The TH400 in my '74 has a leak. It appears to be coming from behind the Torque Converter. Fluid leaks from the hole in the inspection cover and also from the driver side front of transmission. I don’t know if my garage floor isn’t level or the car but the bottom of the transmission pan is slightly lower on the driver side which I think is why I have a leak from that side on the front of tranny. I’m guessing if it’s the front seal to the transmission pump (behind the torque converter), that will mean removing the transmission to fix it. Are there any other things I can check first or any tests to prove for sure that it’s the front pump seal before I pull the tranny? Thks





View of front driver side of TH400 with inspection cover removed.

 

Take a flashlight and try to look between the convertor and the front pump to see if the fluid is leaking from the convertor seal or if it's the pump to transmission seal that's leaking-
I've had both happen and now just make it a habit of replacing both at the same time since dropping the trans is such a pain.

Also, are you sure you don't have any seepage from the trans pan?
I've never seen studs used for trans pan mounting and that one in front doesn't even look straight-

 

Good question on the pan seal ... it is new, I installed it when I changed the filter but I'll try to stuff some towels up by the converter area to see if it continues to show fluid around the seal or not. I'll have to do some research on that converter seal ... have no idea where that is at. I also look up there with a light but man it's tight ... I can't imagine getting to see anything unless you have a special technique.

I bought this car in '83 and those studs were in there at that point. I don't now anything about why they are there unless threads had been stripped but I've never had a problem. You're right that one stud isn't straight.

Prior to installing transmission I took it to a transmission shop to open up and check. They inspected the front pump gears and pulled the pan but said everything looked good but now I'm wondering if they didn't get a seal back in correctly. Nothing was actually done to tranny and it shifts fine ... just has this leak.

Thanks for your suggestions.

 

Does the car get driven regularly of does it sit for months at a time?
I'd had several cars where the converter to pump lip seal would shrink just enough when sitting idle for months for it to start dripping but as soon as I started driving the car again, it would stop.

 

After removing the transmission this is what mine looked like. Started similar to what you see.

Only way to know if the pump seal or torque convert seal or both are bad is to remove the transmission. Replace both to be sure.

 

ezobens ... the car has been mostly sitting as I've been doing almost a complete reconditioning of it i.e. engine/brakes/paint/interior. It's been derivable since late July but only driven probably 6 times and for no more than 30 min. at a time but it's lost enough fluid to be down below the fill mark. Still working on the final details to finish car.

cagotzmann ... nice pic. I won't be able to see that part of my tranny until the converter is removed. Couldn't work on it to-nite but I'll check those towels that I stuffed up there to see if they've soaked up any fluid. Is the converter seal an O-ring?

 

The converter seal is a lip seal that presses into the pump.
The front pump has a square O-ring and the pump bolts have sealing washers.

 

Reseal the front pump assembly complete. Also replace the shift input shaft seal while you're there. I purchased all parts from a local tranny rebuilder for less than $20. T

 

just went thru this 3 weeks ago with my 72, had a major leak...



that was 2 days after a weekend drive.....

dropped trans, and re-builder found that the front pump seal was rock hard, it actually shattered when removed.
decided that i didn't want to go thru the removal process again any time soon,
so had it gone thru and rebuilt with new clutches etc.

i only changed the torque convertor seal when i had the motor out 6mths ago.

many $$$ later, and not a drop to be seen

 

Insure that the trans pan gasket is not the culprit. It took me forever to eliminate the leaks on my th400. Found stripped bolt holes (not providing a proper seal,) a warped pan (original) a thick gasket that wasn't effective and the seal at the vacuum modulator. I fixed all of that - replaced the pan with a heavy cast aluminum type and after talking to a mechanic at a tranny repair shop, I quit using the thick rubber gaskets and went to a thin, paper type properly torqued.
It can be done...
Good luck

 

I may get flamed for this but I had leak issues with my Turbo 400 in my 68 BB. I had gone through the entire transmission but the leaks persisted when the car sat for prolonged periods. I AM NOT a fan of "magic in a bottle fixes" but a bottle of AT-205 Re-Seal stopped my leaks completely in under a week. The car shifts perfectly as it always did. Google it and read up. It worked. Not a drop on the floor even when it sits. Put 1 8 OZ bottle in and take it for a good drive. The theory is that seals dry up and shrink over time and cause leaks. This stuff treats the seals.

It's worth a try.

 

First I really appreciate all the input & pics.

This morning I checked out the the paper towels I stuffed up under the converter & into tranny housing. (see pic). From the outside the towels looked perfect but there was a little fluid on the inside of towel on the pass. side. The odd thing was after installing towels I cleaned off all the other areas that were wet and yet even with the towels there was that drip from the right hand side. A second arrow that points to the rubber boot on transmission linkage is the only other area that is wet. I looked with a mirror and everything above the pan is dry. The Dip Stick is dry, modulator is a little damp but the area that is leaking most appears to be that driver side front pan area, except there was fluid inside the inspection cover that drips out of the hole in the bottom of it.







From what I can see looking past converter with a flashlight ... it looks damp but I'm not sure it didn't look that way when I installed it. Couldn't see anything reddish in there but also couldn't see much.

I checked the torque on pan bolts and each one snugged up about 1/16 or less turn. Maybe I've got several small leaks, converter seal, pump seal and pan at that driver side front.

I believe I lose most of the fluid when the car sits as there isn't a mess underneath the transmission other than under inspection cover, driver side front and that rubber boot on the driver side.

Since it's quite low on fluid I'm going to refill it and then run this test again with the towels to see what happens.

If I pull the transmission I've got a few questions:

1. Do I need to drain the fluid to change the converter & pump seals?
2. If I have tranny on a tranny jack and lowered can the converter & pump seals be changed by an average DIY'er?
3. Do I need any special tools for changing converter or pump seals?

