Fretting - Transmission Digest

Fretting

The ASM Handbook on Fatigue and Fracture (Figure 1) defines fretting as: "A special wear process that occurs at the contact area between two materials under load and subject to minute relative motion by vibration or some other force." Fretting wear is usually associated with electrical contacts rather than non-electrical things, but fretting and fretting wear occur with both.
Fretting

Technically Speaking

Subject: Fretting corrosion
Unit: AW55-50
Vehicle Application: 2002 Volvo XC70 AWD
Essential Reading: Rebuilder, Diagnostician
Author: Wayne Colonna, ATSG, Transmission Digest Technical Editor

Technically Speaking

  • Subject: Fretting corrosion
  • Unit: AW55-50
  • Vehicle Application: 2002 Volvo XC70 AWD
  • Essential Reading: Rebuilder, Diagnostician
  • Author: Wayne Colonna, ATSG, Transmission Digest Technical Editor

The Merriam-Webster dictionary defines the noun form of the word “fret” to mean “the action of wearing away: erosion.” As a transitive verb it means “to eat or gnaw into, to make by wearing away a substance.” As an intransitive verb it can mean to “grate, wear, corrode, chafe or fray.”

The ASM Handbook on Fatigue and Fracture (Figure 1) defines fretting as: “A special wear process that occurs at the contact area between two materials under load and subject to minute relative motion by vibration or some other force.”

Fretting wear is usually associated with electrical contacts rather than non-electrical things, but fretting and fretting wear occur with both.

When it comes to electrical fretting, in the automotive industry this is usually the cause of what I call “ghost codes.” You have a solenoid electrical fault so you unplug connectors to check the solenoid and wiring and find nothing. You plug the connectors back and no more codes. This is usually caused by fretting corrosion. Because of vehicle vibration, electrical contacts in connectors can produce oxidized wear debris due to the small-amplitude fretting motion between the electrical contacts. This buildup of insulation is referred to as fretting corrosion and can interfere with the electrical circuit, causing the “ghost code” to set. In many instances this coating is difficult to see with the naked eye, and unplugging and reconnecting a connector cleans up the contacts enough to eliminate the problem.

A similar principle applies to metals. A great example of this coating developing that was once taught to me is tarnished silver. You polish it, yet the tarnish replaces itself to protect the silver. Oxidation of aluminum oxidizing and rusting of iron are due to the way in which their corrosion-resistant (protective) layer is compromised.

Fretting damage to steel can be quickly identified by a reddish-colored dust, as you can see inside the differential where the axle shaft rides in figures 2 and 3. These pictures were sent to me by Joey Campbell in Virginia from a 2002 Volvo XC70 AWD with the AW55-50 transmission. He had to use a pickle fork and a five-pound hammer to get that axle out of the transmission.

This is an extreme example of fretting damage with steel. This fretting problem is what causes driveshaft slip yokes and bolted flanges to produce ringing, clanking and popping noises; it can occur on just about any spline area and is also the explanation of how a rubber seal can leave a groove in a metal surface. The rubber seal rubs off the protective oxide layer. The oxide will then re-form to protect the base metal, and this repeated process is what causes the groove to form.

So when you are dealing with ghost codes, ringing, popping and clanking noise complaints, fret no more! Unplug and clean all electrical connections and apply some dialectic grease, dress and grease up all spline shafts for a fretless, faultless day.

Wayne Colonna, ATSG, Transmission Digest Technical Editor.

You May Also Like

Trying to Stop the Wheel Hop on Ford Edge with 6F50 Transmission

The 2014 Ford Edge SEL with a 3.5L engine (figure 1) and a 6F50 transmission can also be equipped with an AWD system. This would include a Power Transfer Unit (PTU) attached to the transmission with a rear driveshaft going to the Read Differential Unit (RDU). The RDU comprises a differential assembly along with a

The 2014 Ford Edge SEL with a 3.5L engine (figure 1) and a 6F50 transmission can also be equipped with an AWD system. This would include a Power Transfer Unit (PTU) attached to the transmission with a rear driveshaft going to the Read Differential Unit (RDU). The RDU comprises a differential assembly along with a viscous coupling assembly controlled by an Active Torque Control (ATC) coupling solenoid. The system is designed to monitor vehicle conditions continuously and seamlessly adjust torque distribution between the front and rear wheels. When it is functioning correctly, there should be no perception of this taking place when launching or driving the vehicle. 

Sherlock Holmes Approach to an AB60 No-Move Situation

The effectiveness in diagnosing automatic transmission malfunctions is an art form. Although there are similarities among the wide varieties of transmissions on the road, each transmission has its own peculiarities. Aside from having mechanical, hydraulic, and electrical hardware systems to contend with, software/programming issues and various vehicle platforms make diagnostics much more difficult.  Related Articles –

ab60
GM 6T40 Pump Identification Guide

The 6T40 was introduced in 2008 for General Motors front-wheel-drive cars in the Chevrolet Malibu and has gone through several changes throughout its three generations, specifically in the pump area. The 6T40 is closely related to the more lightweight 6T30 and the heavier duty 6T45 and 6T50. Generation one started phasing out during the 2012

Seeing the Forest AND the Trees

They say that the proverbial phrase “I couldn’t see the forest for the trees” means that a person or organization cannot see the big picture because it focuses too much on the details. Related Articles – TASC Force Tips: Hydraulics Fundamentals: Check Valves – Shift Pointers: Mazda Sensitive to Pressure – Transmission Testing & Repairs:

The Manifold Pipeway

The Honda six-speed transmission has been on the bench of many specialty shops for one reason or another (figure 1). But, for those of you who have yet to lay your hands on one, mounted on the upper side of the unit is one of the largest, if not the largest solenoid and pressure switch

Other Posts
Alto releases GM to Volvo differential conversion kit

Alto has released a new differential conversion kit from GM to Volvo, for GM 4T60E and 4T65E transmissions. Model years 1992 and on are covered. The kit comes with 55.63mm OD and 59.69mm OD bearings, Alto said. Related Articles – Toledo Trans-Kit adds transmission kits for Aisin A466, RE6R01A – Toledo Trans-Kit overhaul kits now available

Alto-GM-4T60E,-4T65E,-Differential-Conversion-Kit-1400
The Subaru mystery burn

The Subaru TR580 transmission is known for having torque converter clutch solenoid failures. An example of this can be seen in Figures 1 (above) and 2 (below). Related Articles – Shift Pointers: Sometimes, a repair needs a little more push – Less is more with cordless work lights – Are cell phone diagnostics the future?

Tech-Speak-May-Figure-1-1400
Ford 8F24 mechanical diode failure

Mechanical diode failure in automatic transmissions is not uncommon. As far back as the AODE/4R70 shops have seen this type of failure. In April 2022 an article was published in Transmission Digest called, “The ins and outs of the Hydraulic Selectable One-Way Clutch (SOWC).” This article provided photos of the type of damage this style

Tech-Speak-April-Figure-1-1400
Sometimes, a diagnostic code is all you need

With ATSG having the opportunity to help shops solve problems, sometimes we get faced with some real doozies. A shop will call and give us a laundry list of DTCs, leaving us to think someone must have a bulkhead connector unplugged. We then go through the arduous task of deciding which codes prompted other codes