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Old 05-29-2009, 11:43 AM
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Tranny or torque converter? (th350 slipping)

Hi guys.
I've recently finished breaking-in my engine and tried some 1/4 mile passes... After first pass tranny started to slip badly at hight RPMs (above 4K). If I hit gas at any gear (1,2 or 3) - I hear rustling sound and car doesn't accelerate (but RPMs rise).

I don't know history of that tranny and TC (bought it used) but it supposed to be built...

So, what's the problem? tranny or converter?

PS: tranny is full of Dexron II. When I check level I can see small bubles on dipstick. At low load and RPMs tranny seems to work ok.

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Old 05-29-2009, 11:50 AM
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Quote:
Originally Posted by Mr. Y
When I check level I can see small bubles on dipstick. At low load and RPMs tranny seems to work ok.
Be sure that the tranny isn't overfilled. Sometimes, different dip sticks can be mixed up and give false readings, though this isn't common. Or the tube isn't all the way home in the case and will read low when full.

If the tranny is too full, air gets whipped into the fluid. Air compresses- fluid not so, so aerated fluid can allow the clutches to slip.

Is the fluid still clean and unburnt-smelling? If so, you may be able to salvage it.

Is the modulator hooked up? What about the detent?
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Old 05-29-2009, 12:21 PM
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I have Lokar dipstick (came with tranny) and IDK how accurate is it. Tranny worked fine at low boost setting (13 psi) but today I've tried more (18psi).

Vacuum modalator is hooked to manifold, detent cable isn't (but afaik it affects shift points only, and I shift mine manually).

Fluid is still fresh, clear and doesn't smell burnt.
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Old 05-29-2009, 12:33 PM
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Quote:
Originally Posted by Mr. Y
I have Lokar dipstick (came with tranny) and IDK how accurate is it.
I'd sure be looking at it being (hopefully) overfilled, then.

Any chance you could sub a stock tube/stick assembly to check?

Quote:
Tranny worked fine at low boost setting (13 psi) but today I've tried more (18psi).
As in turbo- or supercharger boost?
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Old 05-29-2009, 12:41 PM
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it's turbo (Toyota Supra).
I've got whole kit from another supra owner, but he isn't techinically advanced. He just said that this kit have been assembled by reputable shop and was working fine for him.

I'll try to add some more fluid and check that modulator tube is ok...

Any ideas why it operates ok at low RPMs and load but slips at high in any gear?
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Old 05-29-2009, 12:50 PM
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Quote:
Originally Posted by Mr. Y
I'll try to add some more fluid and check that modulator tube is ok...
I'm thinking there may be too much fluid, not too little.

Quote:
Any ideas why it operates ok at low RPMs and load but slips at high in any gear?
You may need to go w/o a modulator if it isn't seeing the right vacuum at cruise and when under a load. But even if plumbed w/o vacuum signals being "correct", if the vac. is low (or the mod. "sees" pressure, not vac.) it will increase line pressure as if the engine were under load.

Was this tranny you are using now ever used successfully in a turbo app?

But first off, check to be sure the fluid level's not too high.

Last edited by cobalt327; 05-29-2009 at 01:26 PM. Reason: Vacuum modulator concerns deleted- unfounded for the most part.
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Old 05-29-2009, 07:46 PM
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Quote:
Originally Posted by Mr. Y
Tranny worked fine at low boost setting (13 psi) but today I've tried more (18psi).

Vacuum modalator is hooked to manifold, detent cable isn't (but afaik it affects shift points only, and I shift mine manually).
Vacuum modulators do not like boost pressure ,,,,,, IF I understand your post on the hook up to the manifold.
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Old 05-30-2009, 02:17 AM
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Well guys, thank you very much for replies.
I've figured out my problem and it wasn't tranny-related at all (boost control and engine management).

And as for modulator: it increases pressure at WOT, right? so in NA applications it sees "zero" boost. Mine sees some positive air pressure and still rises line pressure. So I think it works (more pressure @ WOT, less pressure @ low load).

And please let me ask about brake-boosting. How dangerous is it? How long can I stay at line buillding boost? I have B&M tranny temp gauge and its yellow zone is 220*F. Is it correct? (most part of time tranny sees 170*F and more than it just after hard driving and brake boosting)
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