Is there anything I’m overlooking in swapping a non-turbo 5 speed MT into a turbo AT Loyale?

[Loyalety]

Hey!

Long time lurker here that finally created an account. I just came into possession of a super clean '90 always-on AWD turbo 4 speed AT Loyale. I've owned a non-turbo '91 toggle AWD 5 speed Loyale for years and I love it but it has a few problems that are stacking up and is just generally in much worse shape than the turbo wagon. The original Loyale has 200k and is pretty tired at this point but the transmission was replaced not too long ago and installed along with a new clutch.

Anyway, I'm considering swapping the 5 speed transmission into the turbo wagon that is in much better shape. I know there are several things to consider including:

- I'd have to swap over more than just the tranny because the turbo models have a different number of splines than the non turbo. Obviously I also need to install the pedal and related clutch parts.

- the gear ratios are slightly different in non-turbo MT's than the seemingly super rare turbo MT's (3.7 non turbo vs 3.9 turbo?). I dont really know how to conceptualize this difference as I know next to nothing about transmission gear ratios but I've read that I will need to switch out the rear axle/diff.

- the AWD toggle wouldn't be functional as the turbo wagon is always on AWD

- the instrument cluster wouldn't be quite right as the automatic position indicators wouldn't be necessary and the 'POWER' light wouldn't have a purpose with the MT. Not a big deal.

Is there anything else I should consider with this specific type of swap? Will I have to deal with perpetual check engine lights or problem lights given the instrument cluster isn't going to be happy with the manual transmission? I've read through a great number of threads about swapping between non-turbo models but only a couple where the person is doing this particular swap.

Thank you so much for any wisdom you might be able to share and thanks for all the guidance provided by everyone here over the years.

Edited April 27, 2022 by Loyalety

[el_freddo]

You won’t get check engine light issues for a transmission swap. 

Your NA Subaru is probably a part time single range 4wd. The AWD versions don’t have a push button for AWD, they’re always mechanically driving all four wheels with a push button on the console to lock the centre diff for the 4wd mode. 

Being that your turbo wagon is auto you might find the diff splines are the same as the NA manual box, only because it’s an auto. 

Diff ratios, if the stickers on the back of the rear diffs are the same you’re good to go. If they’re missing just swap the rear diffs over, they’re a direct swap and easy to do in the L series. 

Instrument cluster centre with the auto settings can be swapped out for the manual one, then work out the wiring pins for each light to work properly. Might need to re-route some wiring from the auto shifter to the manual gearbox for reverse and the 4wd lights. 

You will need to bypass the auto start inhibitor switch so this isn’t a problem when starting. 

That’s all I can think of atm from the top of my head. 

Cheers 

Bennie

Edit addition: there might be a vacuum line from the intake to the auto to block off. Not 100% sure on the turbo models, the NA definitely has one so keep an eye out for it  

Edited April 28, 2022 by el_freddo

[Steptoe's photos]

the auto 3 speed turbo were 23 spline

i had a 4 speed awd out of an 89 RXA/GLTA and from memory it's owner did a same swap to PT 4WD 5 speed box from an RX. I think he also gave me a pair of front shafts, which makes me think he needed to use 25 splines for his RX box, these AWD auto 4 speed shafts may have also been 23 - so you might be lucky on that front. The AWD 4 speed auto also used a different rear gearbox mount to the manual box mounts. The 4 speed AWD auto box weighs about 113kg with it's fluids and torque converter. A PT 5 speed 4WD is mid 50 kg plus flywheel and clutch. The last person I spoke to who fitted an awd 4 speed auto commented on how it seemed to sit lower -it would be the extra 30 odd kilos  The wire for the inhibitor switch is easy to find when you remove auto shifter. Thicker black wire maybe white or yellow trace on it. I just bridged mine. I never made any change to the ECU to tell it that it was now a manual, so that did not affect my driving at all, so you may also be able to forget about that, as I did forget  Always an improvement to get 5 gears with feel to it.

[Steptoe's photos]

oh yeah, the 4EAT as many call it, but I saw a Subaru brochure refer to it as E4AT - has a Trans Control Unit TCU, that can stay or go depending on how you feel