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Old 09-28-2004, 03:41 PM   #1
RS25Tuner
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Member#: 59920
Join Date: Apr 2004
Chapter/Region: South East
Location: Winston-Salem, N.C.
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2004 STI
Aspen White

Question 98 RS-T Engine/Trans/Suspension Swap w/ 98 OBS

I have a few questions for you guys. I have done my research on the 98 Impreza line and learned that the MY98 Impreza’s have a lot of features in common across model platforms. I have a 98 RS-T that was rear-ended and totaled a few months ago that I want to bring back from the scarp heap with a little help from a donor 98 OBS wagon I have run across. I know that the wiring harness is the same on RS and the OBS models and that I shouldn’t have to much of a problem swapping out the motor and ECU. As far as the transmission and the drive train, and independent suspension goes, I have a few questions.

1. Is the transmission on the RS and the OBS the same? I have a feeling they may be similar but I don’t know if they would be exact. I thought I might be able to keep the OBS transmission and motor for a raining day if I have an engine problem in the future. Anyone have any thoughts on this?

2. I am not positive on this but I am guessing that there are differences between the OBS transmission and the RS transmission. If there are differences, I may need to use the axles, center drive shaft, and rear trans axle from the RS to get everything to work correctly. Can anyone confirm that I might have to redo the entire driveline if there is a difference in the transmissions?

3. I think question 3 will go along with question 2. If I swap the struts and disk brakes from my RS and install them on an OBS, will this require me to also use the front axles from the RS in the conversion as well or would the OBS axles work with the RS suspension components?

If anyone can help answer these questions, I would greatly appreciate it. Any additional thoughts are appreciated. Also, if you see a potential pitfall involved in this project, please let me know as well. I would hate to get in the middle of everything and find a problem that would prevent its completion.

Thanks for reading this.

RS25Tuner
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Old 09-28-2004, 04:40 PM   #2
stimpy
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1. The transmissions are fundamentally the same, though the gear ratios are different. They are physically the same size, share the same mounting points, can use either the cable or hydraulic clutch system, use the same clutch, axles, and driveline. If you do change them, be sure to change both the transmission and the rear differential. The real difference is the gear ratios. The OBS will have long-winded gears built for economy. The RS has rather short gears that make for a sporty drive. Take your choice on the gear ratios and go for it.

2. The transmissions are virtually interchangeable. No need to swap axles or driveshaft. Since the MY98 RS has an open rear differential, rear axles don't need to be swapped either.

3. Struts and brakes have nothing to do with the axles. Both the struts and the brakes bolt onto the hub in one form or another. The hub shares the same spline count for all Subaru axles. Since the hub remains, the axles don't have to change. The RS struts and brakes will be a nice upgrade over the OBS. You will lower the car and stiffen it up with the RS pieces. The rear hub, rear brake lines, and parking brake cables will all have to be changed to put the RS brakes in the back. The front brakes will swap right over.

-Jon
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Old 09-28-2004, 05:16 PM   #3
RS25Tuner
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Stimpy! - I can't thank you enough. If I can just secure the car I found I might be able to get whats left of my RS back on the road ... just in a new body . She only had 18K on her when she was totalled so I am looking forward to having a newly reconstructed 2.5RS/OBS-Turbo ! Thanks again for answering my questions. I know I will have more questions so please bare with me as I stumple though them. This will be my first conversion.
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Old 09-28-2004, 05:18 PM   #4
RS25Tuner
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Btw.. Sorry forgot to ask this. I know I might need some special tools to complete the conversion. Anything that would jump out at you that I might need upfront that I might not have though of?
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Old 10-04-2004, 03:27 PM   #5
RS25Tuner
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2004 STI
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Well looks like I am back to square one. The OBS that I found was a POS! Rust from head to toe and the owner wanted way to much money for his problems.
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