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Cusco Rear diff install

Old Dec 28, 2011, 05:59 PM
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Cusco Rear diff install

So thanks to Mert at GST, I got my Cusco RS 1.5way rear diff installed.

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So like any diff install, you gotta get those half-shafts and drive shaft out of the way first. Disconnect the AYC lines, 3 bolts, and the diff comes right out. After that, you unbolt the side of the pumpkin that houses the rear diff.

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Then you just slide the old diff off, unbolt the main gear around it, and transfer that gear to your cusco diff.

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You can attempt to transfer the old side bearings too (the ring of bearings on the top of pic 2), but that's definitely not something for the timid. It's better and safer just to buy new ones.

After that, you just bolt everything back together and put the housing back in place. Put new SVG fluid in the diff part, ATF SPIII in the AYC part, and then bleed the lines. Thankfully, I was able to use the new application from Tephra to do that part.
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Old Dec 29, 2011, 06:15 PM
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is there any difference from stock? This looks challenging, good stuff man!
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Old Dec 29, 2011, 07:03 PM
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very nice, i'm running this diff as well.. it's amazing
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Old Dec 29, 2011, 11:04 PM
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Originally Posted by s84kam View Post
is there any difference from stock? This looks challenging, good stuff man!
+1 , also what r u the spec from stock?
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Old Dec 30, 2011, 12:56 AM
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So being a 1.5way is already an improvement from stock. The auto-x season hasn't started yet, so I haven't had a chance to fully test the diff, but what I have found is that you can get on the gas earlier in a turn and stay on it through exit. The back end seems to rotate out better but not kick out in any way like a TRE on an Evo IX.
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Old Dec 31, 2011, 10:21 AM
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Originally Posted by Segfault View Post
So being a 1.5way is already an improvement from stock. The auto-x season hasn't started yet, so I haven't had a chance to fully test the diff, but what I have found is that you can get on the gas earlier in a turn and stay on it through exit. The back end seems to rotate out better but not kick out in any way like a TRE on an Evo IX.
Not kicking out may be in part due to the springs the Cusco has that lets the lock-up be a little more gradual, as opposed to the TRE and other clutch types that have a little more violent lock up? That said if I put my foot down the rear end will kick out, so maybe it's the AYC.

http://www.cusco.co.jp/en/parts_prod...rs_typemz.html
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Old Dec 31, 2011, 05:21 PM
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Yeah, I think the springs are doing a good job at that. If yours is kicking out, it could also be due to power difference between you a I as well as alignment. I run -1.8 degrees in the rear with 1/8" toe out. I know a few TRE guys who run -2.X in the rear to help control that step out better.
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Old Dec 31, 2011, 05:34 PM
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Originally Posted by Segfault View Post
Yeah, I think the springs are doing a good job at that. If yours is kicking out, it could also be due to power difference between you a I as well as alignment. I run -1.8 degrees in the rear with 1/8" toe out. I know a few TRE guys who run -2.X in the rear to help control that step out better.
ahh? i don't make too much more power (380? on a dynojet), but I am definitely running a much milder rear set up. i've been considering adding a front bar lately (stock bars now)
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Old Jul 30, 2013, 10:30 PM
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Could you fit this on a evo 7 rear diff with ayc? does it require other parts like bearings etc?
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Old Aug 3, 2013, 01:16 PM
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I assume you run without AYC once this is installed? (ASC off-off)

If not I'd assume the AYC mapping is no longer anywhere close to optimal. For instance hard breaking in Tarmac will lock up the ACD and make the AYC split 50/50 to the rear. With a 1.5 way does this change the off-throttle feel of the car? Does it do anything to correct the off-throttle understeer which is quite obvious on this AWD car?

It's interesting for sure.. Thanks for posting
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Old Aug 16, 2013, 10:56 AM
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I'm in for all the questions asked above as well...

I also heard that you have to shim the cusco and quaife diffs, was that also the case?

Was the pinion removed as well in order to set backlash properly?

Definitely thinking about this upgrade as well as the front diff
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Old Sep 21, 2013, 01:42 PM
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I would have responded earlier, but missed this thread.

Originally Posted by acidtonic View Post
I assume you run without AYC once this is installed? (ASC off-off)
The ASC button has no effect on the AYC. Off-Off turns off the single-wheel braking aid for the AYC, but has no effect on the AYC, itself.

Originally Posted by acidtonic View Post
If not I'd assume the AYC mapping is no longer anywhere close to optimal. For instance hard breaking in Tarmac will lock up the ACD and make the AYC split 50/50 to the rear.
First, I do not believe that hard braking in Tarmac causes the ACD to lock. I believe that it is the exact opposite; it will open completely (so you can turn in).

Second, the AYC has nothing to do with the front/rear split. The front/rear split is always 50/50 since torque split is determined by the gearing of the center diff. The torque distribution can differ from 50/50 when the ACD locks, but that has nothing to do with the AYC.

Finally, I agree that the maps will be sub-optimal with a 1.5-way rear. But, then again, they are sub-optimal with the OE diffs.

Originally Posted by acidtonic View Post
With a 1.5 way does this change the off-throttle feel of the car? Does it do anything to correct the off-throttle understeer which is quite obvious on this AWD car?
Yes, a 1.5-way will affect off-throttle "feel" because it locks on deceleration, albeit not as much as on acceleration (hence the label "1.5" rather than "2"). As to off-throttle understeer, a 1.5-way will have the tendency to make this worse when compared to an open rear, since the locking of any diff will make the car want to go straight ahead. Lucky for me, at least, I don't feel much if any off-throttle understeer. The idea behind rear diffs that lock (to any extent) on deceleration is to keep the rear of the car behind the front (without having to resort to things like oodles of rear toe-in).
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Old Sep 21, 2013, 01:43 PM
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Originally Posted by nukerj View Post
Definitely thinking about this upgrade as well as the front diff
What front diff would be better than a helical?
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Old Oct 14, 2013, 03:59 PM
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Are the factory front and rear LSD's 2-way?
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Old Feb 17, 2015, 06:26 PM
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Originally Posted by Segfault View Post
So thanks to Mert at GST, I got my Cusco RS 1.5way rear diff installed.



So like any diff install, you gotta get those half-shafts and drive shaft out of the way first. Disconnect the AYC lines, 3 bolts, and the diff comes right out. After that, you unbolt the side of the pumpkin that houses the rear diff.



Then you just slide the old diff off, unbolt the main gear around it, and transfer that gear to your cusco diff.



You can attempt to transfer the old side bearings too (the ring of bearings on the top of pic 2), but that's definitely not something for the timid. It's better and safer just to buy new ones.

After that, you just bolt everything back together and put the housing back in place. Put new SVG fluid in the diff part, ATF SPIII in the AYC part, and then bleed the lines. Thankfully, I was able to use the new application from Tephra to do that part.
Where can you buy the side bearing? I have looked into many difference sources, just can not find them. Anyone knows? I am planning on replacing my rear diff with Cusco RS 1.5 way. Thanks for your input.
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