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Underdog Motorsports - 2015 STI Steering Rack Swap


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2015+ STI Steering Rack Upgrade

Why? The '15+ STI rack has a quicker ratio (13:1, ~2.4 turns lock-to-lock) as compared to the BP/BL LGT/Spec.B (15:1, ~2.8 turns lock-to-lock) and OBXT (17:1). The quicker ratio increases steering response - i.e. less input at the steering wheel for equivalent angle at the front wheels - and also increases steering heft. This makes for a very noticeable improvement in steering feel. The only time I would not recommend this is for users who want the car set up as more of a grand touring highway cruiser - not to say the rack is problematic for highway use, but it is much more direct and engaging than the stock rack.

 

What parts are needed? At a minimum you need only the rack itself (34110VA120).

Optionally, you can also swap out the '15+ STI u-joint (34170VA030) which is solid as compared to the damped version on the LGT/Spec.B. PLEASE NOTE: The OBXT uses subframe spacers requiring a longer u-joint. OBXT owners can use the Perrin Steering Lockdown Kit (PSP-SUS-565), cut and weld in a length of steel rod, or remove the body lift (a project in itself).

I also installed the Cusco rack braces (692 026 ALHD) and Whiteline rack bushings (KSR207, you will use the smaller 45.5mm ID bushing included in the kit), but these are not necessary, and the STI rack comes with new braces and bushings anyways.

The OUTER tie rods appear to be identical to the BP/BL, and the rack comes with new outer tie rods. I am using the Whiteline roll-center correction kit tie rods (KCA313).

 

Are any other modification(s) required? Due to the wider front track of the STI, the tie rods will need to be adjusted almost completely to their inner limit in order to achieve zero toe on the BP/BL platform. By using a M14x1.5 jam nut (e.g. P/N 91938A130 from McMaster-Carr) and trimming ~3-4 threads off the INNER tie rod, you can pick up a few extra millimeters of adjustment. ***This is not strictly necessary*** but is simple and gives you a little margin with your front toe adjustment. Unfortunately we can not swap to the LGT inner tie rods because the stub thread that attaches to the rack itself is M20x1.5 on the STI and M18x1.5 on the BP/BL. To date I have not found another inner tie rod that is a drop-in solution. Fortunately trimming the inner tie rod is simple! Details below. Otherwise all you need to do is tweak the hardlines coming off the rack ever so slightly to mate to the BP/BL power steering hoses - no special tools or parts required for this.

As these cars get up in years and miles, some owners are opting to replace their power steering pump with the '15+ STI unit, which is spec'd for the higher demands of this rack. That said many owners have and continue to use their factory LGT pump without issue.

 

Trimming the inner tie rods (OPTIONAL - SEE ABOVE):

1. Thread two M14 nuts onto one INNER tie rod. Set the outermost nut so that 3-4 threads are exposed. This will serve as a guide for your hacksaw/sawzall/bandsaw/cutting wheel.

2. Cut the exposed threads off. Slow and steady. Use 3-in-1 oil to keep the blade cool (not for abrasive cutting wheels). Keep the cut perpendicular.

3. Thread the two nuts further on to the tie rod, exposing the cut end you just made.

4. Use a file to dress the cut end of the tie rod. Use a metal bristle brush to clean out the threads.

5. Remove both nuts. They will reshape small imperfections in the thread.

6. Repeat on the other inner tie rod.

 

What about VDC? It appears that only the OBXT owners are having trouble with the VDC kicking in at odd times after installing this rack. This is likely due to the extreme difference in ratios between the OBXT and STI racks. LGT owners do not seem to be reporting any issues. Regardless, this is an easy problem to circumvent, as the VDC can be disabled with a press of a button. Work-arounds to keep VDC are beyond the scope of this thread, but as some info has already been posted please feel free to discuss.

 

A brief word about P/S fluid: With the quicker rack, particularly where caster has been added to the front suspension, or aggressive alignment settings are used, it becomes increasingly important to maintain your power steering system. For this reason I recommend flushing the system at the time of the rack install, and using a high quality fluid like Motul Dexron III Technosynthese (1L, P/N 105776). Motorsports users may want to consider additional cooling, as required.

 

Replacement Parts (For Reference Only):

34168FG000 - '15 STI Inner Tie Rod Lock Washer

34128AG000 - '15 STI Inner Boot Band

 

Pictures (moved to attachments due to hosting issues):

 

1. STI tie rods adjusted for max toe in. Just slightly inboard of LGT tie rods which are set for zero toe on my lowered LGT.

326146508_2014_12.02-LGTSTIRackWidthComparison-Copy.thumb.jpg.c15b2a097c2fb15f6c6a901ccd584b02.jpg

 

2. RH bushing braces

453627267_2014_12.02-LGTSTIRHBracket-Copy.thumb.jpg.6efc499f774c837a62b6bb6cbd201e09.jpg

 

3. LGT/STI/Cusco LH braces

457259882_2014_12.02-LGTSTIandCuscoLHBrace-Copy.thumb.jpg.0477ad53ddc50773b86bbe50d666cc47.jpg

 

4. LGT (right) and STI (left) u-joints

2078465988_2014_12.02-LGTandSTIU-Joint-Copy.thumb.jpg.93b19e252b086d555528de0e52bbde5d.jpg

 

5. LGT and STI P/S lines - good clearance to hydraulic lines. May need to tweak hard lines ever so slightly to get good alignment.

