In the August issue of Gears, we covered definitions like flares, bind-ups, and chatters. Shift complaints are challenging, especially when the root cause of the problem has nothing to do with valve body calibration or computer programming. These are dynamic terms and have to do with shift quality. In most cases, shift quality problems are a calibration issue, either with the valve body or computer system.
Let’s talk about friction plates before we get into specific shift-quality problems. As a former rebuilder and Hotline technician, I have practical experience with shift problems caused by incompatible friction plates. Sure, we have to go back many years to draw from these anecdotes, but the same issues exist today, perhaps even more so.
I first realized how friction plates mattered with GM’s THM 400. The complaint was a squawk during the 1-2 shift. I didn’t know enough at the time to recognize the cause of the problem, so I did what rebuilders might do in this situation and threw parts at it. It wasn’t until I discussed it with the late Gil Younger, founder of TransGo®, that I began to learn more about this type of problem. He told me to use a different intermediate clutch plate. Problem fixed. This was an important moment in my rebuilding career and has shaped my thinking ever since. As we continue this topic, I’ll avoid using brand names or innuendos for any friction manufacturer.
While I’m sharing old rebuilding stories, here’s an important one. I was taught to sand the steel plates and drum surfaces with a fine emery cloth to “break the glaze.” I followed this advice for years until I realized I was building complaints into the units. The most memorable example was building a slide bump into every 200-4R I rebuilt by sanding the band surface of the direct drum. I was able to fix the complaint with calibration changes, but it wasn’t until I got serious about the steel plate and drum surface that I could avoid this problem. Years later, I spoke with a friction manufacturer engineer who said, “Dennis, you can’t have a steel plate that is too smooth.” He said using new steel plates was the best choice, but leaving them alone and reusing the old ones was the next best thing. This made me look more closely at micro-finished and Kolene steel plates; they’re very smooth. The takeaway was that a smooth steel plate or drum surface provided a firmer shift, and a rougher surface resulted in a soft or drawn-out shift. In the case of the 200-4R I mentioned, The sanded surface made the shift so drawn out that it couldn’t complete the shift until the accumulator bottomed out, resulting in a bump at the end of the shift.
Another revelation for me as a rebuilder was the converter clutch chatter (often referred to as a shudder). The 1978 Chrysler 904 was the first mainstream transmission with a converter clutch. Soon after came the 727, GM’s THM 200, and THM 350. This was during the gas shortages when manufacturers were scrambling to increase the fuel economy of their vehicles.
In these early years of converter clutches, we struggled to address converter clutch problems. Now, here’s how many converter clutch chatter complaints panned out. You’d deliver the vehicle, and then three weeks later, it’d return with a converter clutch chatter. As I mentioned in the August issue, clutch chatters are not fundamentally a calibration problem. And like a standard transmission clutch, you can’t have a perfect clutch and cause a chatter by the way you apply the clutch. But… if the clutch slips because the pressure plate springs or diaphragm can’t support the load, it’ll slip. This will create hot spots on the flywheel and pressure plate and damage the clutch disc. This damage to the clutch components will likely cause a chatter during the apply.
The same is true with a converter clutch. Initially, it worked fine. However, due to calibration problems, the slipping damaged the friction material and surface on which it works. This is an important distinction. Tuning the calibration to keep the converter clutch from slipping fixed the complaint (the customer returning with a chatter), but it wasn’t the cause of the chatter. The damaged friction material and converter surface (due to the miscalibration) were the cause of the chatter. This is so important that I’ll restate it several times in future articles. The root cause of a chatter is the friction material, the surface it works on, and the fluid.
I used these examples because they’re simple compared to today’s problems and challenges. However, the elements involved (friction material, steel surface, and fluid type) are the same today as they were 40 years ago.
So, let’s look a bit deeper into this topic, and I’ll share a few more anecdotes. Friction material manufacturers make various material types based on engineering from auto manufacturers. Not only does the material composition vary, but some plates are smooth, while others have grooves or a waffling pattern (Figure 1). On top of that, many automatic transmission manufacturers use multiple friction manufacturers for a single unit. That is, they may contract friction manufacturer “A” for two of the clutch packs, friction manufacturer “B” for three of the clutch packs, and friction manufacturer “C” for a single clutch pack. The specifications are rigorous and precise, and the clutches selected are so for a reason. One final thought on friction material manufacturing. Years ago, I toured an Exedy® manufacturing plant. Exedy® is a Japanese firm that made friction plates for JATCO transmissions going back to the 60s. They are a significant player in the manufacturing of friction plates, and while on the tour, I was surprised to learn that they made plates for Mercedes. Imagine a German car manufacturer using Japanese friction plates. This isn’t unique to them; friction manufacturers compete for every clutch pack in almost every transmission.
