The 4L60E sun gear and reaction carrier work as a team. Wear in either causes 3rd-gear flares, slip in reverse, or full failure. Here is how to diagnose and what parts to buy.
What they do
Sun gear:
- Center gear of the reaction planetary
- Splined to the sun shell
- Reacts torque in 1st, reverse
Reaction carrier:
- Holds 3-4 pinion gears
- Splines to the output shaft
- Bears full output torque
Symptoms of failure
Sun gear failure:
- Loss of reverse
- Loss of 1st
- Sometimes loud whine in those gears
- Often paired with sun shell failure
Reaction carrier failure:
- 3rd gear flare
- 4th gear slip
- Sometimes complete loss of 3rd and 4th
- Metal in pan (gear teeth)
Why they fail
Sun gear:
- Splines strip from sun shell wear
- Heat from clutch wear
- Often a chain reaction with shell
Reaction carrier:
- Pinion bearings wear (heat + miles)
- HP applications stress the carrier
- Welded or cracked carrier from extreme HP
Replacement parts
OEM sun gear:
- 27 spline (standard)
- $60-$120 part
- Always replace with sun shell
OEM reaction carrier:
- 4-pinion (light-duty)
- 5-pinion (HD / 4L65E swap)
- $200-$400 part
HD billet sun and reaction carrier:
- $500-$900 set
- Required for 500+ ft-lb builds
- Sonnax or Alto offerings
Always replace together
- Sun gear + sun shell + reaction carrier
- New thrust washers
- Reaction sun bushing
- Output shaft bushing
Install
- Trans must come out
- Major teardown
- Inspect output shaft for spline wear
- Replace if any pitting on output shaft splines
Cost
DIY OEM replacement:
- Sun gear: $60-$120
- Reaction carrier: $200-$400
- Sun shell (always together): $90-$140
- Thrust washers + bushings: $80-$150
- Total parts: $430-$810
DIY HD billet:
- Billet sun + carrier set: $500-$900
- HD sun shell (Beast): $90-$140
- Hardware: $80-$150
- Total: $670-$1,190
Shop rebuild including these parts:
- Parts: $430-$1,190
- Labor: $1,200-$2,000
- Total: $1,630-$3,190
When to upgrade to billet
- Truck makes 400+ ft-lb at the trans
- Heavy tow use
- Already broke OEM once
- Tuned LS swap or HD diesel
Need 4L60E sun gear, reaction carrier, or HD set? Shop our 4L60E catalog. OEM and HD billet parts, complete rebuild kits. Free shipping over $70.
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