Old trannys leak down when they sit--Why? - Hot Rod Forum : Hotrodders Bulletin Board
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Old 07-11-2007, 11:33 PM
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Old trannys leak down when they sit--Why?

I understand there's some kind of seal that's supposed to keep the converter from draining into the pan, and that when that seal gets old & stiff, it lets the converter drain and causes the pan to overflow onto the ground.

I'd like to know what that seal's called, and if it gets a constant bath of ATF when the car's just sitting in park, but running.

I have a couple of old yard-mobiles that could use a dose of "leak remover" if it'd work without having to actually drive them on the road.

Turbo 350, Turbo 400, and AOD are the ones I need to know about.

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Old 07-12-2007, 01:32 AM
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Where the input shaft goes into the tranny pump there is a seal.
Easy to replace once you´ve dropped the tranny and removed the torque converter.
I´ve bought a couple of converters, TCI and B/M, they both came with a new seal.
A little insurance job to do while the converter is off the tranny.
Mine is a 700R4 but the basic setup must be similar to yours.
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Old 07-12-2007, 07:06 AM
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The fluid from the converter will drain back into the trans case after sitting. In most cases the leak is the seal around the dip stick tube when the fluid rises above it.
Bob
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Old 07-12-2007, 07:49 AM
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converter drainback

Torque converter drainback occurs with many types of transmissions, but is especially prevalent with Chrysler trannys.

As soon as you start your vehicle the trans pump will begin to fill, or "charge" the torque converter with fluid. But because of the design of the manual valve, [in the valve body], on most chrysler transmissions, converter charge was inadequate.

In a perfect world, you would park your vehicle, turn off the engine, the converter will be fully charged, get up the next morning, or 5 days later, start your vehicle, then drive right off.

But in the real world, if your pump bushing is worn, or you have wear in pump stator bushings, converter splines, valve body issues, or a host of other issues, the fluid will drain back into the sump [pan].

Then when hop into your vehicle, start it up and expect to drive right off, you may not take off so well.

Let the vehicle run for a couple of minutes, the converter will be "charged" with fluid and the cycle starts all over again.

If you had this condition, you could qualify this concern by removing the trans dip stick, before the vehicle is started [after sitting overnight],then have someone start the vehicle for you and immediately check the fluid level.

If you have converter drainback, the fluid will register very high, or overfull, on the stick. Untill the vehicle runs for awhile, then it will register correctly.
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