Transmission failure from high idle?
 

I just heard a story about MB transmissions failing while sitting in park or neutral and idling at higher rpm - 2500 or so. The examples I heard were during high-idle emssions testing (pre smog dyno) in CA, and when people would rev thier engines while jumpstarting another car. According to the story, some MB transmissions maintain elevated internal pressure when revved up, even when in park or neutral, and the pressure causes pump failure.

Is there any truth to this one?

How in heaven's name could the pressure be any different in neutral than in gear? The pump turns the same speed either way, and that's where the pressure comes from.

However, "rocking" one of the newer trannys while stuck in snow and overspeeding it in low/reverse WILL fry them, I've seen it.

Peter

You're thinking of the ZF automatic made for BMW. The front pump ceases operation at idle, and allows auto-boxes that are used in stop and go traffic conditions to overheat and die an early death. Getting 100k-miles out of a ZF tranny is a big deal as most won't go that far.

Hmmmm.

The ZF22 on the Volvo TurboDiesel has 220,000 on it and is the only thing that hasn't given me trouble yet......


Peter