushing inserts installed.


Impressions
To preface, we were noticing quite a lot of clunking from the rear upon hard shifting and launches in our car. These bushings have reduced 95% of the clunking that we were hearing. We have done a couple launches since the install and have heard very little clunking. Throttle response has also been improved over the OE bushings. When hitting the gas it seems that power is applied just a bit quicker than before. So far I have not noticed any increase in NVH from the install of these bushings under any condition from surface road, to highway cruising.
 

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awesome stuff, it seems like it's a lot easier to work around that area than the previous MY sti's...i know it's a ***** getting to the rear diff bolts on mine :(
 

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While I am looking into this, here are the torques:
Front member underside nuts: 50 N·m (5.1 kgf-m, 36.9 ft-lb)
Rearward mount nuts: 70 N·m (7.1 kgf-m, 51.6 ft-lb)
Front member nuts/bolts: 110 N·m (11.2 kgf-m, 81.1 ft-lb)
 

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Some notes from my profile regarding the install of these:

A little pain in the ass if you don't have much room to get them on if you got a small jack. Even cut my lip from having the diff mount drop on my lip as I was trying to put it back on. I recommend that when putting the bushings from the diff mount on that you take the 2 metal washers and use them to press the bushings in by using the nut and bolt. Not too tight- just good enough to get it in seat very snuggly. Lube well and keep it pressed in for a while and go do something else for 20 mins. Take off the bolt and washers and you'll have an easier time squeezing it in(and you will be).

The diff bushing inserts have a bolt with threads on both sides and a nut. It threads into the diff and the nut to connect to the rear sub frame. If the first one you unscrew only has the nut come off and not the 2 way threaded bolt you won't need a jack to support the diff. If the bolt does come out use a jack to support the diff before taking out the 2nd one. Pretty simple, lube well and press in(be liberal about the lube, you might even have an easier time lubing the bushings, taking them out and lubing them again). It's easier to press in the bushings if you got the whole bolt out. If you only got the nut, push the bushings in as hard as you can. You should be able to see the inside wall of the rear subframe when they get pressed in enough.
 

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I think I'm going to replace all the bushings at once and make a day of it.

It's too bad that most of the GR urethane bushings are not black because these bushings on a stock car could fly under the dealer without warranty concerns. I guess if you buy an aftermarket part, it has to look different so that you know what you're buying.



Thanks for the post. I'll be putting it to good use soon.
 

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Dealers won't concern themselves with people replacing/adding bushings or anything chasis related(untill something breaks). It's pretty hard to fly under the radar from dealers with pretty much any mod(even after you put the stock pieces back on, they can tell when things get swapped around).
 

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Some notes from my profile regarding the install of these:

A little pain in the ass if you don't have much room to get them on if you got a small jack. Even cut my lip from having the diff mount drop on my lip as I was trying to put it back on. I recommend that when putting the bushings from the diff mount on that you take the 2 metal washers and use them to press the bushings in by using the nut and bolt. Not too tight- just good enough to get it in seat very snuggly. Lube well and keep it pressed in for a while and go do something else for 20 mins. Take off the bolt and washers and you'll have an easier time squeezing it in(and you will be).

The diff bushing inserts have a bolt with threads on both sides and a nut. It threads into the diff and the nut to connect to the rear sub frame. If the first one you unscrew only has the nut come off and not the 2 way threaded bolt you won't need a jack to support the diff. If the bolt does come out use a jack to support the diff before taking out the 2nd one. Pretty simple, lube well and press in(be liberal about the lube, you might even have an easier time lubing the bushings, taking them out and lubing them again). It's easier to press in the bushings if you got the whole bolt out. If you only got the nut, push the bushings in as hard as you can. You should be able to see the inside wall of the rear subframe when they get pressed in enough.
Good info. I did this today and space was a problem. On my car the forward member bolts were seized and took quite a while to remove. Fully lubed, my forward diff mount bushings inserted by hand without a fight and did not have to be trimmed. Upon removal, the forward member underside nuts were only as tight as the self-locking nuts permitted, not anywhere near 36.9 ft-lbs and the rear mount nuts were only hand tight. Maybe the robot took a break at that moment during the diff installation. I wonder how long I had before they would have vibrated out.

Pressed the rear bushing inserts in with thumbs and a large flathead screw driver most of the way after greasing the bushings, the voids, and the inside walls of the subframe where they would contact the inserts. The flat washers and nuts pressed them in the rest of the way.

Anti-Seized all threads and torqued as follows:
Front member underside nuts: 50 N·m (5.1 kgf-m, 36.9 ft-lb)
Rearward mount nuts: 70 N·m (7.1 kgf-m, 51.6 ft-lb)
Front member nuts/bolts: 110 N·m (11.2 kgf-m, 81.1 ft-lb)
 

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On my car the forward member bolts were seized and took quite a while to remove.
I also had quite the problem with this. I actually did the rear bushings that go into the diff first and those went super easy. I just pressed them in by hand. 10 minutes tops. However the forward mount bolts were so crazy tight I couldn't get them off. I hit them with some PB Blaster and I'll probably get back around to them tomorrow after I've gotten some 1/2 inch drive 6 point sockets. I was worried about rounding them off with my 12 point sockets. Really pissing me off though :rolleyes:
 

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just a quick tip for anyone installing these. I backed my car up onto ramps. When I put the inserts in the bushing on the left side of the lower mount, as explained above it will make it a real fit tight back into its mount. I put the right side back on the car first since it slid in easily since its still the stock bushing, then i put the nut/bolt back in. I couldnt really swing a hammer to get the left side back in, so i just put a jack under it and jacked it back into place...easy as pie.
 
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