5 and 6 speed automatic transmisions?

[JoLin]

Re: 5 and 6 speed automatic transmisions?

My 2007 Mitsubishi Outlander (FWD, 3.0L V-6) has 2 'overdrive' gears. Turns 2200 rpm at 70 mph. I get about 28 mpg at a steady 70, but my car is 'aerodynamically challenged', i.e., it's a flyin' shoebox.

First Gear Ratio (4.20:1)
Second Gear Ratio (2.41:1)
Third Gear Ratio (1.58:1)
Fourth Gear Ratio (1.16:1)
Fifth Gear Ratio (0.86:1)
Sixth Gear Ratio (0.69:1)

I miss those old 1960's 3-speed trannies, particularly the Chrysler TorqFlyte. That sucker really slammed its way through the gears.

My '64 Dodge Polara w/383, rusted out quarter panels, rear window held up by a coat hanger and exhaust pipe with a tin can and 2 clamps holding it together... could chirp the rear wheels on the 1-2 shift at full throttle. Gave ya whiplash...

 

[Boomyal]

Re: 5 and 6 speed automatic transmisions?

Yep, those were the days. You could even push start cars with automatic transmissions.

 

[River_Lizard]

Re: 5 and 6 speed automatic transmisions?

My Wrangler Unlimited is a 3 speed with overdrive (push button to disengage it). In overdrive at 70 mph the engine rpm is just at 2K...kick overdrive off and it's almost 3K. OD gets me at least 4 mpg difference also.

 

[bruceb58]

Re: 5 and 6 speed automatic transmisions?

My '97 850Ci has:
1st 3.55:1
2nd 2.24:1
3rd 1.54:1
4th 1.00:1
5th 0.79:1

Final drive 2.81

I heard those 850Cis are expensive beasts to fix!

 

[jkust]

Re: 5 and 6 speed automatic transmisions?

I have an 2011 GMC Arcadia that I am told has a 6 speed transmission. When driving above about 50 mph, sometimes there is a hesitation when accelerating. The dealer says that it is "normal" because of the 6 speed transmission downshifting. Twice it appeared that the transmission just shifted into neutral with the engine rpm jumping to over 6K and no acceleration of the vehicle.

Needless to say that I'm not happy with that.

Have driven 2011 Acadias for weeks on end at times and all I can say is the 6 speed needs some work and i'm not buying the gas mileage argument for the 6 speed since all of my much more capable AWD body on frame, suv's with 5.3's and 4 speeds get equaly bad mileage. Hands down the most dissappointing vehicle I've ever driven. Heavy, bad tranny, and underpowered to beat the band with egregious mileage with a light foot. Wanted to love them but did not.

 

[hostage]

Re: 5 and 6 speed automatic transmisions?

They are not only tossing more gears into modern cars, some are tossing the old tranny concept out the window. A lot of vehicles are moving to CVT transmissions. They are the most efficent transmissions and some vehicles are loosing 200lbs by switching as well as gaining ~25% better fuel economy.

 

[jkust]

Re: 5 and 6 speed automatic transmisions?

With the mandated fuel standards skyrocketing in the next decade, I'm guessing we will see a lot of these changes. I'm wondering when diesel will become mainstream. Funny thing though when you watch Top Gear UK, they speak of diesels like their the devil in most cars in the episodes i've seen which is the opposite of the sparse references to them I see on here.

 

[jtmarten]

Re: 5 and 6 speed automatic transmisions?

I heard those 850Cis are expensive beasts to fix!

LOL It depends. Local dealer quoted $4400+ for new tie rods (1 side), center link, new EDC front struts, and 2 rear upper ball joints. I did all the front end work, plus the other side tie rods and idler arm, converted from EDC to Eibach springs/Bilstein sport inserts, and had the rear ball joints replaced, spent ~$1300 total plus a few hours time.
Some things are extremely expensive: plug wires $500, caps/rotors $200+, brake hydroboost unit $1200 (luckily it can be rebuilt completely for $100).

