My tranny is having a similar problem to what has been posted here by others. When the speed of the car reaches 40-50 mph the rpms shoot up to 5000, and the tranny will stay in low gear after that.
I put in some trans-x and the problem seems to have gone away as I only drove it for a few miles.

How long should I run the trans-x in there and should I put more in when I do a filter and tranny fluid change?

Also how many quarts does an 84 300DT take when you drain the torque converter as well. The Haynes manual I have calls for 6.7qts, but according to a friend it should take 3.2 gallons (about 12 qts)?

Also, for those who have used trans-x please let me know how it is doing?

in my old beater 79 300SD the trans wouldn't get into any gear since it has been sitting for some years. i put trans x in there and let it idle while going through the gears for about half an hour. then it started to work again. never drained and replaced it. used the car for a year after that until i blew the engine up. the trans was still working good.

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198? 300D ???K - Future DD
1989 300TE 285K - traded in '12
1984 300SD 186K - Sold in 08
1978 300SD 330K - Died in 05

If it made the trans work.... then I would leave it in there several hundred miles to make sure it has done whatever cleaning it can...... and then change out the fluid and filter... putting one can of trans-x back in to leave long term.......

On my drive to work this mourning. The rpms would flare up and down a few times before shifting into higher gears especially on the third shift. It would only do it for the first few times. I will keep you guys updated.

definitely let us know how the stuff turns out....

Thanks

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Audi TT

Even as a professional mechanic, I'm open minded to the possibilities of snake oil. I put a used trans in an 82 300DT a few weeks ago. It had been sitting on my shelf of used transmissions for a couple of years. After a few days the trans would stay in first several times during the driving day. I had to shift to neutral and back to drive to get it to work. I didn't feel like swapping the trans again even with a hoist and trans jack. I poured a $6.00 bottle of trans x in just to see. The trans has not had the problem in a week of around town driving.

Peter

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Auto Zentral Ltd.

the shifting was acting kind of funky, as in going 50mph then the car would go in to low gear and sometimes get out and sometimes not. The snake oil solved the problem for a few days but it is beginning to come back. This weekend i am going to give it a fluid and filter change and put in only half of a quart of the trans-x and see how that goes.