a little description of the tachometer at the exact moment of the "transmission slip" would help - is there a brief upward blip of rpm, as would happen with true slippage, followed by a reduction as the transmission grabs again a split second later? or does the rpm jolt downwards at that exact moment? The latter could mean that your torque converter lockup is not working well.

 

Great question, I forgot to mention. The tachometer shows no abnormalities when it occurs. It stays steady. I don't think it's actually transmission slip that is happening, it just feels like it.

Not sure if this relates, but I do think my torque converter is a little abnormal. It unlocks at 15mph like everyone else's does, causing the false perception of slight acceleration, which many report. BUT, when the engine/CVT gets really hot (hot, humid Florida days, stop-and-go traffic) the unlock can be quite violent. It can feel like the rear bumper getting tapped. This happens even when my rate of deceleration is very slow. It feels like something in the transmission is slamming into something else. Almost like the TC gets stuck, and then finally unlocks with some anger issues.

Switching dealers, and/or insisting that you yourself accompany them on a test drive seem very wise to me. Especially if you go back to the same dealer make sure you know exactly the kind of drive setup to do to get the misbehavior to happen for them (weather, how long after cold start, speeds, throttle opening, gradient of the road, etc. etc.)

This is really good advice. I've just done this so many times in the past that I'm tired of spending my time with them. If I have a name for what the issue might be, it's easier to direct them to it, or fix it myself.

I'm not really expecting anyone to know what the issue is with what I'll call "virtual slipping," but figured it was worth asking since there is such a broad spectrum of great knowledge and helpful folks on this forum.

 

Switching dealers, and/or insisting that you yourself accompany them on a test drive seem very wise to me. Especially if you go back to the same dealer make sure you know exactly the kind of drive setup to do to get the misbehavior to happen for them (weather, how long after cold start, speeds, throttle opening, gradient of the road, etc. etc.)

 

could be the torque converter, those are known to engage abruptly.

 

Early failure of the belt that connects the torque converter to the main part of the CVT can yo-yo in extremes, tbh you shouldn't notice any behavior like that at all. But if it is failing, that 'boing!' sensation like a spring releasing tension is sometimes a symptom.
Most noticeable with people who like to accelerate aggressively, it was a symptom I noted in a high mileage 2014 Nissan Murano. One mechanic said that he was doing fixes on this lady's car who also owned a CVT murano frequently because she liked to stomp on the pedal, causing torque converter related issues. 🤷‍♂️

Overfilling the oil shouldn't produce a transmission symptom as those are not directly related to each other, what overfilling can do is ruin your engine or the seals at the very least because in that scenario you now have an over-pressure event occurring inside it. When in doubt it's better to have it slightly under filled than overfilled.

 

I don't know if I missed this but did anyone mention if the CVT fluid was checked at operating temperature. All I read was that the engine oil was over full. Also I can't see having engine oil slightly over full would make the CVT slip, engine oil and CVT transmission are different systems. My two cents

 

Those two systems do not directly interact in any meaningful way, it's not like a motorcycle where the engine and trans share fluids, so fluid levels of course not relevant. If you want to travel down that rabbit hole; I saw an in-depth analysis of what happened to an engine with double the amount of oil it was supposed to have inspected during a full tear down, the engine was salvaged and mechanic suspected the original owner totaled the vehicle to hide their costly mistake. Here's the synopsis:

The main shaft journaled bearings tore themselves apart because the oil having nowhere else to go, cavitated inside the engine block at key points. The overfilled state left the journaled camshaft bearings and contact points inside the top and bottom unprotected for long enough periods of time the engine self destructed from the friction points having little or no oil protecting them (signs indicated significant torsion and some surface heating of the metal)..​

​

Anyhoo I digress.​

 

The Subaru cvt is very delicate when it comes to launching or aggressive acceleration, especially with a cold engine. These cvts need to be pampered a bit. Let the engine warm a bit at first start up. Short trips and extended OCI is severe duty.

They’re not like regular transmissions that are less expensive to repair.

 

the sensation of a transmission slip at around 5mph, then "catches" and goes on normally.

The torque converter locks up in two stages, partially at 5mph/9kph and fully at 15mph/24kph. While I often notice it unlocking at 15mph I can't remember ever feeling it locking, but this might account for what you're feeling.

 

hello, is there any update on this?

