Jump to content


Neutral Coasting + auto

Started by _Loki_ , Jul 10 2006 12:04 AM

  • Please log in to reply
51 replies to this topic

#1 _Loki_

_Loki_
  • Guests

Posted 10 July 2006 - 12:04 AM

Heard it's bad for the box, why is this?
Neutral coasting (read: not clutch coasting) in manual's is fine right?
I understand why it's bad in manual to clutch coast at speed for distances in gear, is it a similar reason for auto's?
I sort of understand how an auto determines which is the best gear to use (Through pressurised valves? + kickdown cable + road speed etc. determines which gear the box should be in).

Now my understand was that "1, 2, 3" are one way cogs, while "Drive and overdrive" are 'freewheeled' cogs (i.e. very much like your pushbike freewheel).
Now, my second understanding was that, an auto gearbox actually changes gears by changing the flow of oil through the box? (i.e. pressured valves) which makes the different gears turn.

Not really understanding the connection between how manual synchro and auto synchro works and why it's bad to neutral coast in an auto - but fine in a manual.


Cheers, hope that makes sense ~_~

Edited by Loki, 10 July 2006 - 12:13 AM.

#2 rodomo

rodomo

    To advertise here, call 13TORANA

  • Members
  • PipPipPipPipPipPipPip
  • 18,002 posts
  • Name:R - O - B Dammit!
  • Location:Way out west of Melbourne Awstraylya
  • Joined: 10-December 05

Posted 10 July 2006 - 12:50 AM

I don't see an issue with "coasting" an auto as described. If the motor is still running, the pump is still pumping and I would assume every thing is being sufficiently lubricated given the "no-load" situation. You may be being confused with "towing" a stranded auto, which is not recommended as usually the motor isn't running therefore no pump operating. The old "tow start an auto" subject arises from "old" autos that had a second pump running off the tail shaft that at "X" speed produced enough pressure to engage a gear to roll start an auto. Not many (if any) current autos have this function.
With synchros the manuals have a sychro "clutch" (the brass ring between the gear "dogs") which either slows down or speeds up the gear train to "synchronise" the speed of the gears to be engaged. This synchronisation is overcome in autos due to all the gearsets being in "constant mesh" e.g no gear teeth or "dogs" have to slide and engage another gear. Also the autos have a torque convertor which is not a "positive" connection to the motor like a manual clutch and rather use clutch packs to lock the gearsets to the output shaft. Because of the valveing in autos this also provides "lag" in engagement for smooth shifting. (My brayn hurts and I'm going to bed :ZZZ: )

#3 _Yella SLuR_

_Yella SLuR_
  • Guests

Posted 10 July 2006 - 07:36 AM

Think it's bit of a misnomer, specially considering that most people only ever drive an auto in "D". They go quite well when manualised, even with the T-bar selector. If you drive them in this manner, it's not uncommon to occaisionally slip it into Neutral by accident. Just move it back, to "D" and all is fine.

Jap auto's seem to be quite slow on upshift/downshifts (1,000 RPM lag on upshift). The Holden boxes are quite responsive in this regard, even the old Trimatics.

At the same time I can't see why you'd want to coast in Neutral in an auto. Similarly, I can't see why constant speed in a manual is bad either, other than taking up slack backing off taking up slack, which you sometimes experience in the V8 torries cruising at 100 or 80km/h.

Edited by Yella SLuR, 10 July 2006 - 07:39 AM.

#4 _devilsadvocate_

_devilsadvocate_
  • Guests

Posted 10 July 2006 - 07:55 AM

At the same time I can't see why you'd want to coast in Neutral in an auto.

Not sure on the reason why Loki want to coast in neutral, but a major one would be fuel consumption. A trimatic left in drive provides quite a lot of friction on coast, have a look at the tacho and youll see its also spinning the motor faster(engine braking), this can make a big difference if you are driving for economy....slip it into neutral and it will roll up to the place you need to stop, whereas leave it in gear and youll need to keep applying throttle to get it there. This doesnt apply to when you are crawling when it will then inch forward due to being in drive. Newer autos dont suffer from this type of drag nearly as much.
Have driven trimatics and bw35's for years slipping it into neutral on coast, never had any probs.

