I was wondering if anyone could shed some light on this. When going up the grapevine (a very long steep hill for those not in CA), the convertor clutch will unlock but the trans stays in 5th (top) gear. That's fine, it puts the engine in the powerband but I would think it would build extra trans heat. I manually pull it into 4th gear, rpms go up and then the clutch locks and brings to rpms down to almost exactly where thay were in 5th with the clutch unlocked. Just wondering why it wouldn't automatically shift to 4th with the clutch locked rather than build unnecessary heat.
My TL's shifting strategy. A bit confused.
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In sport shift mode it would reasonably be assumed that you are interested in performance. Leaving the TC unlocked would lessen the shock on the trans when you upshift, presumably at high rpm/horsepower, as well as give more gearing/torque multiplication until the point when it does lock up (delayed when under load?).
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Originally Posted By: TooManyWheels
In sport shift mode it would reasonably be assumed that you are interested in performance. Leaving the TC unlocked would lessen the shock on the trans when you upshift, presumably at high rpm/horsepower, as well as give more gearing/torque multiplication until the point when it does lock up (delayed when under load?).
But it actually locks the convertor going uphill in manual 4th gear.
In sport shift mode it would reasonably be assumed that you are interested in performance. Leaving the TC unlocked would lessen the shock on the trans when you upshift, presumably at high rpm/horsepower, as well as give more gearing/torque multiplication until the point when it does lock up (delayed when under load?).
But it actually locks the convertor going uphill in manual 4th gear.
Maybe it was anticipating a downshift when in 5th but it's logic told it that there probably woudn't be a downshift from 4th?
Or maybe it's programmed to keep the engine RPMs in a certain sweet spot when taking load, incline, throttle position, etc. into account.
My sister drove a TL when her TSX was in for service and she said the transmission is always thinking in that car...downshifting when you begin to brake for a stoplight, etc.
If what it's doing was detrimental to the mechanicals, Honda wouldn't have programmed it that way.
Or maybe it's programmed to keep the engine RPMs in a certain sweet spot when taking load, incline, throttle position, etc. into account.
My sister drove a TL when her TSX was in for service and she said the transmission is always thinking in that car...downshifting when you begin to brake for a stoplight, etc.
If what it's doing was detrimental to the mechanicals, Honda wouldn't have programmed it that way.
and it doesn't know you're on a hill
I know exactly what you're saying, and that's just bad programming or an oversight. Climbing that hill in auto mode would just do exactly what you're worried about; cooking the transmission
Originally Posted By: ViragoBry
If what it's doing was detrimental to the mechanicals, Honda wouldn't have programmed it that way.
LOL Honda also didnt program it to be one of the most unrelaible ATXs ever, either.
If what it's doing was detrimental to the mechanicals, Honda wouldn't have programmed it that way.
LOL Honda also didnt program it to be one of the most unrelaible ATXs ever, either.
The more I think about the stuff I learned working in a GM shop, the more it makes me thing of throttle position logic.
I'd have to drive up the hill you mentioned myself to determine if what I'm about to say is the case, but this is the only conclusion I can come to about TC lockup/non-lockup.
In 5th gear, you have to keep the throttle open to X to maintain speed. The transmission programming may prevent TC lockup at X or >X throttle position.
In 4th gear, isn't the engine making more power and thus causes you to use less throttle? If you're in 4th gear at
The reason I remembered this scenario is because we had a customer come into the shop with his Trans Am GTA complaining that his TC unlocks after 120mph. It was because he needed >X throttle to attain 120mph, thus unlocking the TC.
And most modern cars know when you're on a hill...it's called Grade Logic.
I'd have to drive up the hill you mentioned myself to determine if what I'm about to say is the case, but this is the only conclusion I can come to about TC lockup/non-lockup.
In 5th gear, you have to keep the throttle open to X to maintain speed. The transmission programming may prevent TC lockup at X or >X throttle position.
In 4th gear, isn't the engine making more power and thus causes you to use less throttle? If you're in 4th gear at
The reason I remembered this scenario is because we had a customer come into the shop with his Trans Am GTA complaining that his TC unlocks after 120mph. It was because he needed >X throttle to attain 120mph, thus unlocking the TC.
