STi "rear" diff mount install
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This is a discussion on STi "rear" diff mount install within the Powertrain forums, part of the Tutorials & DIY category; This is the STi Group N "rear" diff bushing. Looks like this:...

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    Moderating on the run! Big Sky WRX's Avatar
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    STi "rear" diff mount install

    This is the STi Group N "rear" diff bushing. Looks like this:
    Attached Thumbnails Attached Thumbnails rdiff1.jpg  
    Last edited by Big Sky WRX; 04-20-2003 at 11:02 AM.

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    Moderating on the run! Big Sky WRX's Avatar
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    This is the area we will be working in. The vehicle needs to be on jack stands.
    Attached Thumbnails Attached Thumbnails rdiff2.jpg  
    Last edited by Big Sky WRX; 04-20-2003 at 11:05 AM.

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    Moderating on the run! Big Sky WRX's Avatar
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    These are the four bolts that hold the bushing (outer two) and rear diff (inner two), they are all 17mm. The two that hold that rear diff are very long and the rear diff won't clear the nount w/ these long bolts. They are actually studs, so instead we will remove them from the rear diff.



    The rear diff should be supported (floor jack) as you will have to raise/lower several times to ease the bolts/studs removal. To remove them we will take off one of the outer (bushing) nuts and put in on the diff stud (it seemed to work better putting the nut on backwards). One tighted down good against the other nut, we will come from underneath and start backing out the stud- go slow and take it easy. If the stud binds raise or lower the diff w/ the floor jack.
    Attached Thumbnails Attached Thumbnails rdiff3.jpg  

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    Moderating on the run! Big Sky WRX's Avatar
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    This is what the stud looks like removed- the coarse threads go into the rear diff:
    Attached Thumbnails Attached Thumbnails rdiff4.jpg  

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    Moderating on the run! Big Sky WRX's Avatar
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    Removing the outer bolts require you lower the diff, as the bolts have to be removed from the rear and the will "bump" into the axle shafts (green portion) without lowering it. Once the bolts clear the axle stubs, remove the bolts and the bushing will drop right out.

    Here's what they look like side by side, notice the voids on the oe piece in the rubber, you could twist them around w/ your finger.
    Attached Thumbnails Attached Thumbnails rdiff6.jpg  

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    Moderating on the run! Big Sky WRX's Avatar
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    Install the new bushing, putting in the outer bolts while the diff is lowered, only hand tighten them as you want a little wiggle room when orientating in the diff studs. Raise the jack till the holes line up (this takes a little bit of time- would be helpful w/ two people because you can easily move the diff w/ your hands). Reinstall the studs- again go careful and slow (both nuts will need to be on to install them). Once tight, you'll need to remove the second helper nut- you'll need both wrenches as it will be on there good.

    The quarters are close and most of your work will be w/ combination wrenches, a "happy" (ratcheting wrench will be helpful). Once everthing is firmed up good- I took my vehicle off the stands and back it up on ramps for final torqueing- the manual recommends the vehicle be unsupended. Torque for all four bolts is 51 ft lbs. You can get a torque wrench on the outer bolts, but not the inner (diff studs) you'll have to cinch them up as best you can w/ an open end wrench (unless you for some reason have more room than me.

    The finished product:
    Attached Thumbnails Attached Thumbnails rdiff7.jpg  

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    Registered User pityr's Avatar
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    Excuse my ignorance. What exactly does adding this accomplish? Did you notice a difference when you drove the car afterward?
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    Registered User AjIsDope's Avatar
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    Originally posted by pityr
    Excuse my ignorance. What exactly does adding this accomplish? Did you notice a difference when you drove the car afterward?
    That's what I want to know. What is the purpose of this part?
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    Moderating on the run! Big Sky WRX's Avatar
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    Firmer bushings in the driveline (engine mounts/tranny mount/rear diff) deflect less than softer ones. Less deflection enables the driveline to put power to the wheels more efficiently (there is less slop), this also helps w/ shifting. The done side to firmer bushings- whether drivetrain or suspension, is they are usually accompanied by more NVH (noise,vibration,harshness). I don't find too much trouble w/ NVH and I'm running STi struts/springs/Group N tops/engine/tranny/pitch rod/rear diff/lateral links/transverse link bushings (trailing arms to go yet). Someone else may however. If you drove this car vs a stock one, the performance difference and feel would be very noticable.

    Many race cars utilize metal bushings (vs rubber) just for the reasons above, ofcourse NVH would probably not be tolerable on the street.

    Big Sky

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    Registered User AjIsDope's Avatar
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    Ok. So it is just a stronger mount like the STi engine mounts. I gotcha.

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    Registered User KanosWRX's Avatar
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    hmm, doesn't look to hard to install. but from doing my rear diff protector I know its hard to get tools up in those areas. so I was wondering how long did it take for the install? also on a side note, did you notice any difference after installing the sti pitch mount?


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    Registered User CustomS10's Avatar
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    i'm surprised no one asked the cost of this
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    Moderating on the run! Big Sky WRX's Avatar
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    Not necessarily "stronger", firmer would be more accurate- less deflection.

    Install about 1.5 hours (I tend to go nice and slow) in my gravel driveway. Can't say that I noticed a difference w/ the pitch mount, but it iwas firmer than stock, again less deflection, thus less "twisting" of the motor.

    Cost on the rear diff mount (bushing) is ~ $100.

    Big Sky

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    Don't you mean "less upward pitching" of the motor?

    I don't see how this thing can do much to prevent the motor from torquing over, that's what the Group N engine mounts are for right?

    I'll see if I can get a good A/B shot of the pitch stops.
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    Moderating on the run! Big Sky WRX's Avatar
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    Less pitching is more correct (although there are some lateral loads placed on the pitch rod as well where the firmer bushings will help resist twisting some).

    Big Sky

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