Low line pressure does not provide the necessary apply force to the OD clutches. Incorrect line pressure, whether too low or too high, can cause 68RFE Overdrive issues as well. Luckily, the aftermarket was quick to respond to this shortfall with strengthened Overdrive drums to stop the flex and keep the frictions within clearance tolerance.įailure Point #4: Incorrect Line Pressure The top of the OE housing is not strengthened or supported and is able to flex, much like squeezing the top edge of a salad bowl. We have seen this same issue in the 4L60-E input drums in the past. The OE Overdrive housing itself can lead to the failure of the clutches by allowing excessive flex that causes the OD frictions to heat up preemptively. If vacuum testing indicates bore wear is severe, the bores should be reamed out and oversized valves installed to restore hydraulic pressure. There are innovative, drop-in parts whose design and material outperform OE components. A detailed guide to vacuum testing RFE units is available free at figure 2Īgain, the aftermarket has developed fixes for this issue. Vacuum testing the bore is an ideal diagnostic technique that will allow you to reliably identify the location of leaks and their severity (Figure 2). While fixing the plugs should be your primary concern, as they have the most to do with OD failure, it is still a good idea to inspect and address the switch valve itself, as it can contribute to the problem. OD pressure losses transfer into a lower clutch holding force, which allows the clutches to slip, heat up and prematurely fail. These valves and plugs cycle frequently and over time wear down the casting, which causes crossleaks into and out of the OD circuit. Failure Point #2: Leaking SolenoidĪrguably the weakest link of the Overdrive clutch system is the solenoid switch valve plugs. Today, the option preferred by most professionals and DIYers is to simply install an upgraded housing designed to hold a taller clutch pack built with thicker steels that can take the heat.Īlthough it is easy to place the full blame on the insufficient clutch pack for the OD failure, distorted clutches are only the first visible symptom there are actually several other underlying causes of this failure. In the past, there were few good options for dealing with 68RFE Overdrive clutch failure, common methods being valve body/pump modifications or adding expensive, extra components. This decreases the overall clearance and causes the clutches not to release fully, eventually burning up. Once these clutches heat up past a certain temperature, they begin to distort. Because of their lack of mass, the 68RFE clutches have a very low tolerance to heat and do not dissipate it well. For comparison, the OE steels in the direct clutch pack of a 4L80-E are. These are some of the thinnest clutches to be installed in any transmission. Taking a look at the clutches first, we find that they are single sided, and the steel core is only. Thin frictions that are prone to warping under heat, and a housing that allows enough flex to increase clearances out of specifications, further contribute to the problem. Add increased engine power, larger tires or a heavy load, and there is a very high probability this will be the first failure of the 68RFE. The OD clutch assembly from OE has significant weak points, even at stock power levels. The most common failure point of the 68RFE is the Overdrive clutches. Failure Point #1: Fragile Overdrive Clutches Overlooking the details will almost always spell trouble in life, though, especially in a transmission. Perhaps it is overlooked because it is more exciting to be bragging to buddies about installing a 6” lift, 35’s and a tuner than telling them about upgrading the input shaft. However, when modifying a vehicle for bigger power, it seems to be a trend to overlook the transmission as a necessary area to upgrade. The diesel aftermarket in general has grown significantly, and the 6.7L is capable of making significantly more power than what it comes with from the factory. Although the 68RFE shares similar design features with the 45RFE, it has come a long way in all aspects considering the 45RFE was used in much smaller applications such as the 3.7L Jeep Liberty.
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