I’ve gone a bit overboard on this point for a reason. Given the exacting specifications for friction plate design, does it make sense that any ol’ clutch is acceptable for a given clutch pack? And does it bring to light that you may suffer a shifting problem just because of the friction plates you used?
I’ll share two anecdotes from my Hotline days. The first is a Mazda F3A. I regularly received calls about a 1-2 slide bump followed by a 2-3 flare. By the time I got the call, they may have fussed with the unit for a couple of days. After receiving so many of these complaints, I began to think about the friction material. Sure, we’d calibrate through the problem, but after a while, it became clear that we were fighting something simple. Then, on one call, I asked, “Do you still have the original band?” Turned out they did. They installed the old band and fixed the problem.
The next one is the KM series 4-speed. I got almost all of these calls since I liked the units. The complaint was a harsh 2-3 shift. It’s an oddball transmission and has a few quirks in its operation. Take a look at the clutch and band chart in Figure 2.
Notice that three friction elements are applied in 3rd gear: the rear, front, and end clutch. This chart is unique in that it illustrates the transitional phases of the clutch applications. The standard chart in the factory manual doesn’t show this. In addition, any combination of two of the three clutches will result in a 1:1 (direct) ratio. The front clutch makes the shift and controls shift feel (labeled, “While shifting).
The end clutch applies after a period of time (Labeled “Shift complete). There’s no computer sensing or any shift-quality assessment needed to trigger its apply, just time. So if the front clutch doesn’t complete the shift by the time that “time frame” elapses then “BANG” the end clutch applies without any shift-feel control. When someone rebuilt one of these with inferior and out-of-design spec front clutch plates, it wouldn’t complete the 2-3 shift before the end clutch slammed on, resulting in a harsh shift complaint. I’m not sharing this to go through the diagnostics of a unit you probably don’t see these days but to expose a friction-based complaint. We saw this complaint every year for about four years. When parts suppliers sold these inferior parts, everyone working on these units suffered the same complaint. After about three months (when suppliers received compliant frictions), the complaint went away (until next year when they bought the same inferior plates). This is not a condemnation of parts suppliers. I’ve known many over the years, and the vast majority take quality control seriously and are quick to purge inferior parts from their inventory once they discover a problem.
Nevertheless, it’s up to you, the rebuilder, to question plates that look different from those that came out of the unit. Is the material the same color? Does it have the same grooving or other textural features? Do the original frictions have a waved core? Toyota likes using friction plates with a slight wave for particular applications. Replacing them with flat plates will guarantee a shift complaint. Some steel plates also have a wave or a “cone” feature. Here, you’ll notice that if you put the steel on a flat surface, you’ll see the wave or that the inside (or outside, depending on which side of the plate touches the flat surface) has a slight gap around the plate diameter. Paying close attention to the replacement friction and steel plates does not guarantee that the parts are compatible, but you can surely identify plates that aren’t.
Now, let’s take a look at fluid types. Increasingly, the fluid you use has a major impact on shift quality. Hondas, for example, are notoriously finicky when it comes to fluid. Using non-Honda fluid will likely result in harsh shifts, particularly with the 1-2 shift.
When Ford released the Torqshift in 2003 they filled it with SP1 fluid. ATRA was flogged with shift complaints on the Hotline, with nothing wrong with it other than using a different fluid.
Ford released a bulletin addressing a shudder complaint and recommended a simple service with Mercon V fluid. Imagine that. Replacing old fluid with new was all it took to fix the complaint. We verified this specific complaint, and it worked.
Today’s transmissions have friction plates and fluid that are so specialized that you can build in a complaint simply by using out-of-spec frictions or fluid. In addition, these units run hotter than past transmissions and have higher demands on the fluid for heat transfer and lubrication.
So, the next time you rebuild a unit, particularly one you’re less familiar with, take a moment to compare the replacement friction components with the old ones. Look for a sticker or label that shows what type of fluid to use. Some manufacturers go so far as to add a tag near the transmission fill plug with the fluid type and even the fluid part number. Use it. You’ll be glad you did.
