CVT TR690 swap from Ascent to FXT 18

daklakfoto

Forum Member
Joined
Oct 19, 2018
Messages
48
Location
US
Car Year
2018
Car Model
Forester XT
Transmission
CVT
I know this may be an unknown questions, but i'm pondering if anyone may have some ideas:

18 FXT: 1st gear 3.50; final drive: 4.11 - CVT TR690
19-20 Ascent: 1st gear 3.23; final drive: 4.44 - CVT TR690-with lots of newer updated

Would you think if any advantage in the full tranny swap + rear diff swap? Does it require ECU/TCU update?

I know it is a CVT, but just wondering....
 
Have you enquired about the cost of a Ascent CVT? I think you'd better sit down when you do, it is probably around $15k or more!! :oops:

Seeing as a CVT doesn't have actual gears, you may be able to program the Forester TCU to use the Ascent programming
 
Even if you are able to swap such mechanically, the biggest challenge that you may encounter is the TCU<>ECU interaction. It will be a proper reprogramming and I am not sure if we have reached that point were the mechanic can do that already, just like what we can with 4EAT and 5EAT transmissions. The ECU and TCU are heavily synced to provide you the best possible ride.

It may be easier and closer to reality to do a full powertrain swap so you won't have to worry about the ECU<>TCU interaction but then they also interact with different computers in the car like EyeSight, ABS, etc., and we are not yet sure how those systems will react once they detect such. Cheers.
 
Someone was able to acquire tr690 in ascent for <$1500. So that is why I was asking.

Yet, you are right about other electric gadgets.
 
That's cheap, relatively. How many kms/miles has that transmission done?

Anyway, in that case, it will be a completely new project as I haven't seen anyone online who has done such swap. It will be a hit or a miss. 4.444:1 must also be the ratio of the rear diff, by the way. SSM IV (Buy a Subaru Select Monitor IV) is going to be mandatory here because of computer interactions.

Again, I haven't encountered anyone who has done this yet but if I would do such swap, an SSM IV must always be around me. Cheers.
 
daklakfoto said:
I know this may be an unknown questions, but i'm pondering if anyone may have some ideas:

18 FXT: 1st gear 3.50; final drive: 4.11 - CVT TR690
19-20 Ascent: 1st gear 3.23; final drive: 4.44 - CVT TR690-with lots of newer updated

Would you think if any advantage in the full tranny swap + rear diff swap? Does it require ECU/TCU update?

I know it is a CVT, but just wondering....
Click to expand...

what are you trying to achieve? They both have almost identical '1st gear' ratios once you factor in the diff.

If you want lower gearing, look at if you can pull the diff from the Ascent and put it into the FXT gearbox.
 
@duncanm by diff, are you talking about both front and rear? I was trying to see if it is even possible to take advantage of that 4.44 final drive gear ratio. I believe to achieve that, i would need the whole set of Tr690 (including front) and rear diff. However, to do that, then you need to update TCU/ECU. :)

Since now I ask the question, it seems IMPOSSIBLE to do. probably the better way is to continue with my research and software tweaking/hacking of ECU to tune for torque or simulate center diff locking :).
 
You can probably start with SSM 4. I've read a lot of good feedback from those who have tweaked their Subarus using SSM 4. Cheers.
 
daklakfoto said:
@duncanm by diff, are you talking about both front and rear? I was trying to see if it is even possible to take advantage of that 4.44 final drive gear ratio. I believe to achieve that, i would need the whole set of Tr690 (including front) and rear diff. However, to do that, then you need to update TCU/ECU. :)

Since now I ask the question, it seems IMPOSSIBLE to do. probably the better way is to continue with my research and software tweaking/hacking of ECU to tune for torque or simulate center diff locking :).
Click to expand...

I mean front diff. Sure, its a CVT, but it still has a diff in it, separate to the 'gear set' (CVT). They're probably easily swapped once the box is split.

Obviously you'd need matching rear diff. If you don't understand that, then step away now and use what you have.

I don't see why that would require any TCU/ECU changes, unless one or them is expecting a fixed ratio between output shaft and wheel speed. That'd be really weird. Its more likely the TCU just worries about input shaft/engine and output shaft relative speeds.


