6T75 Sun Shell

The 6T75 is the transaxle behind the big GM three-row crossovers: the Chevrolet Traverse, GMC Acadia, Buick Enclave and Saturn Outlook. When one of those stops backing up, and the scan tool shows third and fifth are gone as well, the shell that carries clutch torque to a sun gear is on the short list of mechanical suspects. This listing is a used OEM 6T75 sun shell for anyone who has the gear train out and needs to replace that one piece rather than buy a full set of rotating parts.

What the sun shell does in a 6T75

GM built the 6T75 as the heavy-duty version of the 6T70. ATRA's 6T70 introduction rates the 6T75 for 4,500 lb of towing against 1,000 lb for the 6T70, and lists what makes it tougher: a shot-peened output carrier, a five-pinion carrier, a wider transfer gear, a heavier differential carrier and a ribbed case. Inside, it works the same way as its lighter sibling. There are five clutches and one one-way diode, with no shift valves; the control module inside the case swaps one clutch for another to change gears. The sun shell is a stamped steel drum with a splined hub in the middle. Its lugged rim is driven by a clutch, and the hub turns a sun gear in the planetary set. Every time that clutch applies, the full load of a heavy crossover, often with a trailer behind it, passes through the joint where the hub is welded to the shell.

Symptoms of a broken or worn shell

• No reverse, no third and no fifth, while first, second, fourth and sixth still pull
• P0776 in memory, often joined by P2715 or P2723
• Flare or slip on the 2-3 or 4-5 shift in the weeks before the gears disappear
• Steel particles on the pan magnet, or a whine that follows road speed if the sun gear teeth were damaged
• A hub that spins or rocks in the shell, or a crack running around the weld bead

How to confirm it before you order

ATRA's 6T70 issues seminar puts it plainly: unplug the transmission and see whether reverse engages. If reverse works with the connector off, the shell is intact and the fault is electrical, a pressure control solenoid or a pressure switch. If reverse is still missing, the failure is inside. The same seminar notes the no reverse, third or fifth complaint mainly hit units built before the 2010 model year, where a broken 3-5-Reverse wave plate is the more common cause, so inspect the plates and the shell together. Our 6T70 and 6T75 Acadia common problems guide covers the wave plate bulletin and the codes, and the 6T70 common problems and fixes guide explains the pressure switch faults that fake a mechanical failure.

Fitment

This shell is listed for the 6T75 with no model year. A 6T75 shows RPO MH6 or MY9 on the glovebox service parts label; MH2 and MH4 mean you have the 6T70. The 6T75 was built from the 2007 launch through the 2013 Gen 2 changeover and later, so set your old shell beside the photo and match the lug count, the hub spline count and the depth before you install it. If you would like us to check, send your year and VIN with your question. A dated piece is also listed as the 6T75 sun shell 2011, and every 6T70 and 6T75 part we stock is on the 6T70/6T75 collection page.

Install notes

• Pair the shell with a new number 3 thrust bearing. ATRA notes that a new GM shell is supplied with that bearing, which tells you how closely the two wear together.
• Check every bushing and thrust washer the shell touches, and measure pinion end play in the carrier it drives.
• If the pinions are rough or pitted from wave plate debris, replace the gear set with the 6T75 planetary.
• A unit that has thrown metal needs clutches, seals and updated wave plates. The 6T75 rebuild kit for 2009-2013 covers Gen 1 units.
• Flush the cooler and lines, refill with Dexron VI, and check the level hot.
• Clear codes and run the shift adapt relearn before judging the shifts.

Which vehicles use the 6T75 sun shell?

The 6T75 is the heavy-duty version of the GM six-speed, used in crossovers such as the Chevrolet Traverse, GMC Acadia, Buick Enclave and Saturn Outlook. Confirm RPO MH6 or MY9 on the service parts label.

Will a 6T70 sun shell work in my 6T75?

We list them separately. ATRA's list of 6T75 heavy-duty parts covers the output carrier, five-pinion carrier, transfer gear, differential carrier and case, not the shell, but compare spline count and dimensions or send your VIN before swapping.

My Traverse has no reverse. Is it the shell?

Maybe. Unplug the transmission connector and select reverse. If reverse works unplugged, the shell is fine and the fault is electrical. If it still will not back up, inspect the 3-5-Reverse wave plate and the shell.

What else should I replace with the shell?

A new number 3 thrust bearing, any worn bushings or thrust washers, and updated wave plates. Replace the planetary set if its pinions are damaged.

What fluid and relearn does it need?

Refill with Dexron VI, check the level at operating temperature, then clear codes and run the shift adapt relearn with a scan tool.

• 6T70 Acadia Common Problems and Fixes
• 6T70 Common Problems and Fixes
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