My TH350 is leaking fluid like crazy, and I can't find the source. There's been a couple times where I've dried up the puddle on my garage floor, taken the car for a spin around town, brought it home, got underneath and NOTHING. No drips anywhere and everything is dry. When I wake up the next morning and step outside to go to work, the puddle is back, bigger than ever. I've tightened 11 of the 13 pan bolts (the front two are hidden under the crossmember, which I didn't feel like removing at the time); none were really loose to begin with. I've owned the car for less than a month. Everytime I check the dipstick, the fluid is JUST under the full line - nowhere close to the "add" line. I'm not as mechanically inclined as most of you, so I'm at a loss. Any thoughts?

- GoldOlds

 

If it is like stamped steel valve covers, you can have a leak because the surface of the pan is dimpled at every bolt location and not flat, you don't get a good even compression so there is room for leaks around every bolt hole. You may have to remove the pan, flatten out the surface where the gasket mates to, install a new gasket and re-tighten the bolts to specs. As I said, this is just an idea based on my experience with valve covers.

 

Most TH350/400/700R4/200-4R/200c that leak AFTER running then shut off-
Leak begins in about 10-15 minutes, likely culprit may be filler tube O-ring/sleeve (easy fix) or Front pump O-Ring (not easy). Good Luck
KLM.

 

If you can't see the leak source, this tip should help you out.

I would recommend cleaning the transmission (or anything else that may be leaking) with brake cleaner so it is good and dry.

Get an athletes foot spray power (like Desonex), and spray any suspect areas with the spray powder. Wait a little time and the power will change color showing you exactly where the leak is coming from.

I hope this helps.

 

Couple suggestions from the peanut gallery as I found a very similar problem. Check the area around the shift lever. It can leak slightly run down the side of the pan and look as if the front/sides of the pan have a leak. It seems to happen after the car has been driven and parked for awhile (??). Also, the area where the speedometer cable hooks in, the "O" ring can get worn or not fit tight, oil will slowly leak down the side then onto the transmission frame and usually out the bolt holes or around the frame.

 

All good advice, thanks guys! I took the Cutlass for a couple good long trips to make sure the tranny reached normal operating temperature to get a good, accurate reading. The first time I took it for a LONG drive, the oil on the stick almost reached the first kink (well above the "full" line). The second time I took it out for more than just a quick spin around the block (after another night of leaking onto the garage floor), the oil on the stick was JUST above the full line. If the previous owner overfilled it, would THAT make it leak? If so, from where - the dipstick/filler tube where it meets the tranny?
Thanks again!

- GoldOlds

 

I had a 72 cutlass once, and it had a transmission leak that drove me insane, it took almost 3 moths to locate the point she was leaking from, but when I did find it changed out the vacum modeul on the trasmision and the leak stopped. the trans was a 350. now I'm not saying this could be your problem but I thought it was worth sharing with all of you.

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Chip

71 442 Conv.

 

Check the dipstick to trans seal. The fluid level will rise as fluid runs out of the converter overnight. It will run down the body of the trans and look like it is running off the pan gasket.

 

You can remove the inspection cover on the flywheel to better determine if it is the front seal that is leaking. Then again, if it was the front seal you would see tranny fluid leaking from the inspection cover. You should also check the lines going to the tranny cooler in the radiator. The flexible hoses could be old and dry rotted and be giving you a bad seal on the lines. Hope all of this helps.

 

The first 2 places I'd look are the dipstick tube as (W30 said) , and the tailshaft. Especially if your driveway/garage are on an incline.

Also, Overfilling your trans does not hurt it in my opinion. Again this is Opinion only and many would disagree, but I feel the point has been proven having had 2 transmissions grace 170000 plus miles and with fluid always being 1/2 inch above full hot on the dipstick even when the motor is cold. Just change the fluid and filter every 30000 miles and use the right grade for your trans.

There's only so many things that can leak.
Front seal
Tail shaft
Pan plug
Pan gasket
Trans cooler lines
Speedometer
Shift er link
Dipstick tube
trans case (heh)

 

I recently had my '72 gone through after sitting for a number of years without being driven. Initially the Tranny had a leak where the dip stick attaches. That fix was a freebie at the local transmission shop.

After driving it a bit more I also had a leak from the tranny itself, because the seals had dried out. I had a guy pull it and replace the seals and take a general look see that otherwise it was ok.

It cost me about $550 but that is a lot cheaper than a complete rebuild.

Both of these leaks produced a fair amount of stain on the garage floor but a very little fluid can produce a disproportionately large stain. No significant loss of fluid when measured by the dip stick.

 

Just had the same problem, on my VC. It would leak bad when setting, and not when running. I would clean it up, and get under the car a look, and watch and no leak. I changed the pan gasket, took cover off and looked, changed O rings on vac mod, and dip stick. Took the motor and trans out, to put in new motor. Took the trans to the trans shop, and the front pump main seal was bad, not the one that seals the shaft, but the pump itself. Trans guy say that that is more common to leak when setting, and not leak as much if you drive it every day. Glad to get it fixed, it made some big messes.