Anyone know why we don't use a rear bar? (video added)

[StrutlessWonder]

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Chuck is selling a clutch-type R-180 right now in this thread...
http://www.the510realm.com/viewtopic.php?f=10&t=25672
Anyone know if it would be a direct swap for my Torsen, including the axle stubs?

Yes, and I believe the stubs should also fit.

You can also buy these new from Subaru:
(These are old, "retail prices". New list prices are $630-700+ range. You may be able to get them for less...I just Googled and saw them for $500)

2004-5 CLSD unit alone: 38410AA080 $592
2006 CLSD unit alone: 38410AA120 $572
2005-7 unit alone: 38410AA140 $592
Complete 2006 3.54 CLSD PN 27011AB020 $1553
2007 Torsen 27011AB220 $1553

[S15DET]

Thanks Kurt, great to know.

[Sleepys-14]

I would point the camera at the front tire. I want to see how much the outside front wheel is diving. But considering the rear tire didn't even come completely unloaded, makes me think that there is something wrong with the diff.

[S15DET]

So I've determined that the cause of the traction problem is that excessive rear weight transfer is exceeding the TBR of the diff. (3:1). The solution I believe is to reduce rear weight transfer by increasing front weight transfer. To do that it's been recommended that I add the front sway bar and increase my front spring rate from 200# to 250#. For the sway bar, I ordered a 12" sample piece of 1144 alloy in 1" diameter to perform a bend test. The test was a success (photo below) and I now believe that I will be able to make a sway bar that will fit. However, my next event is in 4 weeks, and I'm not sure I'll be able to make it in time. Here's one thought. To simulate the effect of the front sway bar, I'll try 300# springs in the front, just as a test to see if it cures the traction issue. I know this will have a negative effect on ride quality, but that's OK because this will just be a test.

If it works, and the ride is actually intollarable, then I'll design the sway bar to target the new roll rate with the 300# springs, but with a softer spring. New bar + softer springs to equal 300# springs.

If the ride is tollerable, then scrap the sway bar idea and drive on.

What do you think of the idea of a traction test using 300# springs up front as a way to reduce rear weight transfer?

I may also drill out the slow speed bleed hole in the rear damper as described earlier, test that change alone on Saturday, then install the front springs that night for a comparison on Sunday. One variable change at a time.

[bertvorgon]

Clarify the weight transfer issue... was that under acceleration?

If you put #300 in the front, that will help with both weight transfer to the FRONT ( helping lessen it ), under braking, and, help with some lateral transfer under cornering, as you turn in. This will DECREASE body roll, thus helping to keep the rear corner down, diagonal to the loaded corner.

RIDE QUALITY...more a shock issue than springs....

The #300 springs up front will NOT help with rear weight transfer...as under acceleration.....

You either need a better shock to "slow" the rate ( speed )of rear weight transfer / and/or, a firmer rear spring, coupled with a shock that controls that weight transfer...ie ... in the 50/50 bump / rebound range.

If the rear squats very fast, are you running out of shock or suspension travel? Or, if the shock is too stiff, it cannot absorb the rear weight transfer in a controlled fashion, and that will let the rear tires spin very easily. Basically the shock loading causes the traction loss.

Maybe pop back to the suspension thread, and re-read the part on shocks and springs, then evaluate your situation, might shed a hair more light on it, now that you are experiencing the loss.

Just some thoughts.

[Derek]

Just to add a data point, I too ran a Quaife ATB diff and experienced less than ideal performance -- turn 2 at Thunderhill was particularly bad, the car would basically oscillate between traction and no traction and caused a "hopping" effect. My suspension was set up like so:

250#F/225#R, 15/16" front bar
Front strut inserts Tokiko adjustable set to 4/5
Rear shocks Koni Yellow set to 2/5
1/16" Front Toe in
1/4" rear toe in
3 deg castor
2.5 deg neg front camber
2 deg neg rear camber

My solution in the end was to go to a CLSD!

That being said, my dad and brother run one in their 240Z vintage racer and it works GREAT -- huge traction out of corners. It experiences none of the issues I saw on my 510.

[blueridgespeed]

Brad - as far as not missing something basic - and testing things easily for free - you might check for binding of the rear control arm bushings on extension/droop. I'd remove your rear coilover from the lower mount, and since you don't have the stock style springs to remove, this is even easier for you. Does your suspension droop fully, and easily? Can you push it back up easily (without a tire, the control arm, hub, rotor, some of the axle should be relatively easy to lift.) Keeping a floor jack under the control arm will prevent you from dropping it too far - or worse dropping your rotor?drum on the ground. I don't know if you have a "penultimate" rear crossmember or just slots, but the binding of the bushings in the rear is a real thing. If you've converted to spherical bushings, this shouldn't be an issue, but if you've converted to polyurethane, it may be even worse (more likely to bind) than stock rubber.

[HudsonMC]

Clarify the weight transfer issue... was that under acceleration?

If you put #300 in the front, that will help with both weight transfer to the FRONT ( helping lessen it ), under braking, and, help with some lateral transfer under cornering, as you turn in. This will DECREASE body roll, thus helping to keep the rear corner down, diagonal to the loaded corner.

RIDE QUALITY...more a shock issue than springs....

The #300 springs up front will NOT help with rear weight transfer...as under acceleration.....

You either need a better shock to "slow" the rate ( speed )of rear weight transfer / and/or, a firmer rear spring, coupled with a shock that controls that weight transfer...ie ... in the 50/50 bump / rebound range.

