Let's talk about diffs, baby.
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Joined: Mar 2015
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From: CT
We also ran an FD torsen and loved it. However, it will spin up the inside rear if it lifts (like over bumps, such as curbs at a track). It does shock load when it hits the ground again, and it does eventually grenade. Ask me how I know 
I did love that diff though.... but our local autocross site has way too many undulations/bumps that wind up causing us to get thrown up onto two wheels. It's super abusive to the diff especially.
We now run an OSG.
I did love that diff though.... but our local autocross site has way too many undulations/bumps that wind up causing us to get thrown up onto two wheels. It's super abusive to the diff especially. We now run an OSG.
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From: Mid Atlantic
And you also have to know whether it's the diff or something else in your setup causing the problem you're chasing. It's easy to convince yourself you're fighting a suspension problem when it's really a diff problem or vice versa.
If you have a suspension that generally works well it is hard to go wrong with a helical differential, especially one with some sort of preload like a T2R. They do not have the usual bad habits of a clutch-type diff on corner entry. They are very consistent and don't wear out over time like the stock RX-8 diffs do.
If you have a suspension that generally works well it is hard to go wrong with a helical differential, especially one with some sort of preload like a T2R. They do not have the usual bad habits of a clutch-type diff on corner entry. They are very consistent and don't wear out over time like the stock RX-8 diffs do.
was never aware of them offering it for an RX7/RX8 any way and I believe they may be out of business now since their website is dead
but a fitting question I suppose considering that people here in this 2018 thread still weren’t sure or didn’t know that the FD3 RX7 and RX8 differentials are interchangeable despite it being discussed on the forum since back in 2005 if not sooner
it was essentially a torsen with spring loading that allowed the effectiveness to be dialed in wrt to wheel lift and inside wheel spin; stiffer spring(s) more bias towards minimal inside wheel spin and understeer exiting a tight turn, less spring pressure being more neutral but also more susceptible to spinning up the inside tire as Tamra explained in her reply. The RX8 factory diff can do the same thing under certain circumstances. I had a front speedway swaybar fail at a Wendover Pro Solo back in 2008 or 2009 and the excess chassis roll was doing the exact same thing she was explaining about the FD3 torsen.
just bite the bullet for the OSG and be sure to take another bite and use their spec oil too. If you want it to behave more like a torsen then OSG USA can adjust it to a 1-way or 1.1-way bias. Tamra and some others do (or did) it that way.
.
but a fitting question I suppose considering that people here in this 2018 thread still weren’t sure or didn’t know that the FD3 RX7 and RX8 differentials are interchangeable despite it being discussed on the forum since back in 2005 if not sooner
it was essentially a torsen with spring loading that allowed the effectiveness to be dialed in wrt to wheel lift and inside wheel spin; stiffer spring(s) more bias towards minimal inside wheel spin and understeer exiting a tight turn, less spring pressure being more neutral but also more susceptible to spinning up the inside tire as Tamra explained in her reply. The RX8 factory diff can do the same thing under certain circumstances. I had a front speedway swaybar fail at a Wendover Pro Solo back in 2008 or 2009 and the excess chassis roll was doing the exact same thing she was explaining about the FD3 torsen.
just bite the bullet for the OSG and be sure to take another bite and use their spec oil too. If you want it to behave more like a torsen then OSG USA can adjust it to a 1-way or 1.1-way bias. Tamra and some others do (or did) it that way.
.
Last edited by TeamRX8; May 21, 2023 at 09:33 AM.
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Joined: Aug 2015
Posts: 620
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From: Mid Atlantic
was never aware of them offering it for an RX7/RX8 any way and I believe they may be out of business now since their website is dead
but a fitting question I suppose considering that people here in this 2018 thread still weren’t sure or didn’t know that the FD3 RX7 and RX8 differentials are interchangeable despite it being discussed on the forum since back in 2005 if not sooner
it was essentially a torsen with spring loading that allowed the effectiveness to be dialed in wrt to wheel lift and inside wheel spin; stiffer spring(s) more bias towards minimal inside wheel spin and understeer exiting a tight turn, less spring pressure being more neutral but also more susceptible to spinning up the inside tire as Tamra explained in her reply. The RX8 factory diff can do the same thing under certain circumstances. I had a front speedway swaybar fail at a Wendover Pro Solo back in 2008 or 2009 and the excess chassis roll was doing the exact same thing she was explaining about the FD3 torsen.
just bite the bullet for the OSG and be sure to take another bite and use their spec oil too. If you want it to behave more like a torsen then OSG USA can adjust it to a 1-way or 1.1-way bias. Tamra and some others do (or did) it that way.
.
but a fitting question I suppose considering that people here in this 2018 thread still weren’t sure or didn’t know that the FD3 RX7 and RX8 differentials are interchangeable despite it being discussed on the forum since back in 2005 if not sooner
it was essentially a torsen with spring loading that allowed the effectiveness to be dialed in wrt to wheel lift and inside wheel spin; stiffer spring(s) more bias towards minimal inside wheel spin and understeer exiting a tight turn, less spring pressure being more neutral but also more susceptible to spinning up the inside tire as Tamra explained in her reply. The RX8 factory diff can do the same thing under certain circumstances. I had a front speedway swaybar fail at a Wendover Pro Solo back in 2008 or 2009 and the excess chassis roll was doing the exact same thing she was explaining about the FD3 torsen.
just bite the bullet for the OSG and be sure to take another bite and use their spec oil too. If you want it to behave more like a torsen then OSG USA can adjust it to a 1-way or 1.1-way bias. Tamra and some others do (or did) it that way.
.
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Joined: Feb 2018
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I put a brand new cusco diff center in mine and it required different shims to achieve backlash that was within spec. It's not difficult to measure the backlash and calculate the shims required (Mazda stock a few different shims), but if you're not confident doing this just take your diff housing along with your diff center to a transmission specialist and they will set it up for you.
Last edited by RX0004; May 22, 2023 at 06:10 PM.
they *all* have to be checked and set properly; *all*, at least if you have any understanding about it
it’s not just backlash, but also where the pinion teeth engage the ring teeth depth as well
so shimming has to be checked for both the pinion fore/aft (teeth engagement position) and the ring side/side (backlash position)
edit: if it’s just an LSD swap using the same R&P it’s possible that it may only need backlash shimming, but the engagement position should still be checked.
any place that does 4wd offroad work will likely be able to handle setting it up, but you can search for drivetrain shops as well.
.
it’s not just backlash, but also where the pinion teeth engage the ring teeth depth as well
so shimming has to be checked for both the pinion fore/aft (teeth engagement position) and the ring side/side (backlash position)
edit: if it’s just an LSD swap using the same R&P it’s possible that it may only need backlash shimming, but the engagement position should still be checked.
any place that does 4wd offroad work will likely be able to handle setting it up, but you can search for drivetrain shops as well.
.
Last edited by TeamRX8; May 25, 2023 at 08:33 AM.
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