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Old 06-04-2013, 09:16 AM   #1
Mojambo
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Default Adding a front LSD changed the car..

Hey guys and gals,

Just wanted to post this up and share my experience.

I've recently done the 07 STI tranny swap into my 06 ASP STI. While I had the 07 tranny on the bench, I decided now was the time to add in a better front LSD.


I did the install myself and it was very straight forward and simple. I marked the location of the sundials for the OEM diff for refrence and counted the turns to remove them. After the OS Giken installation, backlash setup, pinion depth check, bearing preload and gear pattern check....the sundials were in the same locations. The machining on the OS Giken diff was spot on. The pinion depth did not change at all. I bought all the shims for nothing

Why? For years now, I've been chasing this bouncing/hopping/pogo effect when coming out of corners under throttle. I've tried various spring rates, swaybars, DCCD settings etc. I was honnestly at my whits end.

I've always felt it was the OEM helical front LSD that was a big reason for this problem when on sticky tires and lifting an inside front wheel on exit.

This spring has brought alot of change to my setup. A new built motor on E85 and now an 07 tranny with an OS-Giken 1Way LSD purchased from Forged Performance. It was on clearance too

I softened the springs again 600F/500R to get some compliance from 750F/600R.

setup:
OEM front sway. WL 22mm rear. Carbonetics 1.5Way rear
koni 8611 DA's, GC camber plates front and rear.
-4F, -1.8R, 1/4" toe f, 1/16"rear
10" lexan SP spoiler on trunk

I participated in my first event this season. I was using this as a good shakedown for the car. The surface was a WW2 era Airforce Base. Abrasive asphalt with a high level of grip once swept.

Started the first few runs on some old hard hoosier wets. Coming out of some tight corners, I immediately noticed the front having more grip and pulling out of tight corners. the most amazing, was the bouncing I was previously experiencing was gone. For the 2nd heat, I put on some A6's to really feel this diff. I was blown away by the grip level the diff was providing to the setup.

Accelerating mid corner was really coming alive and NO bouncing!! This same feeling was felt on on long sweepers and tight corners with hard acceleration on exit.

I did experience understeer at first and changed the rear bar to the WL 22 soft setting from the stock bar. But I am not sure if it's the front diff or the rear lexan spolier I added creating more down force at speed. I still have a slight push, but will be working on that by giving it more rear bar.

All of this to say that my experience with the OS Giken front diff has been nothing short of spectacular. I highly recommend it to anyone looking to gain more mid corner to exit traction.

Eric
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Old 06-04-2013, 09:30 AM   #2
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Shhh! You're posting all the secret sauce about the bounce out of corners!

:beer:
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Old 06-04-2013, 09:42 AM   #3
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Damn, making me want to redo some diffs on my cars... do you have any pics of your car? I'm interested in see this thing.
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Old 06-04-2013, 10:55 AM   #4
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werd

check your breakway. Too high and it will be hard to fully tune out the push through other items. In my experience.
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Old 06-04-2013, 12:21 PM   #5
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^^

That's why I was really happy to be purchasing an OS Giken. They have more plates than most LSD's and the lockup is very smooth ( as per the GRM review). I would hate to have to pull the tranny again to re-adjust the plates...Lets hope I can change the balance with the swaybar.

The push was minimal at the soft 22mm bar setting. Then I corded the inside of the 2 fronts and the push was evident
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Old 06-04-2013, 01:07 PM   #6
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Greg is talking about the preload springs, not the lockup setting that re-stacking plates would change.

The sway bar change seems odd. You went from full stiff or middle setting? Going to soft should have increased rear grip while allowing more body roll up front. If you're cording the inside of the tires up front maybe you have too much front camber and the reduction of rear sway bar allowed a greater tire contact patch during the increased body roll.
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Old 06-04-2013, 02:05 PM   #7
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Quote:
Originally Posted by Mojambo View Post
^^

That's why I was really happy to be purchasing an OS Giken. They have more plates than most LSD's and the lockup is very smooth ( as per the GRM review). I would hate to have to pull the tranny again to re-adjust the plates...Lets hope I can change the balance with the swaybar.

The push was minimal at the soft 22mm bar setting. Then I corded the inside of the 2 fronts and the push was evident
Quote:
Originally Posted by subydude View Post
Greg is talking about the preload springs, not the lockup setting that re-stacking plates would change.

The sway bar change seems odd. You went from full stiff or middle setting? Going to soft should have increased rear grip while allowing more body roll up front. If you're cording the inside of the tires up front maybe you have too much front camber and the reduction of rear sway bar allowed a greater tire contact patch during the increased body roll.
Yep. I was gonna respond but figured Tim would.

I hope it's set perfect for you because dropping and splitting is a pain. I know.

Tim is way more versed and articulate than I am in chassis dynamics. What I do know is a, clutch 1 way front cusco with a setting of 76 ft lbs breakaway, made the car do some suspicious things.

But yeah intial tq and aggressiveness of lock-up are seperate, to an extent. Cone springs/Plates.

