Having worked at the ATRA Hotline for many years, I know that words have meaning. Communication between two “techs” can fall apart if they call the same symptom (or part) by two different terms. I’ve heard of adjectives like “Ruent” or “slap up.” I’m a quick study and figured this out pretty quickly.
ATRA is devoted to training the next generation through the VTS (Virtual Training Solutions) and ATRA University Project. Part of this is to establish a common language. In the September issue of Gears magazine, you’ll see a complete list of definitions we use in the transmission industry. But before we get to that (it’s a long list), I’ll share some of my favorites. Most of these are dynamic terms, meaning it’s how a transmission works and shifts. These are in no particular order.
SLIDE-BUMP
We see this less today than years ago, but even a computer-controlled system can do this. A slide-bump occurs when shifting pressure runs out of time and holding pressure goes to work. In the old days, transmissions used accumulators to apply a controlled leak so the shifting element had a lower pressure than line pressure. If the shift wasn’t complete by the time the accumulator bottomed out, you’d have a bump at the end of the shift. I often hear this on the Hotline as a harsh shift. The harsh part of the shift is so prominent that techs overlook the slide that occurred just before it. The fix for a harsh shift is the opposite of a slide bump, so remedies for a harsh shift make the matter worse. Too often, a slide bump is caused by incompatible frictions (clutch or band) and ATF. Today’s transmissions are so finicky that by using the wrong oil, you can create a slide-bump shift.
FLARE
A flare shift is where one holding element releases too early before the next applying element. Look at the 8L90 clutch apply chart in Figure 1. The 1-3-5-6-7 clutch is applied in 3rd gear and releases during the 3-4 shift, whereby the 4-5-6-7-8 clutch applies and takes over. If the releasing clutch or the applying clutch don’t coordinate properly, you can have a “brief ” moment where neither is applied; you effectively have… neutral. You feel this as a momentary engine rev in the driver’s seat. That’s a flare. To make matters worse, during the 4-5 shift, two clutches release while two clutches apply. This isn’t uncommon for transmissions with so many gears; to avoid this problem, manufacturers will shift past that gear to prevent the problem. In this case, it’ll be a 3-5 shift.
Most transmissions today use a clutch-to-clutch shift strategy (versus a shift that includes a sprag or roller clutch), so shift timing is critical for a smooth and proper shift. Fortunately, today’s computer systems can cope with timing issues and accommodate most irregularities resulting in timing issues. But here, too, the proper ATF plays a role in shift timing. While you might be going through a teardown or valve body replacement, you may be suffering from simply… using the wrong fluid.
BIND UP
A bind-up is the opposite of a flare. In this case, a shifting clutch applies before the applied clutch releases. Let’s use the 8L90 3-4 shift again as an example. If the 4-5-6-7-8 clutch applies while the 1-3-5-6-7 clutch is also applied, then the geartrain will seize momentarily while the exchange takes place. It could feel like someone momentarily hit the brakes or a harsh shift, depending on the severity. An important note here is that the clutch shifting into the bind will suffer more than the already applied clutch. In our 3-4 shift scenario, the 4-5-6-7-8 clutch will likely suffer more than the 1-3-5- 6-7 clutch. You’ll see this in the form of burnt 4-5-6-7-8 clutches. You might falsely condemn the 4-5-6-7-8 drum or a feed circuit.
CHATTER
This is a challenging topic. Too often (particularly with converter clutch chatters), technicians look toward solenoid or valve body problems or even problems with the computer. But let’s step back for a moment and examine this.
We can use a standard transmission clutch as an example. Imagine you have a perfectly good clutch, no hot spots or scoring of any kind. There are two factors at work when applying and using the clutch. Consider the following:
- The rate at which you work the clutch pedal: You can apply the clutch aggressively or very slowly, slipping it during the apply.
- Once the clutch is fully applied, the force applied to the clutch becomes a factor. This determines the amount of torque transfer before the clutch breaks loose and begins to slip.
The question is (Think hard on this): Can you create a chatter if you have a perfectly working clutch by the way you operate the clutch pedal? The answer is, No!
You won’t have a chatter until you have hot spots or a glazed clutch (through repeated slipping). The same applies to an automatic transmission clutch (or converter clutch). The apply rate of a clutch doesn’t affect (or create) a chatter. Therefore, you can’t fix a chatter problem with valve body or calibration changes. And you certainly can’t fix a chatter by replacing solenoids. One additional factor is the fluid. Today’s transmissions have a compatibility matter with the clutches and fluid. You can create a chatter simply by using the wrong fluid. We see this commonly with Honda and Chrysler transmissions (41TE and 62TE, as examples), but the list is getting longer. Based on this, a chatter will occur when either:
- You have incompatible frictions (including bands) and ATF.
- An underlying problem has damaged the frictions (glazing of the frictions or hotspots on the steel plates). In this case, you can rebuild the transmission and deliver it working great, only to have it return months later with a chatter.
We use these phrases in the transmission industry to characterize shift concerns (among others). In the next Gears issue, we’ll include a complete list of terms. We’ll also include a file you can download for future reference.
Now, in closing, I mentioned in the beginning that words matter. Here’s a pet peeve of mine. Take a look at Figure 2. It’s commonly referred to as a “stator.” It’s actually called a “stator support.” Figure 3 shows a stator. It’s a part that’s inside the torque converter. I don’t expect this miss-naming to get fixed with today’s lexicon because it’s been so misused for years.
That’s it. Learn the language and understand the terms. It’s easy once you know what “words” mean.