 

Seems to be software related, and starts happening more when I spend lots of mornings crawling along in the school drop-off line with my kids. Going a while without short bursts of acceleration (school vacation), or doing one of the "throttle reset" procedures outlined somewhere on this forum makes it go away.

 

just an FYI it's not normal. take it to your dealership. Ask the mechanic to drive it with you in it.

 

I agree, it's not the way the car is supposed to drive. That said, all indications point to a "learning" behavior of either the throttle sensing software or transmission. Since it is resolved by a reset, or by changing driving behavior, I'm going to ignore it.

Your advice is solid, but I've wasted soooooooo much time pursuing more tangible issues (very harsh torque converter unlock in hot conditions, endless interior rattles) with zero resolution from the dealer. I don't waste my time going there anymore unless it's an issue with 100% concrete symptoms and close to 100% repeatability. Example: I will ask them to address my windshield washer fluid nozzle that sprays 20ft to the right every time I use it. 🥳

 

Not normal in any of 3 CVTs (Subaru) I have owned

 

I may have good news for a lot of people. I took my 2021 Forester in for a jerky transmission at the start of driving. They kept the car for 2 days trying to figure out the problem. Then we all got lucky. A new Subaru transmission software update appeared the second day, February 8, 2023.
That update fixed the problem. The car runs great.

 

@Raygolf1 Good afternoon, would you have a reference number for this software update? My daughter just bought a Subi Forester which is experiencing this issue and she can still return it today, if need be. Subaru dealer and independent mechanic tells her there are no updates available. Thanks!

 

My wife and I are having the same problem with our 2021 Forester. We took it in a 18k miles and they said it needed a new transmission. The dealer did it under warranty. It fixed the problem for about 1k miles and it slowly started to get worse again. Took it back in at 27k miles, they said it needed ANOTHER transmission. They got approval from Subaru corporate and they put ANOTHER brand new transmission in the car under warranty. It has been about another 1k miles and the same probem is starting up again. Not as bad yet, but still there. If anyone has a real fix for this problem, that would be great. We love the car, but this is getting out of hand.

 

@21ForesterTour Welcome to the forum from DFW, TX. Please update your forum profile with details of your vehicle: https://www.subaruforester.org/threads/your-forum-public-profile-how-to-fill-this-out.824165/

Thank you,
bman

 

I'll add a few data points here:

The first 2 clips being the most egregious, you can see the large drop in RPM at around 7mph. In the second clip, you can definitely see the jerk in my camera (despite phone optic stabilization). Some mornings it's barely noticeable, other mornings I seriously considered there could be something wrong with my Forester.

I've always slightly felt that jerky motion since brand new, but I attributed it to a CVT thing. Once it started doing a noticeable jerk, I started searching the forums. The fact that it's not consistently doing it upon a morning cold start makes me think it is computer related. What's keeping me from going to the dealership is that I have a 2" lift since about 20k miles (now around 32k) + CVT drain and fill @ (30k) from an independent Subaru shop. I think the dealership would happily blame it on either of those 2 items before considering it as a widely known warrany issue.

 

Have you found a solution?

 

I am experiencing exactly what you are describing. I bought a 2021 Forester (previously owned a 2001), and noticed this hesitation and jolting when I got back from a long road trip out West. You are the only person I have found that accurately describes the sensation of the chain slipping on a bike. Its is annoying and my kids make fun of me when they are riding with me. Anyway, thanks for confirming that the dealership is a waste of time. Can you send a link to the throttle reset procedure?

 

Actually, " the sensation of the chain slipping" is likely to be exactly what it is doing.
The chain slips on the spindle. It's amazing that it works at all.

 

I kinda doubt it. If the chain was slipping, there would be less resistance and RPMs would jump. My RPMs go down during that jolt. I think it has something to do with the torque converter locking up.

 

@Francisco300
My reply was to post #25, not your post which preceded it.
As to your issue, I agree that it is likely to be the TC and that issue has been identified numerous times on other threads.
It's a common complaint for they way the TC locks and unlocks at low speed.

 

@Francisco300
My reply was to post #25, not your post which preceded it.
As to your issue, I agree that it is likely to be the TC and that issue has been identified numerous times on other threads.
It's a common complaint for they way the TC locks and unlocks at low speed.

@Francisco300 Could you point me to the other posts you refer to?
thanks!

 

@wonder1999 look back up to post # 20.

There is a software update available.

Seems to fix the problem.

Talk to your dealer.