1873708039_2014_12.02-STIHydraulicLineClearance.thumb.jpg.be53ac2f8f3bcd0d2ffa84419f61582f.jpg

 

6. P/S lines installed

614533838_2015_01.31-PSLinesInstalled-Copy.thumb.JPG.c00bc21ccf63836c3f70285887a9b2b8.JPG

 

7. STI u-joint installed. Fits just like the LGT joint.

1349147259_2015_01.31-U-JointInstalled-Copy.thumb.JPG.6e8b3d4df3a7230d4bb2316db7f1a39e.JPG

 

8. Cusco LH brace

1122277996_2015_01.31-RackLHBraceInstalled-Copy.thumb.JPG.9a66a80e1d92b86497013735e8609f0c.JPG

 

9. RH brace

1365397903_2015_01.31-RHBraceInstalled-Copy.thumb.JPG.b8798d83bcdd5911e8891fd0b2a2fa23.JPG

 

10. Rack installed - bottom view

546777237_2015_01.31-RackInstalled01-Copy.thumb.JPG.160064dde50be8845a2e2f336f6c017b.JPG

 

11. Rack installed - side view

747775160_2015_01.31-RackInstalled02-Copy.thumb.JPG.e748cbc71e11e0bd2e11e11f818e5560.JPG

 

12. Rack installed - top view

614619717_2015_01.31-RackInstalledFromEngineBay-Copy.thumb.JPG.f77c13750b8c5064d50092c3c4c9a581.JPG

 

13. Rack Label

Rack Label

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Damn I didn't even think about the VDC steering angle information I might not be able to do this if it causes a problem with the VDC. Wonder if simply resetting the steering angle like after an alignment will be sufficient...

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Really not sure with the VDC stuff. I believe the steering angle sensor is incorporated into the roll connector assembly so it's possible swapping that over would send "correct" information, but I'm not sure if it will play nice with whatever algorithm is at work behind the scene. Going to take an adventurous VDC-equipped LGT/OBXT owner to find out. In fact - this applies to my plan to swap the LGT rack into my OBXT as well. Who knows... I may end up tackling this in the spring.
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I am an OEM and aftermarket parts distributor so I sourced these parts from myself. :lol:

 

I can provide these racks for $640. One of my competitors is selling them at dealer cost but way overcharging for shipping, like they do for short blocks. Kickbacks anyone? If they didn't charge 3x actual shipping costs it would have been cheaper to order from them rather than my wholesale distributor. The reality is that even at $640 I am only making single-digit margins.

 

Anyways, this felt incomplete without some pics of the rack installed in the car so I installed the OEM bushings and put the rack in the car so we could get an idea of clearances for the hydraulic lines and any other fitment issues. Everything bolted up without issue. More pics in the first post.

Edited by Underdog
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that's with a 2015 STi rack. what about other STi racks, will any of them fit. I'm sure you can get aftermarket rebuilt racks for less money.

305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD).  CHECK your oil, these cars use it.

 

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Did a lot of measuring and I'm going to be right at the inner-most adjustment limit due to the longer inner tie rods. While probably not strictly necessary, I would prefer to have a bit more positive adjustment range. Rather than modify the STI inner tie rods and buy thinner jam nuts to pick up ~4mm of positive adjustment, I'll just replace them with LGT inner tie rods. The STI rods do not appear to be different from the LGT rods in any other way than length, so assuming they fit it would be crazy to not just do it right.

 

Ordered new LGT inner tie rods, lock washers, and inner boot bands. P/Ns will be added to the first post.

 

that's with a 2015 STi rack. what about other STi racks, will any of them fit. I'm sure you can get aftermarket rebuilt racks for less money.

 

The GR rack should fit but I don't think there is any difference in the ratio.

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The steering angle sensor is in the roll connector behind the steering wheel. There are no sensors built into the rack itself.

 

I don't know if the sensor is scaled differently or if the algorithm takes care of scaling, so there would need to be more research before slapping parts into a VDC car. Could always disable the VDC in the meantime.

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I would imagine that the sensors are the same - just measuring the angle of the steering wheel - and the scaling is applied within the algorithm. Purely speculation though. If the sensor is indeed outputting the steering output angle and not the steering wheel angle then I suppose it would be possible to retrofit the STI roll connector, assuming it fits.
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I read through this thread: http://forums.nasioc.com/forums/showthread.php?t=1757077

 

Unfortunately no one was able to figure it out - quicker rack = VDC off. Bummer. Hopefully I can figure out something (maybe there is a value in the ECU that can be modified). Would really really like the STI rack with VDC .

 

It also looks like only the STIs are able to turn off VDC? All others have to turn off VDC, ABS, and EBD.

Edited by Rhitter
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Unfortunately the LGT inner tie rods will not swap in. The LGT inner tie rod male threads (to connect the inner rod to the rack) are M18x1.5 and the STI inner rods are M20x1.5. Back to modifying the STI inner tie rods and getting a thinner jam nut. Please note: the thread for the inner/outer tie rod connection is the same between the LGT and STI (M14x1.5), so LGT outer tie rods and the Whiteline KCA313 replacements will work. Edited the first post with this information. Edited by Underdog
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