Last post on Sep 07, 2011 at 7:13 PM
You are in the Buick Lucerne
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Buick Lucerne, Sedan
#673 of 2217 Re: A6 . . . . . Re: The 2006 Buick Lucerne [bunky36]
Jan 17, 2006 (3:23 pm)
A 5 speed would add several things, bunky36...
First, it would fulfill the "expectation" that a car in this sedan category today has 5 forward gears (even if 5th is overdrive).
Second, the 0 to 70 times (approx) would improve slightly and be closer to the competition. This is meaningful to some potential buyers.
Third, the gas mileage would probably go up a little.
Fourth, the transmission would probably last longer if it were properly designed. Even with the extra shift and gears the load distribution would probably be make a longer life cycle.
To the average Lucerne shopper, #1 is probably the most important. And that is the same possible buyer who will accept the outdated V6 as a standard engine and be content.
#674 of 2217 Re: A6 . . . . . Re: The 2006 Buick Lucerne [bunky36]
Jan 18, 2006 (8:44 am)
The 4 speed automatic you have gives you 4 basic gears: a low gear to start off in; a passing gear; and two driving gears, 3rd gear is good for up to say 50 MPH, while overdrive is better for highway cruising. These gears are all spaced far apart. A six speed transmission will add a lower first gear, and a higher overdrive and will space the gears closer together. A 4 speed automatic can be engineered with two planetary gear sets. A six speed will require one additional planetary set. A 5 speed also requires 3 planetary gearsets, so six speeds makes far more sense.
#675 of 2217 Re: A6 . . . . . Re: The 2006 Buick Lucerne [sls002]
Jan 18, 2006 (8:59 am)
Are 6-speed with more parts more prone to failure? Do they have the same long life of the 4T65E with 4 speeds in most people's driving?
Jan 18, 2006 (9:20 am)
Very generally, a good A6 vs an A4 will provide (potentially) an opportunity to deliver:
1 - a wider ratio spread between first and sixth (as SLS002 said above)
2 – a lower first gear \ higher torque multiplication can provide better take-off & associated feel.
3 – a higher (lower RPM) top / sixth gear can provide lower noise and wear and better MPG, if all other things remain roughly equal.
4 – the steps between gears can also be closed somewhat – such that gear to gear RPM drop is less – and transitions more nearly ‘seamless’.
The A6 would typically (ironically) help the lower displacement and ‘torque challenged’ motors more than one with a relatively broad, flat torque curve. The supercharged 3800, for example, has a relatively flat TQ curve, and generates good torque from low rpm. The A4s (4T65E as in the GPs and 4T80 as in the Lucerne) have a reasonably wide ratio spread already – and the torque generated (similarly with my 5.3L V8) tends to largely offset having only 4 gears to choose from.
Additionally, the newer 5 and 6 speed automatic trans. design features ** should ** allow for smoother and quicker (more efficient) shifts. And (one hopes) that they will have been engineered to be more reliable.
“3rd gear is good for up to say 50” – SLS002
Well – I am not exactly certain what you mean here by ‘good for’.
First, in my current GM V8 Sedan w/A4 (GP GXP), second gear is ‘good for’ up to just over 100 mph. Meaning that it will achieve that road speed before requiring an upshift to third. Since you can force it to start in second gear, the speed range for second is (ahem) pretty wide: 0 – 100. So, in that sense, I’d say that second gear is good for 0 mph to 100 mph. [ And in fact, first gear in my GXP is good for over 50 mph. ]
Third gear can be (manually) engaged in my GXP at speeds as low as 10 mph. And it will pull quite happily – though certainly not as quickly as if the trans. were in second – or even first gear. And the actual (drag limited) top speed would typically (I have not tried it) be achieved in third gear, not fourth – as the deep OD ratio in fourth will kill acceleration. In third gear, at 6,000 rpm, the GXP would be at over 150 mph.
