Transmission oil pan gasket. Leaking after installing new

Hello, Im wondering if someone can share the tips and tricks one uses in order to instal a leak free transmission oil pan gasket on my TH400?

I recently installed a rubber gasket and the car just sits (only ran it about 5 miles since) leaks considerably.  I looked under the car and seems like its leaking from all sides of the oil pan gasket. 

What type of seal is better Rubber, cork?  do you guys use any RTV or silicon?

Does anyone have a part number for a gasket that has worked well for you?

 

 

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Comment by Manuel Cerda on January 23, 2014 at 4:05pm
Just purchased a new gasket.. Wow what a difference in quality compared to the rubber one that came with my filter kit. ATP part number JG-50 Is looks thick and made out of black fiberlike material. I see a lot of aftermarket producing aluminum pans for a th400 but do not have a side transmission dipstip tube adapter on it. Was the 64 Cadillac the only car with a th400 and dipstick tube coming out if the oilpan?
Comment by Miki on January 23, 2014 at 3:52pm

Maybe design isn't the correct word, I might be mistaken but modern GM transmissions and engines use aluminum pans, so the bend of the metal pan is eliminated, since the aluminum is stiff (but pron to crack if to over tightened) it has more of a clamping force, at least that's what I think 

Comment by Dan on January 23, 2014 at 3:32pm
I don't think the pan design has changed. It's just that fewer people are changing their own because the problem is caused by someone using the cheap gaskets that you get at auto parts stores over tightening the bolts when they reinstall the pan. Most modern cars come with the good gasket.
Comment by Miki on January 23, 2014 at 3:12pm

Off topic, but I think the biggest issue was the poor design to begin with, modern cars don't have these issues due to better design of the mating surfaces along with pan design and material, just my rant..

Comment by Dan on January 23, 2014 at 11:59am
As far as I know the pan gaskets are all the same on 400s.
Comment by Manuel Cerda on January 23, 2014 at 11:51am

Thank You Dan,  I did locate a supplier here locally that carries a similar gasket but only as a filter/gasket kit.

TCI #890-228500

Are all th400 gaskets the same?

 

Comment by Dan on January 22, 2014 at 9:28pm

another thing on the gasket.....about the only place you will find them is at a transmission shop or a transmission parts supplier. I've never been able to get them from auto parts stores.

Comment by Dan on January 22, 2014 at 9:26pm

I use to work at a transmission shop and fixed a lot of leaks. The best gasket to use is the black cardboard type gaskets( can't remember the actual name).Cork and rubber just don't work well for very long. Before reinstalling the pan you need to do some straightening around the bolt holes. If previous mechanics have over tightened the pan bolts using a soft cork or rubber gasket the bolt will pull the inside edge of the hole in. This "pucker" causes problems. Get something to flatten out the area around the holes before you reinstall the pan. If you flatten out the area around the holes and use the black cardboard gasket you won't have a leak from the pan. Some other areas that leak will look like they are the pan leaking. The shift shaft seal will disguise itself as a pan gasket leak as will a pump o-ring leak and a dipstick tube grommet leak.

Comment by Manuel Cerda on January 22, 2014 at 6:58pm

Thank You Lee.. I did see this moroso gasket and looked tempting.   I do notice a slight leak around where the gear shifter rod goes in.  The transmission also has a hard time engaging into reverse and first from the neutral position but might be due to the low oil lever. I  have another perfectly working, non leaking transmission in my garage.  I might just drop that one back in save some $$ and avoid do over..

 

 

Comment by Lee on January 22, 2014 at 6:50pm

 I had the same problem. I ended up buying a rubber/steel  Moroso Transmission Pan Gasket # 93103 and it fixed my problem . Don't forget to use a torque wrench on the pan bolts,  I do believe I used a very thin layer of rtv . I also had a leak around where the gear shifter rod went in that would run down and look like a pan gasket leak.

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