[Schurkey]

"Pan leaks" are often fixed by re-sealing:
1. Shift shaft seal. At least on the TH350s, you might as well buy a shift shaft along with the seal. The old shift shafts make great pin punches.
2. Dipstick tube. They tend to crack in the O-ring groove. Impossible to see with the O-ring in place.
3. Modulator O-ring. I use two o-rings on modulators ever since I had a trans that leaked after it wasn't run for a couple of days. Torque converter drains, raises fluid level in pan.
4. Torque converter (front pump) seal
5. Kickdown cable seal or TV cable seal (doesn't apply to TH400)
6. Servo seals
7. Loose front pump (bolts not torqued) can push fluid out the vent at the top of the case when trans is in reverse. This drools down the case and could be mistaken for a pan leak. I had this happen on the first TH400 I built. My screwup was to torque the pump in "inch-pounds" instead of "ft/lbs". No mistaking for a pan leak on mine, the thing would leave a six-inch puddle or larger on the ground every time I backed-up.
8. Speedo gear assembly inner and outer seals. May or may not drool onto the pan. Often the driven gear is eroded from the little inner seal. Then you need a speedo driven gear, too.

Basically, ANYTHING above the pan that seeps, is going to look like a "pan gasket leak".

[HWYSTR455]

The true fix is a cast pan, and to make sure it isn't leaking elsewhere, as others have stated.

As Cliff mentioned, the composite/fibre gasket is the best, and true too that 'gas, oil, and water' sealers don't last with ATF, ATF is super high in detergents.


.

[Kenth]

It sure would be nice with a cast aluminium TH400 pan that takes the original shifter cable bracket. Haven´t found one yet.

[Formulajones]

Hmm, we run 2 of the aluminum 400 pans and use the factory shifter cable brackets on both of them (GTO and Chevelle) Works fine.

What is it exactly you're having a fitment issue with?

[dataway]

I'm all for the OEM pan (with bolt holes fixed), cork gasket, OEM flanged head bolts and tightening to the service manual specs.

I find the filler tube to be harder to seal.

[Kenth]

Originally Posted by Formulajones

Hmm, we run 2 of the aluminum 400 pans and use the factory shifter cable brackets on both of them (GTO and Chevelle) Works fine.

What is it exactly you're having a fitment issue with?

Screw holes are too close to the thicker wall of the aluminium pan to mount the original cable bracket.
Just don´t want to "mickey mouse" the original bracket.

Do you have pictures on your pan/bracket?

[Formulajones]

Originally Posted by Kenth

Screw holes are too close to the thicker wall of the aluminium pan to mount the original cable bracket.
Just don´t want to "mickey mouse" the original bracket.

Do you have pictures on your pan/bracket?

I'll look through my pics and if I don't have one I can take one. I'm trying to remember now what brand these pans are. They were both bought in the 80's and are both the same. Might be able to tell from the pictures..

[mchell]

Originally Posted by Kenth

Screw holes are too close to the thicker wall of the aluminium pan to mount the original cable bracket.
Just don´t want to "mickey mouse" the original bracket.

Do you have pictures on your pan/bracket?

Yep....that’s what I’ve found

I went Mickey Mouse on the bracket and ground the bracket mounting ears down so the the bracket would lay on the aluminum pan rail properly.... works

Figured if I ruined the bracket I’d get a new one....that was 10yrs ago

[ponyakr]

Got a light & took a good look at the trans. I think I MAY have found at least one leak source. In the 1st pic, it appears that there is ATF at the bottom of the speedo cable housing. I assume the O-ring seal on it leaks, when the engine is running. That ATF then drains down onto the pan gasket, and drips off the lowest part of the pan, which is shown in the 2nd pic.

The shifter shaft & lever looked dry. And, as shown in the 3rd pic, don't appear to be any leak coming from vac modulator.

I wiped everything off. Will see how it looks tomorrow. If no leaks appear, I'll start adding a little ATF every day, to make sure it gets back up to the pan gasket. That should tell if the gasket is leaking. It looks suspect to me. There actually appear to be 2 gaskets, in certain areas. You can see this in the 1st pic below.

When I had this trans in a '68 Bird, I thought the only leak was the dipstick tube. So, for install into this car, I put in a new FitzAll tube, with a "top hat" style seal. Obviously, that was not the only leak.

[lust4speed]

One of the goofier things is you buy a B&M deep aluminum pan and then you buy their shifter that comes with the cable and new bracket -- and their own bracket won't clear their pan.

[Schurkey]

Originally Posted by lust4speed

One of the goofier things is you buy a B&M deep aluminum pan and then you buy their shifter that comes with the cable and new bracket -- and their own bracket won't clear their pan.

