6T40 Planetary 2019

Late-model 6T40 owners, especially in a 2017-2019 Buick Encore, Chevrolet Trax, Cruze or Sonic, usually start looking for a gear set after a road-speed whine shows up or a gear goes missing while the others still pull. This is a used, genuine GM 6T40 gear set carrying part numbers 19125743 and 181310631, removed from a 2019 Buick Encore Preferred FWD with the 1.4L turbo four. That donor showed 12,346 miles, so this is a low-wear part from one of the last model years of the 6T40 in that family, not a high-mileage core.

What the planetary gear set does in a 6T40

The 6T40 makes six forward ratios and reverse with three simple planetary gearsets. Five clutches, two rotating and three stationary, choose which sun gear, ring gear or carrier is driven, held or left free, and that combination is what gives you each gear. Every ratio passes through pinion gears riding on needle bearings, so wear in a carrier or ring gear does not stay hidden in one range: it shows up as noise that follows road speed and, in worse cases, as a gear that no longer transmits torque. The 6T40 input gearset uses four pinions, where the heavier 6T45 uses five, which is one reason the two models should not be mixed when you replace gear train parts.

Symptoms that lead buyers to this part

• A whine or hum that rises and falls with vehicle speed rather than engine rpm
• One forward gear or reverse missing while the rest of the range still works
• Hard steel slivers, needle rollers or broken plate pieces on the pan magnet
• Slip or no reverse, third and fifth with P0776, the 3-5-R circuit problem that can send wave plate debris through the gear train
• Pinions that feel rough or rock on their shafts when the old assembly is spun by hand

How to confirm the gears are the problem

Do not buy hard parts on noise alone. Check the fluid level hot at the level set plug first, since a low 6T40 can make noise and slip. Then drop the pan: fine gray paste is normal wear, but chunks of steel or loose rollers mean something mechanical has let go. Shift complaints with a clean pan are more often clutch or control faults, and our 6T40 common problems and fixes guide sorts those from gear train damage. If you also have speed-related codes, rule out a sensor with the 6T40 speed sensor guide before you open the case.

Fitment

This assembly is listed for a 2019 6T40 and came out of a 2019 Encore 1.4L turbo. The valve body was removed before it was pulled, so you receive the gear set as pictured and nothing more. GM revised the 6T40 several times, with Gen 2 controls arriving for 2012 and further changes later in the run, so gear train pieces from a late unit are not automatically a match for an early one. The reliable check is the GM number: match 19125743 or 181310631 to your old part, compare the splines, gear teeth and overall shape against the photo, or send us your year and VIN before you order. Older units have their own listings, such as the 2013 6T40 planetary, while a 6T45 owner should look at the 2016 6T45 planetary set instead.

Install notes

• Measure pinion end play and inspect every thrust washer, thrust bearing and bushing it touches; replace anything worn or discolored.
• If the old gear set failed from debris, find the source. A cracked 3-5-R wave plate or a worn clutch pack means the whole unit needs attention, and the 6T40 overhaul kit covers the seals and gaskets for that job.
• Inspect the low one-way clutch while the unit is apart; the 6T40 sprag clutch is the matching replacement if it slips or binds.
• Flush the cooler and lines so old debris does not return to the new gears.
• Refill with Dexron VI, cycle through the ranges, set the level hot at the check plug, and run the scan tool fast learn before road testing.

What vehicle did this 6T40 gear set come from?

A 2019 Buick Encore Preferred FWD with the 1.4L turbo engine and about 12,346 miles on it.

Does it include the valve body or any other transmission parts?

No. The valve body was removed, and you receive only the gear set shown in the photo.

Will it fit my older 6T40?

Match GM part number 19125743 or 181310631 to your old part and compare it with the photo. GM revised the 6T40 over its run, so send us your year and VIN if you are unsure.

Can I use it in a 6T45?

No. The 6T45 uses a five-pinion input carrier and other heavier-duty parts, so a 6T45 should get 6T45 gear train parts.

What fluid does the 6T40 use after the repair?

Dexron VI. Set the level hot at the level set plug after cycling through the ranges, then run the fast learn so the shift adapts reset.

What else should I replace while the transmission is apart?

Thrust washers, thrust bearings and worn bushings at minimum, plus seals, a filter and a cooler flush. If debris came from a clutch failure, rebuild the clutches too.

• 6T40 Common Problems and Fixes
• 6T40 Input and Output Speed Sensor Symptoms: How to Tell a Bad Sensor From a Bigger Problem
• 6T40 Gear Ratios and Specs: The Numbers a Builder Actually Uses
• 6T40 Fluid Change Cost