6T40 Sprag Clutch 2008

Early first-generation 6T40 transmissions in 2008 GM front-drive cars are now well past the mileage where the low one-way clutch starts to wear. When yours begins to flare on launch, or the car revs in Drive and only gets going once it grabs second, this remanufactured GM sprag clutch for 2008 units is the part that restores first gear. It carries reference number 24274198 on the listing, which you can use to compare against the part you take out.

How the low one-way clutch works in a 2008 6T40

The 6T40 uses five clutch packs and a single mechanical one-way clutch. According to the Sonnax apply chart, first gear in Drive is the 1-2-3-4 clutch applied plus the one-way clutch holding; nothing else. From second through sixth the one-way clutch overruns, and in reverse and manual first the low/reverse clutch is applied hydraulically to do the holding instead. On a Gen 1 unit like this 2008 one, the TEHCM still uses internal pressure switches to monitor clutch apply, and those switches have a high failure rate, which matters when you diagnose a first-gear complaint.

Symptoms on a 2008 Gen 1 unit

• Slip or flare on takeoff in Drive, worse when the fluid is hot
• Engine flares with little movement until the 1-2 shift
• Manual first and reverse still drive normally
• A light clunk or ratchet sound coasting to a stop
• Metal particles on the magnet, often mixed with 3-5-R wave plate pieces on high-mileage early units

How to confirm the sprag is the cause

Gen 1 6T40s have more than one failure that feels like a mechanical slip. Pressure switch and solenoid faults inside the TEHCM can drop gears or set P2723 and P0878, and those point at the 1-2-3-4 circuit, not the sprag. Our 6T40 shift solenoid guide explains how to rule those out. A clean code scan plus a no-first-in-Drive condition that disappears when you select manual first is the classic one-way clutch pattern. Check the level at the plug first, though, because a low 6T40 can slip on launch too; see the common problems guide for the level procedure and the early-unit failure list.

Fitment

This sprag is listed for 2008 6T40 transmissions, which are first-generation units built before GM's 2012 Gen 2 changeover described in bulletin PI0604C. Sonnax warns that many internal parts do not interchange between generations, so do not assume a 2008 sprag fits a 2012-up unit. Match the reference number 24274198 or the part stamped on your old one-way clutch, compare the photo, or send us your year and VIN. If your transmission is a 6T45, use the 2008 6T45 sprag clutch listing; for a unit built anywhere from 2008 to 2013, compare the 6T40 sprag clutch for 2008-2013 as well.

Install notes

• Mark the freewheel direction on the old part before teardown and confirm the new sprag locks the same way by hand before the unit goes back together.
• Replace the race if it is pitted or shows flat spots from the old rollers or elements.
• On a 2008 unit, inspect the 3-5-R wave plate and the bonded pistons while it is apart. The 6T40 master rebuild kit for 2008-2011 matches this generation.
• If the TEHCM pressure switches are suspect, address the controls as well; the 6T40 valve body listing covers later controls, so match your generation before ordering.
• Fill with Dexron VI, set the level hot at the check plug and clear adapts before the road test.

Is this 2008 sprag the same as a 2013 or 2014 6T40 sprag?

Not necessarily. 2008 is a Gen 1 unit, and parts changed with the Gen 2 and Gen 3 updates. Compare the reference number 24274198 and the physical part, or send us your VIN.

My 2008 6T40 has no first but reverse works. Is it the sprag?

That pattern fits a freewheeling one-way clutch, especially if manual first also works. Scan first, since P2723 or P0878 points to the 1-2-3-4 circuit or a solenoid instead.

Is this part new or used?

It is a remanufactured GM part listed for 2008 6T40 units.

What else should I replace on an early 6T40?

Inspect the 3-5-R wave plate and replace the bonded pistons and frictions if the unit is coming apart anyway. A rebuild kit for 2008-2011 covers the soft parts.

What fluid and relearn does it need?

Dexron VI, level set hot at the check plug. Clear the adaptive values and drive through gentle shifts so the TEHCM relearns.

• 6T40 Shift Solenoid Symptoms and Replacement
• 6T40 Common Problems and Fixes
• 6T40 Valve Body Symptoms: What Wears, What It Does to the Drive, and How to Test It
• 6T40 Delayed Engagement: Causes and Fix