LET’S PLAY BALL by Lance Wiggins - · PDF fileIn this issue of Let’s Play Ball,...
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18 GEARS September 2003 LET’S PLAY BALL J ust like most every other auto- matic transmission out there, there are some problems where it’s easy to go down the wrong path dur- ing your diagnosis. That’s the case with the 4R100 when it comes to flare shifts; particularly on the 3-4 shift, and it’s a question that comes up often. In this issue of Let’s Play Ball, we’ll enter the world of the 4R100 to find out why a flare can’t happen… and what really is happening. A Little Background Information The definition of flare is “to erupt or intensify suddenly or to expand or open outward.” Although this is only one of the many definitions in the dic- tionary, in our world flare means sliding through a gear, coupled with a rise in engine rpm. It may include a momen- tary neutral condition. In order to do this, one friction component must release earlier than normal during the shift; before the next shifting element engages, so that for a moment the trans- mission is not completely in one gear or the other, almost like neutral Looking at the application chart (figure 1), what clutch comes off during any of the upshifts? That’s right: there isn’t one. So how can you get a flare on a shift? The short answer is: You can’t. So let’s look at a few facts about trans- mission operation in general, and the 4R100 in particular, and see what’s really happening. As the application chart shows, these units employ a continuous clutch application; which means, as the trans- mission upshifts, it simply adds an ele- ment. No clutches come off during a shift, so if a clutch didn’t apply on time, the transmission just wouldn’t upshift; it would remain in the original gear. So what is happening, and why does it feel like a flare shift? To answer that, we first need to clear up a few mis- conceptions about the torque converter clutch and the electrical commands that control its operation. Although the E4OD only came with an on/off converter, the 4R100 came with a PWM converter on some models; beginning with the 1998 Diesel applications (figure 2). Let’s talk a little about the feel of both styles of convert- ers. On/Off Converter Clutch Feel The E4OD used an On/Off style converter clutch; the 4R100 uses a PWM style converter clutch. The differ- ence? Apply feel. Remember back when customers liked how a shift felt? Now, if they feel the shift, they assume we did something wrong, hence the reason for the PWM converter. And this leads to the flare scenario. The complaint usually sounds something like this: “During the 3-4 shift the transmission flares.” My ques- tion is always “what did the torque con- verter clutch do?” The converter clutch strategy for the computer is simple: Slightly release the converter clutch before the shift, so the shift doesn’t lug the motor. Then reapply the converter clutch right after by Lance Wiggins Figure 1 Figure 1
Transcript of LET’S PLAY BALL by Lance Wiggins - · PDF fileIn this issue of Let’s Play Ball,...
18 GEARS September 2003
LET’S PLAY BALL
Just like most every other auto-matic transmission out there,there are some problems where
it’s easy to go down the wrong path dur-ing your diagnosis. That’s the case withthe 4R100 when it comes to flare shifts;particularly on the 3-4 shift, and it’s aquestion that comes up often.
In this issue of Let’s Play Ball,we’ll enter the world of the 4R100 tofind out why a flare can’t happen… andwhat really is happening.
A Little Background InformationThe definition of flare is “to erupt
or intensify suddenly or to expand oropen outward.” Although this is onlyone of the many definitions in the dic-tionary, in our world flare means slidingthrough a gear, coupled with a rise inengine rpm. It may include a momen-tary neutral condition. In order to dothis, one friction component mustrelease earlier than normal during the
shift; before the next shifting elementengages, so that for a moment the trans-mission is not completely in one gear orthe other, almost like neutral
Looking at the application chart(figure 1), what clutch comes off duringany of the upshifts? That’s right: thereisn’t one. So how can you get a flare ona shift? The short answer is: You can’t.So let’s look at a few facts about trans-mission operation in general, and the4R100 in particular, and see what’sreally happening.
As the application chart shows,these units employ a continuous clutchapplication; which means, as the trans-mission upshifts, it simply adds an ele-ment. No clutches come off during ashift, so if a clutch didn’t apply on time,the transmission just wouldn’t upshift;it would remain in the original gear.
So what is happening, and whydoes it feel like a flare shift? To answerthat, we first need to clear up a few mis-
conceptions about the torque converterclutch and the electrical commands thatcontrol its operation.
Although the E4OD only camewith an on/off converter, the 4R100came with a PWM converter on somemodels; beginning with the 1998 Dieselapplications (figure 2). Let’s talk a littleabout the feel of both styles of convert-ers.
On/Off Converter Clutch FeelThe E4OD used an On/Off style
converter clutch; the 4R100 uses aPWM style converter clutch. The differ-ence? Apply feel.
Remember back when customersliked how a shift felt? Now, if they feelthe shift, they assume we did somethingwrong, hence the reason for the PWMconverter. And this leads to the flarescenario.
The complaint usually soundssomething like this: “During the 3-4shift the transmission flares.” My ques-tion is always “what did the torque con-verter clutch do?”
The converter clutch strategy forthe computer is simple: Slightly releasethe converter clutch before the shift, sothe shift doesn’t lug the motor. Thenreapply the converter clutch right after
by Lance Wiggins
Figure 1
Figure 1
the shift is complete. (The only exception is the diesel, whichkeeps the converter clutch applied during the shift, so it does-n’t lose its torque.) This results in a very smooth shift. If theconverter clutch releases too much it feels like a flare becauseof the increased engine rpm.
So how do you identify whether you’re dealing with a realproblem or normal operation? Check the command from thecomputer (figure 3). You’re looking for one of two possibleconditions:
1. The computer is turning the TCC off (or down)before the shift, and back on immediately afterward, whichthe customer is interpreting as a flare. Usually caused by thewrong converter, modifications to the converter apply system,or may even be normal depending on the intensity of the flare.
2. The computer is momentarily commanding thewrong gear (overrunning the desired gear). This is a problem
in the computer system, and must be diagnosed further. Youcan verify this with a shifter box or simple signal monitor.
3-Disk Converter Clutch Some 4R100s use a 3-disk converter with their PWM
systems (Figure 4). This allows for more holding capacity ofthe converter. It also requires a different computer strategythan the 2-disk version.
The “flare” problem sometimes occurs when the techni-cian modifies the converter clutch system from PWM toon/off, or installs a single or 2-disk converter where a 3-diskconverter belongs. That’s why it’s important to understandexactly what the modification you’re performing is designedto do, and what converter originally came with the vehicle.
While modifications to the PWM system may increasethe system’s durability under certain driving conditions,
20 GEARS September 2003
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Figure 2: These two converter plates show the difference between PWM and Non PWM converter plates. Figure 3
My 4R100 Flares During the Shift!
PWMNonPWM
there’s one thing for sure: TheTCC apply will feel different.And it may create that verysame “flare” complaint that weget with the earlier On/Off con-verter clutch systems.
The reason is that while thecomputer commands a slightrelease of the converter during ashift, on/off conversions willcause the converter to releaseentirely. This then feels like aflare (remember the definitionincludes an increase in enginerpm).
To determine if the convert-er clutch is the source of thecomplaint, touch the brakepedal lightly during the upshift.This prevents the TCC fromapplying. If the “flare” goesaway, you’ve identified thesource of the complaint. And inmany cases it’s just a matter ofusing the wrong converter.
So what does this mean about a flare shift on an E4OD or4R100? Because of the continuous clutch application, even ifa clutch didn’t apply, the transmission can’t flare during ashift. But the converter clutch operation can feel just like a
flare shift. So, before you start tearing the transmission apart,looking for a flare problem, be sure to check the TCC opera-tion… and That’s the Game!
GEARS September 2003 21
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Figure 4: 3-Plate PWM Converter
