727 Transmission leaking

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Longgone

Longgone

John/68 Barracuda & Dart
Joined
Jul 12, 2005
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Newport News, Virginia
I`ve got a monster leak from the 727 transmission in my Dart. It leaks when the car is just sitting. In 24hrs. it`ll create a puddle 6 inches in diameter. I`ve replaced the shift selector seal, pan gasket, tailshaft seal, speedometer O-ring, and filler tube o-ring. It still appears wet all around the pan, I replaced the rubber pan gasket with a cork one. I don`t know what else to replace? Can the front pump seal leak with the car just sitting?
 
My car was the selector shaft seal. After I turned the car off the convertor would drain back into the case and put the fluid level above the selector shaft seal. I suppose the front seal could leak if the fluid drained back enough.
 
try some uv dye for atf in your transmission and find some dopers black light. lol you can pick up the dye and light from NAPA. then look for the leak in the dark, believe me you can see it you can see it just like the detectives use luminal for blood spatter. One other area to check is seal at the very top of the manual shaft a lot of us forget about this seal, it sould not leak that much unless your convertor drain back a lot.
 
Did you use a ball pien hammer to dimple the bolt holes outward or toward the bottom ? Then lay the pan flange down on a flat surface to check it ?
Trans pans get beat up and warped. If its done right cork or vulcanized rubber gasket will seal it without added sealant.
Old school method of finding the leak... wash it all down good and use toilet paper to wick the leak. Poke it in around line fittings, selector shaft, dip stick tube, then wrap the pan flange. Come back in a couple hours and find the leak evidence.
 
I had that happen recently on my Cuda and it ended up being the kickdown adjustment bolt leaking. I just tightened the locknut real tight and it fixed it.

BTW: The pump seal can leak setting but it don't usually appear on the pan. It comes out of the bellhousing.
 
I have a similar problem too, leaks only when the car is sitting around for a little while, so I will go tighten some stuff up and if I find anything that might apply to you I will let you know!

Don't want to thread hijack, but a quick question, how do you tell the difference between a 904 and a 727? I have a 360 so I'm assuming it's a 727 but don't know for sure.
 
Look at the trans pan,the 904 is nearly rectangular with a corner cut off, the 727 has a projection on the passenger side.

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It appears that the shift selector seal is still leaking, it`s going back Monday for a do-over. Lol! This time they`re going to pull the valve body and install it that way.
 
Where the selector shaft and kick down are a shaft in a shaft the inner O ring between the 2 might be the problem. To pull the valve body and do it right is the best way. Good luck
 
RedFish said:
Where the selector shaft and kick down are a shaft in a shaft the inner O ring between the 2 might be the problem. To pull the valve body and do it right is the best way. Good luck
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That's right that one does cause problems also but it isn't an O-ring, it's a lip seal. Just a small one. I have seen them leak before. Real easy to change too.
 
RedFish said:
Where the selector shaft and kick down are a shaft in a shaft the inner O ring between the 2 might be the problem. To pull the valve body and do it right is the best way. Good luck
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fishy68 said:
That's right that one does cause problems also but it isn't an O-ring, it's a lip seal. Just a small one. I have seen them leak before. Real easy to change too.
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Thanks guys, I will mention that to them.
 
Longgone said:
Don`t sell the 904 short, they have a lot of performance parts for that transmission to make it tough.
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That's right. Even a stock parts 904 with just a Trans-go TF-2 kit will handle 400 hp all day long. There alot better than guys think. Plus they have a lower 1st gear ratio than a 727 so their a little faster.
 
Okay, I`ve replaced all of the gaskets except for the front pump seal. It looks all good but the pan gasket still leaks! This is the 3rd gasket on it. First rubber gasket was replaced with rubber, then the rubber was replaced with cork, then the cork was replaced with rubber with the addition of silicone. The last gasket swap was accompanied by a thorough cleaning and careful straightening of the pan. I`m at wits end with this thing. The only other thing I can think of is to try a new gasket that Mopar makes now that has a steel center with rubber coating. Anybody used one? What`s better cork, rubber, steel/rubber, silicone?
 
Longone I've only used the new Mopar steel coated rubber once and it did work real good so I think I'd give it a try since you've tried all else. Like Dart-swinger said don't use silicone anytime. Apparently something in ATF eats it up.
 
