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Discussion Starter · #1 ·
Quite simply, my '71 automatic Opel GT slips out of first gear when I turn a corner. All I need to do is let off the gas and reapply to get it to re-ingage. Fluid level is good and I don't see any leaks. Any ideas?
 

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Vendor
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It does sound like a classical case of low transmission fluid. The TH-180 is pretty fussy when the fluid levels drop, and checking the level can be somewhat tricky. I recall that the transmission fluid level needs to be checked after the transmission is warmed up, while running, on level ground.
 

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I recall that the transmission fluid level needs to be checked after the transmission is warmed up, while running, on level ground.
…and in neutral, not in park.

The lines on the dipstick relate to pints, not quarts. Even 1/2 a pint low (or high) will cause issues.
 

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Über Genius
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…and in neutral, not in park.

The lines on the dipstick relate to pints, not quarts. Even 1/2 a pint low (or high) will cause issues.
It's amazing how many people check their auto transmission fluid with the engine off, just like engine oil.
 

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Just Some Dude in Jersey
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Very common problem. Too low on fluid. In fact, slipping out of gear is how I have always judged if I have enough fluid in the tranny after draining it for the numerous engine removals I've done. It's impossible to drain all the fluid out of an Opel tranny, which makes it tough to judge how much to put back in. I always put in one quart less than I think I need, then start and put it in drive, if the car moves you're almost there. If not, add 1/2 a quart. Then I drive around the block making sharp right hand turns and accelerating halfway through the turn. This causes the fluid to slosh to the left, which allows air to get sucked in to the tranny pump via the fill tube, and if the tranny slips out of gear with a whining sound, then I add another 1/2 quart. If it doesn't slip out of gear while applying gas and making a sharp right hand turn, then your fluid level is perfect. However, you can sometimes not have a fully inserted fill tube which can partially cause the air sucking thing during right hand turns, but you usually end up with a noticable tranny leak. Adding just 1/2 of a quart PAST the NO SLIPPING out of gear on a right hand turn point will often cause an OVERFILL situation and the excess fluid will slowly leak out a drain hole on the top of the tranny for WEEKS and make you think you have a tranny leak.

Other than getting the leak thing straightened out with new front and rear seals, a new fill tube o-ring and a fully inserted fill tube, and installing the relatively new high quality pan gasket(and not over tightening the bolts/no sealer/and making sure the pan isn't bent), the auto trannies are bullet proof and will outlive you and the car and never need maintenance or rebuilding and can handle all the HP you throw at them.
 

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Discussion Starter · #7 ·
OMG, I knew this was the place to ask. You all are a wealth of information! Turns out I need a new transmission tube (it seems to be too short) and so my dip stick isn't accurate. I will look into all of your suggestions and get back to you. Thank you again everyone!
 
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