If the rear squats very fast, are you running out of shock or suspension travel? Or, if the shock is too stiff, it cannot absorb the rear weight transfer in a controlled fashion, and that will let the rear tires spin very easily. Basically the shock loading causes the traction loss.

Maybe pop back to the suspension thread, and re-read the part on shocks and springs, then evaluate your situation, might shed a hair more light on it, now that you are experiencing the loss.

Just some thoughts.

We're still not sure if this is a weight transfer problem (inside rear tire getting too unloaded for the LSD action to work) or a traction problem (inside tire geometry getting too negative for it to provide enough traction for the LSD action to work). There is also that weird thing OP was referencing earlier about the rear shock rebound being WAY too stiff...I feel like we're missing something...what about the rear camber issues talked about a couple pages back...I would hate for him to start throwing parts at what may be an adjustment issue or even a bushing issue like blueridge is suggesting.

Either way, I'll throw this in just to give you something to think about contrary to Bert's advice (not because I don't like Bert but because there are many ways to skin the proverbial cat). I think the front would be a good place to start provided all other likely causes have been eliminated. You're on the right track. Increasing the front springs/bar will limit overall body roll and provide higher roll stiffness in the front, reducing the weight transfer in the rear. Weight transfer does not equal body roll. Body roll is caused by weight transfer, but body roll itself does not create any appreciable amount of weight transfer. What I'm saying is that a flat cornering attitude is not the end-all-be-all of handling setups. Nothing inherently wrong with body roll provided it's managed correctly and creating a suspension around this constraint might create tuning headaches for you down the road.

[bertvorgon]

Hudson is right, staying with the basic symptoms first, to see what is going on, is the right approach, before throwing parts at things..

[S15DET]

Thanks for the thoughtful replies; I'm not ignoring, just taking it all in, and I'm right with you. Agreed, the body roll isn't the enemy. Repeatable and consistent loss of traction at the inside rear tire (while trying to put power down coming out of a turn) is the enemy. The diff. seems to be working as it should, the problem is the tractive grip of the inside tire, and you're all right that it could be caused by 1) excessive rear axle weight transfer (unweighting the tire) and/or by 2) poor camber curve severely reducing the contact patch while cornering. My belief is that I need to try and address BOTH of these possibilities.

1) Excessive weight transfer; To reduce weight transfer I will add additional roll resistance to the front axle. I'll do this by installing new front springs or by adding a front sway bar, or both.

2) Contact patch; I will have another look at static rear camber, and try to reduce it to keep that inside rear tire more square to the road. I cannot alter the camber curve before Sept., so it is what it is. Altering this curve will require a total re-design. maybe a winter project, but not a near-term option. I WILL make sure the rear suspension is free to travel and isn't binding.

I doubt I'll be able to make it to a skid pad before Sept. 7th, oh well.

[S15DET]

Well folks, I'm happy to report that that above plan worked. The ONLY change I made for this weekend was to swap the front springs from 200 to 300. The geometry is the same, didn't drill out the rear shock, same tires. Saturday AM, turn one, I know the problem was solved. I can apply nearly full throttle through the turns and I couldn’t be happier. If I try to spin a tire by jerking and stepping on it, I can, but driven normally the corner exit speeds are impressive. The impact on perceived ride harshness is barely noticeable, which is as I understood it would be, but still was a surprise. Also surprising was that there was no added understeer. It’s hard to understand but I can’t tell you if the car is understeering, oversteering or is neutral. For these street tires I was carrying impressive mid-turn speed, and if I wasn’t clearly fighting over or under steer, then I can only assume that it’s pretty close to being well balanced. That or I’m a terribly insensitive driver?

I have the option to add a sway bar, but will have to think about that. My assumption is that more front weight transfer would take me towards in the understeer direction. Maybe I still need to take that trip to the skidpad to get a baseline for the fine-tuning that I can finally get to start, fine tuning alignment, tire pressures, that sort of stuff. This was the first weekend that I was blown away by the cars’ performance, what a rush it is. I can’t’ wait to compare my lap times to my old ITS RX7.

[bertvorgon]

GREAT...that's why we run 300!

By limiting the weight transfer to the front, which you got with body roll and softer springs, that actually decreases the understeer...to a point.

No, you sound like you have got it, the car will likely understeer at a steady state, high speed situation.

It sounds like you have the well balanced situation, that we have, very controllable with the throttle.

In the hands of a smooth driver, this is what you want. Once you "leave" the traction circle, the final characteristic of the car will come out, but, stay within the traction limits..and, you have the well balanced chassis situation.

It is a blast when the car gets to that point, as the confidence level is so high, you can just drive and not THINK about what it is going to do.

As a test..if you can, try getting OUT of the throttle suddenly, in a corner, with some good steering lock, and see what the car wants to do. IF,,it does not have a huge tendency to oversteer, and only just tightens up the line a bit...your there..in my opinion....

[S15DET]

I will do that, and should have Sunday as towards the end of the day the run groups were getting pretty light.

I need to go to the setups thread to see what spring rates you're running in the rear to go with the 300 up front. I have 200 in the rear now with no sway bars on either end.

[Uber Deaf One]

Also surprising was that there was no added understeer. It’s hard to understand but I can’t tell you if the car is understeering, oversteering or is neutral. For these street tires I was carrying impressive mid-turn speed, and if I wasn’t clearly fighting over or under steer, then I can only assume that it’s pretty close to being well balanced. That or I’m a terribly insensitive driver?

When I swapped the front springs in my KA 510 from 225 to 275, it seemed to have actually gained front grip.

[bertvorgon]

I run 1200 in the rear, no rear bar, 1 1/8th front bar.

That will let you know your rear toe is good, on the sudden throttle lift.