And most modern cars know when you're on a hill...it's called Grade Logic.
Originally Posted By: BuickGN
Originally Posted By: oilyriser
and it doesn't know you're on a hill
Actually, it does.
I'm with BGN on this. Not sure about other makes, but the Honda and Toyota transmissions DO know whether you're on a hill, and whether you're going up or down. Honda calls it "grade logic" and
Toyota accounts for the feature with an "i" at the end of the trans name, as in "ECT-i". The off-road Toyotas also have a hill climbing or descending feature that goes by a name I forget at the moment...
As for the original question, it's tantalizing IMO, but something that will be difficult, if not totally impossible, to ever get a clear answer about from the source. I'm sure that the unit got programmed to behave in what the designers feel is the optimal manner for the design. That said, sometimes even carefully programmed "things" exhibit odd behaviors under some circumstances that the designers may not have foreseen. Good luck figuring it out...
Originally Posted By: oilyriser
and it doesn't know you're on a hill
Actually, it does.
I'm with BGN on this. Not sure about other makes, but the Honda and Toyota transmissions DO know whether you're on a hill, and whether you're going up or down. Honda calls it "grade logic" and
Toyota accounts for the feature with an "i" at the end of the trans name, as in "ECT-i". The off-road Toyotas also have a hill climbing or descending feature that goes by a name I forget at the moment...
As for the original question, it's tantalizing IMO, but something that will be difficult, if not totally impossible, to ever get a clear answer about from the source. I'm sure that the unit got programmed to behave in what the designers feel is the optimal manner for the design. That said, sometimes even carefully programmed "things" exhibit odd behaviors under some circumstances that the designers may not have foreseen. Good luck figuring it out...
They just need to look at the engine load vs. throttle position to determine if you're on a hill or not. I wonder, though, if you could confuse them into thinking you're on a hill by driving with the parking brake on? (Assuming the ECU doesn't have a connection to the parking brake switch).
Originally Posted By: brianl703
They just need to look at the engine load vs. throttle position to determine if you're on a hill or not. I wonder, though, if you could confuse them into thinking you're on a hill by driving with the parking brake on? (Assuming the ECU doesn't have a connection to the parking brake switch).
It does. The first time I drove my new TL in the rain and pulled the E-brake for some fun it let me know quickly I was being an idiot.
I understand the strategy for the most part and I guess what I was wondering too, is if there's an inherent weaks spot in the trans and they don't want it downshifting unless absolutely necessary. Don't get me wrong, if I give it enough gas it will go to 3rd or 4th.
My scenario is:
A. 5th gear TCC unlocked= 2,500rpm
B. Same speed 4th geear TCC locked= 2,500rpm.
I would think B would put less load on the engine and produce way less heat in the form of convertor slippage.
The funny thing is, on the way down it will keep me in 4th to maintain a steady 70mph without using the brakes. If I hit the gas just a little, as it should it goes into 5th.
They just need to look at the engine load vs. throttle position to determine if you're on a hill or not. I wonder, though, if you could confuse them into thinking you're on a hill by driving with the parking brake on? (Assuming the ECU doesn't have a connection to the parking brake switch).
It does. The first time I drove my new TL in the rain and pulled the E-brake for some fun it let me know quickly I was being an idiot.
I understand the strategy for the most part and I guess what I was wondering too, is if there's an inherent weaks spot in the trans and they don't want it downshifting unless absolutely necessary. Don't get me wrong, if I give it enough gas it will go to 3rd or 4th.
My scenario is:
A. 5th gear TCC unlocked= 2,500rpm
B. Same speed 4th geear TCC locked= 2,500rpm.
I would think B would put less load on the engine and produce way less heat in the form of convertor slippage.
The funny thing is, on the way down it will keep me in 4th to maintain a steady 70mph without using the brakes. If I hit the gas just a little, as it should it goes into 5th.
Buick, most auto transmission do what your TL does in auto mode. I fully agree that 4th lockup is just smarter in certain scenarios, and it should have been programmed in when writing the D grade logic. Perhaps the TCM uses torque converter slippage to determine how much load is on the transmission itself and needs to see it until it's in top gear? But either way, most autos as long as they have another gear to upshift to, will not lockup.
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