PUZZLLED over an s60 feature...wld it do harm to an XC90?

1370 Views 13 Replies 12 Participants Last post by dmd, May 2, 2009

bikz

Discussion Starter · Apr 28, 2009

heya guys...was just reading through the s60 threads and came across an interesting feature in the earlier auto trannys which had a "stop neutral" feature which kinda screwed up the tranny box!

my question is if that feature did more harm and than good, wld changing the position from Drive to Neutral on my 04 2.5 XC90 with an auto tranny lets say while waiting at a trafffic light 10 times a day do any harm? (this also applies to all other auto trannys from other carmakers)

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dmd

· #2 · Apr 28, 2009

Re: PUZZLLED over an s60 feature...wld it do harm to an XC90? (bikz)

I doubt it would do any good to do it... What are you trying to accomplish? If trying to save fuel
then I doubt it is worth it, these trans are pretty disengaged when stopped in drive. Anyone with
a mild slope to their driveway can attest to that. I would guess that shifting in and out would cause
more harm than leaving it as it was designed to be.

You can save much more fuel by accelerating slowly and not racing up to red lights. Can save much more
money just by skipping a Fancy coffee once a week.

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ss60

· #3 · Apr 28, 2009

Re: PUZZLLED over an s60 feature...wld it do harm to an XC90? (bikz)

It would lead to very premture wear, yes. Auto transmissions are made to remain IN gear. That is how they are designed/engineered.

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cdauerer

· #4 · Apr 28, 2009

Re: PUZZLLED over an s60 feature...wld it do harm to an XC90? (bikz)

moving from d to n while waiting at a stop light is definitely a bad idea. Leave it in drive!

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cdnx90

· #5 · Apr 30, 2009

I'd like to know the technical detail (if there is any) why its a bad idea. In our 850's and V70 (one had 400,000km and the V70 has 300,000 with the original transmission) I've told the wife and daughter to pop it into neutral if you were stuck in traffic or a lineup where you were not moving for several mins. (not at stop lights) The reasoning is that if you take your foot off the brake, you start moving. Hence, the transmission is trying to overcome the brake... just like slipping the clutch in a standard. Drag is wear on something (clutch pack??) so it can't be good. I also thought I read somewhere that the XC90 goes into neutral automatically after some time period when not moving and in gear then engages drive again when you go to accelerate, but I haven't been able to reproduce that in our V8. Maybe it was in the horrid T6 GM version and they were trying to make it live longer ??

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drevilkep

· #6 · Apr 30, 2009

Re: (cdnx90)

It's not really like slipping the clutch. The torque converter sits between the gears and the engine and acts as a "buffer" of sorts. The torque converter is full of transmission fluid and has two discs with vanes on them, one connected to the engine and one connected to the rest of the transmission. When you accelerate, you spin the disc connected to the engine, which causes the fluid to move and spin the disc connected to the transmission. When you're sitting at a light, the engine disc is just moving fluid around the transmission disc, which is "stuck" because you have your foot on the brake. Putting the transmission in neutral disconnects the flywheel from the engine, keeping the torque converter from spinning at all. The reason people say to put the car in neutral when waiting at a traffic light is that the movement of the torque converter fluid generates heat. Heat wears out transmission fluid and ultimately kills the transmission. With modern torque converter designs, this is not the issue it once was. I would still put the car in park if you know you're going to stopped for a while... just keep your foot from getting tired.

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Pinstripe

· #7 · Apr 30, 2009

^
The V8 does not use a GM transmission. It's a 6-speed from Aisin.

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sol

· #8 · May 1, 2009

Re: (drevilkep)

To set some facts straight ...

The [flywheel] flexplate is never disconnected from the engine (unless you dissemble the engine) as it is part of the engine. The torque converter is not disconnected from the [flywheel] flexplate by shifting the transmission into neutral or park, as it's [bolted] attached to and turns with the [flywheel] flexplate. The disconnection occurs within the transmission itself, "downstream" of the [flywheel] flexplate and torque converter.

With the transmission left in drive and the car stopped, the housing (or pump or impeller) of the torque converter turns while the output turbine remains stationary. With the transmission in neutral or park, both the housing and turbine will turn at similar speeds.

http://auto.howstuffworks.com/...r.htm

Modified by sol at 8:24 AM 5-1-2009

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Dextrobrick

· #9 · May 1, 2009

FWIW an automatic transmission does NOT use a flywheel at all since there is no conventional clutch as would be the case with a manual transmission.

Instead the torque converter is keyed (not bolted) to a flat disc called the flexplate that itself is bolted to the engine's crankshaft. BTW the flexplate is what the stater engages with and spins to start the engine.

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aintsheswede

· #10 · May 1, 2009

Re: (cdnx90)

Page 89 of my 06 owner's manual states shifting into park or neutral when idling at a standstill for prolonged periods will prevent overheating of the transmission fluid, which can lead to premature wear. Unfortunately, it does not define "prolonged periods".

But obviously, when stopped for some length of time (anyone have Volvo's definition of "prolonged"?) it does make sense to shift into N or P.

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sol

· #11 · May 1, 2009

Dextrobrick: I probably stand corrected by your posts, but the concept (other than the name of the part and method of attachment) is still essentially the same as what I posted. Note edits inline in previous post.

aintsheswede: I'll stick my neck out and hazard a guess at to what constitutes "prolonged". A red light would not be prolonged. A stalled (not creeping) traffic jam or railroad grade crossing would constitute prolonged. And along the Volvo concept of safety, please put the transmission in park when discharging or admitting passengers, even if you're only stopping for a few seconds to do this.

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Cabot

· #12 · May 1, 2009

Re: (aintsheswede)

Quote, originally posted by aintsheswede »

Page 89 of my 06 owner's manual states shifting into park or neutral when idling at a standstill for prolonged periods will prevent overheating of the transmission fluid, which can lead to premature wear. Unfortunately, it does not define "prolonged periods".

My '07 manual says the same thing, but also neglects to define "prolonged periods." I took it to mean stop lights, some of which can make you wait over four minutes in my town. It sounds like I should stop putting it in neutral.

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rnb

· #13 · May 2, 2009

Re: (aintsheswede)

Perhaps if the stop is "prolonged" it would make even more sense to put the transmission in Park and turn the engine off.

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dmd

· #14 · May 2, 2009

Re: (rnb)

Quote, originally posted by rnb »

Perhaps if the stop is "prolonged" it would make even more sense to put the transmission in Park and turn the engine off.

Unless it is July or Aug in Texas

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