TH400 Leak Source?
Thread Starter
Melting Slicks
Joined: Oct 2013
Posts: 2,569
Likes: 126
From: San Diego California
TH400 Leak Source?
I'm wondering what exactly could be the component leaking on this '73 transmission.
First, this project car sat for at least 10 years without running. When I trailered it home, there were no leaks from the tranny.
After a few times of raisng & lowering the various front & rear wheels for suspension & brake service, I noticed some transmission fluid dripping from these two points;
At first I just wiped it up. But then I observed it didn't stop. It was a slow drip, of maybe one drop every 20 seconds. And it didn't stop. I first put a jar under it to catch the fluid, but by the next day saw it overflowing. So I then put an oil pan under it. And it leaked. And it leaked. For a month and a half (!!) it filled the oil pan. It finally stopped leaking, and by then I had collected a little over a half gallon of transmission fluid.
What could be the source of the leak?
Clue: the dipstick still shows FULL.
Thanks in advance.
Steve
First, this project car sat for at least 10 years without running. When I trailered it home, there were no leaks from the tranny.
After a few times of raisng & lowering the various front & rear wheels for suspension & brake service, I noticed some transmission fluid dripping from these two points;
At first I just wiped it up. But then I observed it didn't stop. It was a slow drip, of maybe one drop every 20 seconds. And it didn't stop. I first put a jar under it to catch the fluid, but by the next day saw it overflowing. So I then put an oil pan under it. And it leaked. And it leaked. For a month and a half (!!) it filled the oil pan. It finally stopped leaking, and by then I had collected a little over a half gallon of transmission fluid.
What could be the source of the leak?
Clue: the dipstick still shows FULL.
Thanks in advance.
Steve
Race Director
Joined: Apr 2011
Posts: 11,183
Likes: 3,335
From: North of Toronto - Ontario
Problem with trans is they leak and it runs to the lowest point.
Trans that sits for a long time, seals dry out. Sometimes when they start moving again the seals may swell back up and re-seal (and then start leaking again for no apparent reason a month or two later
)
Anyway, typical leak points on the TH400 are (in no order)
O-ring on the filler tube
Seal around the shifter shaft
Speedometer cable
Pan gasket
Front main seal
Tailshaft seal
I'd probably look at the seal on the shifter shaft first based on how much you're saying it's leaking (lower point on the trans), but it's usually more likely to be the front main leaking around the TQ-converter.
Unless the pan has been disturbed, it's unusual to have the pan gasket just start leaking. but they are cheap and easy to replace. We used to put a fresh fluid and filter change in any of the old cars we bought something to be done anyway.
HIH
M
Trans that sits for a long time, seals dry out. Sometimes when they start moving again the seals may swell back up and re-seal (and then start leaking again for no apparent reason a month or two later
)Anyway, typical leak points on the TH400 are (in no order)
O-ring on the filler tube
Seal around the shifter shaft
Speedometer cable
Pan gasket
Front main seal
Tailshaft seal
I'd probably look at the seal on the shifter shaft first based on how much you're saying it's leaking (lower point on the trans), but it's usually more likely to be the front main leaking around the TQ-converter.
Unless the pan has been disturbed, it's unusual to have the pan gasket just start leaking. but they are cheap and easy to replace. We used to put a fresh fluid and filter change in any of the old cars we bought something to be done anyway.
HIH
M
Racer
Joined: May 2012
Posts: 259
Likes: 11
From: Kennesaw GA
When I discovered there was transmission fluid dripping from the bottom of my th400 pan I replaced the pan gasket using cork. That didn't work so I used a new gasket and used sealant. That didn't work so I used a rubber and cork gasket. That didn't work so I then installed a drain on the pan to make taking the pan off easier and used a rubber and cork gasket with sealant. That didn't work either and someone suggested the O-ring on the fill tube. I replaced it twice and still had a leak. I finally traced the leak to a pin hole in one of the transmission lines coming from the radiator. The trans fluid was running down the line and onto the transmission and down to the pan. Working on jack stands at that time only gave me a limited view of things.
Thread Starter
Melting Slicks
Joined: Oct 2013
Posts: 2,569
Likes: 126
From: San Diego California
Thanks guys.