#5 _Yella SLuR_

_Yella SLuR_
  • Guests

Posted 10 July 2006 - 08:03 AM

Off the gas, don't they slip into top gear anyway? Must say, my only Auto is the VN Commondore with electronic gadgets inside and overdrive.

Edited by Yella SLuR, 10 July 2006 - 08:04 AM.

#6 _devilsadvocate_

_devilsadvocate_
  • Guests

Posted 10 July 2006 - 09:06 AM

Off the gas, don't they slip into top gear anyway?

Yes they do(if going at least 20kmh), but that still provides signficant resistance, just as it does in a manual.

#7 _Loki_

_Loki_
  • Guests

Posted 10 July 2006 - 01:10 PM

devil is right, my t350 even going down hills creates noticeable resistance when in drive (3rd gear) - if you pop it in neutral you notice it and begin to get alot further rolling.
Haven't been doing it because i heard its bad for the box though - used to neutral coast on the freeway in the 202 + 4 speed on the ipswich motorway in the wee hours of the morning goig to work - i was able to neutral coast over 5km's of that journey.
that;s 5 clicks at 750 rpm instead of 3000 =]

#8 _munro_

_munro_
  • Guests

Posted 10 July 2006 - 01:54 PM

the problem with coasting is engine braking and the ability to accelorate (don't pic on my spelling)
if something happens you've got less control of the car
and the reason the motor is reving at 3grand is cause the turbo and trimatic boxes lock meaning the input shaft is spinning at the same speed as the motor
this happens ova a certain rpm (i don't know the exect figgures)

:spoton: tom

#9 _devilsadvocate_

_devilsadvocate_
  • Guests

Posted 10 July 2006 - 03:39 PM

the problem with coasting is engine braking and the ability to accelorate (don't pic  on my spelling)
if something happens you've got less control of the car
and the reason the motor is reving at 3grand is cause the turbo and trimatic boxes lock meaning the input shaft is spinning at the same speed as the motor
this happens ova a certain rpm (i don't know the exect figgures)

:spoton: tom

Dont agree with any of that Tom.
The effect is there all th time, regardless of whether the torque convertor is locked up at 3000rpm or not.
Drive a new car with auto and lift your foot off the accelerator, it barely slows down at all compared to an older auto trans(i find newer auto trans disconcerting to drive for that reason.....but just a matter of getting used to, engine braking is useful for preserving brakes on a downhill run or racing or for going down slippery slopes, but gives no more control than just putting a permanent brake on the tailshaft otherwise.
If you need to accelerate in an emergency, perhaps yes, but selecting D again is bit quicker than trying to change down a gear in a manual for some sudden acceleration. So no its not reccommended procedure while doing your driving test, but used appropriately will save fuel on older cars. Dont know if regs have changed but the only time one could put the car in neutral on a driving test was if the car was stationary with the handbrake applied.

Edited by devilsadvocate, 10 July 2006 - 03:41 PM.

#10 _Loki_

_Loki_
  • Guests

Posted 10 July 2006 - 05:52 PM

and the reason the motor is reving at 3grand is cause the turbo and trimatic boxes lock meaning the input shaft is spinning at the same speed as the motor

O.o

Was my 202 and 4 speed that used to sit on 3k :P

T350 + 5.2L + 3.08 diff sits on about 2750 :(

Might begin to do some neutral coasting with the all clear that it's ok for the box :)

One other thing I heard was that it saves fuel to sit in neutral instead of Drive at a set of lights? Is there truth behind this as well?
I usually sit in neutral at traffic lights or when stopped simply because my extractors like to tap the sway bar when I do and it's slightly annoying :P

In drive I idle at about 750 rpm and idle at just below 1000rpm in neutral.

