e36 3i6i auto box doesnt change down

Hi guys , i have a 93 bmw 316i automatic. It often changes into a higher gear and doesnt change down...imagine driving around in 3rd all day! This has plagued me for over a year and i lived with it as it
didnt happen all the time.
I have found that if i switch of the car and restart its fine for a while. I dont know if its temperature related cos its did'nt bother me much over the past few months but with summer coming around and the increase in temp it seems to be happenning more often.
Sometimes whilst stopped at a traffic light theres a thud from the box as it changes into a higher gear.
Any help will be appreciated.
Thanks. javs
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Summer coming? Temps increasing? I get it, you're south of the equator.
My first thought -- well, the thought after my confusion over climate -- was that your kick-down linkage was on the fritz. You can make gear selections manually by moving the shifter, can you control the transmission this way, or does it still refuse to downshift?
If your car won't shift down when you mash the gas pedal, then you have problems with the kick-down linkage -- you can spot at least a portion of this linkage connected to the carburator/throttle body adjacent to the cable that goes to the gas pedal. Since your car "shifts" while stationary, I'm thinking the kick-down is not the trouble -- I described the operation just to give you a point from which you can do a test. I think your transmission is close to making you walk home. You need transmissiion service beyond what most of us can do at home.
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South Africa to be exact!..so things definitely hottin up down here.
Trying to shift gears manually with the lever doesnt work...the only thing that helps when the box acts up is switching off and restarting. Maybe its a control unit?
But i agree that its unlikely a kick down problem.
Thanks for the input Jeff.
Jeff Strickland wrote:

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Easy thing to check is the switch on the brake pedal. Some take a 'sniff' off the brake switch rather than a separate one, so even easier to check it's working normally. If the brake is effectively 'on' and the throttle open it effects the down changing.
--
He who laughs last, thinks slowest*

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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I think your problem is bigger than kick-down linkage. At first, it seemed the kick-down was the trouble, but with your current list of symptoms, I'm thinking the kick-down is not the trouble anymore. Me thinks you need transmission work.

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