Automatic Transmission Question: Slipping vs Flare
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Flare is usually a brief increase in rpm on an upshift, rpms normally drop on an upshift. Slipping, also an increase in rpm can occur while in gear, under acceleration or load and happen for a longer time. When the slipping stops the rpms drop to the normal range for the gear and speed being driven.
This is an obnoxious trick question.
Everyone knows slippage and flares don't exist because our transmissions are sealed for life.
The automotive industry always has our best interests at heart.
Everyone knows slippage and flares don't exist because our transmissions are sealed for life.
The automotive industry always has our best interests at heart.
Thanks! That helps to clarify the difference for me.
Great answer.
Most multispeed transmissions must apply and release multiple clutches (double-transition shift) to shift. That is, multiple clutches must disengage and multiple others must engage to complete a shift. This is in comparison to older single-transition shifts, which only required one clutch to release and another to apply.
More clutch activity requires more of control and very specific timing to make occur as seamlessly as we expect transmissions to shift.
A shift flare can certainly be caused by worn friction material (as many people expect causes it), but it is just as likely, maybe even more likely, to be caused by something impacting the timing of a double-transition shift.
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What might impact the timing of a shift? Is there a way to determine if the flare is caused by worn friction material vs a timing issue? If worn friction material, would the flare be, at least frequently, repeatable?
All kinds of things. Software calibration, fluid properties and viscosity, small internal leaks (like a nicked seal), sticky valves or components. The list is pretty large and you'd have to look at it in a transmission-specific and shift-specific scenario.
Even then, you may end up with the odd flare or weird shift that's unavoidable. I can tell you that there are modern transmissions that just have funky shifts sometimes. One example involves a particular transmission that has an accumulator that drains after sitting for a while (like, overnight). On the first shift involving that accumulator the next morning, it presents a funky shift as the accumulator refills, then it shifts fine until the next day when the accumulator drains again. Now, the software calibration accounts for these circumstances as much as it can but a perceptive driver may notice it (others may never feel it). That's a situation you're never going to correct. It will be very consistent but it's a result of the transmission design and not an indicator of an issue. The transmission is operating as designed and will live it's entire normal life doing it.
Good point. The answer was kind of hard to put into print, a flare is just that, a quick flare up in rpms when upshifting. A slip is longer in duration and can come before or after a shift with a flare in between shifts too. LOL It's hard to explain, but very easy to show someone while driving with an eye on the tach.
Thanks for the compliment on my 2016 JK Rubicon. I bought it new, and when they upgraded Bitog I learned how to create an avatar. I've been using the avatar for quite a while now.
On top of that it's a TOYOTA! Everybody knows they don't have problems EVER.
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