1994 merc s420 tranny

Asked by Apr 19, 2010 at 02:52 PM about the 1994 Mercedes-Benz S-Class S 420

Question type: Maintenance & Repair

'94 S420, transmission started slipping gears. I had a new(used 84k miles) tranny put in. Works fine when cold but when gets hot and i am on the frwy, gears suddenly wont shift down. it will be go 45 mph and rev 4000 rpm. if i go faster, rpm goes higher. if i let go of gas, rpm wont go less than ~3700 rpm.
    If i pull over and wait 30 min, it works fine again only for a while.
The guy who i bought the used tranny from said problem is the brainbox.
    My mechanic who installed it says  the tranny is bad.
What is the "brain box"? Could that be the problem?
   ALSO of note, the AT Kickdown cable is broken. Could this be problem?
Guy who sold me the tranny says to take it to a shop he recommended to let it be checked, but i dont think i can trust bc its his best interest to say its the brainbox, not tranny.
What should I do?

2 Answers


I am interested to know if you were able to sort your problem. I have a really similar problem with my 95 - e320. The car has 400,000 km on it and the tranny has been excellent. This summer with the hot driving it has started jumping out of top gear when on the highway. It only happens on the hottest days and only after driving for a long way. When the temperature is lower or the drive shorter... then no problem.

2 of 2 people found this helpful.

Its the Kick down cable you should get it fixed because it its messed up it wont shift down or if it does it will shift down late

1 of 1 people found this helpful.

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