...and both the pan and the shifter are Chinesium, and WAY overpriced.

[Formulabruce]

At the Pontiac dealership we used a product called 'GMS"
(general Motors Sealer) GM had started in the 70's using this vs a gasket
on many items with pans, or covers. The Modern version is below.
I assume the Permatex Red RTV would work.
Genuine GM # 1052943

[Rhagolin]

Originally Posted by ponyakr

Please don't tell me to do a search.

I realize that this has probably been brought up many times. And I've recently Googled up lots of opinions. And there are lots of differing opinions. Some say use a plain cork gasket ONLY, no sealant. Some say use no gasket at all, just some Right Stuff.

My TH400 was built many years ago. The gasket appears to be cork. When there is fluid up to that level, it seeps constantly, while not running, pretty much all around. Snugged the bolts up some. Didn't make a difference.

I don't wanna have to do this more than once.

So, I'd like to hear what some of you guys have done to stop the leaks/seepage between the pan & trans. It's a factory pan.

Like mentioned above make sure some one didnt over tighten and warp bolt holes , Also check shift shaft selector seal. If it is leaking it will appear to be pan gasket ..............................

[dataway]

Yep, looks like someone put two gaskets on it because the bolt holes are all stretched/bent. All that does is bend them more.

[4 bucket gTo]

Originally Posted by ponyakr

Please don't tell me to do a search.

I realize that this has probably been brought up many times. And I've recently Googled up lots of opinions. And there are lots of differing opinions. Some say use a plain cork gasket ONLY, no sealant. Some say use no gasket at all, just some Right Stuff.

My TH400 was built many years ago. The gasket appears to be cork. When there is fluid up to that level, it seeps constantly, while not running, pretty much all around. Snugged the bolts up some. Didn't make a difference.

I don't wanna have to do this more than once.

So, I'd like to hear what some of you guys have done to stop the leaks/seepage between the pan & trans. It's a factory pan.

I had a 200 in mine that leaked until I put a Farpak brand gasket in. It fixed that one. I've since replaced the trans with an original 400, and going to add Gearvendors overdrive, to be durable. This new trans pan started leaking from the rubber gasket within 2 weeks. I've replaced with Farpak, but haven't ran it yet. I also have an aluminum pan for rigidity. These gaskets are inexpensive, and available online. I hope this works for you.

[Bill Eveland]

Im not sure what the factory spec is, but a torque wrench at 10 ft lbs going around a few times would be good insurance not to overtighten pan bolts.

[1968GTO421]

Originally Posted by Sun Tuned

What Cliff and Brad and formulajones said!!!!

Now let's talk a minute about how crappy Rtv from the box parts houses has gotten...

I bought my last tube of that about 3 months ago and gave it to a buddy free.

Trust me on this. Go to the Ford dealer and buy a tube of TA-31. It has more chemicals in it than the box store stuff by far. I assure you it is NOT the same grey stuff you get at advance auto.

If you really want the current stuff float a loan for a tube of the TA-357.

I'm sure GM has their version. I won't ever buy permatex rtv at a box store ever again.

Originally Posted by Formulabruce

At the Pontiac dealership we used a product called 'GMS"
(general Motors Sealer) GM had started in the 70's using this vs a gasket
on many items with pans, or covers. The Modern version is below.
I assume the Permatex Red RTV would work.
Genuine GM # 1052943

Thanks to all for excellent info. I'll be checking out these sealers at the dealers parts dept's.

[Sirrotica]

The GMS has also changed what the letters stand for, back in the 80s it was General Motors Sealer. Used it on every engine pan, and rear axle covers, trans pans, about any tin cover on the car got GMS instead of a gasket.

No aromatics in it to foul oxygen sensors is why GM used it over run of the mill RTV. I used to have cases of that stuff from working at a GM dealer, every time you needed a gasket you got a tube of GMS, pretty easy to build a stockpile of it.

[geeteeohguy]

Originally Posted by Bill Eveland

Mine was a selector shaft seal leak, napa had the removal tool and seal kit . But for gaskets ive used the moroso reusable gasket . If you glue it with the right stuff its going to be a real pia to get off .

Mine too. Got the tool at NAPA, de-burred the shaft, installed the new seal. That was in 2010 or 2011.....hasn't leaked a drop since. More often than not, it is the shift shaft seal or the dipstick tube.

[geeteeohguy]

Just looked at your pics: you have a leaking O ring at the speedo gear fitting, and those two cork gaskets and deformed pan are doing you no favors. Replace the O ring, and drop the pan, peen the rails straight, and install only ONE gasket, and go EASY on the torque....I like to use a nut driver and not a ratchet. Just snug is all you need.