Transmission problems

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Nov 22, 2025 | 05:11 PM

dicairem

Thread Starter

3rd Gear

Joined: Nov 2025

Posts: 3

Likes: 3

Transmission problems

Hi everyone,

Looking for help on my 2017 250 lariat 6.7. It has 170,000km.

I am having trouble with a 1-2, 2-1 and 5-6 shifts. The shifts are fairly harsh regardless of throttle input or temperature. No codes or issues with other gears. I have reset adaptive tables multiple times and did a fluid/filter change with no luck.

The shifts are better with exhaust break on or tow/haul mode. Even better when towing a trailer but still there.

Any thoughts?

Nov 22, 2025 | 08:49 PM

Dustin F450

More Turbo

Joined: Mar 2022

Posts: 537

Likes: 223

Change the fluid and filter and report the results after.
I don't care if it was done 50k miles ago, do it again. 90% of the 6r140 issues are lack of maintenance.
use a dedicated LV fluid.

Nov 23, 2025 | 05:38 PM

dicairem

Thread Starter

3rd Gear

Joined: Nov 2025

Posts: 3

Likes: 3

Quote:

Originally Posted by Dustin F450

Change the fluid and filter and report the results after.
I don't care if it was done 50k miles ago, do it again. 90% of the 6r140 issues are lack of maintenance.
use a dedicated LV fluid.

I replaced the fluid a couple weeks ago with no change to the problem unfortunately.

Nov 23, 2025 | 05:41 PM

Dustin F450

More Turbo

Joined: Mar 2022

Posts: 537

Likes: 223

Is it tuned, engine or transmission?

Last edited by Dustin F450; Nov 23, 2025 at 05:43 PM.

Nov 29, 2025 | 02:44 PM

dicairem

Thread Starter

3rd Gear

Joined: Nov 2025

Posts: 3

Likes: 3

I just put in a new oem valve body and it’s shifting perfect!

Nov 30, 2025 | 07:10 AM

HorizontalHunter

Laughing Gas

Joined: Aug 2021

Posts: 898

Likes: 501

Quote:

Originally Posted by dicairem

I just put in a new oem valve body and it’s shifting perfect!

Glad that took care of it and thanks for reporting back with the solution. Not everyone does and it is helpful to other members as well.

Bob

Nov 30, 2025 | 08:18 AM

Toreador_Diesel

FTE Leadership Emeritus

Joined: Sep 2003

Posts: 12,242

Likes: 758

From: Houston, Texas

Quote:

Originally Posted by dicairem

I just put in a new oem valve body and it’s shifting perfect!

9 times out of 10, that's what it is on the 6R140, it's all around a solid transmission

Keep up on your fluid changes every 30,000 miles. Dorman makes a pan with a drain plug to make the service easier. Always use Motorcraft Mercon LV, the parts store stuff may say it's compatible but it's too thin.