6T70 Sun Shell

When a 6T70-equipped Equinox, Malibu, Impala, Terrain or LaCrosse drives forward in some gears but has no reverse, no third and no fifth, a failed shell is one of the mechanical causes worth ruling in or out. This is a used OEM 6T70 sun shell for the rebuilder or do-it-yourself owner who has the unit apart and needs the one hard part that failed, not a whole gear train.

How the sun shell works in a 6T70

Inside the 6T70 there are no shift valves. The internal control module times every shift by filling one clutch while releasing another, using five clutches and a single one-way diode across three planetary sets. The sun shell is the stamped drum that carries clutch torque down to a sun gear. Its outer edge is lugged to engage the clutch, and a splined hub welded into its center turns the sun gear. That weld is where these shells give up. ATRA's 6T70 issues seminar lists shell weld breaks as a source of the no reverse, third or fifth complaint, and points out that the replacement shell comes with the number 3 thrust bearing because the two wear together.

Symptoms of a failed sun shell

• Reverse, third and fifth missing, with first, second, fourth and sixth still working
• P0776 stored, with P2715 or P2714 possible in the same event
• Slipping or flaring into third or fifth before those gears are lost
• Steel debris on the pan magnet, or a scored thrust bearing race at teardown
• A hub that turns inside the shell, or a visible crack around the weld

Rule out the cheap causes first

The same symptoms show up from a broken 3-5-Reverse wave plate, a stuck pressure control solenoid or a failed fluid pressure switch, so do not tear the unit down on a code alone. Unplug the transmission connector and select reverse. If reverse works with the harness disconnected, the shell is fine and the problem is electrical. GM Service Bulletin 09-07-30-012F lists the P0776 related codes, and our 6T70 Malibu common problems guide covers the pressure switch faults. For harsh or flared shifts with no mechanical noise, read the 6T70 Equinox shift problems guide before buying hard parts.

Fitment

This sun shell is listed for the 6T70 without a model year. The 6T70 is coded MH2 (front-drive) or MH4 (all-wheel-drive) on the glovebox service label; units coded MH6 or MY9 are the heavy-duty 6T75. 6T70 production spans the 2007 launch, the 2009 carrier update and the 2013 Gen 2 control update, so compare your old shell to the photo for lug count, hub spline count and overall height before installing. If you would rather we check it, send your year and VIN with your order question. All of our 6T70 and 6T75 parts are on the 6T70/6T75 collection page; a dated 2011 shell is also listed as the 6T70 sun shell 2011.

Install notes

• Fit a new number 3 thrust bearing with the shell, and replace any bushing that shows copper or scoring.
• Check the sun gear splines and pinions for debris damage. A carrier with rough or pitted pinions should be replaced with the 6T70 planetary.
• On units built before the 2010 model year, put updated wave plates in every clutch while the case is open.
• Install a new filter and pan gasket with the 6T70/6T75 filter and pan gasket kit, then refill with Dexron VI.
• Clear codes and perform a shift adapt relearn with a scan tool.

Which vehicles use this 6T70 sun shell?

It is for the GM 6T70 six-speed, used in models such as the Equinox, Malibu, Impala, Terrain and LaCrosse. Match the RPO code (MH2 or MH4) and compare the old shell before installing.

Can a bad sun shell cause no reverse in a 6T70?

Yes. A broken weld between the hub and shell is one documented cause of no reverse, third or fifth. Unplug the transmission connector first; if reverse returns, the shell is not the cause.

Do I need a new thrust bearing with it?

Yes. Install a new number 3 thrust bearing with the shell, since a worn bearing will damage the new part.

Is the 6T70 sun shell the same as the 6T75?

We list them separately. The 6T75 differs mainly in its carriers, transfer gear and case, but always compare spline count and dimensions or send your VIN to confirm.

What fluid goes back in after the repair?

Dexron VI. Check the level hot and follow up with a shift adapt relearn.

• 6T70 Malibu Common Problems and Fixes
• 6T70 Equinox Shift Problems: Diagnosis and Fix
• 6T70 Common Problems and Fixes
• 6T70 Equinox Common Problems and Fixes