I haven't specificlly looked at it yet, but can the bottom of the torque converter be seen/inspected with that bottom thin steel cover (with the 4 bolts) removed? I've got a hunch that's the guy leakin. The fact that the dipstick shows a normal level makes me go in that direction. But then again, I don't know crap about car transmissions.
I haven't specificlly looked at it yet, but can the bottom of the torque converter be seen/inspected with that bottom thin steel cover (with the 4 bolts) removed? I've got a hunch that's the guy leakin. The fact that the dipstick shows a normal level makes me go in that direction. But then again, I don't know crap about car transmissions.
Melting Slicks
Joined: Mar 2009
Posts: 3,126
Likes: 15
If it continually leaks then there must be a reservoir of fluid for it to leak from. That leaves the torque converter or the pan. Remove the dust cover and look at the rear of the torque converter. If the front seal is leaking it must run down the rear of the converter and there should be fluid dripping from the hole in the bottom of the dust cover. If no fluid at the dust cover hole then it is coming from the pan gasket or dipstick o-ring. Fluid level must be checked with fluid warmed to operating temp., car level and trans. in park with engine running. I am confident that the real experts will correct me if I am wrong.
Good luck with it. mike...
Good luck with it. mike...
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Thread Starter
Melting Slicks
Joined: Oct 2013
Posts: 2,569
Likes: 126
From: San Diego California
No. The engine hasn't ran in years. Many, many years. The tranny fluid just started dripping for no apparent reason (no engine/transmission operational movement anyway).
Thread Starter
Melting Slicks
Joined: Oct 2013
Posts: 2,569
Likes: 126
From: San Diego California
If it continually leaks then there must be a reservoir of fluid for it to leak from. That leaves the torque converter or the pan. Remove the dust cover and look at the rear of the torque converter. If the front seal is leaking it must run down the rear of the converter and there should be fluid dripping from the hole in the bottom of the dust cover. If no fluid at the dust cover hole then it is coming from the pan gasket or dipstick o-ring. Fluid level must be checked with fluid warmed to operating temp., car level and trans. in park with engine running. I am confident that the real experts will correct me if I am wrong. Good luck with it. mike...
Good luck with it. mike...But what about a converter leak; where are it's leaks likely to be from exactly?
Melting Slicks
Joined: Jun 2011
Posts: 3,116
Likes: 598
I'm wondering what exactly could be the component leaking on this '73 transmission.
First, this project car sat for at least 10 years without running. When I trailered it home, there were no leaks from the tranny.
After a few times of raisng & lowering the various front & rear wheels for suspension & brake service, I noticed some transmission fluid dripping from these two points;
At first I just wiped it up. But then I observed it didn't stop. It was a slow drip, of maybe one drop every 20 seconds. And it didn't stop. I first put a jar under it to catch the fluid, but by the next day saw it overflowing. So I then put an oil pan under it. And it leaked. And it leaked. For a month and a half (!!) it filled the oil pan. It finally stopped leaking, and by then I had collected a little over a half gallon of transmission fluid.
What could be the source of the leak?
Clue: the dipstick still shows FULL.
Thanks in advance.
Steve
First, this project car sat for at least 10 years without running. When I trailered it home, there were no leaks from the tranny.
After a few times of raisng & lowering the various front & rear wheels for suspension & brake service, I noticed some transmission fluid dripping from these two points;
At first I just wiped it up. But then I observed it didn't stop. It was a slow drip, of maybe one drop every 20 seconds. And it didn't stop. I first put a jar under it to catch the fluid, but by the next day saw it overflowing. So I then put an oil pan under it. And it leaked. And it leaked. For a month and a half (!!) it filled the oil pan. It finally stopped leaking, and by then I had collected a little over a half gallon of transmission fluid.
What could be the source of the leak?
Clue: the dipstick still shows FULL.
Thanks in advance.
Steve
Transmission Leak
I stuffed some paper towels up in the bell housing after replacing the pan gasket and I still had a leak. The paper towels obsorbed the fluid and the pan was dry so I new it was leaking from somewhere in the bell housing.
Melting Slicks
Joined: Mar 2009
Posts: 3,126
Likes: 15
In your photo you can see the converter seal, that is one place. The front pump seal is also in the area at the front of the case and is shown in cagotzmanns linked photo. Converter could have a crack but I have never had it happen. You just have to wipe everything down and start looking. Hope it is simple. mike...
Last edited by mds3013; Jan 24, 2014 at 04:17 AM.