TH350 leak parked level or nose up only

[demian5]

Hey everyone, i have a leaky trans that leaks a little when parked level but way more when in the driveway nose up.

Nose down, no leaks at all (so i park it like this as much as possible).

This is my first 350 and I never had any issues with TH400s or 4l60-e's.

Maybe someone has some tips. i checked my pan bolts and cleaned it up the other day. Im trying to think of components towards the rear of the trans that would not have fluid when parked nose down.

I saw mention of some switch that can leak.
Also saw mention of a plug in the yoke or maybe wrong yoke.
Some stuff about the modulator - does it have an o-ring?
Is speedo gear housing low enough to leak oil parked on level and incline like this?

Thanks in advance.

[Maximus]

really your first step in this journey is to crawl under your truck and identify the area of the leak.

if its based on an angle, I would start at the tailshaft seal as leaks like the pan would normally occur regardless of tilt, but knowing where you see the fluid is step one. if its too hard to tell, take the truck to a self-car wash and do what you can to pressure wash the underside to get a clear area to observe.

leaks are found by looking. I had a leak in an 90's company owned ford truck. I TOLD a local tranny shop that the tailhousing was leaking, they insisted it was the pan. they replaced the pan seal and it still leaked. My company was fed up with the truck and I bought it cheap. I crawled under the truck and TWO bolts were missing out of the tailhousing extension. I TOLD this idiot shop owner that area was leaking and he didnt even take the time to LOOK. that was the last time this shop ever saw a vehicle I was involved with....

anyways, moral of that story was you really gotta put your eyes on the trans and identify where the red fluid is coming from... then we can help you stop the leak. take some photos under there and post em for a better response....

[Keith Seymore]

Look at the forward slip yoke of the driveshaft.

Is there a vent hole in it? Often that is the source of a leak that occurs only when the front of the truck is elevated.

K

[demian5]

Looks like pan but its tight. Ill clean it off and see. Always a challenge on a lowered truck.

Definitely not tail shaft seal or yoke from what I can see.

Bigger puddle is on the passenger side. Really clean under the vacuum modulator...

[toolboxchev]

Mine looks the same way, yet I try to pressure wash it about every 3-6 months. The front torque convertor seal and the pan are the main culprits I would look at in your shoes.

[RPBurris]

Check your detent cable. Mine leaked like a SOB. When you buy a new one at the store they don't sell the little sleeve that helps seal the plastic housing to the transmission. When sitting it will leak from there. A guy at a transmission shop gave me a few of them after i was talking to him about it. No leaks.

[LockDoc]

Originally Posted by demian5

Looks like pan but its tight. Ill clean it off and see. Always a challenge on a lowered truck.

Definitely not tail shaft seal or yoke from what I can see.

Bigger puddle is on the passenger side. Really clean under the vacuum modulator...

If it's really clean under the modulator I bet that's where it's leaking from (or that corner of the pan). The leaking fluid keeps the dirt washed off of it.

LockDoc

[randy500]

There is also an o ring on the servo in front of the modulator that can leak. That is a hard one to change because of high spring pressure on it. You can make a tool to depress it, some guys use a heavy wire with loop from 2 pan bolts as a fulcrum point, then a spacer under a pry bar to depress it.
I just re-sealed my 400, did the pan, the shift selector seal, the modulator and the speedo gear housing, no leaks now....

[special-K]

Lock Doc has a good point. Is it clean AND dry or just clean?

[Grumpy old man]

pressure wash it down or use brake clean , once dry liberally coat it with talcum/baby powder then park it in the position you normally notice the leak , inspect it again and you will notice the wet /discolored powder that will lead you directly to your leak . and the powder easily washes off when done .

[Mike_The_Grad]

The best thing about a leak is that it can be traced back to its point of origin. Other than that fact, I despise leaks.

There are at least 5 points of origin on the passenger side of a th350 to leak from, beginning at the front of the transmission main body. (This is not including the pan, because the photo provided earlier in the post indicates differently.)

The brass trans. cooler line adapters are the first in order starting from the front of the trans. body. The upper port is "out," lower "in". Mine leaked until I learned they were piped the wrong way.

The next possibility is the "Transmission-Contolled Spark" switch. This switch threads into the transmission case with 1/4" NPT threads and is mostly related to 1972 models. Its a "smog era" device wired into the distributors vacuum advance.

