Re: [diesel_mercedes] Re : GM Dual Hyr

 

Except on the original Hydra-Matic, the rear band required pressure to RELEASE.  Also, the front and rear pumps worked independently of each other.  (In fact, the front pump was variable output, and had negligable effect at speeds over 40 mph.)  If Brian never slipped the car into Neutral while coasting, he may have been able to get away with his stunt.  But, once the engine was stopped, pressure to the rear band would drop.  Going back into Drive would get the engine spinning again and the band would release, but only after the forward momentum and weight of the car had to overcome the friction of the applied band, which would take up to five seconds.  A few cycles of Neutral/Drive/Neutral/Drive, and that band would get pretty hot.

Also, they didn't have any sort of fluid cooling, other than whatever was cycled through the fluid coupling, which was minimal in the higher gears.

BTW, Mercedes transmission models 722.0, .1 and .2, the ones with the four-bolt oil pan, used up til '81-ish, retained the rear pump, and yes, ARE push-startable.

(Wow.  Got this back around to Mercedes....)

Mark in Lakewood, CO

From: "Bobby Yates Emory" <liberty1@gmail.com>
To: "diesel mercedes" <diesel_mercedes@yahoogroups.com>
Sent: Wednesday, August 31, 2011 11:27:36 PM
Subject: Re: [diesel_mercedes] Re : GM Dual Hyr

 

Brian,

I don't think you should think it is your fault.  The original Hydra-Matic had a rear pump.  It should have been able to deal with being operated without the engine running.

(Reality note - since about 1970 ? auto trans have not had rear pumps - they cannot be towed or operated with the engine running.  Most earlier trannys had the rear pump so they were less touchy.)


Bobby

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