Can't get into 6th gear

[hat_man]

Hello everyone.

This time the question is about our 2009 Saturn Aura.

We didn't buy the car for mileage reasons but because my wife liked it and she is the one driving it 80% of the time. It has the "manu-matic" type trans that I really never liked because it doesn't allow me to shift to the gear I want when I want. It downshifts when it wants to, not when I want to. To get into 5th gear I have to be going almost 40 mph. It will cruise at 35mph (even as low as 32) in 5th, but to get there I have to risk a speeding ticket in town. I always watch the tach and speedo when I'm driving to get an idea of where the sweet spots are at but have a terrible time keeping them there so the few times I drive it I just use in "automatic" (no paddle shifting).

The other day I was taking my sister in law to work and she asked what the paddles were for. I pulled over and put in "manu-matic" mode and showed her. When we took off I shifted as normal, knowing that I never usually use it and had never really tried it at highway speeds. When I hit 5th gear at 60mph I was around 2000 rpm. I hit the paddle again and M6 popped up in the DIC. What??? I didn't know it had a 6th gear. It dropped to around 1600 RPM and cruised so quietly that you would have never thought the engine was running. After dropping her off I tried to replicate the 1600ish RPM in "automatic" mode. It would never drop below 2000 RPM. I even tried going faster to make it change gears thinking that if I had to go faster in "manu-matic" mode to reach 5th (and then could cruise slower) maybe "automatic" mode was the same. I didn't mash the throttle and make it downshift to "passing gear" just a steady increase to make it want to go into 6th. Even at 80 MPH (good thing I was on the interstate) it would never drop below 2000 RPM. So I pull over and switch to "manu-matic" mode and take off. I was able to get into 6th at 62 MPH and watched the RPM's drop accordingly.

So after all that back story the question is......why can't I get into 6th gear in "automatic" mode? I mean if 6th gear is available in the mechanics of the trans, why will it only engage in "manu-matic"???

Luckily I do most of the driving on our get-away trips and will be using "manu-matic" on the highway from now on. But it is frustrating that it won't engage in "automatic" mode.

[Hersbird]

If it was 2000 rpm at 60 in 5th then when at 80 and 2000 rpm it had to be in 6th. I don't like how when in auto some cars just say D and not what gear its actually in. You can try counting them from a standstill but there may seem to be an extra drop when the torque converter locks up. At 80 steady state in drive try shifting it to manual and see if there really is another gear. Also I bet the difference in ratios 5-6 is pretty slight.
Ps- I bet any kind of tow/haul mode will lock out 6th in drive also.

[hat_man]

I guess I should clarify that. When I was at 80 MPH in "automatic" it was above 2000 RPM. I don't remember exactly what it was but I was watching it and the road at the same time. Usually when it shifts in "automatic" you can see a pretty good RPM drop. At least enough movement to catch your eye. And when I shift from 5th to 6th in "manu-matic" mode it definitely drops. I wish it was at 2000 RPM at 80 MPH in "automatic". That would mean much lower RPM's at more realistic speeds.

If I can get 1600ish RPM's at 60 MPH in "manu-matic" why can't I get it in "automatic"?

[redpoint5]

I'm assuming you have the 6-cylinder engine? 1600 RPM at 60 mph is a very low engine speed. My car is doing 2600 RPM at that speed in 6th gear.

1600 RPM at 60 mph is 26.7 RPM per mph. This would equate to 2133 RPM at 80 mph. So, if you are around that RPM when in auto-shift mode, then the car is getting into 6th gear. At 75 mph, you should see an even 2000 RPM.

Auto transmissions generally rev higher than ideal on purpose, because the consumer demands quick throttle response. People would complain if the car accelerated slowly at low RPM while they pressed the gas pedal 3/4 of the way.

[hat_man]

Some times I wish it was the 6 cyl. Nope just the little I4. I'll try and get a pic of the dash at 60 mph both automatic and manu-matic.

[2000mc]

to complicate matters, the torque converter might behave differently in the manual vs automatic range. in auto the converter clutch could slowly ramp up to only 50% duty cycle, for a seamless feel, and maintain a low slip speed. driven in manual it might quickly go up to 80-100% with no slip

[baldlobo]

GM 6T40 transmission - Wikipedia, the free encyclopedia

[redpoint5]

Originally Posted by hat_man

Some times I wish it was the 6 cyl. Nope just the little I4. I'll try and get a pic of the dash at 60 mph both automatic and manu-matic.

An automatic will never select a cruising gear of around 1600 RPM in a 4-cylinder engine. As mentioned, the typical driver would complain of the lack of throttle response from the 2.4L engine, even though it is more efficient for steady cruising.

My guess is your car doesn't select 6th until around 65-70 mph.

Having the option to manually select 6th at 60 mph would make for extremely efficient cruising on longer trips. I'd be interested to know what your fuel efficiency is at this speed.

[RobertISaar]

Originally Posted by 2000mc

to complicate matters, the torque converter might behave differently in the manual vs automatic range. in auto the converter clutch could slowly ramp up to only 50% duty cycle, for a seamless feel, and maintain a low slip speed. driven in manual it might quickly go up to 80-100% with no slip

GM started doing this in ~98 or so on nearly everything. supposedly reduces vibration felt by the passengers, but i don't buy it. it also likes to make trans temps shoot through the roof.

[niky]

Most likely, they want to avoid people putting up with the vibration and the sluggish and jerky response when the converter is locked and the engine is lugging at such a low rpm.