This is a normal feature of the transmission, designed to use engine braking on downhill grades. Honda has a trade name for this feature, but I can't remember what it is. Check your owner's manual.AZRonS said:
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If you are traveling down hill with no throttle and your torque converter unlocks then you will notice less rpm's not more.dlginnc said:
Sounds like Grade Logic is doing it's job correctly. I wouldn't worry.
My observation is that when I'm crusing at 50-70 MPH and let off the throttle and look at the Tach the RPMs increase as the torque convertor unlocks resulting in a higher gear ratio. It just has to be a momentary lift of the throttle as the transmission is programmed to allow engine braking.funfinder4 said:If you are traveling down hill with no throttle and your torque converter unlocks then you will notice less rpm's not more.
Think about it, when the torque convertor lock/unlocks how does that affect the gear ratio?
Ok, lets think this through a little more...dlginnc said:
Torque converter allows slippage between the engine and the transmission (kind of like a clutch on a standard) so the transmission can make smooth shifts (up and down). It can not turn the engine faster by "unlocking" unless it also down shifts to the next lower gear then starts to lockup again. If you drive a standard and push in the clutch while in top gear (no throttle applied) what happens? Does the engine race? It shouldn't!
Under power (throttle) a torque converter does (virtually) change the gear ratio by letting the engine's rpms rev higher than if the torque converter was fully engaged. I can't see how it can work backwards without shifting to the next lowest gear.
I haven't noticed this type of behavior with my Ody. or any other auto transmission I've ever driven. If I take my foot off the accelerator (on flat surfaces) to coast I see my rmp's drop to almost idle not raise higher than before I took my foot off the gas.
Now with Grade Logic this can happen, on hills with a downshift.Let's look at a couple of definitions.funfinder4 said:Ok, lets think this through a little more...
Torque converter allows slippage between the engine and the transmission (kind of like a clutch on a standard) so the transmission can make smooth shifts (up and down). It can not turn the engine faster by "unlocking" unless it also down shifts to the next lower gear then starts to lockup again. If you drive a standard and push in the clutch while in top gear (no throttle applied) what happens? Does the engine race? It shouldn't!
Under power (throttle) a torque converter does (virtually) change the gear ratio by letting the engine's rpms rev higher than if the torque converter was fully engaged. I can't see how it can work backwards without shifting to the next lowest gear.
I haven't noticed this type of behavior with my Ody. or any other auto transmission I've ever driven. If I take my foot off the accelerator (on flat surfaces) to coast I see my rmp's drop to almost idle not raise higher than before I took my foot off the gas.
Torque converter - The torque converter converts rotational energy from the crank to the transmission. It slips by design to allow smooth transfer of power.
Lock-up torque converter - The lock-up torque converter was designed to eliminate slippage resulting in improved fuel economy.
The converter is locked at 1:1.
Grade logic - Advanced transmission control that uses inputs to the PCM and decides what gear is required. Engine load, vehicle speed, barometric pressure, etc are used to determine the gear.
Gear ratio - The 04 Odyssey has 5 forward gears and the ratios are as follows:
1 - 2.563
2 - 1.552
3 - 1.021
4 - 0.727
5 - 0.520
The torque converter locks up in 4th and 5th gears.
Here’s what happens. You are traveling along on a flat road at 70 MPH in 5th gear with constant throttle. The torque converter is locked up to provide maximum economy. You lift off of the throttle and the torque converter unlocks. Because the torque converter is not 100% efficient when not locked you just changed the effective gear ratio to something in between 4th and 5th gear. I'm not saying that the transmission downshifted to 4th gear but there is no longer a direct 1:1 connection between the engine and transmission because the torque converter is no longer locked-up.
If you look at the Tach you will notice the RPMs increase. As soon as you restore throttle the torque converter lock-up and the
RPMs drop again.
Here's some more good reading:
Neo Fender said:
5 speed tranmission question
Re: I have to chime in
Did I confuse ya'll more?
One quick addition; grade logic is engaged by braking and when it is engaged the tranny will down shift, and as you dropped one gear and grade logic is trying to keep the vehicle at the same speed the rpm will increase. For example, you are going down the hill at 60 mph at 4th gear with converter locked, and because of the slope the van starts to increase it's speed (just because of the gravity not because of your right foot). You start applying the brakes slightly to keep it at 60, this is when grade logic kicks in and drops the tranny to the 3th gear. Now you are going at 60 mph at 3rd gear instead of 4th. That's why the rpm increases when grade logic kicks in.renew82 said:
Did I confuse ya'll more?
I agree with this definition but can't see how it supports your idea of the torque converter increasing the engines rpm's while unlocked with zero throttle.dlginnc said:
The definition you listed does support the idea of the torque converter "converting rotational energy from the crank to the transmission," but not the other way around. When Grade Logic does kick in it downshifts the transmission and forces torque converter lockup, not torque converter slippage. I'll repeat again, I have never driven a car with an auto that increased rpm's when I let off the gas and the torque converter unlocked. If this is happening to you this doesn't sound normal and I'd get it checked out! Maybe your engine's idle is set too fast?
One last thing... I thought the torque converter also locked up in 3rd gear? Is this only true for the 4-speeds? What about those that have the 5-speeds and tow in 3rd? Are they towing with an unlocked torque converter?
I meant I had my foot on the brake and was braking and slowing down and my foot was not any where near the accelerator, and it downshifted and slowed me down (really fast, since I was going uphill .) Still normal? It hasn't done it like that since.
And since my van has only @ 46,000 miles on it, I was thinking of purchasing an extended warranty (from another company we used before, not honda) to cover it (and pretty much everything else mechanical-doesn't cost but a few dollars more). Think this is a good idea? I don't see honda extending the tranny warranty out past 7 yrs.
.) Still normal? It hasn't done it like that since.And since my van has only @ 46,000 miles on it, I was thinking of purchasing an extended warranty (from another company we used before, not honda) to cover it (and pretty much everything else mechanical-doesn't cost but a few dollars more). Think this is a good idea? I don't see honda extending the tranny warranty out past 7 yrs.
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