Budperm

I was leary about the CVT tranny, I hope what I am experiencing is normal for one. My 2.5S w/ CVT ony has 3500 miles, so far, so I am still learning.

My tranny only seems to freewheel below 15mph. I get engine breaking at higher speeds unless I keep my foot on the gas. Is no coasting at higher speeds normal? I see that if I am going downhill or grade (with my foot off the gas) between 45 and 60mph the tranny will actually down-shift and run the engine rpm up to ~3K RPM and slow the car down. It doesn't take much of a downhill slope for this to happen. If i put the car in neutral then she gains speed. Yeah baby...free momentum, no gas required.

This doesn't seem right to me and I would think it is NOT a fuel effecient way of operating.

Can someone with more CVT experience clue me in to what is normal with these trannies?

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AltimaSL

I don't know what is up with my CVT. It vibrates and sputters at around 3-4K. My Altima coasts... Also, the CVT doesn't have gears so i don't see how it downshifts. Something must be up with your Altima.

__________________
2010 Mazda 6i Grand Touring
Navi/Tech Pkg.
Brilliant Silver Metallic/Gray
Mileage - 21,+++.

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Budperm

AltimaSL, Your not giving me any warm fuzzies about these CVTs.

What kind of problems have you experienced so far?

__________________
08 Altima Coupe
2.5S CVT
Super Black

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Budperm

AltimaSL,
When I said the tranny downshifts what i mean is that as I coast downhill very slowly picking up speed the rpm is ~1500-1800rpm, after I pick up about 3-5mph from coasting the rpm jump up to ~3K and the car noticably slows (engine breaking) if I momentarily shift to neutral and back to drive the rpm will fall back to 1500-1800 until I gain about 3-5 mph again, due to slope then the tranny will do the same thing again causing the rpm to jump to ~3K and start slowing the car thru engine breaking.

This behavior actually makes sense in that it would limit a downhill run-away situation if you lost your brakes. The no coasting thing gets on my nerves and I am sure is costing me $$$MPG$$$

We need A CVT expert

__________________
08 Altima Coupe
2.5S CVT
Super Black

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AltimaSL

With CVT, the only problems i've had are with the sputtering at 3-4K RPM and a lack of power during the sputter. After about 4K the engine will gain speed slowly until about 6K, then it will act normal. It can really scare me when passing people.

__________________
2010 Mazda 6i Grand Touring
Navi/Tech Pkg.
Brilliant Silver Metallic/Gray
Mileage - 21,+++.

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DJ

The "jerks", which I've had many times with quick stopping and going is part of emulation. Unfortunately, It can't keep up with certain scenarios sometimes.

Heres some useful information..

The CVT emulates downshifting and upshifting. It's controlled by the ECU and how it works is:

Continuously Variable Transmission (CVT) is a type of automatic transmission that can change the "gear ratio" (gears are not generally involved) to any arbitrary setting within the limits. The CVT is not constrained to a small number of gear ratios, such as the 4 to 6 forward ratios in typical automotive transmissions. CVT control computers often emulate the traditional abrupt gear changes, especially at low speeds, because most drivers expect the sudden jerks and will reject a perfectly smooth transmission as lacking in apparent power.

Variable-diameter pulley (VDP) *Which is the design Nissan uses.
This type of CVT uses pulleys, typically connected by a rubber-covered metal belt. A chain may also be used. A large pulley connected to a smaller pulley with a belt or chain will operate in the same manner as a large gear meshing with a smaller gear. Typical CVTs have pulleys formed as pairs of opposing cones. Moving the cones in and out has the effect of changing the pulley diameter since the belt or chain must take a large-diameter path when the conical pulley halves are close together. This motion of the cones can be computer-controlled and driven, for example by a servo motor. However, in the light-weight VDP transmissions used in automatic motorscooters and light motorcycles, the change in pulley diameter is accomplished by a variator, an all-mechanical system that uses weights and springs to change the pulley diameters as a function of belt speed. In higher power types, for example that produced by Van Doorne's Transmissie (part of the Bosch Group), an oil-cooled laminated steel belt is used.

But in Nissan's case.. A kevlar belt is used.

http://www.motorcars.in/transmission/cvt.htm

http://en.wikipedia.org/wiki/Continu...e_transmission

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2007 Altima 2.5s [Dark Slate, CVT] - RIP
2005 Titan SE King Cab [Black, AT]
2008 350z [Silver, 6MT]

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Budperm

OOOOooo Input! Thanks DJ. I appreciate the info and links! I hate being clueless about anything in my car. This is my first experience with a CVT. Actually the car is doing great, I am just trying to learn its nuances and qwerks. My CVT doesn't seem to freewheel or coast. It is like a manual, if you take your foot off the gas pedal she starts engine braking. That and the rpm jumping from 1500 to 3k rpm on coasting downhills are the only complaints I have. I looks like I was lucky enough to get a very solid 08 Altima2.5S. No creaks, rattles, popping or other strange noises. This is a very good thing because I live in Pennsylvania where the roads are TERRIBLE!

Again...Thanks for the info!!

Bud

__________________
08 Altima Coupe
2.5S CVT
Super Black

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DJ

No problem man! Knowledge is everything and I know what you mean about owning something and being clueless on it. Everytime I buy a car, I do extensive research on it.

Enjoy that beautiful car of yours!!

__________________
Administrator
Email: admin@altimaforums.net

2007 Altima 2.5s [Dark Slate, CVT] - RIP
2005 Titan SE King Cab [Black, AT]
2008 350z [Silver, 6MT]

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