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Car jerks like it's being hit from behind


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I have a 2011 JDM Legacy GT Wagon. Sometimes after applying the brake to slow down then back to stepping on the gas pedal the engine revs as if the car is in neutral for about a second then gets back into gear.

 

This is when it slams/jerks as if the car was hit from behind. The first time it happened I thought someone rear ended me.

 

I am assuming it may be the rear diff or something transmission wise.

 

Anyone ever experienced or having this issue. Or a diagnosis as to what is causing this?

374e924e94ef8c6a29bd33b836a4b1f0.jpg

 

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You've got the 5-speed auto in there, correct? Does this only happen when you really stomp on the gas, or does it happen under light throttle input as well? Sounds like a clutch isn't engaging correctly in the transmission. I'm not sure how the 5EAT is set up, but it almost sounds like either an overrunning clutch that's not reliably re-engaging when you get back on the power, or maybe a sticky solenoid valve that's delaying engagement of a clutch pack. Hopefully one of the 3.6R guys knows more about these transmissions than I do- USDM 5th-gen LGTs are manual trans only, and the 3.6R has the 5EAT that went into the LGT elsewhere.
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The 5eat has been known to be a bit slow reacting to gear changes and throttle input, especially abrupt input like you are describing. I seem to remember someone either on this forum or the Tribeca forum having a similar issue.

 

I personally would shoot a pm over to XRT tuning and see what they say, or take it in to the dealer and see if there is an updated ROM for the transmission.

 

For the DIYr there are only a few things you can do, check front diff play, change trans fluid, check rear diff play. Maybe if you download freessm there is transmission relearn you can do yourself which may temporarily "fix" the issue.

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You've got the 5-speed auto in there, correct? Does this only happen when you really stomp on the gas, or does it happen under light throttle input as well? Sounds like a clutch isn't engaging correctly in the transmission. I'm not sure how the 5EAT is set up, but it almost sounds like either an overrunning clutch that's not reliably re-engaging when you get back on the power, or maybe a sticky solenoid valve that's delaying engagement of a clutch pack. Hopefully one of the 3.6R guys knows more about these transmissions than I do- USDM 5th-gen LGTs are manual trans only, and the 3.6R has the 5EAT that went into the LGT elsewhere.
That's correct, it does have the 5-speed auto. The jerk/bump mostly happen under slight acceleration.

 

What your saying about the clutch not engaging at times seems to Make sense, I will be doing some further checks into that.

 

Thanks for your input

 

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The 5eat has been known to be a bit slow reacting to gear changes and throttle input, especially abrupt input like you are describing. I seem to remember someone either on this forum or the Tribeca forum having a similar issue.

 

I personally would shoot a pm over to XRT tuning and see what they say, or take it in to the dealer and see if there is an updated ROM for the transmission.

 

For the DIYr there are only a few things you can do, check front diff play, change trans fluid, check rear diff play. Maybe if you download freessm there is transmission relearn you can do yourself which may temporarily "fix" the issue.

 

Thanks for the info, I will reach out to the guys at XRT and hear what they have to say also.

 

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Thanks for the info, I will reach out to the guys at XRT and hear what they have to say also.

 

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Thanks guys for the information provided thus far, I planned on changing the front Trans oil and rear diff oil over this weekend. Start my trouble shooting there and see if an these oil change makes a difference.

 

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  • 3 weeks later...

Hiya, if you head over to the Aussie forums (being migrated at the moment so give it a few days) http://forum.liberty.asn.au/index.php?sid=2b72fc63c64cd1624739ea7e232ed2e0

They are up again - use this link: http://forum.liberty.asn.au/viewtopic.php?f=73&t=35044

There are a couple of people with similar issues as we have the Auto GT here, dropping out of gear and back in. The suspicion was that one of the valve body solenoids was acting up but no result yet and can't see bc forum is temporarily out.

I and others with auto GTs have had the occasional soft thump/push like someone had rear-ended you softly, often at low speeds in slow moving traffic when you are lightly on/off the throttle, we think due to catching the auto between downchanges and the extra throttle grabs the gear too quick.

The auto and valve body is the same between 3.6 and GT and it's nothing like the previous 5 speed. The only difference is the TC, it's more slippy in the GT, high torque.

Sounds like a good start with a flush and check of the basics, also a reset to forget whatever it has learned may help.

Edited by Muzza03
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when was the last time you changed the trans oil?

 

I do mine every 30k on my 2003 legacy and it runs like a champ....and I do not use the Subaru stuff because in cold weather it exposes a known issue with the first 2-3 shift being delayed due to long accumulator initial charge time. You need to change the trans fluid more often if you are in stop and go traffic a lot as the fluid really takes a beating under those conditions. Valvoline synthetic ATF is what I use and never seen that problem come back since I started using it at 60K. car now has 120K on it and I will change the fluid when it gets a bit warmer outside.

 

I tried to get the Subaru dealer to do a drain and fill on my '14 at 30K and they said nope....but I am sure they will say yes at 60K even though the new trans (if it lives that long as the car now tries to stall when coming to a stop after driving a bit) will have only 20K on it

Edited by YeuEmMaiMai
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  • 3 weeks later...
Hiya, if you head over to the Aussie forums (being migrated at the moment so give it a few days) http://forum.liberty.asn.au/index.php?sid=2b72fc63c64cd1624739ea7e232ed2e0

They are up again - use this link: http://forum.liberty.asn.au/viewtopic.php?f=73&t=35044

There are a couple of people with similar issues as we have the Auto GT here, dropping out of gear and back in. The suspicion was that one of the valve body solenoids was acting up but no result yet and can't see bc forum is temporarily out.

