Using the wrong snap ring to retain the 3-5 reverse piston on a 6L80E will result in snap, crack, and pop: the snap ring pops out!
There’s been a change to the snap ring and groove on the 6L80/90E 1-2-3- 4, 3-5 reverse drum. If you aren’t aware of this change and use the wrong 3-5 reverse snap ring, the snap ring won’t snap in when you install it. And later, it’ll pop out, resulting in a failed unit.
When was the change and exactly how do you identify early drums from late? The exact Julian date isn’t known, but we do know it was sometime in late 2011 when GM changed the snap ring groove depth and diameter, and diameter of the snap ring. The Julian date is stamped into the drum.
Use the graphics to determine whether you’re working with an early or late drum (figures 1 and 2).
The change made to the drum was to increase the depth of the snap ring for the 3-5-reverse piston for better retention and clamping force. When they did this, they also changed the diameter of the snap ring, from 74mm to 73mm.
Use the same procedure to measure the groove diameter on both early and late drums, using an outside caliper (figures 3, 4, and 5).
The early drum uses a snap ring with a 74 mm inside diameter (figure 6).
The late drum uses a snap ring with an inside diameter of about 73mm (figure 7). The lower snap ring was painted white, and you can see it’s slightly larger (figure 8).
You can use an early snap ring on either the early or late drum; the problem comes when using a late snap ring on an early drum (figure 9). That’ll create what we like to call 3-point contact and you don’t get the snap sound when you install the snap ring.
This leads to the snap ring blowing out, cutting the 3-5 reverse-to-drum O-ring (figure 10). Then, if you select drive or reverse, the 1-2-3-4 and 3-5 reverse clutches will be applied all the time, causing wrong gear starts and a bind in reverse.
There’s a snap ring kit available from ACDelco (figure 11), part number 24260139 that has the three snap rings for the 1-2-3-4, 3-5 reverse, and 4-5-6 drums (figure 12). This is an early snap ring kit, which you can use in both the early and late drum. Remember, you can’t use the late snap ring in the early drum; it’ll pop out.
Your best bet is to replace all three snap rings on every rebuild; the snap ring for the 4-5-6 drum is known to break.
About the Author
Brian Workman career spans over 42 years, he began his transmission career in 1975 while attending Union County Technical Institute and working as an installer. In 1977, Brian went to work for AAMCO Transmissions, in 1987 went to work for Technical Services Dept. of AAMCO Corp, where he soon became manager of Technical Services. Brian is currently the warranty analysis supervisor for LKQ Corp /Global Powertrain Systems, Newnan Ga.