leaking th400
 

Fresh unit, deep pan...leaks out a qt. just sitting there, not running. have tried new pan gasket, new o/ring & a touch of silicone on dip stick tube & modulator valve. have tightened all fasteners and cant see any obvious spots...any idea please? how aggrivating !

Re: leaking th400
 

I chased something similar. It was my deep aluminum pan. I put it on a machined flat surface and found it to ever so slightly rock back and forth. Had it machined flat and solved the problem.

Re: leaking th400
 

If it leaks that much, clean it with starting fluid/ brake clean, put a piece of paper down and wait for the drip.

Re: leaking th400
 

Also look at all the front pump bolts for wet

Re: leaking th400
 

I'm assuming the trans.isn't overfilled.The best thing would be to get the car on a hoist,and as stated check the frt. pump and converter seal,also the weld around the hub on the converter.Also the gear selector seal, and look if there's any fluid around the vent on top of the trans...gsa612

Re: leaking th400
 

checked the pan its flat. going to scuff both alum. surfaces, found a thicker gasket @ .065" compaired to the first one @ .045"...and a thin coat of RTV.

Re: leaking th400
 

A quart from the pan is a lot. Overfilled would make sense. Usually silicone doesn’t work with ATF. You need to pinpoint where the leak is. Do the front pump bolts have sealing washers on them?

Re: leaking th400
 

The torque converter is draining back into the transmission. It will drain fluid until it reaches half way down. There are two fixes. Number 1 is to pull the transmission and replace bushing in front pump and the seal. The easier fix is to remark the dipstick lower to the amount the depth the new pan added. If the deep pan is 2" deeper, then mark the dipstick that amount lower. That way you will have the same amount of fluid as original with the shallow pan. That gives enough room for the torque converter to drain back into the pan. The leaks are showing up because the fluid level after draining back is going above the pan rail.

Re: leaking th400
 

Did you reference the mark on the dipstick related to the pan rail when the pan was off?

Re: leaking th400
 

Make sure the pan is flat.

Re: leaking th400
 

thankyou everyone for your help! ive have the fluid level to the dipstick full mark, WITH the deep pan on...did not remark the full mark...2 3/4" deep pan.

Re: leaking th400
 

Fluid level cold should be at “add 1 pint” ATF will expand as it heats up.

Re: leaking th400
 

1 1/2" ...full mark to dipstick end.

Re: leaking th400
 

Are you using the oem dipstick and tube or an aftermarket ? Even with a deep pan I believe the fluid level should be below the pan rail. If it’s an aftermarket dipstick try draining the pan so the oil level shows about 1/4 up the dipstick cold. Then go for a test drive heat cycle the trans and recheck to see if the oil level is at full when hot.

Re: leaking th400
 

we originally had a fancy milodon unit. i thought it was the leak source, went back to the factory piece. will get it sorted out and go back to fancy...

Re: leaking th400
 

You just need Flex Seal

Re: leaking th400
 

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

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.

Re: leaking th400
 

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.

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...

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 .

Re: leaking th400
 

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.

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....

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.

Re: leaking th400
 

Just a heads up.....

GM used that Orange RTV on TH700-4R transmissions and HT4100 engines for years....The surface has to dry and the RTV given time to completely set up.....

It's your choice...

Just sayin'

Re: leaking th400
 

That RTV ended quickly after we in Engineering discovered the problems with the RTV's effect on the anti Foaming additives , and Off gassing that would rust internal transmission parts . Cadillac may not have had those problems with their engines , but most anything that was designed after GM's experience with "orange" RTV was either done with a gasket or the PA material I mentioned before .

Re: leaking th400
 

ok tks everyone! milodon unit installed, nice piece.... . marked the gasket/panrail installed height on dipstick. i have an additionail .125'' more capisity before level would reach the modulator valve bore. (which i believe is the seepage) sooo where does the operating level go? above or below the pan rail & gasket height? new fiber gasket to be install dry.

Re: leaking th400
 

The best / sure way to check dipstick height is to get a stock dipstick tube and stick. Insert in the trans and with the pan off measure in relationship to the pan rail. Transfer this known height to your new / aftermarket stick. This way you can't be wrong.

Re: leaking th400
 

The add one pint level is about 1 1/4” from the tip of the dipstick on a stock piece.You can figure about another 1/2” to the full mark.Although it’s permissible I don’t usually run the oil level right at the full mark.Make sure you’re checking the level with the engine running/trans in park or neutral. With the engine off and the trans sitting the fluid level may well be above the full mark.
I would try the oil level right where you have it.Again, road test and heat cycle the trans.Then check the level.If the level when hot is above the .125 you measured,lower the level until it is even or slightly below.