Trans.dipstick guide tube is next and most likely the culprit, especially if it's the original guide tube and transmission. One o-ring seals the transmission fluid level. There is a remedy to this though. You can get a later style 200r4 or 700r4 guide tube with a "top hat" multi-lip grommet. Fits with no modifications to the trans case BUT you have to get a different dipstick to compensate.

The next in line leak prone area is the intermediate servo piston seal. Big round thing cast into the passenger side of the case with an o-ring type seal under spring pressure.(Mine leaks here.)

Second to last*~is the vacuum modulator. According to the picture you provided it appears you still have the stock modulator installed. One way to check if it's still good is to disconnect the vacuum supply line and stick a pipe cleaner down inside the port. If it has trans fluid on it, the modulator is bad. If it has engine oil or smells of gasoline on it, it may not be bad but consider this, anything that old with a diaphragm in it should be replaced by now. Luckily, a new one only costs about $12 at your local parts store. And some of them have shift point adjustability within a certain range.

Lastly is the tailshaft gasket and bushing. Not to say that yours isn't leaking, but based on the photo provided I know for a fact it isn't the only thing leaking.

Best case scenario for narrowing down the source of a leak is pretty easy once you know where to start.
Start by cleaning the s*** off the transmission. That way old engine oil leaks don't get confused with trans fluid leaks.

Fluid leaks follow a few basic principles.

Gravity is king. Fluid can only leak down,unless it's under pressure. The title of this post clearly states what you are facing.

Airflow will divert a leak. Liquid follows the path of least resistance.
Once you clean the s*** out of your trans, let it sit for a day if possible. Then get under there and take a look. The truck hasn't moved, so the leak will follow gravity and the path of least resistance.

I've experienced ALL of these instances myself. Obviously there are more areas that leaks can originate, but this info is based on the OP's first post.

[demian5]

Originally Posted by Mike_The_Grad

The best thing about a leak is that it can be traced back to its point of origin. Other than that fact, I despise leaks.

There are at least 5 points of origin on the passenger side of a th350 to leak from, beginning at the front of the transmission main body. (This is not including the pan, because the photo provided earlier in the post indicates differently.)

The brass trans. cooler line adapters are the first in order starting from the front of the trans. body. The upper port is "out," lower "in". Mine leaked until I learned they were piped the wrong way.

The next possibility is the "Transmission-Contolled Spark" switch. This switch threads into the transmission case with 1/4" NPT threads and is mostly related to 1972 models. Its a "smog era" device wired into the distributors vacuum advance.

Trans.dipstick guide tube is next and most likely the culprit, especially if it's the original guide tube and transmission. One o-ring seals the transmission fluid level. There is a remedy to this though. You can get a later style 200r4 or 700r4 guide tube with a "top hat" multi-lip grommet. Fits with no modifications to the trans case BUT you have to get a different dipstick to compensate.

The next in line leak prone area is the intermediate servo piston seal. Big round thing cast into the passenger side of the case with an o-ring type seal under spring pressure.(Mine leaks here.)

Second to last*~is the vacuum modulator. According to the picture you provided it appears you still have the stock modulator installed. One way to check if it's still good is to disconnect the vacuum supply line and stick a pipe cleaner down inside the port. If it has trans fluid on it, the modulator is bad. If it has engine oil or smells of gasoline on it, it may not be bad but consider this, anything that old with a diaphragm in it should be replaced by now. Luckily, a new one only costs about $12 at your local parts store. And some of them have shift point adjustability within a certain range.

Lastly is the tailshaft gasket and bushing. Not to say that yours isn't leaking, but based on the photo provided I know for a fact it isn't the only thing leaking.

Best case scenario for narrowing down the source of a leak is pretty easy once you know where to start.
Start by cleaning the s*** off the transmission. That way old engine oil leaks don't get confused with trans fluid leaks.

Fluid leaks follow a few basic principles.

Gravity is king. Fluid can only leak down,unless it's under pressure. The title of this post clearly states what you are facing.

Airflow will divert a leak. Liquid follows the path of least resistance.
Once you clean the s*** out of your trans, let it sit for a day if possible. Then get under there and take a look. The truck hasn't moved, so the leak will follow gravity and the path of least resistance.

I've experienced ALL of these instances myself. Obviously there are more areas that leaks can originate, but this info is based on the OP's first post.

Excellent information! Thank you so much.

And the talcum powder idea from another post sounds great as well.