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Underdog Motorsports - 2015 STI Steering Rack Swap


Underdog

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It seems like the majority of the VDC issues here is the massive change from a 19:1 rack to the 13:1 rack, that's like 50% difference in the angle when the car thinks VDC should come on. Whereas going from 15:1 to 13:1, or 19:1 to 15:1 would only be a 15% or 25% difference, respectively, and may not show up as readily during daily spirited driving to the point where VDC erroneously interrupts.

 

I have VDC issues in my car too. The OBXT doesn't have 19:1 (like the Forester), but it is higher than the Legacy rack.

 

Most of them are solved by turning off traction control. However, the system is not fully defeatable, so quick decreasing radius turns I get ABS pulsing way too easily. But I don't get that one brake dragging hard that happens with the system on.

 

Eventually looks like I'll need to look into scaling the signal up....

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I know you were having issues too. How many turns lock-to-lock for you? My Forester is 3.2 and I was just assuming that was approx. 19:1. EDIT: Thanks for correcting me with the 16.5:1. Edited by GTEASER
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I know you were having issues too. How many turns lock-to-lock for you? My Forester is 3.2 and I was just assuming that was approx. 19:1 (because I saw that number here somewhere) but might be more like 17:1.

 

OEM is 3.2 lock to lock, 16.5:1

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I edited my older posts to get rid of my erroneous 19:1 number.

 

I think that may be why you and oldskoolbiker are having problems, the angle difference between 16.5:1 and 13:1 is too big. 16.5:1 to 15:1 would have been safer, although probably not as huge an improvement in feel, and that's what I plan to do. A guy on http://www.subaruforester.org did just that with his 2011 FXT, installed a 2013 STi rack (15:1) in his FXT (stock rack is 16.5:1), and he has had no issues with VDC.

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Anectdotal but I recall VDC OBXTs switching to LGT racks previously without issue. It seems that stepping down to the 13:1 '15+ STI rack will cause issues in VDC LGTs and OBXTs alike.

 

The 13:1 STI rack is so nice though....

 

I am not sure how the VDC issues show up at the track. But just turning off the system in every day normal driving is 100% worth it in my opinion.

 

I edited my older posts to get rid of my erroneous 19:1 number.

 

I think that may be why you and oldskoolbiker are having problems, the angle difference between 16.5:1 and 13:1 is too big. 16.5:1 to 15:1 would have been safer, although probably not as huge an improvement in feel, and that's what I plan to do. A guy on http://www.subaruforester.org did just that with his 2011 FXT, installed a 2013 STi rack (15:1) in his FXT (stock rack is 16.5:1), and he has had no issues with VDC.

 

WRX USA installed a 15:1 rack in his Outback with VDC and also has no issues.

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I think taking both steps in ratio is where the problem lies. One step and you're fine.

 

Somewhere here there was a link to a NASIOC thread where a guy put a little converter box in. Maybe that is your solution rhitter.

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Can confirm, VDC re-calibration procedure does not fix the issue.

 

Arduino is my next step. Honestly though, just turning off VDC works for now. so it will probably be awhile before I do that.

 

Especially because I have no experience with Arduinos.

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Random question but couldn't we also upgrade the VDC sensors to STI ones? Then recalibrate.

 

It's not the sensors. It's the brain that's the issue. The fix wasn't a recalibration of the sensors, it was to scale the signal into the range that the brain accepted.

 

If you could replace the VDC module with an STI one (not sure that that's possible) it should work fine. No idea what that would take though.

Edited by Rhitter
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Any concern in buying a rack from a wrecked car? I just may pick that one up.

 

I would say only if it was hit in the front or side front. I have a pic of the totaled car that the one I may buy is coming from, and it was hit in the driver's side B-pillar, so the wheels didn't take any impact.

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I'm sure it LOOKS like new, but the one pic on the posting showing the dash shows a shattered windshield and a driver airbag deployed, which doesn't give me much confidence that the rack wasn't jolted and possibly will have internal damage that will show up later. Maybe it was just in a rollover?
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The gearbox can back drive so the crash would have to have been under very specific circumstances to damage the internals. Even so, i would think the inner tie rod would take the brunt and would be deformed.

 

Any used part is a risk but 1) IMO the risk is low, 2) the cost/savings is pretty good, and 3) the buyer is protected somewhat from some risk (if the part is fraudulently listed). I'd snatch it up.

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Its only the stub threads - the rest of the ITR is identical (save for the length). Only the 15+ STI rack got the 20mm stub threads. The ITR spherical joint is the same size between the LGT and STI as well.

 

So just to confirm - to get back some of the toe-in adjustability, all I need to do is install thinner jam nuts on the ITRs, correct? And these are M14x1.5 regardless of what year the rack is?

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So just to confirm - to get back some of the toe-in adjustability, all I need to do is install thinner jam nuts on the ITRs, correct? And these are M14x1.5 regardless of what year the rack is?

 

Yes just thinner jam nuts. Underdog linked the site earlier in the thread. I bought those. I also cut 2-3 threads off the tie rod for some more adjust-ability, but as you can see it probably wasn't needed. This picture was taken after the rack was aligned.

http://i.imgur.com/g4ugK3j.jpg

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WRX USA installed a 15:1 rack in his Outback with VDC and also has no issues.

 

It's actually a SpecB rack, and I know it is different part number than the LGT one. You are correct that I've had zero issues.

 

Underdog (or anyone else) - Can you confirm the ratio on the SpecB rack?

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SpecB rack is the same ratio as the lgt at 15:1.

 

Has anyone with a VDC legacy (non-outback) gone from the 15:1 rack to the 13:1 Sti rack and had issues?

 

It seems like the WRX guys that went to the Sti rack didn't have issues, and most of the issues I see are people making very large changes in ratio, i.e., 15:1 going to a 11.5:1 Q rack, or the outback/foz guys going to the new 13:1 rack.

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It seems like the WRX guys that went to the Sti rack didn't have issues, and most of the issues I see are people making very large changes in ratio, i.e., 15:1 going to a 11.5:1 Q rack, or the outback/foz guys going to the new 13:1 rack.

 

This is exactly what I was getting at.

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