And I'm not saying it's right or wrong. Just things I went through along the way. Some will be driver induced. Some like front bias, some like neutral, some (like me) like maximum oversteer.
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Old 06-04-2013, 02:41 PM   #8
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Quote:
Originally Posted by mccanixx View Post
Yep. I was gonna respond but figured Tim would.
Legitimate for that one!

Quote:
Originally Posted by mccanixx View Post
And I'm not saying it's right or wrong. Just things I went through along the way. Some will be driver induced. Some like front bias, some like neutral, some (like me) like maximum oversteer.
I remember hearing your car described as "being sideways in grid"

I've gone from massive understeer to massive oversteer to neutral in my preferences. However, all the people I've co-driven with say I'm more comfortable sideways than straightways....maybe I need to go back to understeer to calm things down
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Old 06-04-2013, 07:31 PM   #9
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This is exactly the thread I was waiting for. Except I don't have a problem with front wheels lifting only the rear. I've tried different sprig rates, and sways and with my v710's on the car I cant get on the throttle at all mid corner. I kept blaming the center diff and was planning to rebuild it. Maybe I'll bite the bullet and replace the front too.
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Old 06-04-2013, 07:35 PM   #10
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sorry for the confusion about the sway. I had understeer, so I removed the stock rear bar and added the WL 22mm on soft. this helped and had the car feeling close to neutral.

The reason I corded the front inside tires, is that I went from -3.2 zero toe, to -4.2 with about 1/4" or more of toe. The tires were 2 years old and at the end of their life and tread. I normally have pretty even wear patterns all around. I should have removed some toe when I swapped tires, but failed to do so and I paid for it....boo

I just ordered a set of BFG R1-S's some 285's. Pretty pumped to see what they are all about. Just came off 295 A6's.

Thanks for the comments and tips guys. I'll be sure to keep a close eye on things to see if the diff is making tuning the handling difficult.

Thanks
Eric
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Old 06-04-2013, 08:09 PM   #11
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Yes, diffs are awesome. If you have the means, I highly recommend picking one -- or two -- up.
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Old 06-07-2013, 01:41 PM   #12
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When driving the car like a grandma on the street do you still get any pogo'ing on slow 90* turns under acceleration?
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Old 06-07-2013, 02:54 PM   #13
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No, you wouldn't be lifting a wheel under those conditions.
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Old 06-07-2013, 09:41 PM   #14
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Quote:
Originally Posted by Deuce Cam View Post
When driving the car like a grandma on the street do you still get any pogo'ing on slow 90* turns under acceleration?
Depending on how "slow" and how "grandma" you're talking about. I have both front and rear diffs, and the rear diff definitely makes going up the "express ramp" at a particular parking deck interesting.
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Old 06-08-2013, 02:40 PM   #15
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I'm curious because I have a cusco rs 1.5 and it pogo's a lot on slow tight turns under acceleration when normally daily driving it (it has the default 100% lockup ). I haven't noticed any bouncing under heavy load; it's very stable.

I've heard the engagement on os diffs is really smooth which I'm guessing would really help on the street. My cusco diff works great when driving spiritedly, but it's kind of like an on/off switch which is a pita on the street.
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Old 06-08-2013, 10:36 PM   #16
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The rear diff only has about 60ish ft/lbs of preload on the springs, so if you're accelerating out of tight corners I could see the diff popping at that time. I don't think it's due to a wheel lifting up or anything, it's just due to the lockup and preload of the diff.

I had a carbonetics rear that is supposed to be decently like the OSG diff and it didn't pop. However I switched to Cusco and found that this one does pop a bit more. It's just the name of the game with spring loaded diffs it seems since our cars make more than break away torque very easily.
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Old 06-08-2013, 11:29 PM   #17
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All I know is, if you install a rear spool, use rear coilovers with 0" of droop travel, a 29mm rear bar, and more than 15* of positive caster, You can finally live up to the hype that your car "handles like a go-kart"...
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Old 07-24-2013, 10:30 PM   #18
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Any particular reason you chose 1-way for the front diff vs 1.5 way?
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Old 07-25-2013, 12:51 AM   #19
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Quote:
Originally Posted by rwheelz View Post
Any particular reason you chose 1-way for the front diff vs 1.5 way?
because understeer is bad?
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Old 07-25-2013, 07:08 AM   #20
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^^

Didn't want more understeer.

The 1.5W rear is ideal with the 1W front from what I've read. Also, after driving it the car really feels nice and grips very well

Eric
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Old 07-09-2019, 03:55 PM   #21
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Default How do you learn to adjust clutch style racing diffs?

Pardon me if you find that I am taking a shotgun approach to finding answers to my questions. I may be asking this elsewhere.

