Rear Diff clutch plates installed incorrectly from factory
Thread Starter
Joined: Jun 2003
Posts: 2,202
Likes: 20
From: Orlando, FL
Rear Diff clutch plates installed incorrectly from factory
I've been debating sending my rear diff in to Shep or TRE lately, but then a member sent me a thread on how to unlock an 8-plate locking diff by merely re-arranging the clutch plates in the oem diff. The finding dates back to 2008. Apparently, by re-arranging the plates correctly, it has been reported that you'll gain throttle oversteer, much like a 1.5 way locking diff.
So I immediately took the rear diff off. Luckily I did, because I found a leak and then cleaned it off. The case is held together with RTV sealant in between, so I'll be making sure the seal is good when I put things back together.
Cracked open the diff cover.
Took the diff carrier out.
Unbolted the final gear and opened the carrier. Sure enough the plates were assembled wrong from factory. You can see that the factory stacked the plates as follows, top to bottom: plate, plate, disc, disc, plate---plate, disc, disc, plate, plate
The service manual calls for plate, disc, plate, disc, plate---plate, disc, plate, disc, plate.
So I rearranged it to specs.
I'll be putting the car back in the next couple days and testing it this weekend to report back the difference.
REVIEW (post #49)
Here's a 5min parking lot review. I did a friction circle test and at steady state turning at the tire's grip threshold, the car still wants to understeer. It was neutral at best, but the circle kept getting larger and larger with the front tires slightly sliding out more so than the rears. BUT as soon as I smashed the gas, the rear end kicked out. It needs the torque to lock up. By the way, I have no clunks and noises whatsoever.
Video showing friction circle test:
http://www.youtube.com/watch?v=X2k9Nn5vySk
AUTOCROSS REVIEW (post #93)
I had an autocross event today and was finally able to test this mod out in real world applications. My suspicion was that this mod would benefit road racers more. I confirmed it today. With autocross, the turns can be excrutiatingly slow at times, and you will not slide the rear end out until the boost hits. During really slow corners, the boost may not kick in until you are at the corner exit, which you probably don't need rear end rotation anymore.
I was able to capture a video of the rear end catching me off guard today, so I countersteered in reaction to the slide, as opposed to anticipation. This scenario would have definitely been understeered in the past--more gas would have pushed me off line, outward.
http://www.youtube.com/watch?v=uJlZZ7x9OMI
If you have corners that are faster and you're already in boost rpm mid-corner (road race corners, or bigger autocross venues), you'll do better with this mod then. It'll allow you to rotate the car as you approach the corner exit, therefore, letting you get on the gas sooner.
HOW-TO's
Removing the Rear Diff
How to Assemble the Rear Diff
So I immediately took the rear diff off. Luckily I did, because I found a leak and then cleaned it off. The case is held together with RTV sealant in between, so I'll be making sure the seal is good when I put things back together.
Cracked open the diff cover.
Took the diff carrier out.
Unbolted the final gear and opened the carrier. Sure enough the plates were assembled wrong from factory. You can see that the factory stacked the plates as follows, top to bottom: plate, plate, disc, disc, plate---plate, disc, disc, plate, plate
The service manual calls for plate, disc, plate, disc, plate---plate, disc, plate, disc, plate.
So I rearranged it to specs.
I'll be putting the car back in the next couple days and testing it this weekend to report back the difference.
REVIEW (post #49)
Here's a 5min parking lot review. I did a friction circle test and at steady state turning at the tire's grip threshold, the car still wants to understeer. It was neutral at best, but the circle kept getting larger and larger with the front tires slightly sliding out more so than the rears. BUT as soon as I smashed the gas, the rear end kicked out. It needs the torque to lock up. By the way, I have no clunks and noises whatsoever.
Video showing friction circle test:
http://www.youtube.com/watch?v=X2k9Nn5vySk
AUTOCROSS REVIEW (post #93)
I had an autocross event today and was finally able to test this mod out in real world applications. My suspicion was that this mod would benefit road racers more. I confirmed it today. With autocross, the turns can be excrutiatingly slow at times, and you will not slide the rear end out until the boost hits. During really slow corners, the boost may not kick in until you are at the corner exit, which you probably don't need rear end rotation anymore.
I was able to capture a video of the rear end catching me off guard today, so I countersteered in reaction to the slide, as opposed to anticipation. This scenario would have definitely been understeered in the past--more gas would have pushed me off line, outward.
http://www.youtube.com/watch?v=uJlZZ7x9OMI
If you have corners that are faster and you're already in boost rpm mid-corner (road race corners, or bigger autocross venues), you'll do better with this mod then. It'll allow you to rotate the car as you approach the corner exit, therefore, letting you get on the gas sooner.
HOW-TO's
Removing the Rear Diff
How to Assemble the Rear Diff
Last edited by Thoe99; Jul 22, 2011 at 02:45 PM.
This is how it was set up for all usdm ct9a evos, not as the manual calls for
while it definitely increases lock up in the rear diff i dont know about actual throttle oversteer - i'm interested to hear how much more though - https://www.evolutionm.net/forums/9410547-post613.html according to this it doubles the friction surface - but stock didn't lock up that much at all to begin with
while it definitely increases lock up in the rear diff i dont know about actual throttle oversteer - i'm interested to hear how much more though - https://www.evolutionm.net/forums/9410547-post613.html according to this it doubles the friction surface - but stock didn't lock up that much at all to begin with
Thread Starter
Joined: Jun 2003
Posts: 2,202
Likes: 20
From: Orlando, FL
Thanks for clarifying.
Before anyone blindly goes out and does this, keep in mind that people also report that you'll hear clunks and noises at low speeds while turning. I don't really care about that, so long as I know it's normal
Before anyone blindly goes out and does this, keep in mind that people also report that you'll hear clunks and noises at low speeds while turning. I don't really care about that, so long as I know it's normal
after looking into it a little more i think it's going to create a more power oversteer than i had initially assumed..
good luck
Last edited by kyoo; Jun 22, 2011 at 10:13 PM.
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Evolving Member
Joined: Apr 2007
Posts: 185
Likes: 0
From: Coronado, CA
I took my car to a local shop for an inspection and was told the rear diff is acting like an open diff. Apparently this is a common occurrence with the 9's? Does anyone think getting in there and switching the plates and cleaning it up is a good idea or does it sound like it should be sent to TRE for an overhaul?
Evolving Member
Joined: Jun 2007
Posts: 156
Likes: 0
From: NorCal
I took my car to a local shop for an inspection and was told the rear diff is acting like an open diff. Apparently this is a common occurrence with the 9's? Does anyone think getting in there and switching the plates and cleaning it up is a good idea or does it sound like it should be sent to TRE for an overhaul?
However if you are going for some heavy duty racing ie autocross/circuit/drag then sending to TRE for overhaul/strengthening may be a better idea.
For now, I'll be doing this myself.
