300D Transmission Slipping

Will switching from Dextron to Synthetic ATF stop my transmission slipping between gears? I was thinking of Switching to Mobil 1 or AMSOIL Synthetic. I've heard it stops transmissions from slipping.
Thanks and Happy Holidays to all...!
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No... simply changing the fluid and filter might help. When I got my car, it was slipping on takeoff... occasional. After fluid change and filter, it hasn't slipped since then. The tranny has 209,000 miles now.
I use Valvoline Dextron ATF or Pennzoil Multi-Vehicle ATF. For the 5 speed transmission, I use Amsoil synthetic Universal ATF.
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I would have thought this too, but the transmission fluid and filter were just changed this Fall after I had the engine rebuilt. So the fluid is new, and transmission slipping. What are other fixes for this short of a rebuilt trans.?
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Did he do a full drain including the torque converter? If not, then that is not enough... what I do on mine... without draining the torque converter is to drain, fill, drive 10 miles and repeat 3 time.
On the third time, I then change the fluid.
What gear is it slipping? Only when starting to move? Or certain gear? How many miles on the tranny?
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Tiger:
I was contemplating doing the "drain and fill" method, but am not sure if I want to do that if I am going to convert to synthetic trans fluid. Then on the other hand, maybe I don't want to switch to Synth. During the engine overhaul, the transmission fluid was drained twice (once to change, another because they pinched the gasket upon installation). However, I do not know if they drained the torque converter--I would like to think they did, bur not being certain, I would have to say, maybe not. The transmission is slipping in all gears.
Randall
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P.S. Only 218,000 miles on transmission.
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218,000 miles and you didn't spring for a rebuilt tranny while your engine is out? Yeah, the engine cost a fortune...
Slipping in all gear is not possible unless catastrophic failure. Usually it is slipping upon start that the engine revs and then tranny jerk...
Have you tried adjusting your vacuum modulator? Adjust it counter clockwise for less vacuum assist... and more firm gear. Improper asjustment cause slipping in all gears.
Or from an old engine to new rebuilt engine is enough to cause slipping because new engine got more vacuum pressure.
Other possibility is improper tranny throttle cable adjustment. It should be slightly loose on idle position... just follow the cable from your tranny. it should be loose a bit.
Don't waste your money on synthetic.
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Tiger. OK, forget synthetic. I was about ready to take that decision anyway, after reading all the posts here about it.
No, I didn't think about a rebuilt transmission at the time that the engine rebuild became necessary, because I was somewhat in shock from the notion of needing an engine rebuild at just over 200K miles, and insofar as the transmission was not slipping or showing any signs of needing maintenance at that point, the thought of replacing the transmission never even occurred to me.
Your point about the vacuum adjustment seems to be the most plausible, although I will certainly check the throttle cable adjustment. The transmission does slip as it goes through each gear, which makes this seem more than a likelihood.
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