#11 _devilsadvocate_

_devilsadvocate_
  • Guests

Posted 10 July 2006 - 07:14 PM

One other thing I heard was that it saves fuel to sit in neutral instead of Drive at a set of lights? Is there truth behind this as well?

I wouldnt think so, unless there is some throttle position sensor connecting drive to the carby.
If its a basic setup, then putting the car into drive puts some resistance on the motor and would slow it down, which also reduces the amount of petrol/air it sucks in, most drivers adjusting the idle speed so it wont stall in drive and consequently it idles faster than it needs to in neutral.
Yes, it would be different in a computerised car, they are programmed to idle at exactly the same low speed whether in drive or neutral, so to have it idle at the same speed in drive requires the computer to activate the throttle to have it maintain the same desired engine speed, it also does this with other varying loads whether it be the aircon, powersteering or alternator.

#12 Tiny

Tiny

    Oh My, Don't you post alot

  • Administrators
  • PipPipPipPipPipPipPip
  • 10,018 posts
  • Name:Tiny
  • Location:Sydney
  • Joined: 04-February 07

Posted 10 July 2006 - 08:21 PM

I havent read every word of every post here... So bear with me if i makea bit of a mistake... BUT... neutral coasting or "angel gear" is one of my all time pet hates....

Coasting a car in neutral means that there is no ( or less).. drivetrain friction put onto the engine I agree.. so your chances of coasting further are increased BUT... you are at IDLE... your throttle blades are closed ( EFI or Carby), so NO MORE FUEL is entering the engine...

Whether the engine is still turning at 3000 Rpm or at idle it simply CANT be using more fuel cause the throttle blades are shut!! you are feeling the effect of engine braking and of course the resulting friction etc.

As Munro has said your not in control of the car and you cant even accelerate into a curve if needed ( and dont tell me you dont need to... try driving on cruise control and NOT varying speed around bends...) let alone avoid an emergency situation.

I woudlnt do it, I reckon its false economy!
Cheers

#13 WhiteA9XS

WhiteA9XS

    .

  • Members
  • PipPipPipPipPip
  • 1,646 posts
  • Name:Shaun
  • Location:Billys Creek
  • Car:LJ LX
  • Joined: 08-November 05
Garage View Garage

Posted 10 July 2006 - 09:17 PM

i select neutral after a 160 mph 1/4 mile pass , then pull the chute .

does no harm to the powerglide and less stress on engine components..

can be dangerous if you select reverse if no lock out on shifter..

#14 _JBM_

_JBM_
  • Guests

Posted 10 July 2006 - 09:41 PM

This sums up this debate.

Whether the engine is still turning at 3000 Rpm or at idle it simply CANT be using more fuel cause the throttle blades are shut!!

Neutral in a Trimatic auto idles faster.

You also generate extra changes from N to D that just aren't necessary.

James

Edited by JBM, 10 July 2006 - 09:43 PM.

#15 makka

makka

    A m��se once bit my sister

  • Members
  • PipPipPipPipPipPip
  • 3,559 posts
  • Name:Cohen
  • Location:ya daughters place
  • Joined: 08-November 05

Posted 10 July 2006 - 09:41 PM

or manage to put it into park.......

#16 _Loki_

_Loki_
  • Guests

Posted 10 July 2006 - 09:45 PM

I havent read every word of every post here... So bear with me if i makea bit of a mistake... BUT... neutral coasting or "angel gear" is one of my all time pet hates....

Coasting a car in neutral means that there is no ( or less).. drivetrain friction put onto the engine I agree.. so your chances of coasting further are increased BUT... you are at IDLE... your throttle blades are closed ( EFI or Carby), so NO MORE FUEL is entering the engine...

Whether the engine is still turning at 3000 Rpm or at idle it simply CANT be using more fuel cause the throttle blades are shut!! you are feeling the effect of engine braking and of course the resulting friction etc.

