Transmission hard downshift.

[LankyGap]

I have a 2015 Hyundai Accent with a 6-speed auto transmission. I just did two drain and fill with maxlife, but I am pretty sure this has occured before that, and now I am just really focused on the problem.

The transmission shifts smooth almost all the time. But at certain speeds , if I completely completely dxepress the throttle from like 0%-100% rapdily (essentially stomp it), the car downshifts very hard with a thud that reverberates throughout the body of the car.

For example, if I drive along at 40kmh with the rpm at like 1500, in 4th gear, and throttle just barely pressed to maintain speed, and then immediately mash the throttle, there is a very abrupt thud / impact in the tranmission before the downshift. I have never experienced this is a auto transmission before.

What could be causing this, and it this a sign of transmission failure?

 

[Eddie]

Like the Dr. said if it hurts don't do it or pay the price. Good advice, I think. ED

 

[wpod]

Maybe there is a programming problem ? It is like when I hear the engine is missing, I think to my self when you find the engine we can fix it.

 

[GSCJR]

Your foot is causing the problem, stop mashing on it. I mean, you demanding instant acceleration and therefore the transmission downshifts to deliver your request.

 

[JavierH19]

Try driving it more like a grandpa by easing in and out more. The 10 speed in my escalade acts similarly if hit it too much. Pretty much why i always have it in snow mode now since that really detunes the gas pedal which i like.

 

[atikovi]

Get rid of the maxlife and put in the oem fluid for starters.

 

[LankyGap]

Get rid of the maxlife and put in the oem fluid for starters.

I scoured these forums and all I could find was good things about maxlife in Hyundai's....

 

[LankyGap]

Your foot is causing the problem, stop mashing on it. I mean, you demanding instant acceleration and therefore the transmission downshifts to deliver your request.

It is anything but a normal downshift though. Its not like I have never punched it in an auto transmission before.

In regards to not doing that, it is literally required in this slow car for freeway driving.

 

[GSCJR]

It is anything but a normal downshift though.

Okay, it might be a good idea to have your motor/trans mounts checked first.

 

[JustN89]

Get rid of the maxlife and put in the oem fluid for starters.

This is not the fluid.

@LankyGap have you checked fluid level? Mounts? I'd start there and then move on in the diagnosis if those are good.

 

[CKN]

Get rid of the maxlife and put in the oem fluid for starters.

The Maxlife in the past has been a satisfactory OEM replacement. In the case of my wife's Santa Fe (gone now) it actually improved the shifting.

 

[The Critic]

I scoured these forums and all I could find was good things about maxlife in Hyundai's....

The Maxlife in the past has been a satisfactory OEM replacement. In the case of my wife's Santa Fe (gone now) it actually improved the shifting.

New formula (ATF/CVTF) Maxlife or the old formula? A new formula went into circulation about a year ago that is completely different.

 

[CKN]

New formula (ATF/CVTF) Maxlife or the old formula? A new formula went into circulation about a year ago that is completely different.

If that's the case it would have been the old one. I am assuming the current one is "new and improved"????

 

[LankyGap]

This is not the fluid.

@LankyGap have you checked fluid level? Mounts? I'd start there and then move on in the diagnosis if those are good.

I have visually inspected the mounts and they seem good. But TBH this feels like 100% a hard transmission downshift.

Level is confirmed to be good via check level port.

Another note, this problem only occurs when transmission is at operating temp. When it is cool the problem is not reproducible.

 

[The Critic]

I have visually inspected the mounts and they seem good. But TBH this feels like 100% a hard transmission downshift.

Level is confirmed to be good via check level port.

Another note, this problem only occurs when transmission is at operating temp. When it is cool the problem is not reproducible.

Could be viscosity related.

 

[Greasymechtech]

I have visually inspected the mounts and they seem good. But TBH this feels like 100% a hard transmission downshift.

Level is confirmed to be good via check level port.

Another note, this problem only occurs when transmission is at operating temp. When it is cool the problem is not reproducible.

Did you use a scan tool to verify ATF temperatures for that check level port level?

 

[LankyGap]

Did you use a scan tool to verify ATF temperatures for that check level port level?

I measured what came out and put the same back in. Then I let the engine run till at operating temp, and then checked the level port and there was a steady trickle.

 

[LankyGap]

Could be viscosity related.

Could be. Some points though, I think this was always occuring, just I never figured out how to reproduce....now I am fixated on it lol. Point two, is that maxlife has a viscosity of 5.9 @100c, the Eneos SP4 sepcific fluid is 5.75 @100c, and the Idemitsu SP4 specific fluid is 5.31 @100C. Are these differences considered large or small?

 

[The Critic]

Could be. Some points though, I think this was always occuring, just I never figured out how to reproduce....now I am fixated on it lol. Point two, is that maxlife has a viscosity of 5.9 @100c, the Eneos SP4 sepcific fluid is 5.75 @100c, and the Idemitsu SP4 specific fluid is 5.31 @100C. Are these differences considered large or small?

Very similar. Viscosity is not likely your issue, but the friction modification properties may be different and could be a contributing factor.

Also, keep in mind that trans fluid rarely reaches 212F on a passenger car under light duty service. The viscosity curve could also be different between the OE and aftermarket fluids.

 

[The Critic]

I measured what came out and put the same back in. Then I let the engine run till at operating temp, and then checked the level port and there was a steady trickle.

Fluid level is probably wrong - need to verify the AT fluid temp before pulling the check plug. It is different than the engine coolant temp.

https://static.nhtsa.gov/odi/tsbs/2016/SB-10081115-0699.pdf