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Hi everyone! I’m the proud new owner of a ‘99 Boxster 2.5L. 


Recently, I noticed that when my transmission automatically shifts from second to third gear, it’ll jerk very slightly, as if the transmission is stuck for the briefest moment in second gear right before it shifts.


More noticeably, when I’m driving to slow down and breaking, as the transmission begins shifting from fourth to third and second, there is some jerking again—the sort of jerking you get when a transmission shifts into a slower gear and the car slows down suddenly because of the lower gear. 


So when I’m slowing down, I will be going at a given speed, the car will downshift a gear, I will feel that sudden slow down, the car will run at a lower speed, downshift again, and I’ll feel that sudden slowdown again. This keeps happening until the car reaches second gear, of course. 


Because of this, I recently had the transmission fluid changed. My mechanic showed me that the old transmission fluid was black and smelled like smoke, but that he hadn’t found any metal shavings so he thought the transmission was probably still okay. He told me to check in after a couple hundred miles to see if the transmission adjusts and drives better.


It’s been a hundred miles, and I’m still seeing this behavior—should I be worried, or is this common in tiptronics? I’m hoping that best case scenario, the car’s sensors are miscalibrated and the trans is downshifting at the wrong times (thus the gap between the speed it’s going at and the slowing down effect of a lower gear). Worst case would be having to buy a new transmission. 


Please help! Would appreciate some advice or expertise. 

Edited by Ordonezp

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It is not common behavior.  You need to recognize that when you changed your old fluid, you only got about 35-40% of it out, the lion’s share is still inside the converter which does not gravity drain.  Unfortunately, Porsche instructions are to change the Tip fluid at 90K miles, which is WAY to long, we typically service customer’s Tips around 40-50K miles.  When we see one with fluid as bad as yours, we typically drain it, change the filter, and then do three fill, run, and drain again cycles to try and flush out as much of the old fluid as possible.  And before you ask, no, there is no way to pressure flush this trans like many other brands can easily be done.  


Good luck.

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“ when I’m slowing down, I will be going at a given speed, the car will downshift a gear, I will feel that sudden slow down, the car will run at a lower speed, downshift again, and I’ll feel that sudden slowdown again. This keeps happening until the car reaches second gear, of course. “


Mine does the same, you feel the down shift and then the deceleration braking, I have a 97 2.5 if the trans slips and them jams into gear that is not normal, JFP is right about changing the fluid a friend of mine suggested an additive that their shop puts in Mercedes that works well on the sticky selenoids when the hard shifting happens, but I don’t have the name handy, will check tomorrow and post back!

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Did you have the codes read? If you have durametric it will read the transmission codes if there are any. These won’t result in a CEL on the display but could still be stored. I would check that to see if that gives you any ideas. Could be a solenoid issue or one of the sensors on the valve body.  Sometimes clogs on a solenoid or something as simple as a bad o-ring on the valve body can cause similar behavior. I would also ask if there was any fiber residue in the retrieved ATF which could indicate wear in the fiber discs inside the trans. Did he also change the trans filter?

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As you are no doubt aware, there is a precise procedure for refilling the transmission to ensure the correct fill level.


Your mechanic presumably knows that?


If in doubt, it may be a good idea for you yourself to ensure that the transmission has been filled to that correct level; with the fluid at a temperature of between 35C and 40C.



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Hi everyone, thanks for your replies! I touched base with my mechanic, and he said that because it doesn't seem like my transmission has ever been serviced (going on 122K miles), that he thought it was better to replace the fluid gradually as to avoid slipping or damaging the transmissions. He told me to come back after 1000 miles to replace the fluid again. I think the transmission fluid has been filled to the right level--I trust that my mechanic knows what he's doing. For now, the transmission is okay, just not shifting as smoothly as I would like. Definitely better after the original transmission fluid change than before.

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