auto gearboxes

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It won’t do any harm to your transmission but you’re likely to use more fuel that way. An engine requires fuel to idle. Left in ‘D’, at least up to the point that it reaches the 2-1 rollout shift, the vehicle inertia on overrun will be driving the engine speed above idle and it won’t therefore be being fuelled.
 
I have done this in the past dowl long hills - the mpg on the trip computer definitely increases...may therefore depend on where you are "freeheeling"
 
Datatek said:
The gearbox internals will be turning over at road speed but the input shaft and therefore the oil pump will be running at idle speed. Is that a good idea?
Click to expand...

Well at least with the engine running the pump is being driven, but i don't think it is a good idea personally.
 
Lubrication flow rate in the 5HP24 is around 15 litres/min at tickover but around 45 litres/min at any engine speed above 2000 rpm (flow control valve characteristic). Wouldn't matter much just for rolling up to the traffic lights in neutral but if you were to engage neutral while coasting downhill where the engine speed in gear would have been 2000+rpm in 'D' then you only have a third of the lubrication flow to the transmission running gear.
 
wammers said:
Might be interesting the first time you accidentally stick it in reverse.:D:D:D
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To put it in reverse you have to press the button on the shift, but to move between D and N to can just move it without pressing anything so it's impossible to put it into reverse by accident without pressingnthe button

Matt
 
Incidently, there’s a shift solenoid (MV-3) in the 5HP24 valve block whose job in life is to prevent reverse gear being engaged if it’s selected at forward speeds above 5mph. It does this by activating the reverse gear lock-out valve which bypasses the manual selector valve. There you go, we can all sleep tonight now :)
 
Woof ! good knowledge there Bemble. Can you tell me why ZF4HP Whatever in my P38 is gradually increasing the time it takes for 4th to lock in. I used to be able to get it in at 35MPH now its usually 45. ???
 
rewmer said:
Woof ! good knowledge there Bemble. Can you tell me why ZF4HP Whatever in my P38 is gradually increasing the time it takes for 4th to lock in. I used to be able to get it in at 35MPH now its usually 45. ???
Click to expand...

It could be something to do with the weight of your right foot and degradation of the muscles as part of the normal ageing process:screaming_bug_eye_f
 
rewmer said:
Woof ! good knowledge there Bemble. Can you tell me why ZF4HP Whatever in my P38 is gradually increasing the time it takes for 4th to lock in. I used to be able to get it in at 35MPH now its usually 45. ???
Click to expand...

Mine seems to come in about 25 - 30 ish but it feels harsh & jerky when it changes.
If it changes about 35 - 40 feels a lot smoother. I have a service kit for it so thats the next job.
 
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