As Munro has said your not in control of the car and you cant even accelerate into a curve if needed ( and dont tell me you dont need to... try driving on cruise control and NOT varying speed around bends...) let alone avoid an emergency situation.

I woudlnt do it, I reckon its false economy!
Cheers

Tiny: When you're in gear and the drivetrain is pulling engine speeds up, would not a a higher vacuum be created that would pull the required fuel and air through the carby for proper combustion at those revs and thus more fuel?

And more to the point, neutral coasting in my manual when I was driving to ipswhich hospital and back for work every day (twice per day) equated to nearly 50k's per week of neutral coasting over having to have the throttle open to maintain speed!
That's alot of distance travelled and fuel saved in a week... Fake economy? I don't think so...

#17 FastEHHolden

FastEHHolden

    Steptoe

  • Members
  • PipPipPipPipPipPipPip
  • 5,114 posts
  • Location:Central Coast NSW
  • Joined: 16-November 05

Posted 10 July 2006 - 09:54 PM

why not turn the engine off..save more. :fool:

I am sure its illegal..and I would definately fail and trainee who did it in a test.

#18 _Loki_

_Loki_
  • Guests

Posted 10 July 2006 - 11:24 PM

Oh PFFFT to that high-horse.

I'm pretty sure if a situation arises where I need power and don't have 0.2 seconds to flick the T-Bar down to drive you're pretty well f-ckd already.

Show me where at 4.45am you require emergency power in a straight line on the freeway downhill that the aforementioned of flicking the shifter down a notch to drive (you dont even need to push the button in) can't be had.

Most situations involve deceleration, shit if you had to power down that hard it'd probably take longer in a manual already in gear to downshift anyway.

I'll take everything I have and put it on red/black over betting that situation arising inf fourteen lifetimes of driving.

Next.

Edited by Loki, 10 July 2006 - 11:26 PM.

#19 _devilsadvocate_

_devilsadvocate_
  • Guests

Posted 11 July 2006 - 12:43 AM

Let Loki coast on this one, has any one watched the tour de france on the downhill stages yet��..I didn�t notice anyone without a freewheeling hub? Ok I hear you, cars are different.
Many have their opinions on the need for a car to instantly be able to accelerate in an emergency, good in theory�.justifies fast cars, but as stated previously, comparing it to a manuals that require a downchange: to do any good here, its going to be faster to put the auto into D as Loki has suggested. As for the car needing to be in gear to be in control, basically new automatics are in neutral once you take your foot of the pedal. There are circumstances where the feel of braking without touching the brake is warranted and this is part of why one can select lower gears on an auto. Not all these things are best practise for everyone but one needs to use judgement about when it is safe to do things and to whom the advice is given, driving downhill through sharp bends in neutral isnt recommended and certainly using the auto selector to keep it in a lower gear keeps the speed of the vehicle more steady in these situations. There are quite a few things they tell you can instantly get failed for when doing a driving test which even I threw out the window as soon as the test was over��.
Also the ability to be able to accelerate out of trouble is a much overrated safety feature, how many accidents are caused by underpowered cars? often I suspect its a cause of the accident becoming worse, the "advanced" driver using their training to power out of trouble, still losing it and crashing at higher speed.

EH: turning the engine off(you were just kidding, yes?), well I�ve done it myself on a long mountain descent when I was low on fuel(circumstances). The fuel to the engine was switched off but road it down in gear(manual), so brake booster would still work and brakes wouldn�t burn out, just turned fuel back on so could change gears without shaking the thing to bits. Get increased engine braking this way, less brake fade in a full loaded torrie. Possible not a good thing if you are running one on those �dinosaur� petrol carby things as there would be quite a delay in refilling the float bowl.
Don�t most of the newer cars do this too, shut off fuel to the cylinders on overrun.
Ive got a 2km section on my trip to work where the slope of the road appears insignificant , if put it into neutral it will go the whole length maintaining 60kmh�..now that�s gotta be better for the hip pocket and the environment.

