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Old 09-15-2003, 03:04 PM   #1
foreSTir
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Member#: 43077
Join Date: Sep 2003
Location: Texas
Vehicle:
05 OB-XT
GRP

Default Limited Slip Differential interaction with ABS Braking?

How do the WRX's limited slip diffs affect ABS performance? Assuming that ABS is trying to keep any single tire from locking up during braking, and if the limited slip diff is trying to limit the difference in rotation rate all the time (not sure to what degree this happens), would the limited slip's mechanism also affect braking (with engine-braking or otherwise)?

This may explain the WRX's odd ABS behaviour observed in other posts complaining about braking ability.

If a tire loses traction, say under heaving braking and crossing railway, ABS would detect the sudden locking of that wheel. At the same time, the limited slip mechanism can/can't (this is where I'd appreciate some discussion) transfer torque between the wheels and try to keep the tractionless tire from actually locking.

I still don't have a strong intuitive grasp of how the various limited slips work... could this be the culprit of the WRX ABS gremlins?
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Old 09-16-2003, 08:43 AM   #2
Orson
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Member#: 25254
Join Date: Sep 2002
Chapter/Region: MWSOC
Location: Livonia, MI
Vehicle:
2003 WRX wagon

Default

Here's what I've written:
http://www.geocities.com/nosro/abs_f...%20about%20AWD

Here's other odd-end pieces of info I know:
1) Bosch has very very little experience with ABS on AWD vehicles
2) the LSD is not a direct culprit. Plenty of other manufacturers have excellent ABS on AWD vehicles. From my time driving the WRX, it feels like Bosch, in their inexperience, tuned to a very very conservative control. (In the ABS world, conservative means resisting oversteer on ice.) This conservatism impacts all areas of performance and looks like the root cause of all the complaints I hear.
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Old 09-16-2003, 07:29 PM   #3
Merdock777
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Join Date: Jul 2002
Location: Fort Collins,CO
Vehicle:
2002 Impreza 2.5RS
BlindYoAssPlatinumSilver

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I know that certain types of LSD only work when power is applied, not sure about the viscous LSD in the WRX though. But if you are braking there is no power being applied, therefore the LSD is acting like an open diff durring braking. I know that the ABS problems we all see have nothing to do with LSD's as I have an 02 2.5 with NO LSD in the back, and I get all the same crappy ABS charateristics. My solution for the ABS was to install an ABS switch. Now I can turn off the ABS whenever I feel like it and since we all know the curcumstances and road conditions when these crappy ABS characteristics appear it is easy to avoid them. best $10 Mod ever! and if you do it right you can actually use the switch WHENEVER you want the people who have to restart the car to turn the ABS back on have put a switch on the wrong fuse (unless ofcourse they want it that way).

Dan
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Old 09-16-2003, 09:49 PM   #4
foreSTir
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Join Date: Sep 2003
Location: Texas
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05 OB-XT
GRP

Default

I like the idea of having an ABS-disable switch if you're planning to be on gravel, snow, or just for practice. How did you set it up so that it goes back to ABS-enabled whenever the car is restarted (so that you don't forget that it's disabled and get in an accident)?
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