leaking th400

richie 2 · 08-10-2020, 01:48 PM

pan manufacturer says fill to the factory full mark...WTF... the flex seal idea is sounding better adger...

Mark Ruset · 08-10-2020, 02:34 PM

Before you start throwing parts at the transmission you really need to locate the source of the leak. My days as a GM tech when I had a complaint of a transmission leak, I cleaned the entire surface areas with brake clean and then used air to make sure it was completely dry. Next I used spray tracing powder and sprayed the entire area., in a short time you should be able to see the powder turning a pinkish color at the source of the leak. It may be as simple as transmission fluid leaking around the front pump cover bolts that would make it look like a pan rail leak.

Mark Ugrich · 08-10-2020, 03:11 PM

Quote:

Originally Posted by richie 2

pan manufacturer says fill to the factory full mark...WTF... the flex seal idea is sounding better adger...

I’d say the manufacturer is wrong. In 40 years as a tech, I’ve never started a trans with the level at the full mark.

richie 2 · 08-10-2020, 08:35 PM

with the pan off, dipstick in, the full mark is higher than the trans/pan surface. the modulator valve bore is right there too....sure seems to be seeping out there. the valve and o/ring fit feels sloppy. measured it all up and installed theres not much crush on the o/ring, .020" roughly...

Tom Goldman · 08-10-2020, 09:56 PM

Definitely run the fluid level at the add mark.
Another area I've had issues with lately is the shift shaft seal .
It appears the newer seals are not as tight on the shaft as ones I had from old kits.
My solution has been to machine a groove in the shift shaft and install an o ring .

Lenny5160 · 08-11-2020, 12:20 PM

Quote:

Originally Posted by Tom Goldman

Definitely run the fluid level at the add mark.
Another area I've had issues with lately is the shift shaft seal .
It appears the newer seals are not as tight on the shaft as ones I had from old kits.
My solution has been to machine a groove in the shift shaft and install an o ring .

That's interesting. I was just laying under my car last night after installing the engine and trans (glide) over the weekend, and noticed some fluid on the end of the shift shaft which I've not noticed before.

Bob Mulry · 08-11-2020, 02:15 PM

Just a quick heads up.....

Don't use RTV sealer on gaskets because it acts as a lubricant and allows the gasket to push out. Just completely clean both surfaces and use brake clean to remove any residual oil and use the gasket only...

OR

You can do like GM did, which was do not use a gasket at all. You can use anaerobic sealer or RTV, with the surfaces clean and bone dry put it together. Woks on engines and transmissions, just make sure it is allowed to dry and set up before exposing it to oil. This isn't for a race engine or transmission which is constantly being worked on, but it works great on a stock rebuild for the street.....

Your results may vary....

ss3011 · 08-11-2020, 03:18 PM

You really don't want to use any RTV sealants that will come in contact with ATF . Most ATF has an anti-foaming additive and RTV will destroy that additive . Most manufacturers that seal structures ( like case halves) will use a Poly-Acrylic sealer. PA has no effect on ATF.

08-10-2020, 01:48 PM	#1
richie 2 Senior Member Join Date: Feb 2009 Posts: 971 Likes: 426 Liked 205 Times in 93 Posts	Re: leaking th400 pan manufacturer says fill to the factory full mark...WTF... the flex seal idea is sounding better adger...

08-10-2020, 02:34 PM	#2
Mark Ruset Member Join Date: May 2006 Location: Southwest Florida Posts: 263 Likes: 35 Liked 43 Times in 29 Posts	Re: leaking th400 Before you start throwing parts at the transmission you really need to locate the source of the leak. My days as a GM tech when I had a complaint of a transmission leak, I cleaned the entire surface areas with brake clean and then used air to make sure it was completely dry. Next I used spray tracing powder and sprayed the entire area., in a short time you should be able to see the powder turning a pinkish color at the source of the leak. It may be as simple as transmission fluid leaking around the front pump cover bolts that would make it look like a pan rail leak. __________________ Mark Ruset 2048 STK

08-10-2020, 08:35 PM	#4
richie 2 Senior Member Join Date: Feb 2009 Posts: 971 Likes: 426 Liked 205 Times in 93 Posts	Re: leaking th400 with the pan off, dipstick in, the full mark is higher than the trans/pan surface. the modulator valve bore is right there too....sure seems to be seeping out there. the valve and o/ring fit feels sloppy. measured it all up and installed theres not much crush on the o/ring, .020" roughly...

08-10-2020, 09:56 PM	#5
Tom Goldman VIP Member Join Date: Jan 2003 Location: Allentown,PA Posts: 2,476 Likes: 889 Liked 882 Times in 236 Posts	Re: leaking th400 Definitely run the fluid level at the add mark. Another area I've had issues with lately is the shift shaft seal . It appears the newer seals are not as tight on the shaft as ones I had from old kits. My solution has been to machine a groove in the shift shaft and install an o ring . __________________ Tom Goldman 1500 SG , 1506 STK

08-11-2020, 02:15 PM	#7
Bob Mulry VIP Member Join Date: Apr 2002 Location: Coarsegold, CA Posts: 1,016 Likes: 57 Liked 320 Times in 102 Posts	Re: leaking th400 Just a quick heads up..... Don't use RTV sealer on gaskets because it acts as a lubricant and allows the gasket to push out. Just completely clean both surfaces and use brake clean to remove any residual oil and use the gasket only... OR You can do like GM did, which was do not use a gasket at all. You can use anaerobic sealer or RTV, with the surfaces clean and bone dry put it together. Woks on engines and transmissions, just make sure it is allowed to dry and set up before exposing it to oil. This isn't for a race engine or transmission which is constantly being worked on, but it works great on a stock rebuild for the street..... Your results may vary.... __________________ Bob Mulry 7516 STK A & M Motorsports

08-11-2020, 03:18 PM	#8
ss3011 Senior Member Join Date: Feb 2002 Location: Southeast Michigan Posts: 909 Likes: 70 Liked 239 Times in 114 Posts	Re: leaking th400 You really don't want to use any RTV sealants that will come in contact with ATF . Most ATF has an anti-foaming additive and RTV will destroy that additive . Most manufacturers that seal structures ( like case halves) will use a Poly-Acrylic sealer. PA has no effect on ATF.