Third gear in the Lucerne then I’d suggest ought to be ‘good for’ 10 or 15 MPH to top speed. With the gearing and HP \ TQ specs, top speed on the Lucerne, I expect would also to be achieved in third gear – not fourth. So, again, the useful range of third gear (it is likely ‘good for’) 15 or 20 mph to somewhere well north of 100 mph. [ Assuming no limiter in the PCM. ]
Still hoping for a Lucerne Grand Sport . . .
#677 of 2217 Re: A4 A6 [rayainsw]
Jan 18, 2006 (9:25 am)
Now that would raise the 'buzz' factor for the Lucerne.
#678 of 2217 Re: A6 . . . . . Re: The 2006 Buick Lucerne [imidazol97]
Jan 18, 2006 (9:26 am)
Perhaps we should return to the days of the powerglide with one planetary gearset. The question of failure rates depend on how well the transmission is engineered and built. I see no reason to expect it to have more problems.
The northstar automatic has a 2.96:1 first gear, and a 0.68 overdrive. The overall ratio is 2.96/.68 = 4.35:1. The gear ratio averages about 1.63 from higher to lower gears. The six speed automatics are designed with an overall ratio of 6:1 or about 1.43 per gear. So the gears are closer together. Basically this means that shifting down will speed up the engine from 2000 rpms in the 4 speed to 3200 rpms while in the six speed it will go to 2800 rpms. In reality, the gears are not spaced evenly.
#679 of 2217 Re: A4 A6 [rayainsw]
Jan 18, 2006 (10:00 am)
What I meant by 3rd being good to 50 MPH was that my Seville in 3rd gear will cruise 50 MPH at 2000 RPMs, which is a fairly reasonable speed for the engine. Above 50 MPH overdrive will be more fuel efficient. But I find that on hilly/mountinous roads with 50 MPH the speed limit, running in 3rd gear is better than letting the transmission try to use overdrive.
#680 of 2217 Re: A4 A6 [sls002]
Jan 18, 2006 (10:21 am)
“running in 3rd gear is better than letting the transmission try to use overdrive.”
As I recall, the previous (FWD) SLS & STS did not offer manumatic control of the A4 trans., so that does make sense.
One thing (of many) that I enjoy and utilize almost always is the ability to exercise some additional control over the automatic trans. shift \ don’t shift algorithms. It seems that many people do not understand that a true manumatic will allow much, much more control than simply placing a ‘normal’ automatic in third or second gear, which (typically) only locks out the gears above the one selected.
I will need to drive a V8 Lucerne at some point – one reason is that (though I have read the brochure) I am not sure exactly how much control they have engineered into this manumatic as they have implemented it in the Lucerne.
(Trans.) control freak . .
#681 of 2217 Re: A4 A6 [rayainsw]
Jan 18, 2006 (10:42 am)
I don't think that the Lucerne's 4T80 transmission has a manumatic mode. It should be the same transmission that I have on my 2002 Seville.
The Corvette's six speed automatic (same as Cadillac's STS_V automatic) has the following gears: 4.02:1, 2.36:1, 1.53:1, 1.15:1, 0.85:1 and 0.67:1. So the top three gears are close together. Third gear is also close to 4th actually. My Seville has the same top gear nearly at 0.68:1, but then 3rd is 1:1 and 2nd is 1.63:1. So, my 3rd is between the six speeds 4th and 5th gears, while my 2nd is a lower gear than the six speeds 3rd, although both of these gears are passing gears. On the six speed, with a 2.93:1 axle ratio, 2nd gear will go to about 65 MPH at an engine speed of about 6000 RPM's, making this gear a lower speed passing gear.
#682 of 2217 Re: A4 A6 [rayainsw]
Jan 20, 2006 (4:30 am)
Great A6 A4 discussion! Very informative. I'm convinced! I'll be in my Bonneville GXP for another couple years. A Lucerne V8 is on my radar. Hopefully by then it will have an A5 or A6. Better yet an A6 GS!