[Shop-talk] Coast in Neutral -the next great debate

John Miller jem at milleredp.com
Mon Dec 12 10:32:09 MST 2022


>     If you put a manually car or truck in neutral and release the clutch
>     while going down long hills or coming to a stop at a intersection,
>     are you doing any damage?

Ah, Mexican Overdrive as it used to be called.

You said 'release the clutch' so that's assuming it's a manual 
transmission.  You're pretty safe, most traditional manuals are 
splash-lubricated and will do fine.

Maybe some DSG-type quasi-manuals maybe not so much.

Automatics it's potentially a problem, it depends on which end of the 
transmission the hydraulic pump(s) that lubricate and cool things is/are 
driven from.

The ZF 4HP18 was a notorious case, the hydraulics were driven off the 
output side.  Perhaps what you need for this, but they routinely blew up 
a couple weeks after e.g. California smog tests where the engine was run 
at 2500RPM in neutral for a few minutes.

John.




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