My point is if you change the whole box, you'll get no 'final drive' advantage, as the first gears are different.
FXT: 3.50 x 4.11 = 14.385
Ascent: 3.23 x 4.44 = 14.341
That's only 0.3% difference. Quite amusingly exactly equal to 3/10's of f' all!
 
lineartronic_kopie-jpg.28112


I'm not sure that looks like fun to pull apart
 
That picture confuses me. Is the bottom 'pulley' fixed? if so how does that work?
Or is it just a lot smaller than the one coming from the engine? I always thought they were more equal in size.

edit: NVM this shows it:
 
i was thinking of only doing front and rear diff as well. However, it is not the same for CVT as the front is part of the CVT tranny.

Also, i was not so sure if it is even useful.

I was thinking taking advantage of the 1st gear of fxt at 3.5 with the 4.44 somehow.

What i found out across subies, the overal. gear ratio has always been at around 14.4x. There is no documentation on what XMODE would add to that.


duncanm said:
I mean front diff. Sure, its a CVT, but it still has a diff in it, separate to the 'gear set' (CVT). They're probably easily swapped once the box is split.

Obviously you'd need matching rear diff. If you don't understand that, then step away now and use what you have.

I don't see why that would require any TCU/ECU changes, unless one or them is expecting a fixed ratio between output shaft and wheel speed. That'd be really weird. Its more likely the TCU just worries about input shaft/engine and output shaft relative speeds.


My point is if you change the whole box, you'll get no 'final drive' advantage, as the first gears are different.
FXT: 3.50 x 4.11 = 14.385
Ascent: 3.23 x 4.44 = 14.341
That's only 0.3% difference. Quite amusingly exactly equal to 3/10's of f' all!
Click to expand...
 
I see what you mean. You want to get your lowest possible crawl ratio with the Ascent transmission plus with that transmission, you get 80% newly designed and formulated components. The cost-benefit ratio will be too high for you especially with that 0.3% difference.

For me, what will help you a lot will be tuning using SSM. Look for a technician who has been using SSM for quite a while now a Subaru dealership can but won't do this because of warranty and liability concerns. The technician can give you a setting where you will have more torque at lower RPMs. In 4EATs and 5EATs and using older SSMs, the full auto shift points can be manually selected instead of giving the computer time to program those based on your driving behaviour. With the CVTs, I was told you can even reprogram the virtual gear ratios for the Manual Mode or remove the virtual shift points for good!

I have only seen the FreeSSM version but it is for older Subarus only. I think it's one of the biggest secrets/treasures for non-manual Subaru owners. There is also good community writeup with the use of FreeSSM.

I didn't bother using it because I am pretty satisfied with my 4EAT SportShift. Prodrive did a good job with the tuning.

Regarding X-mode, I can't still find any sort of community writeup about it. Based on what others experience, it seems that it regulates throttle input to prevent abrupt torque input and makes VDC become extra sensitive to provide maximum traction. Cheers.
 
The newer app is RomRaider but I have not find out much about it yet.

I'm still r&d this thing.
 
Yes, RomRaider is one of those that can be used to tune and diagnose Subaru and some BMW ECUs. Not sure if you can tune the TCU with it though. SSM is just Subaru-specific but can do much, much deeper tuning, even with the TCU. Cheers.
 
daklakfoto said:
i was thinking of only doing front and rear diff as well. However, it is not the same for CVT as the front is part of the CVT tranny.
Click to expand...

looks like a diff to me.. whatever.

The diffs in all subarus are 'part of the tranny' - but that just means the tranny has to be split to change the diff.
 
Thanks for the vid. I could hear the urgency in his voice.

I wonder how many of those mistakes are DIY and through lube shops. I bet the mistakes are through lube shops/mechanics. I was told by CVT technicians before that when CVTs entered the mainstream market around 20 years ago, technicians/mechanics filled them in with ATF and when the recently filled-in transmissions broke, they would just blame the manufacturer when it was actually their fault, hence, producing hate with such design.

That fill level indicator is very, very handy, by the way.
 
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