#20 _Loki_

_Loki_
  • Guests

Posted 11 July 2006 - 12:56 AM

^ Definately not talking about neutral coasting where it has the potential to be "dangerous" anyway (down steep sweeping hills etc.)
The reason I brought the whole issue up was that with rising fuel prices, and remembering driving to ipswhich on the old ghost-town freeway in the old 202 at 4am in the morning - I found certain sections I could neutral coast for a few kilometers instead of having to having to keep the throttle down to maintain 100kph even on slight down hills (due to gearing and engine retardation slowing the car down).

I noticed with the 308 + T350 that even Drive has some resistance but I haven't been neutral coasting it, particularly because I heard it was bad for the box; which otherwise seems to have been debunked.

Ive got a 2km section on my trip to work where the slope of the road appears insignificant , if put it into neutral it will go the whole length maintaining 60kmh�..now that�s gotta be better for the hip pocket and the environment.

Same here: There are a few roads near me that are very slight down-hill gradients that even in the T350 at 60kph, I have to very lightly accelerate to maintain speed, whereas neutralling it would maintain speed, although I wouldn't switch the engine off :blink:

Either way, my main question of whether or not neutral coasting is bad for the box has been answered, as has N/D at lights.
Not interested in continuing to argue with high-horses about the 'danger to manifold floorpan falling off doors unbolting themselves because not in gear' argument.

Edited by Loki, 11 July 2006 - 12:58 AM.

#21 Tiny

Tiny

    Oh My, Don't you post alot

  • Administrators
  • PipPipPipPipPipPipPip
  • 10,018 posts
  • Name:Tiny
  • Location:Sydney
  • Joined: 04-February 07

Posted 11 July 2006 - 12:20 PM

Loki: I thought about the vaccum pulling fuel etc and to the best of my understanding of carbies, it wouldnt happen. You;d have a massive vaccum in the manifold thus causing considerable engine braking, but it cannot open the butterflies and thus cant give any more fuel ( Well.... Any more fuel than the idle circuit can supply i spose!).

I understand wehre your coming from about the time it takes to flick it back into D from N if you need the power suddenly and your location etc etc, but I belive its still false economy on a road car.
I knew a lady who was in financial trouble and coased around in neutral in her manual car alot of the time... with her kids in the car and in places that were definitely dangerous... Its not something i would encourage at all and i dont really think you could measure the fuel you may save.

I think the best thing to do would be to have the car tuned for highway driving with a lean top end and idle set so there is as little unburnt fuel from the exhaust as possible. I know i spent $300 chasing that in my torana when i had the webber on it and the guy who did the job was amazing! The fuel economy was nothing short of excellent ( when my lead foot allwed it!) though i did loose considerable power.

That's my opinion on the matter, but to answer your question, No i cant see it damaging anything in the drivetrain.

Cheers

#22 _munro_

_munro_
  • Guests

Posted 11 July 2006 - 02:15 PM

the problem with coasting is engine braking and the ability to accelorate (don't pic� on my spelling)
if something happens you've got less control of the car
and the reason the motor is reving at 3grand is cause the turbo and trimatic boxes lock meaning the input shaft is spinning at the same speed as the motor
this happens ova a certain rpm (i don't know the exect figgures)

:spoton: tom

Dont agree with any of that Tom.
The effect is there all th time, regardless of whether the torque convertor is locked up at 3000rpm or not.
Drive a new car with auto and lift your foot off the accelerator, it barely slows down at all compared to an older auto trans(i find newer auto trans disconcerting to drive for that reason.....but just a matter of getting used to, engine braking is useful for preserving brakes on a downhill run or racing or for going down slippery slopes, but gives no more control than just putting a permanent brake on the tailshaft otherwise.
If you need to accelerate in an emergency, perhaps yes, but selecting D again is bit quicker than trying to change down a gear in a manual for some sudden acceleration. So no its not reccommended procedure while doing your driving test, but used appropriately will save fuel on older cars. Dont know if regs have changed but the only time one could put the car in neutral on a driving test was if the car was stationary with the handbrake applied.

devels your clueless
where talking 30year old technology not new cars
new cars can coast and have the revs drop but the older ones can't ,accept that fact.