Thanks

 

You may want to start with the 'easy' leaks first-
Based on your pictures and description, it does appear that at least some of the leakage is from the pan gasket.
As stated by others, if the sealing area on the pan isn't flat or if the areas around the bolts holes are deformed from over-torquing, you're gonna have leaks.
Since the trans fluid is above the gasket line when sitting, this is a critical sealing area that must be as close to perfect as possible.
I still suspect that front stud that isn't straight- You can't get an even torque on that nut if it's not perpendicular to the mounting flange.

If re-sealing the pan doesn't help, then go to plan 'B' (dropping the trans).
Yes, you need to drain the fluid to do the front pump seal (unless you like a big mess) but the torque converter seal can be done without but the torque converter is full of oil so you will get a little spillage from that if you aren't careful.

'Special' tools- Not really.. Converter seal can be removed with a screwdriver / chisel and a hammer (if you are real careful and don't nick the casting).
Removing the front pump will require a makeshift puller that threads into the 2 threaded bolt holes in the pump so you can gently remove it in a 'slide hammer' fashion.

 

ezobens ... that sounds like a good plan ... can't argue with any of it. Looks like I've found a nice weekend project ... like any of us needed another one ... but it is what it is. Thanks again to you and the others that responded.

I'll post the final outcome!

 

OK ... I removed the pan and found that the hole in the pan where the stud is located was deformed and I believe I got that repaired to look like the other holes in pan. Also I straightened that stud and re-installed the pan with a new gasket. Filled tranny and drove the car enough to get everything up to temp. and then parked it.

The next day another puddle but this time it wasn't coming from that bent stud area but from the right corner of the pan. Looking at the pan from the drivers side of car it's quite noticeable that the right front corner of pan is slightly bent so I removed the pan again to see if that could be straightened with plans that if that doesn't work I'm buying a new pan.

The problem is when I removed the bolt from the stud that was bent ... it looks like a Helicoil that must have been used for the stud has started to back out. (See pic of right front of tranny area with pan removed).





What is the recommended way to fix that? Do I need to have a new Helicoil installed ... can that one be re-installed. I've never had any experience with Helicoils so I need some advice from someone experienced. I have tried putting some light pressure on it to turn it but it doesn't seem to want to go in or out. Thanks

 

Yikes.. It's hard to tell from the pic but it appears the Helicoil is also at an angle?
If that's the case, you really can't 'straighten' it as is-
If the Helicoil was installed ****-eyed, it's worthless.
Gotta love Bubba..

My suggestion would be to drill and tap that hole (Straight!) to the next larger size (even metric if need be) and drill the hole in the pan accordingly and pitch the Helicoil.
I realize that isn't the optimum solution but your options are limited.
Elm

 

I'll put $100 on a shift selector shaft seal leaking.
Anyone want any of that action?

 

I would say replace it on principle if you already have the pan off.
They are notorious for leaking.

 

Ezobens & AZMotorhead … thanks for your replies. I can’t get to this tonite but tomorrow I’m on it and I’ll check to see if that hole (w/Helicoil) is perpendicular to the bottom of Tranny housing. It could just be the optics of the camera that makes it look crooked or the portion of Helicoil that is out of the housing is damaged.

Today I had lunch with a group of guys that are into cars. One of the guys suggested I talk to a older guy that works at a local CarQuest … saying he had a lot of experience and has helped others. Beside ezobens suggestion of re-tapping to a larger size he showed me they had an assortment of kits and replacement Helicoils, should I just want to replace it and the process didn’t seem bad at all. With my current progress of one step forward and two steps back as of late I really hate to drill out/tap the housing hole and then enlarge the hole in the pan for fear of creating another problem some how.

Current plan is to extract the helicoil, then check the straightness & thread integrity using another bolt that fits. If hole isn’t perpendicular then I’ll go with ezobens suggestion. If it is perpendicular and threads seem to be fine then I’ll clean it & dry it out and try another Helicoil with Loctite on the Helicoil to housing threads.

AZMotorhead … I’m guessing you’ve had shift selector shaft seal problems. I’ve check that area with a mirror and that seal area is bone dry but will check out getting one of those seals since it may be an opportune time to change it. I’m guessing the exhaust on drivers side may have to come off.

capevettes … so far you haven’t got flamed and I’ll keep that in mind but I really hate the idea of putting in additives … glad to hear it worked well for you!

Each time I’ve tested this for leaks I’ve removed the inspection cover and stuffed paper towels up between the converter and housing and I’m not collecting any fluid from that area on the towels so if the converter seal was leaking, I think it’s sealed itself back up after getting some miles on the transmission after sitting, similar to what ezobens mention earlier in post.

I’ve sealed leaks from areas like JimT mentioned stripped bolt hole, warped pan, modulator O-ring (in my case also the filler tube O-ring too). Everything else is looking dry except this right front corner. I should be able to fix current issue and test within next few days. If you think of anything else … let me know. Thanks again for your thoughts and ideas. JP

 

Yep just went a round or 2 with a Trans leak.
I can say with almost certainty your selector shaft seal is leaking.
PO probably overtorqued the pan bolts on that corner,causing them to strip out. Thinking the leak was coming from that corner of the pan.
Her's the tool you'll need.Trans seal tool.
Here's the GM seal you'll need

Pan does not need to be off to replace the seal. Be careful when you put the seal over the shaft. the rubber on the seal is easy to cut on the flats of the shaft. My trick is to put 1 wrap of permacel(ptfe) tape over the shaft when installing the seal.
Once I get my lathe up and running I'm going to make some bullets that seals will slip over