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Discussion Starter #1
I've had a transmission fluid leak since I bought my 66 Galaxie that had a 460 / C6 conversion before I bought it. Both were rebuilt. Previous owner had the cooler lines plugged off so no cooling to the radiator. It leaks even with the car off from the front and rear seals. I always assumed it was from the seals being blown by the previous owner plugging the tranny cooler line inlet and outlet ports on the C-6. I am now wondering if the dipstick is wrong and I am simply over filling it. Looks a bit shorter to me than it should by just looking at it.



How long should a Mid 1970's C-6 dipstick be? (Tip to tube top)
I have to put about a quart of fluid in it every time I drive it just to get it back on the stick. Shifts good. Just leaks.


Thanks
 

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I've had a transmission fluid leak since I bought my 66 Galaxie that had a 460 / C6 conversion before I bought it. Both were rebuilt. Previous owner had the cooler lines plugged off so no cooling to the radiator. It leaks even with the car off from the front and rear seals. I always assumed it was from the seals being blown by the previous owner plugging the tranny cooler line inlet and outlet ports on the C-6. I am now wondering if the dipstick is wrong and I am simply over filling it. Looks a bit shorter to me than it should by just looking at it.



How long should a Mid 1970's C-6 dipstick be? (Tip to tube top)
I have to put about a quart of fluid in it every time I drive it just to get it back on the stick. Shifts good. Just leaks.


Thanks
For most domestic rear wheel drive 3 speed automatic transmissions,
with the trans warm and engine running in Park or Neutral,
the full mark should be at the level of the trans pan gasket.

Use what ever length dipstick gets that level.

Even if slightly overfull (or even a lot overfull) it still should not leak.

Seriously overfull it would leak out the vent, which is very high up and it would need to be about 4-5 quarts overfull to leak there.

Get those leaks fixed!
 

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Discussion Starter #3
For most domestic rear wheel drive 3 speed automatic transmissions,
with the trans warm and engine running in Park or Neutral,
the full mark should be at the level of the trans pan gasket.

Use what ever length dipstick gets that level.

Even if slightly overfull (or even a lot overfull) it still should not leak.

Seriously overfull it would leak out the vent, which is very high up and it would need to be about 4-5 quarts overfull to leak there.

Get those leaks fixed!

Thanks.
I've got a local tranny shop to replace them and check the front pump. Previous owner did not hook up oil lines to the radiator and plugged the ports with bolts. Pretty sure that blew the front seal around the torque converter. I have it plumbed correct now.



Shifts good. Just leaks.
 

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Thanks.
I've got a local tranny shop to replace them and check the front pump. Previous owner did not hook up oil lines to the radiator and plugged the ports with bolts. Pretty sure that blew the front seal around the torque converter. I have it plumbed correct now.



Shifts good. Just leaks.
Plugged cooler lines would not "blow the front seal"..... plugged cooler lines cause far more serious damage.

On the C6, the front port is "OUT" to the cooler and the rear port is "IN" from the cooler.

The rear port return line from the cooler feeds the lubrication circuit inside the trans. IMPORTANT!!!!
It lubes the sprag clutch and planetary gears.

If there is no oil flow into that rear port,
very serious hard part damage can and will happen if the car is driven any significant distance.

Case in point.

Years ago I built a C6 for a friends 67 Mustang GT 390.
When he re-installed the trans he kinked the rear cooler line so badly it stopped oil flow into that lube circuit. (basically the same as plugging the ports)
(also he had headers on the car and the tight fit of the headers made it hard to get the cooler lines hooked up, so he "mangled them" into place :surprise:)

He drove the car about a week and then took it to the 1/4 mile track.
Shortly after that the trans failed.

When we got the trans apart the sprag was destroyed along with the case bushings and sun gear bushings.
He's lucky the planets didn't fail.

Good on you for hooking up the cooler line properly :smile2:

...and hopefully the previous doofus that plugged the ports didn't drive the car much with them plugged.

In any case... your leaks have not been caused by the plugged ports.

Something else is going on and it may just be a matter of replacing some seals..... OR...

The bad news is, the previous doofus drove the car far enough with the ports plugged
that there is the beginning of hard part damage and metal particle contamination in the oil that is damaging seals and causing leaks.

