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I could live with the fake shifts if they programmed out that 'shudder'!
Catastrophic Transmission Failure 2021 Ascent 10k Miles
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As could I! I've a mental checklist of all the programming-related symptoms I decided I could live with if they'd only fix "this" or "that". I could live with the simulated shifts (most of our driving is way under 50% throttle anyway, and we rarely experience them). I'd really like them to smooth out the step-off bog (probably not with this programming fix), I'd really like them to smooth out the on/off throttle transitions at slower speeds (probably not with this programming fix), and I'd really like them to fix the stumble/shudder (some of which apparently may happen with this programming fix).
If our VIN is not part of the affected bunch...
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Probably not?
Probably?
probably due to what TCM software they're running, which will be dependent on when recall service was done, or if TCM code was updated during a service (eg: for the people who've reported back that their TCM was updated due to complaints).
We'll know more when the official NHTSA filing is done, and the related TSB's and memos are posted.
I believe that they can be related programming. There's a set of conditions which trigger an upshift subroutine to execute. As mentioned previously, the fake upshifts are sequence of events which includes a backing off of the throttle. The shudder appears to be a premature upshift which triggers an engine bog. Could possibly be the same upshift subroutine causing a throttle rollback when you're accelerating gently.
I wonder how much Subaru can change the CVT programming without altering the certified mileage specifications.
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For the issues at hand, pretty easily, I'd guess. Might improve gas mileage a tiny bit too.
I guess I was referring more to the fake shift and shudder behaviors. The EPA doesn't take kindly to changes that make certs invalid.
The whole pressure variability issue is interesting to say the least. The only CVTs that I've worked on were in tractors and they were entirely mechanical. The movement of the variators are in lock step. They just couldn't move one in without moving the other out the corresponding amount.
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Well, most of the shudders shouldn't be (sans the occasional lockup clutch engagement, or turbo wastegate), so, fixing that shouldn't hurt anything. Getting rid of the fake shifts wouldn't affect EPA gas mileage negatively. I bet most testing doesn't even make the car faux shift, as it is probably light on the throttle.
Alas the TR690 uses a calculation based on the input torque (including a safety margin) to determine and set clamping pressure so it's not unnecessarily super high on light throttle. Somewhere Shaeffler has a paper on it, with LuK (the people who helped come up with the original math, and who designed and built our CVT chains) that explains it, and even how much the safety margin is. Shaeffler owns LuK, so, finding anything from either of them can be quite informative, and quite accurate.
CVTs are interesting from an engineering perspective. Like the Wankel engine, they seem like a "no brainer". When hitting on all cylinders, they work well, but perhaps they require meticulous maintenance/programming. You can drag an old Fordomatic or Powerglide through the mud, reinstall it and it will likely get you down the road. The 2.4t/CVT combo seems to demand a lot of asks...durability, performance, faux shifts (to satisfy the public?), MPG numbers, etc, etc.
I'm reminded of the McCulloch VS57 superchargers from the 50s & 60s. They had a vacuum actuated variable diameter driven pulley that changed the effective ratio on demand (drop in vacuum).
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I'm a "car guy"...have been into building cars and modding cars for a long time (though those days are mostly behind me now), and one of the things that drew me to the Ascent was the CVT. I really wanted to try one. I like how you stated it above -- this technology seems like a "no brainer" from a variety of perspectives. They probably aren't as simple as they seem like they should be, but there's something appealing to me about a transmission that, at its core, is simply a set of pulley sheaves and a chain (Subaru/Audi) or a belt (others) with the ability to give you an infinite number of drive ratios with those three basic components. As stepped automatics get more complex and are fitting an increasing number of gears into smaller and smaller packages, the CVT has even more charm to me. My mother-in-law has a 2019 Acura RDX with Honda's (pretty good) 10-speed auto and it generally does behave very well, but it's shifting all the time, and I think while I'm driving it that it's basically trying to mimic a CVT already (keeping the engine in a narrow speed range) that it might as well just be a CVT.
The engineering challenges are not lost on me with regard to keeping a CVT happy (fluid pressure, manufacturing tolerances, etc.), programming it well (it seems like this is a challenge, at least when forced induction is also involved), designing it so it's capable of handling abuse, etc. But I still really like (and agree with) what you said above: they're very interesting devices and seem like an excellent solution to the problem of how to transmit power from the plant to the wheels.
Gear proliferation happened with manuals and manumatics as well. I drove 3 speed manuals before 4 speeds became common, then some 5 speeds and ultimately 6 and even 7 speeds. There was even a 4 speed with a 2 speed rear end (overdrive). That was just the cars. Trucks had more.
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My first car was a 1963 Chevy Biscayne. It had a 2-speed Powerglide and a top speed of 79 mph. A cop did once clock me at 81 miles per hour after I just came over a slight hill and had it floored for 2 minutes straight.
I flipped many 60s and 70s Chevys and even owned a Corvette 327/325 with Powerglide. That car had enough torque to shift into drive by about 15 mph. If you floored it at any speed up to about 45mph it would drop back into "passing gear" (low). With open headers, the sound was way more exhilarating than the acceleration.
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As promised, Cindy, Subaru (a) did the right thing, and (b) started the recall. So, don't let it stress you - if yours is affected, they'll, step up and fix it. Everyone will get physical mail notifications within the NHTSA required notification period - and then receive app and head unit notifications.
RECALL: WRK21 / NHTSA Campaign 21V955000 - Ascent CVT...
RECALL: WRK21 / NHTSA Campaign 21V955000 - Ascent CVT Chain Slip/Chain Guide Breakage Type: Safety Safety Recall: WRK21 NHTSA Campaign: 21V955000 Date: December 9, 2021 Title: Ascent CVT Chain Slip/Chain Guide Breakage Remedy: Open - remedy not yet available RECALL DOCUMENT FILES: To...
www.ascentforums.com
And, to everyone else... the remedy is what I mentioned the other day.
"the chain guide will be visually inspected" I understood that the trans was sealed and not serviceable at the dealer level. I'm not sure how the guide can be visually inspected without opening up the trans case. Perhaps there is an inspection plate to access the innards?As promised, Cindy, Subaru (a) did the right thing, and (b) started the recall. So, don't let it stress you - if yours is affected, they'll, step up and fix it. Everyone will get physical mail notifications within the NHTSA required notification period - and then receive app and head unit notifications.
RECALL: WRK21 / NHTSA Campaign 21V955000 - Ascent CVT...
RECALL: WRK21 / NHTSA Campaign 21V955000 - Ascent CVT Chain Slip/Chain Guide Breakage Type: Safety Safety Recall: WRK21 NHTSA Campaign: 21V955000 Date: December 9, 2021 Title: Ascent CVT Chain Slip/Chain Guide Breakage Remedy: Open - remedy not yet available RECALL DOCUMENT FILES: To...
And, to everyone else... the remedy is what I mentioned the other day.
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It's not "sealed" in the standard sense. For instance, it has a vent/fill tube (it's under your TMIC). But, there are also plugs and ports on the side that could likely be used to get a boroscope inside. This is something Subaru is very skilled at doing (they use such a method to check the A-C/D pillars on the cars), and is easy for a tech to do. Once done, the plug goes back into place.
I think this is the other part of the remedy that needs to be handled before they start servicing cars (any tools necessary need to be shipped to dealers).
But, yes, the dealers will NOT be servicing it if something broken or damaged is found inside - it will be replaced.
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Sounds like a free cvt fluid change! My luck though, they’d be poopholes and put the same fluid back in after draining for an inspection!
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