Author Topic: ST300 transmission pan sealing  (Read 1700 times)

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Offline Brian

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ST300 transmission pan sealing
« on: September 17, 2012, 09:06:50 PM »
How is everyone sealing the transmission pan to their ST300 auto transmission.  My '66 gets driven very little (once every couple months), and in the 25 years I have owned it, I have never been able to get the pan gasket on the trans to no leak when sitting around.  I have one of the composit rubber gaskets on it and that has worked best (compared to the cork gaskets).  Has anyone ever tried putting the pan on with a thick bead of silicone RTV with no gasket installed?  I know that is how alot of modern engines and transmissions seal their joints now and it works very well. 
'64 Skylark 2dr ht 4 speed, 300-4
'65 GS ht, 4 speed,2-4s,AC,PS,PB,PW,Pseat,Tilt
'66 Skylark 2dr ht 300-2 automatic
'78 Yamaha DT 400 2 stroke
'88 Ford F-150 4x4 (used to be 4x2)
'89 Ford F-350 4x4
'03 Honda Accord Coupe V6 6-speed manual (daily driver)

Offline Dr Frankenbuick

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Re: ST300 transmission pan sealing
« Reply #1 on: September 18, 2012, 06:29:11 AM »
Mine also seems to leak from the band adjustment port as well as the transmission pan!  I want to to fix this all at once when under there, and am very interested in the answer to Brian's question.

Offline mdkd

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Re: ST300 transmission pan sealing
« Reply #2 on: September 18, 2012, 11:42:35 AM »

    Me too.

65 White GS HT My Pride & Joy
31 in Registry
65 Red White GS Convert 99 in Registry
SOLD to a good home in Ohio
65 Black GS HT - SOLD to a good home local
Several 64-65 non GS HT & Convert Sold
64 Special 4dr parents bought new not 4 sale

Offline WkillGS

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Re: ST300 transmission pan sealing
« Reply #3 on: September 18, 2012, 06:12:46 PM »
I generally use a THIN layer of silicon on my gaskets as an adhesive and to fill pinholes. Also makes removal and future clean-ups much easier.

My Special had an annoying leak at the o-ring seal on the (servo cover?)
My final solution was to install a 5 speed. :icon_biggrin:
Walt K
Eastern Pa

66 GS Astro Blue/blue 425 auto
66 GS Silver Mist/black 401 4 spd
66 GS Flame Red/black 401 5 spd
66 GS Saddle Mist/black 401 L76 auto
66 Special Flame Red/black 300 5 spd
65 GS vert Verde Green/ Saddle buckets 401 4 spd
79 Turbo Regal

Offline gs spoken here

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Re: ST300 transmission pan sealing
« Reply #4 on: September 19, 2012, 07:40:47 PM »
I had a 68 300 that was a reak leaker, turned out to be the connector for the kick down, I bought a new one from a local trans supplier for $3.00 and it stopped 99% of the leaks, thanks Bill.