Transmission pan
+4
ant7377
dynchel
JB2wheeler
driveit
8 posters
G3GM :: G3 Tech :: Engine & Driveline
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Transmission pan
My TH400 pan just wont stop seeping, even after fooling with it for s few months, so today I received a cast aluminum stock size pan from Summit, and bolted it on. Being a flat surface for the gasket, maybe it will finally quit leaving oil on the floor.
Couldn't determine why the stock pan would seep, even after the usual tapping the mounting holes flat again etc. Didn't get time to refill it today, so tomorrow is the "acid test" to see if will finally stay dry. Sometimes the simple things can drive us nuts....
Couldn't determine why the stock pan would seep, even after the usual tapping the mounting holes flat again etc. Didn't get time to refill it today, so tomorrow is the "acid test" to see if will finally stay dry. Sometimes the simple things can drive us nuts....
pila- Donating Member
- Street Cred : 43
Re: Transmission pan
Agreed. My trans is leaking too. There is so much fluid everywhere under the car that I can't tell where it is coming from.
driveit- Donating Member
- Street Cred : 15
Re: Transmission pan
I believe these snythetic oils are harder to keep contained than old time oil. JB
JB2wheeler- G3GM Fanatic
- Street Cred : 28
Re: Transmission pan
When i got my car the trans pan leaked. After I had it rebuilt i had the trans shop install a TCI 2 qt extra pan. After picking up the car i noticed the trans leaked worse than ever. I took i back and they blamed the sealing surface and claimed to use permatex. That was in 1997, It hasn't leaked since.

dynchel- Donating Member
- Street Cred : 40
Re: Transmission pan
THey get bent up and dont seal no matter what, just have to replace them sometimes.
ant7377- G3GM Addict
- Street Cred : 36
Re: Transmission pan
I could have used some aircraft sealant on it, but it would likely be difficult to get the pan off later on, for oil changes etc. Never had a leak in a TH350 pan, but this 400 is a different story....
pila- Donating Member
- Street Cred : 43
Re: Transmission pan
I like to use the pan gasket that is "reuseable". Its the rubber one (no cork) that has the metal frame embedded in the rubber. The rubber also has small "ribs" on the top and bottom. I had one my Tahoe (4L60 trans same as the 700R4) and on my Uplander and Lesabre. I've reused it 3 times already on the lesabre. Gasket costs more but its heavy duty and no issues lining up the bolt holes because its stiff.
If you do like to use the flimsy type of gasket I put it on the pan and tie some thread through a couple of bolts holes to hold her in place while installing. She wont lead with the thread and it saves some cursing.
If you do like to use the flimsy type of gasket I put it on the pan and tie some thread through a couple of bolts holes to hold her in place while installing. She wont lead with the thread and it saves some cursing.
Joe73- Donating Member
- Street Cred : 80
Re: Transmission pan
I used a FelPro gasket this time. It has the smaller holes in it, to hold the bolts in place during installation, and it's thicker than the cheapie gaskets.
pila- Donating Member
- Street Cred : 43
Re: Transmission pan
i also have a few drips each day under the trans . hope its my pan but looks like its coming from the front of the transmission . car is so damn low though so will have to jack it up to check it out . as soon as i get the time .
magic marouke- G3GM Member
- Street Cred : 3
Re: Transmission pan
I had one pan bolt missing, from the kit with the pan, and today I found another one ( socket head) to finish bolting it up in place. Tomorrow I'll see if the leak is finally stopped........if it's still leaking, maybe the case has a porous spot in it, or...?
Anyway, it's full of oil..........
The engine hadn't been run for a few months, so I ran it for a bit today. It starts very quick. Maybe due to the MSD module in the distributor. The 100 octane avgas n the tank likely helped too !
Anyway, it's full of oil..........
The engine hadn't been run for a few months, so I ran it for a bit today. It starts very quick. Maybe due to the MSD module in the distributor. The 100 octane avgas n the tank likely helped too !
pila- Donating Member
- Street Cred : 43
Re: Transmission pan
Good news today !
The new cast pan did the trick, no leaks or seeps !
I was getting tired of mopping up ATF ! I have a mop bucket with mineral spirits in it, for messes created by cars & airplanes !
Next fairly big project is fitting a Sanden AC compressor and the hoses, to the GM dryer and condenser etc...

The new cast pan did the trick, no leaks or seeps !
I was getting tired of mopping up ATF ! I have a mop bucket with mineral spirits in it, for messes created by cars & airplanes !
Next fairly big project is fitting a Sanden AC compressor and the hoses, to the GM dryer and condenser etc...
pila- Donating Member
- Street Cred : 43
G3GM :: G3 Tech :: Engine & Driveline
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