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Old 05-25-2009, 12:06 PM   #1
Sylvain b
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Default Rear LSD issue and DCCD setting.

Hello everyone.

I am autoxing for the last two years with my impreza L swapped impreza version 6 (engine + tranny + etc).

The car is setupped more like a FWD than a RWD due to it's natural tendency to understeer AND my experience as a former FWD rally driver.

This situation cause my exterior rear wheel to be lifted during low speed/high G corners. In the past, when applying throttle a little before the apex, the car was power oversteering a little bit so no understeer ans great speed.

Since the end of last summer, the exterior rear wheel spin when the rear LSD is a LITTLE bit hotter than ambiant temperature.

MANY seconds left here and there in slow corner.

A solution that works but is only a temporary "patch" to the problem is to set the DCCD to partialy locked (first orange light). It is helping the car to exit the corner and when spped is better and the rear wheel hit the grount, the cars exit very well.

My question is:
- Do setting the DCCD like this with slick tire on dry asphalt will destroy my DCCD in a short period of time?

I know it will probably worn it faster. But I much faster?

And my next 2 questions:
- If I can find a cheap R180 LSD from a recent STI, will it be clutch type or helical?
- If it is helical, will it cure my exterior rear wheel spin issue?

Thanks.
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Old 05-26-2009, 08:28 AM   #2
KC
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Default

The only thing that's really going to help the exterior rear wheel spin is suspension setup to keep it in contact with the ground while taking a hard turn.

There are plenty of posts in how to set up a Subaru to limit this tendancy, yours being no different because it's an L and/or a swap.

--kC
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Old 05-26-2009, 08:39 AM   #3
Sylvain b
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Quote:
Originally Posted by KC View Post
The only thing that's really going to help the exterior rear wheel spin is suspension setup to keep it in contact with the ground while taking a hard turn.

There are plenty of posts in how to set up a Subaru to limit this tendancy, yours being no different because it's an L and/or a swap.

--kC
Thanks. I know how to keep the rear wheel on the ground. I tried that last year and the car was not as fast as i was with the LSD working properly and the exterior wheel lifted. Acceleration corrected but I was not able to apply throttle as soon as before (understeer).

With the DCCD in "medium lock" position, the car is still fast. The only concern is about the potential problem with the DCCD.

A completly locked rear diff COULD be something to try but I heard that it will cause understeer in corner entry! Not better.
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Old 05-26-2009, 05:21 PM   #4
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Quote:
Originally Posted by Sylvain b View Post
Thanks. I know how to keep the rear wheel on the ground. I tried that last year and the car was not as fast as i was with the LSD working properly and the exterior wheel lifted. Acceleration corrected but I was not able to apply throttle as soon as before (understeer).
So your suspension setup to keep the rear wheel down caused understeer.

What did you change to keep the rear wheel down?
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Old 05-26-2009, 09:06 PM   #5
Sylvain b
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Originally Posted by maxQ View Post
So your suspension setup to keep the rear wheel down caused understeer.

What did you change to keep the rear wheel down?
I did what I could without changing parts.

- Setting the rear sway bar to lowest setting (20mm) did not solve the problem.
- Removing it completly did not solve the problem completly. So I had to set the front damping to maximum setting to keep the rear wheel on the ground.
- I had no front sway bar (it is extreme, but it was working pretty well), so I installed the front sway bar back.

At that time, the car was understeering even with some trail braking. I tried to put some old front pad to make the car turn in better when trail braking and it helped a little. But the car beging to be very unstable. The track (a parking lot with some up and down section to help drain the water) was bumpy as hell.

This was during the worst event I had last year. After that event, I tried to add some toe out in the rear. Help a little bit but the car was ok on entry but oversteering on exit So I was not able to accelerate as hard as I did in the past.

This is when I tried to set the DCCD more toward full lock. The car was then easier to predict. I beging to set it back to its original setup and it worked correctly.

And here we are.

I have found a good deal on a used resr LSD. I will try that.

If you have some answer or suggestion, I am open to try things.

Thanks.
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Old 05-27-2009, 09:23 AM   #6
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Quote:
Originally Posted by Sylvain b View Post

If you have some answer or suggestion, I am open to try things.

Thanks.
I have my rear camber under -1.0, while my front camber is 3. Car is very neutral, tending towards oversteer.

I agree with you, rear toe doesn't really solve this problem.

If the above camber doesn't help, then I'm afraid the only really better solution I can suggest is stiffer front springs.
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Old 05-27-2009, 10:46 AM   #7
Sylvain b
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Quote:
Originally Posted by maxQ View Post
I have my rear camber under -1.0, while my front camber is 3. Car is very neutral, tending towards oversteer.

I agree with you, rear toe doesn't really solve this problem.

If the above camber doesn't help, then I'm afraid the only really better solution I can suggest is stiffer front springs.
I have about the same camber setting as you. Rear is -1.25 and front -3.25.

I recently receive my new coilover kit from stance. I order the wrong front rating (8k). I should receibe my 10k very soon to remove some roll and help keeping the rear on the ground.

Also, by installing the camber plate with camber AND caster position, I get 1.2deg of added caster So I will try to remove some static camber. Something like 3 or even 2.75. With the added caster and stiffer front spring, I will probably get more grip in the front (less understeer) and keep the rear wheel on the ground.

I will also install the 8k spring in the rear.
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Old 05-27-2009, 11:14 AM   #8
maxQ
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Quote:
Originally Posted by Sylvain b View Post
I have about the same camber setting as you. Rear is -1.25 and front -3.25.

I recently receive my new coilover kit from stance. I order the wrong front rating (8k). I should receibe my 10k very soon to remove some roll and help keeping the rear on the ground.

Also, by installing the camber plate with camber AND caster position, I get 1.2deg of added caster So I will try to remove some static camber. Something like 3 or even 2.75. With the added caster and stiffer front spring, I will probably get more grip in the front (less understeer) and keep the rear wheel on the ground.

I will also install the 8k spring in the rear.
Yeah, I'm over 10k on the front with a massive front bar... but I'm also on street tires and ~3200 lbs so your setup might have to be even further on the crazy side.
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