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TH400 pan gasket

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Old 01-09-2005, 01:25 PM
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Default TH400 pan gasket/or some leak

Search and read tips on how to stop the pan gasket from leaking. All my local part store carries is and cork/rubber combo gasket.
Anyone have a part # for a better gasket? Are there metal gaskets that can handle more torq?
EDIT: Read on for more discription, sorry for being so short the first time.

Last edited by Tim 98z; 01-09-2005 at 07:36 PM.
Old 01-09-2005, 05:11 PM
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Default leak

Originally Posted by Tim 98z
Search and read tips on how to stop the pan gasket from leaking. All my local part store carries is and cork/rubber combo gasket.
Anyone have a part # for a better gasket? Are there metal gaskets that can handle more torq?
there is a good chance your pan is not leaking. look where the shifter shaft is, place to leak, where the kick down wire connects, and the biggest leaker of all the fill tube "O" ring. question, does it leak while engine is running or when it sits overnite? if it only leaks overnite it is not the pan gasket. the tc will drain back over nite and the trans oil level will be above the places l mentioned and the trans will leak. good luck
Old 01-09-2005, 07:07 PM
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Just last night I decided to take the HotRod out to dinner. Got on the freeway and decided to give her hell for a couple gears. Then about two miles up the road just cruisin at about 65mph I see smoke.
So I pull over and it smells like burning oil. I grab a rag, wipe the headder, and notice the fluid is red. So I look under no drips... Check fluid all is good so I continue on to the next exit about .5 miles.
Get under the car and the only sign of anything is tranny fluid on the exhaust and looks like it might have came from the gasket. There was a couple small drips on the bolts and the gasket was saturated. That's all I know to do as of now is change the gasket. It dont leak sitting there at all. Only under WOT I'm assuming. I limped it home and all was fine.
Old 01-09-2005, 07:42 PM
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John is correct. It probably isnt the gasket. And pan gaskets dont go torqued very much at all. If it is the gasket, You might have overtightend it. Make sure when you install the gasket, you install it dry. Tranny fluid will eat through most silicones. The only one approved for tranny fluid is the gray one.....
Old 01-09-2005, 07:52 PM
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The only reason I think it's the gasket is
#1 that's the only sign of moisture on the tranny (atleast from a quick look at night with a flash light)
#2 Two weeks ago the gasket looked a little wet in that area. So I retightend it down. Now I have a bigger leak. And after searching I read NOT to go to tight on the rubber gaskets. And it looks to be bulging out in that area.
Where else would spew fluid under a load?
Old 01-09-2005, 07:52 PM
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Originally Posted by Tim 98z
Just last night I decided to take the HotRod out to dinner. Got on the freeway and decided to give her hell for a couple gears. Then about two miles up the road just cruisin at about 65mph I see smoke.
So I pull over and it smells like burning oil. I grab a rag, wipe the headder, and notice the fluid is red. So I look under no drips... Check fluid all is good so I continue on to the next exit about .5 miles.
Get under the car and the only sign of anything is tranny fluid on the exhaust and looks like it might have came from the gasket. There was a couple small drips on the bolts and the gasket was saturated. That's all I know to do as of now is change the gasket. It dont leak sitting there at all. Only under WOT I'm assuming. I limped it home and all was fine.
Sounds like you blew fluid out the vent, to much or too little fluid can cause this.
It won't blow out of the gasket.
Old 01-09-2005, 07:56 PM
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Where is the Vent on the tranny? Top i'm assuming? Rear, front, left/right side...
Sorry I dont know much about Auto's, This is my first and the tranny was in the car when I got it or I would know more about it.
Old 01-10-2005, 05:39 AM
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The vent tube on a th400 is located on the passenger side right above the vacuum modulator. Almost on top of the trans, maybe in the 2 o'clock position.
Old 01-22-2005, 01:44 PM
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Well it was the gasket. It wasnt spraying out, from what I can see it was leaking when hot and the drips fell back onto the exhaust.
I replaced the gasket with a ruber one and what do you know I guess I over tightened it. It's leaking now just sitting there. AHHRGG LOL I did not go very tight at all either.
I tried to do all the recomendations. Cleaned it up well, put it on DRY, tightened by hand then went back with a 3/8 wratchet and tightend them down. Not anywhere near TIGHT. I could have went a lot further. I'd say les than a turn past fingertight with a socket in hand.
The only thing is one area of the gasket(front) was saturated before I got them tight. I would wipe it off and fluid would drip onto it before I could get the pan up and tight. I dont see how I could prevent that.
I guess ill look into a GOOD gasket if I can find one and try this all over again.
Old 01-22-2005, 02:44 PM
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if you have a stamped steel pan and you overtightened it a couple times it will never seal right again unless you spend a lot of time on it with a hammer. A cast alumunim pan will stay flat and spread the load if you crank the bolts, on a steel pan it will bend the rail and in between the bolts it will leak.

If you have a cast aluminum pan, never mind



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