If it is indeed the pan... The way I do them is cork gasket or the rubber reinforced cork, clean and flattent he pan flanges. There can be no oil of any kind on the pan or tranny's gasket flanges. Clean with brake cleaner and clean cloth/rag. I do not ever use silicone on the tranny pans. Over time, the gasket will loosen up with it and it doesnt grab the metal like it should with silicone on it. If you've done afew services on them you might note it's usually a bear to remove a cork gasket when it's been installed dry and on for a while. Also, when the pan goes bcak on, you need to be careful to tighten evenly going accross the pan. Not just around the outer edge in one direction. Start with one bolt, snug it, then go accross the pan to the second, snug it, go back accross to the next one, etc until they are all snug. then go around again going maybe 1/2 turn tighter and they are done. They should not be torqued very high. The spec is only 150 inch pounds. that's only a hair over 12 foot pounds...
 
67yelodart said:
longone,did you replace the O-ring on the neutral start switch?
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I have not but I have cleaned the trans thoroughly with brake cleaner and have narrowed it down to the left front corner of the pan. Thanks for the info though.

moper said:
If it is indeed the pan... The way I do them is cork gasket or the rubber reinforced cork, clean and flattent he pan flanges. There can be no oil of any kind on the pan or tranny's gasket flanges. Clean with brake cleaner and clean cloth/rag. I do not ever use silicone on the tranny pans. Over time, the gasket will loosen up with it and it doesnt grab the metal like it should with silicone on it. If you've done afew services on them you might note it's usually a bear to remove a cork gasket when it's been installed dry and on for a while. Also, when the pan goes bcak on, you need to be careful to tighten evenly going accross the pan. Not just around the outer edge in one direction. Start with one bolt, snug it, then go accross the pan to the second, snug it, go back accross to the next one, etc until they are all snug. then go around again going maybe 1/2 turn tighter and they are done. They should not be torqued very high. The spec is only 150 inch pounds. that's only a hair over 12 foot pounds...
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Each time I`ve replaced the pan gasket I have cleaned both the pan and transmission surfaces thoroughly and wiped both clean with lacquer thinner. I`ve also observed a cross pattern when installing the bolts in a two step torquing process. The second or third time I replaced a gasket I also checked the pan for true and straightened anything that was not flat. I`m at wits end. I installed a new reusable gasket on the pan yesterday and so far no drips but it does appear the corner of the pan is getting wet again. I`m starting to think the pan has some microscopic holes in it.??????
 
Longgone said:
I`m starting to think the pan has some microscopic holes in it.??????
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That's always possible. I had an oil pan that had that problem. Wouldn't leak sitting on the bench but when installed on the engine I guess the heat opened up the pores and it leaked.
 
I think I`ve finally got this thing fixed! I went to the dealer and bought a new "reusable" pan gasket which is made from hard plastic. It`s about 1/8" thick and has a dual ridge on both sides. I used this gasket in conjunction with the sealant (The Right Stuff) as recommended by Dart-swinger. I ran a bead between the ridges on both sides and then installed it quickly, torquing the pan to 13 ft.lbs.. So far so good.
 
moper said:
If it is indeed the pan... The way I do them is cork gasket or the rubber reinforced cork, clean and flattent he pan flanges. There can be no oil of any kind on the pan or tranny's gasket flanges. Clean with brake cleaner and clean cloth/rag. I do not ever use silicone on the tranny pans. Over time, the gasket will loosen up with it and it doesnt grab the metal like it should with silicone on it. If you've done afew services on them you might note it's usually a bear to remove a cork gasket when it's been installed dry and on for a while. Also, when the pan goes bcak on, you need to be careful to tighten evenly going accross the pan. Not just around the outer edge in one direction. Start with one bolt, snug it, then go accross the pan to the second, snug it, go back accross to the next one, etc until they are all snug. then go around again going maybe 1/2 turn tighter and they are done. They should not be torqued very high. The spec is only 150 inch pounds. that's only a hair over 12 foot pounds...
Click to expand...

fishy68 said:
That's right. Even a stock parts 904 with just a Trans-go TF-2 kit will handle 400 hp all day long. There alot better than guys think. Plus they have a lower 1st gear ratio than a 727 so their a little faster.[/QUOTE

Only some 904's had the lower 1st gear before 1980-81
Click to expand...
 
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