On the plus side, the V12 will go 500,000+ miles before needing major work; and that V12 smoothness is well worth the effort!

 

[drrpm]

Re: 5 and 6 speed automatic transmisions?

Overdrive refers to gear ratios which turn the drive shaft at a higher rpm than the engine. Some of the new 7 and 8 speed transmissions have several overdrive gears.

 

[JoLin]

Re: 5 and 6 speed automatic transmisions?

They are not only tossing more gears into modern cars, some are tossing the old tranny concept out the window. A lot of vehicles are moving to CVT transmissions. They are the most efficent transmissions and some vehicles are loosing 200lbs by switching as well as gaining ~25% better fuel economy.

I always thought that regulating an engine to run at a constant RPM (peak torque), then mating it to a CVT would return phenomenal fuel economy. I don't suppose that consumers would accept the 'feel' of it, tho.

 

[Harritwo]

Re: 5 and 6 speed automatic transmisions?

Had an 08 Acadia with the 6 speed auto gear box. 3 times before it had 30000 miles on it, it left my wife stranded 200 miles from home. The trans would get stuck in 5 or 6 gear and would not shift into 1 at a light. Then it did not have enough power to pull itself away from teh light. Had it towed to the local dealer and they would get it working, finally my dealer replaced the trans computer and solved it. Then had the engine overhauled at 59000 miles due to oil and antifreezed consumption. GM says a 1 quart every 2000 miles is acceptable, mine was using a quart every 1000 miles and the antifreeze tank would be empty. Traded it off for a 12 Acadia, no problems with it.

The 08 had a towing package, would only get about 11 mpg towing a pop-up at 55 mph. Glad it is gone, but the wife loves them.

 

[TorchedGT]

Re: 5 and 6 speed automatic transmisions?

This seems to have been covered fairly well, but it should also be noted that while 6 speed transmissions can offer less of an increase in ratio going into the last gear, the 6th gear can also have many different purposes depending on the vehicle. 6 speeds are now being used in most economy-based vehicles which offer a much greater drop in rpm, since acceleration isn't required when entering this ratio - a performance -based vehicle needs to enter a ratio that lands the engine in its' peak power band (granted a 5 speed will still have a significant ratio change, since it's traveling slower when entering the final gear than a 6 speed - my 2005 mustang was an example of this, 300hp stock + 5 speed = BIG overdrive gear)

My range rover has some interesting ratios, with two that are overdriven and a high ratio 1st - the engine has many variable cam/plenum systems so it can deliver power in a broad band so I suppose the ratios become less important. It's also one of the ZF units that has the ability to lock-up the torque converter in any of the 6 forward gears, which essentially offers a much greater range of options for ratios/power. Then again it also weighs 5,500lbs so it needs them haha.

My old land rover discovery has a 4 speed with a significant overdrive (acceleration comes to a stop when it shifts into 4th/OD which bugs me, you need to then apply more gas to just maintain the same level of accel.) luckily this was fixed with later generations - in fact there's rumor of the 2013 RRs getting the 8 speed ZF unit but that seems totally pointless given the new 400/510hp (sc) engines and broad power bands.

It's important to keep in mind that some engines NEED a close-ratio 6+ speed trans just to keep the engine in the power band (very small engines and/or very high performance small-displacement engines like the BMW M 8/10cyl engines) since these engines make absolutely zero power down low. HP is a function of RPM (i forget the exact equation) but I know F1 engines can stall if they fall below like 3k rpm for example haha.
First: 4.17:1
Second: 2.34:1
Third: 1.52:1
Fourth: 1.14:1
Fifth: 0.87:1
Sixth: 0.69:1
Reverse: 3.40:1
Final Drive Ratio: 3.73:1
Transfer Ratios High: 1.00:1
Low: 2.93:1