I and others with auto GTs have had the occasional soft thump/push like someone had rear-ended you softly, often at low speeds in slow moving traffic when you are lightly on/off the throttle, we think due to catching the auto between downchanges and the extra throttle grabs the gear too quick.

The auto and valve body is the same between 3.6 and GT and it's nothing like the previous 5 speed. The only difference is the TC, it's more slippy in the GT, high torque.

Sounds like a good start with a flush and check of the basics, also a reset to forget whatever it has learned may help.

Muzza03 Thank you, this helps alot gonna check the forum out. I did a flush and things seems ok but gonna read up on other fix people find if any.

 

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  • 2 months later...
Thanks guys for the information provided thus far, I planned on changing the front Trans oil and rear diff oil over this weekend. Start my trouble shooting there and see if an these oil change makes a difference.

 

Sent from my SM-N950U1 using Tapatalk

 

Any update on the problem so far?

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Mine does this every so often, I ended up taking the throttle body off and cleaning it.

I also used BTSSM and my Tactrix 2.0 cable to reset the ECU and allowed it to idle for 10-15 minutes to re-learn the idle and it seems to have gotten better.

 

The only issue I still have is harsh downshifts to first under deceleration.

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Mine does this every so often, I ended up taking the throttle body off and cleaning it.

I also used BTSSM and my Tactrix 2.0 cable to reset the ECU and allowed it to idle for 10-15 minutes to re-learn the idle and it seems to have gotten better.

 

The only issue I still have is harsh downshifts to first under deceleration.

 

Ok, thanks for that update. So basically the transmission flush might not work? and I don't have the adapter nor the software to play around with the tuning, so what other options can I explore ?

 

My gt still does it from time to time and it is literally driving me crazy, always have a feeling that something is about to happen, that's not a nice feeling at all.

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Replacing the valve body could do it, but I think I would try a few drain and fills with fresh fluid, maybe amsoil synthetic. Then maybe datalogging the tcu if that is possible I imagine there has to be fluid pressure and temperature data somewhere in the TCU.

 

On a side note, does your 2011 have eyesight? I just noticed the picture in the OP has what looks like the dual cameras in the windscreen.

Edited by FLlegacy
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Same problem here..

I did factory reset and changed fluid.

It shifts very smooth after the change. But the problem is still there.. It happened 2 months and 3000kms after trans fluid change. I guess valve body will to be the next step. Hopefully final step.

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Similar to what happened in my Altima SER - Valve body solenoid was messed up... ended up replacing transmission.... hope its not that extreme.. good luck!

Really hope not, i would be so disappointed with Subaru if that is the case. Thanks for suggesting the possible problem

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Replacing the valve body could do it, but I think I would try a few drain and fills with fresh fluid, maybe amsoil synthetic. Then maybe datalogging the tcu if that is possible I imagine there has to be fluid pressure and temperature data somewhere in the TCU.

 

On a side note, does your 2011 have eyesight? I just noticed the picture in the OP has what looks like the dual cameras in the windscreen.

 

Ok thanks, will try the draining of the transmission fluids and hope that works for now and will have to check out the datalogging, hope someone apart from the dealer here knows how to do that.

 

Yes mine is a 2012 and it has the very same eyesight camera system as the one in the picture..

Really appreciate the suggestions.

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of course we do.... http://legacygt.com/forums/showpost.php?p=5467518&postcount=1744

 

BtSsm (software) and BtSsm or a few other dongles/cables (hardware) are your friends.

 

http://btssm.com/

 

http://legacygt.com/forums/showthread.php/btssm-bluetooth-adapter-app-v-2-267811.html

 

Aside from an ECU reset and idle/tps relearn, you should also perform a TCU reset and transmission relearn procedure (outlined in a few threads and PDFs, shop manual, vacation pix floating around). Thats only if you opt to do it yourself, else a dealership (any around the globe can perform the steps).

Edited by Perscitus
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  • 6 months later...
I did the flush but it came back couple days after. We ended up changing the filter and topped up after, checked the valvebody to see if there were any loose wires but couldn't visibly find any. The filter change resulted in only one slight bump , but it has been ok now for 2 months since the filter change. It will downshift harsh at times but no bump. The error code will be speed sensor 2 which is located within the valvebody and is hardwired in the system. So new valvebody will be needed if that doesn't work. Once again thank you all for the advice..
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Geezus,

 

LGTalex, that's quite a whack from the transmission. Although I have had it react that way once (I believe I manually shifted to 1st and gassed simultaneously and it paused for a second followed by a whack from behind. This only happened one time.

 

I tend to get odd hang ups when slowing down sometimes too. It's every couple of weeks I'll be coming to a stop and it'll thunk pretty good when slowing quickly to a stop. This is following having the torque converter replaced for other reasons by Subaru a few months back. For myself this seems to just be a transmission shifting oddity. It doesn't happen often enough to concern me.

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  • 2 weeks later...
I used the amsoil hp, same oil that the dealer supplies for it, I was skeptical about the valvoline because I believe I read somewhere on the forum that it causes issues in the 5EAT trans..so maybe next oil change I will give it a go.
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  • 5 months later...

Hi everybody,

 

finally I diagnosed what is the problem.

 

Code P1710 appeared. Then I googled it and found out that many people are experiencing the same issue. In Japan there was also a free replacement for it.

 

The cheapest way to repair it is buying turbine speed sensor 2 ($100) which is located on valve body and have it replaced. The more expensive one is having replaced valve body. In every authorised dealership, that is what is going to happen...

 

I found one sensor on ebay, so I am waiting for it to arrive, then I am going to change it.

 

I will let you know what is the result.

 

It's crazy that it took almost 2 years to show the code...

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