Hope it's not that... :frown2:

You say it shifts good... so there is hope no significant damage has occurred.

Good luck!

PS, I'm a transmission re builder with over 45 years experience so I might know 1 or 2 things about automatic transmissions. :grin2:
 

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Discussion Starter #5
Thank You for that in depth info. I know very little how the transmision actually works so I was thinking the internal pressures just blew the seal. I don't think it was driven much, but I'm sure it decreased the life of the transmission and I will have to have it rebuilt again someday sooner than later. I just hope the seals fix it for now. The previous owner was building it for a drag car, but the owner between he and I didn't drive it much. He was an old dude just trying to flip it for some $$.


Thanks again
Jim


Plugged cooler lines would not "blow the front seal"..... plugged cooler lines cause far more serious damage.

On the C6, the front port is "OUT" to the cooler and the rear port is "IN" from the cooler.

The rear port return line from the cooler feeds the lubrication circuit inside the trans. IMPORTANT!!!!
It lubes the sprag clutch and planetary gears.

If there is no oil flow into that rear port,
very serious hard part damage can and will happen if the car is driven any significant distance.

Case in point.

Years ago I built a C6 for a friends 67 Mustang GT 390.
When he re-installed the trans he kinked the rear cooler line so badly it stopped oil flow into that lube circuit. (basically the same as plugging the ports)
(also he had headers on the car and the tight fit of the headers made it hard to get the cooler lines hooked up, so he "mangled them" into place :surprise:)

He drove the car about a week and then took it to the 1/4 mile track.
Shortly after that the trans failed.

When we got the trans apart the sprag was destroyed along with the case bushings and sun gear bushings.
He's lucky the planets didn't fail.

Good on you for hooking up the cooler line properly :smile2:

...and hopefully the previous doofus that plugged the ports didn't drive the car much with them plugged.

In any case... your leaks have not been caused by the plugged ports.

Something else is going on and it may just be a matter of replacing some seals..... OR...

The bad news is, the previous doofus drove the car far enough with the ports plugged
that there is the beginning of hard part damage and metal particle contamination in the oil that is damaging seals and causing leaks.

Hope it's not that... :frown2:

You say it shifts good... so there is hope no significant damage has occurred.

Good luck!

PS, I'm a transmission re builder with over 45 years experience so I might know 1 or 2 things about automatic transmissions. :grin2:
 

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PS, I'm a transmission re builder with over 45 years experience so I might know 1 or 2 things about automatic transmissions. :grin2:
Hey Galx
My COM was acting up so I swapped it out for a rebuilt 1959 MX. It shifts fine but there is fluid dripping from the bellhousing. I pulled the tranny and everything looked nice. I did put in a new gasket but the seal was nice and flexible so I left it but after all that it still leaks, just sitting in the garage. I suspect the TC since it might be original but do those things even leak?
I am loathe to pull it again if I am just guessing. I'm looking for advice!
 

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Hey Galx
My COM was acting up so I swapped it out for a rebuilt 1959 MX. It shifts fine but there is fluid dripping from the bellhousing. I pulled the tranny and everything looked nice. I did put in a new gasket but the seal was nice and flexible so I left it but after all that it still leaks, just sitting in the garage. I suspect the TC since it might be original but do those things even leak?
I am loathe to pull it again if I am just guessing. I'm looking for advice!
Which gasket?

There are many places an automatic can leak.

Hard to diagnose over the internet....

Torque converters can leak.
Usually a pin hole in the weld, either at the hub, or the weld joining the 2 halves.
If equipped, the TC drain plug can leak too.

Torque converter re-builders have equipment to pressure test the TC for leaks.

If there is a groove worn on the hub where the front seal rides, that can leak too.

Just because a seal is soft, does not mean it is good or can't leak. It can be soft yet worn out.

Any time you have the trans out, it is a good idea to replace the front seal, even if it looks/feels good.
 

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Torque converters can leak.
Usually a pin hole in the weld, either at the hub, or the weld joining the 2 halves.
If equipped, the TC drain plug can leak too.
Torque converter re-builders have equipment to pressure test the TC for leaks..
Sorry OP for the hijack... One more question, can my TC be tested while still in the car?
 
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