December 09, 2014

GM 4L60-E Friction Material Options

You have probably seen that popular TV commercial that advertises for a major credit card company. At the end, a celebrity spokesperson asks “What’s in your wallet?” An aftermarket torque converter variant of that question might well be “What’s in your 4L60-E converter?”

First, a little history: Years ago, relining torque converter damper assemblies with friction material was relatively basic. Most transmissions, like the Chrysler 727 LU or the GM 350-C had simple on/off lockup strategies. TCC friction material was relatively hard and dense and the material was easy to bond, but complaints of TCC chatter were common.

Fast forward a few years and the strategies for TCC control have become much more sophisticated. The 4L60-E is a good example of this evolution; the early 4L60-E had a simple on/off control system, while late-model 4L60-E units are designed for constant, controlled slip. As apply strategies evolved, TCC material also progressed through many variations – later models use much softer and more porous materials to reduce NVH (noise, vibration and harshness), while still providing high-temperature protection and long service life.

So what is a converter rebuilder to do when faced with choosing friction material for 4L60-E units? Is the converter going into an early ‘on/off’ unit, or a late model ‘constant slip’ application? Or maybe a mid-generation unit with a relatively short ‘PWM’ apply? Often, converter builders do not have this information.

To further complicate matters, worn-out TCC hydraulic circuits in the transmission valve body can be overlooked by transmission rebuilders. Still more confusion and potential problems can be added due to simple, cheap (and common) valve body mods made by rebuilders. These ‘shortcut’ modifications can eliminate OEM features, drastically raise TCC apply pressure, and potentially build problems into units. To keep some level of sanity here, we won’t even discuss the potential issues that might arise if the converter goes into a vehicle that has been reprogrammed with aftermarket software.

If you know that:

​​​​​​​1. The unit is a constant slip application.

2. The transmission hydraulics are in good repair and have not been modified to function differently from OE.

3.The software controlling the transmission is OE.

Then HTS (High Thermal Slipping material from BorgWarner) is a definite option. It’s nothing like the dense materials from the old days; it’s a much ‘softer’ material that is engineered to act more like a sponge. These qualities are very helpful in controlling NVH, and if all variables are right HTS can provide trouble-free service for 100,000 miles and beyond.

If you are building 4L60-E converters and don’t know what version of transmission they might end up in, HTE (High Thermal Engagement material, also from BorgWarner) is a better choice. HTE has a higher density, but still has great friction and heat-resistant characteristics. While it isn’t as good with NVH issues, it’s still a great long-lasting material that works when you don’t know all the transmission rebuild specifics.

Understanding the variables you control – as well as the variables you don’t – will help you provide a better unit to your customer. And that will allow you to keep more of the good stuff in your wallet.

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