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-   -   8speed: torque converter behavior in OD? (http://www.jeepgarage.org/f109/8speed-torque-converter-behavior-in-od-70155.html)

Rexlion 01-08-2014 04:43 PM

8speed: torque converter behavior in OD?
 
Hi, new member here with first post. I read quite a bit here though during the last week or so, picking up tidbits about the new GC. I am currently looking at vehicles with an eye toward purchase this summer.

I tow all the time, for work and on vacations. Nothing too big, just 3500 lb or so. With my current vehicle, 2008 Toyota Highlander, I always lock out overdrive by going into select-shift mode (tap the shifter to the left) because the torque converter doesn't stay locked in OD and too much tranny heat would result from that. My old 2000 Mercury Mountaineer is similar, it has a OD lockout button on the shifter, same result.

My question is: will the 8 speed ZF trannies keep the torque converter locked up in the top gear or gears? If not by default, is there a way to lock out OD without going into the paddle shift mode?

Ok, now you're probably wondering why I said that last thing about paddle shifters. Here's the thing. On my current vehicles, when I lock out OD the other gears are all still totally automatic; if I slow or stop the vehicle, it kicks down but then also shifts back up as I accelerate again. The paddle shifters work completely different, right?

I test drove a GC diesel. Really liked it. Yes, I know I probably don't absolutely need all that torque, but I want all that torque! :lol: However, when I experimented with using the paddles to lock out high gear, then I came to a stop light and tried turning left while accelerating, I got a real shock! You can guess, the engine was roaring like a lion and then finally shifted up to avoid damage. My hands were busy turning the steering wheel, and were not in any position to mess with paddles!

So here's my thing. For towing I don't want to burn up my tranny from an unlocked TQ. But I don't want to shift through 8 speeds every time I come to a stop and speed up again, either. And it seems like it would get old quickly if I had to remember to pull the shifter back at every stop, to get out of that mode (autostick, is that the name?). Therefore I want to find out whether the TQ is going to stay locked up at high gear or is it going to allow heat-building slippage? And if it will, have I overlooked an easier way to cope with this shifty situation?

I would like my questions to apply to any WK2 8 speed, since I'm still not certain if I'd spring for the diesel I have always wanted or if I'd economize with a Laredo V6. TIA.

200sxr 01-08-2014 06:13 PM

Re: 8speed: torque converter behavior in OD?
 
My feeling with the 8 speed is the converter is always locked or at least with minimal slip.

Instead of unlocking the torque converter it would just drop down a gear or two. It works very differently to the traditional 5-6 speed auto transmission.

Also in the situation you have described, what you can do is to take the transmission out of manual mode by holding the + lever for a couple of seconds, once you get back up to speed and want to set it to certain gear use the levers again.

Rexlion 01-08-2014 07:37 PM

Re: 8speed: torque converter behavior in OD?
 
I looked through the manual (online) and didn't see any instructions about driver input to stay out of high gear during towing. Although if I missed something, let me know. If this is correct, that seems to imply that they don't consider it necessary for the user to do anything special (like stay out of OD) while towing... even with the gas V6. Is that right? It's hard to believe, after all these years of locking out OD.

TurboRush 01-08-2014 09:24 PM

Quote:

Originally Posted by Rexlion (Post 956820)
I looked through the manual (online) and didn't see any instructions about driver input to stay out of high gear during towing. Although if I missed something, let me know. If this is correct, that seems to imply that they don't consider it necessary for the user to do anything special (like stay out of OD) while towing... even with the gas V6. Is that right? It's hard to believe, after all these years of locking out OD.

I'll say yep. 2011 to 2013 had a tow/haul mode which presumably did the same basic thing as just turning off OD. That's no longer present in the 2014s as the transmission figures it all out for you. Personally, and you're the same way I think, it's tough to stop doing things you've been around forever... 3k oil changes, change oil at 500mi in new motors, etc.... But it seems to be the case. So I've decided to just let the tranny do its thing and adapt to what it's doing at the time. So far so good.

racer-xerols 01-10-2014 10:00 AM

Re: 8speed: torque converter behavior in OD?
 