I am about at my wits end with my OS Giken racing diffs.
Searching for books, articles, OSG documentation, how-to's, etc. about adjusting diffs has basically led me on wild goose chases and circular searches. I've only found a couple of general articles on the subject.
I'm looking for who's knowledgeable about racing diffs. Specifically, my OS Giken diffs. I had them custom tuned by OS Giken in California when I purchased them.
Being in Connecticut, I am reluctant to send my diffs all the way to their headquarters in CA for adjustments (diffs which might or might not be correct when I get them back).
So, back in 2014, I felt OSG's were the best of what was offered for my “road racing only” car and shelled out about $3,500 for them. I installed them, doing a close-ratio gearset in the transaxle at the same time. To compound things, I have a new OSG diff to go into the 818R I'm building as well. So, I have three OSG diffs.
After 50 or so hours on them in the STi I feel I am getting increasing slippage in the rear diff in tight turns (like the toe at Watkins Glen and several at Palmer) especially once the diff gets up to temp. BTW, the car handles great otherwise.

Diffs are about the last frontier for me in regards to my abilities to work on a car. I design and build my own race engines, transmissions and do lots of fab/machine work too. I am told the Giken's are fairly sophisticated. I've yet to find an OSG dealer on the East coast that adjusts them! I found one that will rebuild them but they will not attempt to make any adjustments and will not warranty any work on OSG diffs.

Anyone know how I can learn to do them myself? Are there specs out there for torque changes or what I would accomplish by engaging one more of the clutch plates that is normally disengaged? Those kind of things, or is it black magic, trade secrets and so on that make it so hard for me to find anyone to help or teach me?
I do have the specs of how the diffs are set-up now. I understand that I need axle stub tools so I can measure torque. That's about all I know other than the basic design and the concept of how they work.
I don't know if 50'ish hours is enough to mean that the plates should be replaced or whether they last two to four times that long.

I'd appreciate any advice that anyone has to offer! I am in central Connecticut and it'd be great if I can find help in the N-E. If I can do this myself then so much the better. If all I need is a little verbal/texting hand-holding then that would be cool too.
I just don't relish wasted days at the track and the diff in and out of the car a bunch of times with hit and miss adjustments.
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Old 07-09-2019, 11:12 PM   #22
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Some time ago OSG killed off the “do it yourself” market of diff rebuilds and tuning after what I heard were unfavorable results. I’ve talked to Lugod at length at OSG about setting up an autox tune for the diffs and have gone further in regards to tuning/etc there recently. Track tuning would likely be different vs autox so I won’t offer advice there when I honestly don’t know.

What I would suggest is calling and talking to someone there in depth. Preferably Jon Lugod as he does a lot of the tuning and can explain what you’re feeling vs what the diff was setup for. AFAIK none of the true hard parts are available in terms of plates for replacement. The springs and preload washers are around, but without the tuning chart for what preload they give it’s not something you can really do. I know that the current autox tune is a good bit different than the original one they had on file so it’s possible what you got from years ago has been updated.

If you want more info or a phone call doesn’t pan out shoot me a PM.
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Old 07-10-2019, 12:16 AM   #23
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interested in see this thing
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Old 07-10-2019, 11:46 AM   #24
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Quote:
Originally Posted by subydude View Post
Some time ago OSG killed off the “do it yourself” market of diff rebuilds and tuning after what I heard were unfavorable results. ...
What I would suggest is calling and talking to someone there in depth. Preferably Jon Lugod as he does a lot of the tuning and can explain what you’re feeling vs what the diff was setup for. AFAIK none of the true hard parts are available in terms of plates for replacement. The springs and preload washers are around, but without the tuning chart for what preload they give it’s not something you can really do.
... it’s possible what you got from years ago has been updated.
The dealer/service business owner I talked to said he felt like OS Giken's were problematic and unreliable. This might be from what you mentioned above.
I paid the extra premium to have my diffs tuned to my specifications which was based on replicating what they had done for other AWD race cars. I honestly cannot remember what it was other than I gave them my HP, torque weight and tire data. Those notes were lost by them. I have all of the supposed values. The settings for my rear unit should be 25/38 cam angle and 376kg of negative resistance. I guess that's 272 foot pounds. I really need a glossary for diff terms as I have heard some strange words bandied about.
It is inconceivable that new clutch plates are unavailable or at least unavailable to me. Several places (I think OSG in CAli was one) who said they would not sell me parts. I'll try Jon once again. All he offered in February was that I could make a rough stab at increasing clamp force by removing one set of springs. I have not tried that yet. Thanks!
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Old 07-10-2019, 01:58 PM   #25
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That's a lot of negative preload on the diff. They use that as lock timing, so the more negative preload you have the longer it takes for the diff to lock. Total lock is determined by plate stack and to a lesser extent how much negative preload is in the center section.

The negative preload is the secret sauce for the OSG's. It allows zero understeer when the diff is disengaged and then allows lock timing to be fine tuned. The downside is if lock timing is too long it can allow what feels like the diff to slip before it locks, and if it spins up fast (quick spool or some such) when it does lock it can shock things. To an extent the secret sauce is what makes it more prone to damage from the shock loads while other diffs (like Cusco or Kaaz) lock much quicker (and understeer more) but don't experience the same loads.

Long story short, if you have that much negative preload, I'd see about less of that which should help the diff to lock quicker. If it's still slipping after lock then I'd look at stacking the plates differently (assuming they're not already stacked at like 80-100%).
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