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Transmission downshifts suddenly

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Old 07-16-2009, 09:57 AM
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Transmission downshifts suddenly

I could use some help from you guys,

I have a 1995 4runner with 168k, 3.0L 4wd etc. Every once in a while i'll be driving on the freeway at about 60mph and suddenly the tranny will downshift quickly and go right back to normal. This "slip" happens really fast from over drive to 4th gear (shoots up to about 4k rpm) and back into OD in a blink of an eye. When this slip happens the A/T oil temp light AND CEL blinks on and off during the downshift moment. The lights blink on and off as fast as this slip happens. If these lights would stay on then that would help me figure this out but they don't for some reason. this slipping occurance can happen after 10 minutes of regular driving or an hour or sometimes it doesn't happen during a drive at all. I drive normally, i'm not offroading it when this happens and i checked the fluid level and it read normal for my tranny. This occurance can also happen when just driving in a parking lot and accelerating normally but it's rare. Can anyone give me some advice? Thanks for looking.
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Old 07-20-2009, 02:09 PM
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Some more info for anyone that can help.

I just jumped Te1 and e1 to read any codes that may be stored and there isn't any. The check engine light continuously blinks with no pauses. That confuses me further, i was hoping for a code since my CEL flashes on real quick when this problem occurs.

Another idea may be my speedo cable? When i drive my speedo waves back and forth as i drive and accelerate. It sways about 5mph. If i'm driving around 55 mph the speedo is swaying from 53-57mph. I heard a bad speedo cable (i think mine is mechanical) can mess up your transmission by something called 'lock up'?
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Old 02-14-2012, 08:39 AM
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I have a similar problem with a 95 6cyl auto. Most of the time all is well then suddenly it will downshift. No light s or gauges are affected. My experience has been at speed under 50mph on the level. Is there a sensor involved? Any help appreciated.
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Old 08-05-2012, 06:43 PM
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random transmission shifts

Might have found a possible solution. I decided to replace the radiator due to pin holes that developed in the tank. In the course of doing so, I found out that there were different sensors that send coolant temperatures to the transmission. Since the radiator replacement, the problem has gone away.
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Old 08-05-2012, 07:44 PM
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While I've never figured out exactly which vehicle has an electronic speedo, I'm pretty sure that a '95 4wd would be electronic. The easy way is to look at the back of the transfer case: is there a fat cable or a supple wire coming out of the sensor?

Unfortunately, a failure of the electronic VSS1 is more commonly "drops to zero for a second or two, then springs back up to the right speed." Your wavering sounds more like a cable type. Under the vehicle for you!

Either way, VSS1 (whether it is the electronic one in the transfer case, or the reed-switch inside the combo meter driven by the speedo cable) is an input to the Transmission (missing VSS1 is the first diagnostic code http://www.ncttora.com/fsm/1990-1995...2/troubles.pdf ) so I would definitely look in that direction.
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