Tow/haul did NOT lock out OD. you still had access to all gears. what it did was modify shift programming - faster shifts, less slipping between gears, snappier feel, holding gears longer while accelerating and downshifting sooner on decel. And in my old 05 Cummins that would knock about 100 degrees off the trans temp, even running empty (no cargo or trailer).

For my money in the WK2 ( I have a Summit diesel), if I'm towing or hauling I'll be in Sport mode. Behavior seems pretty much the same as tow/haul did in my Ram.

TurboRush 01-10-2014 02:07 PM

Re: 8speed: torque converter behavior in OD?
 
Quote:

Originally Posted by racer-xerols (Post 957574)
Tow/haul did NOT lock out OD. you still had access to all gears. what it did was modify shift programming - faster shifts, less slipping between gears, snappier feel, holding gears longer while accelerating and downshifting sooner on decel. And in my old 05 Cummins that would knock about 100 degrees off the trans temp, even running empty (no cargo or trailer).

For my money in the WK2 ( I have a Summit diesel), if I'm towing or hauling I'll be in Sport mode. Behavior seems pretty much the same as tow/haul did in my Ram.

Thanks for the clarification on Tow/haul in previous models. I was under the (incorrect) assumption it worked like a few other vehicles that lock you out of top gear.

lstowell 01-10-2014 04:29 PM

Re: 8speed: torque converter behavior in OD?
 
Quote:

Originally Posted by Rexlion (Post 956820)
I looked through the manual (online) and didn't see any instructions about driver input to stay out of high gear during towing. Although if I missed something, let me know. If this is correct, that seems to imply that they don't consider it necessary for the user to do anything special (like stay out of OD) while towing... even with the gas V6. Is that right? It's hard to believe, after all these years of locking out OD.

The false presumption would be that it will or can fall out of torque convertor lockup.

I never had that happen in couple hundred K miles on the very first model GC with the 4 speed overdrive auto.

The ZF and Mopar/ZF 8 [and 9] speeds are an entirely different architecture that use dog clutches internally. Nice writeup on Mopar web. Timing of those dog clutches was I understand, one of the reasons for delaying the Cherokee availability.

If I were towing with the V6, I'd think about turning off ECO mode and possibly even using sport mode to hold the shifts longer. The diesel uses the same native ZF as the Hemi [happy 50th birthday btw] and doubt it would be needed.

Rexlion 01-10-2014 11:56 PM

Re: 8speed: torque converter behavior in OD?
 
Well, that would be a welcome improvement over my current vehicles. They do come out of TQ lockup quite readily while in high gear and towing; I know it's happening when I see the RPMs climb about 300-500 but it hasn't shifted. I'm glad to find some trannies that don't act that way.

By the way, did I just find a misprint in the owner manual? On page 395 it says:
When frequent transmission shifting occurs (such as
when operating the vehicle under heavy loading conditions,
in hilly terrain, traveling into strong head winds, or
while towing heavy trailers), select TOW mode (refer to
Selec-Trac in Starting and Operating) or use the
AutoStick® shift control (refer to AutoStick® in this
section) to select a lower gear. Under these conditions,
using TOW mode or a lower gear will improve performance
and extend transmission life by reducing excessive
shifting and heat buildup.
But upon searching the file, I found that this is the only mention anywhere in the manual of TOW mode or Selec-Trac. Is this an accidental carry-over from the previous model year's manual? There is no tow mode, is there?

Rexlion 01-11-2014 01:08 PM

Re: 8speed: torque converter behavior in OD?
 
I was thinking for some reason that the Eco button toggled between Eco and Sport modes. Now I see that they are separate, but so similar I can't understand the differences. Can someone explain?

With Eco mode off (via button on panel), it seems that the transmission maintains higher RPM overall by upshifting less readily and downshifting more quickly. Also the idle speed is higher and performance is 'less conservative' (more sporty?).

With Sport mode engaged (by tapping the shift lever back), the manual says,
"This mode alters the transmission’s automatic shift schedule
for sportier driving. Upshift speeds are increased to
make full use of available engine power."
It sounds like the same thing to me as turning off Eco mode! What am I missing?

If I drive with Eco off and Sport on, is it much different than Eco on and Sport off? With Eco and on and Sport on, what then?

racer-xerols 01-13-2014 10:50 PM

Re: 8speed: torque converter behavior in OD?
 
If you watch the green light...ECO goes off when you toggle Sport.