LOKI if you figgure that no cars can come out of a side street and cut you off then go for it.
the reason i mention the fact that you can't accelorate is cause if you get cut off both your hands are on the steering wheel trying to avoid a crash having to engage g'box is another distraction at the worst possible moment.


:spoton: tom

#23 _devilsadvocate_

_devilsadvocate_
  • Guests

Posted 11 July 2006 - 02:49 PM

devels your clueless
where talking 30year old technology not new cars
new cars can coast and have the revs drop but the older ones can't ,accept that fact.

Munro, stick to facts, personal insults doesn't improve your case...... If you disagree with something, state it politely and back it up, while we all would like to be right about things, thinking we are right and actually being wrong is a worse position to be in, sensible discussion means we can all learn......dishing out insults to those that simply disagree with you is really playground behaviour.
Perhaps get some correct first hand facts, get in a trimatic with a tacho, drive the thing at 60kmh observe the revs,(perhaps do it at all speeds) then take your foot of the throttle.

Edited by devilsadvocate, 11 July 2006 - 02:56 PM.

#24 _Loki_

_Loki_
  • Guests

Posted 11 July 2006 - 03:32 PM

Loki: I thought about the vaccum pulling fuel etc and to the best of my understanding of carbies, it wouldnt happen. You;d have a massive vaccum in the manifold thus causing considerable engine braking, but it cannot open the butterflies and thus cant give any more fuel ( Well.... Any more fuel than the idle circuit can supply i spose!).

I understand wehre your coming from about the time it takes to flick it back into D from N if you need the power suddenly and your location etc etc, but I belive its still false economy on a road car.

Yep, fair enough mate on the fuel idle issue.
Only where I'm talking about you have to actually keep your foot on the throttle to maintain speed due to that engine braking (thus you are putting more fuel in).

Tiny: Would not having enough fuel for the revs (rpm being brought up by drivetrain) then, be infact detrimental to the block then due to improper and lean combustions (this is why some cars tend to pop, gurgle and have small backfires when engine braking right - improper combustions; wouldn't this be bad?).
I know my 202 used to do that down hills alot and I thought it sounded pretty tough :)
The old 308 doesn't do it, just bubbles along like a normal v8 when engine braking :(

As for the side street incident mentioned by someone else. I don't see too many side streets at 4am in the morning on a freeway driving to work ~_~

#25 _munro_

_munro_
  • Guests

Posted 11 July 2006 - 03:43 PM


devels your clueless
where talking 30year old technology not new cars
new cars can coast and have the revs drop but the older ones can't ,accept that fact.

Munro, stick to facts, personal insults doesn't improve your case...... If you disagree with something, state it politely and back it up, while we all would like to be right about things, thinking we are right and actually being wrong is a worse position to be in, sensible discussion means we can all learn......dishing out insults to those that simply disagree with you is really playground behaviour.
Perhaps get some correct first hand facts, get in a trimatic with a tacho, drive the thing at 60kmh observe the revs,(perhaps do it at all speeds) then take your foot of the throttle.

sticking to the facts
well we all talking about g'boxes that came out in the torries.
if we were talking new cars then i'd agree with you.
if i'm driving an auto i prefer the little engine braking the old g'boxes give.
i belive it gives you that little more control ova the car.
and devils the reason i'm having a go at you is cause your arguing with everyone based on new car specs which i fell is irelivant to this thread.

loki the back firing was proberbly caused by ignition timing


cheers tom :spoton:
Back to General Questions and Help


1 user(s) are reading this topic

0 members, 1 guests, 0 anonymous users

  1. GMH-Torana
  2. → Holden Tech
  3. → General Questions and Help
  4. Privacy Policy
  5. The Rules! ·