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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.

[unclemat]

There is one confusing thing. The picture of all the inserts show only two for the lower support. But you installed both on one side. Should there be four inserts for the lower support? Or only two - i.e. one per side?

[MaStA]

Originally Posted by unclemat

There is one confusing thing. The picture of all the inserts show only two for the lower support. But you installed both on one side. Should there be four inserts for the lower support? Or only two - i.e. one per side?

Yeah I was wondering the same thing, but it looks like the other bushing doesn't have places to insert something so maybe just the other side gets them.

[unclemat]

Good catch! Weird isn't it? Looks like Subaru by purpose makes one side softer. Adding inserts stiffens that side.

FWIW, on LGT both bushings are solid without space for an insert.

[cky3396]

do you have the torque specs for this install?

[CJCAMERON]

Was an easy install with copeous amounts of Grease

[hokie_sti]

A few questions:

1. What are the torque specs for the nuts/bolts that are removed?

2. If the reward mount studs come out with the nuts, how do you reinstall the studs?

[Endymion]

Bump for torque specs.

[hokie_sti]

Originally Posted by Endymion

Bump for torque specs.

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)

From this thread: New Whiteline 2008 rear diff bushing inserts

Those two threads should probably be merged seeing how they are the same thing.

[Endymion]

Bah, I agree. Thanks for digging that up for me.