My suspicion is (pure guesstimation here), they do the same thing but to different degrees. ECO is the most conservative - lower RPMs, earlier upshifts, later downshifts, more freewheeling, and the most conservative fuel and boost tables (mine's a Summit diesel). Non-ECO/D (drive mode) is a slight bump in RPM, slightly longer gear holding on accel, slightly earlier downshifts, and slightly more aggressive fuel and boost tables. Non-ECO/S is likely the most aggressive - much later upshifts, much earlier downshifts, much more aggressive fueling and boost response.

To be honest...I don't think I've touched the ECO button twice. I toggled it once to make sure it worked, but all my "changes" come from a shifter tug into S. If I feel the need to change it at all - which I rarely do. Sometimes I'll use the paddles (in regular D mode) on the way to work, just to kick it down a few gears for engine braking on mountain twisties...but basically I'm just fine in regular ol' D mode.

TurboRush 01-14-2014 08:04 AM

Re: 8speed: torque converter behavior in OD?
 
Quote:

Originally Posted by Rexlion (Post 958150)
I was thinking for some reason that the Eco button toggled between Eco and Sport modes. Now I see that they are separate, but so similar I can't understand the differences. Can someone explain?

With Eco mode off (via button on panel), it seems that the transmission maintains higher RPM overall by upshifting less readily and downshifting more quickly. Also the idle speed is higher and performance is 'less conservative' (more sporty?).

With Sport mode engaged (by tapping the shift lever back), the manual says,
"This mode alters the transmission’s automatic shift schedule
for sportier driving. Upshift speeds are increased to
make full use of available engine power."
It sounds like the same thing to me as turning off Eco mode! What am I missing?

If I drive with Eco off and Sport on, is it much different than Eco on and Sport off? With Eco and on and Sport on, what then?

I think its really 3 modes... Eco on, Eco off, Sport... when in Sport the Eco button is essentially ignored by the vehicle. I will say Sport mode definitely holds gears longer, less likely to up shift when coasting and pretty quickly to downshift. You see it a lot more if you're getting up on the highway. Its a pretty apparent difference (to me at least) as compared to just Eco off.

One thing that is definitively different is when in sport it can/is sending 80% of power to the rear wheels in auto it appears to be 40/60 split. (Jeep Grand Cherokee WK2 - Selec-Terrain)

lstowell 01-14-2014 02:59 PM

Re: 8speed: torque converter behavior in OD?
 
Quote:

Originally Posted by Rexlion (Post 957966)
Well, that would be a welcome improvement over my current vehicles. They do come out of TQ lockup quite readily while in high gear and towing; I know it's happening when I see the RPMs climb about 300-500 but it hasn't shifted. I'm glad to find some trannies that don't act that way.

By the way, did I just find a misprint in the owner manual? On page 395 it says:
When frequent transmission shifting occurs (such as
when operating the vehicle under heavy loading conditions,
in hilly terrain, traveling into strong head winds, or
while towing heavy trailers), select TOW mode (refer to
Selec-Trac in Starting and Operating) or use the
AutoStick® shift control (refer to AutoStick® in this
section) to select a lower gear. Under these conditions,
using TOW mode or a lower gear will improve performance
and extend transmission life by reducing excessive
shifting and heat buildup.
But upon searching the file, I found that this is the only mention anywhere in the manual of TOW mode or Selec-Trac. Is this an accidental carry-over from the previous model year's manual? There is no tow mode, is there?

It would sure seem that someone oopsed there.
Further on there is a towing tips, which just says use drive position and use the manual levers if you get too much shifting and select a lower gear to keep temperature down.

The section on ECO notes it actually locks up the torque convertor quicker than sport mode does, maybe that's why sport mode isn't noted for towing.

6th gear is straight thru, 7 and 8 are overdrive.

You can show the transmission temp to keep an eye on it while towing as well as oil temp.

I don't know if this is actually what the transmission control is doing, but I've noticed that when in auto mode, if I am about 50 mph, it will stay in 7th gear if I'm going downhill and more or less coasting [and won't upshift with the paddle], but as soon as I reach level ground I can upshift to 8th with the paddle, then go back to full auto mode by pulling the + paddle for several seconds and it will stay in 8th until the terrain changes again.


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