1972 transmission leak FMX

I tried this elsewhere on the site but no response. Maybe hoping I posted in the wrong place so here is my question:

Looking for some insight on my "ghost leak". Mycar has been sitting for a while and I noticed a leak that appeared to be coming from where the shift linkage attaches to the shaft. I was down about a 1/3 quart. It's been very cold here in Dallas up until to last weekend so I was able to finally get it out and drive it around for a few hours. I expected to be low again when I got back, but so far no leak? Any idea what could have caused the leak to be somewhat substantial and then disappear after driving? i know there are a couple of seals in that area but that is about the extent of my transmission knowledge. I've heard that it's possible for the torque converter to "bleed down" but that's a new one to me. i would appreciate any feedback/ideas that you may have. the transmission has been rock soild as long as i have owned the car (6 years) and still shifts like new. i really don't want to do a tear down on this thing since it's an FMX. I hear that they are unique compared to a typical C4 or C6 and if the mechanic is not familiar with the differences you can really make things worse during a rebuild which i don't feel is necessary anyway. Thanks in advance for your input.

If it stopped after driving it, it may be just the seals dried out.

I have a 73 with a C-6 that leaves a puddle over the winter and when I drive it in the summer it stops or at least becomes a small drip.

I would just keep a close watch on it for awhile.

Don

thanks. I was hoping that might be the case.

My FMX used to do that, while using the car no leaks. If I let it sit for a long time couple weeks or more it would leak near the shifter shaft. Could be the converter letting fluid back into the pan slowly until the level goes over the shifter. Once you start it it sucks the oil back up and doesnt leak since the level is now below the shifter again.

That seal is cheap, getting to it requires taking off the valve body though.

Thanks. Hopefully that's all it is. I really don't want to tear the thing apart. It's really been a good transmission to this point.

Well how hard is to take off valve body can I do with trans still in. It been thirty yrs since I did one

My FMX used to do that, while using the car no leaks. If I let it sit for a long time couple weeks or more it would leak near the shifter shaft. Could be the converter letting fluid back into the pan slowly until the level goes over the shifter. Once you start it it sucks the oil back up and doesnt leak since the level is now below the shifter again.

That seal is cheap, getting to it requires taking off the valve body though.

Click to expand...

That's exactly what the problem is. +1

You can probably avoid it by starting it once a week, put the tranny through the gears and turn it off again.

I also had the issue with oil weeping through the pan after leaving it standing a while.

I fixed that after many attempts by using "the right stuff". Amazing stuff.

Well how hard is to take off valve body can I do with trans still in. It been thirty yrs since I did one

Click to expand...

It can be done with the tranny in the car but if you're unfamiliar with the springs and levers in there, don't bother.

I had an fmx on my work bench earlier this year and had to reposition the shifter lever to go from a column shift to a floor shift for a truck project. It was simple with no fluid being able to see everything. Unfortunately, I did not replace the lever seal while I was in there.

Fastforward to the tranyy in the truck and full of fluid......and a leak at the shifter lever. Rolled under the truck, dumped the fluid filled pan. Pulled the valvebody again, fuild dripping in your face and down your arms. Springs and levers falling out of the tranny. PITA. If I hadn't already pulled this before I would have never been able to figure out where everything went.

If it's just a drip.. save yourself the aggrivation

My daily driver is a 1979 Thunderbird with a FMX shortcase tranny. Whether I drive it or let it sit, it leaks--because the shift seal has hardened and needs to be replaced. But replacing it is a major undertaking; tranny needs to be dropped down to replace it. No easy way around it.

My 72 has the same FMX selector shaft leak to varying degrees. It is worse when it is not driven for a while. I keep cardboard under it in the garage. I am capable of replacing the seal but it works so well with over 150 K miles on it that I just don't want to mess with it. I have a spare unit on standby in the event I need it. So I live with it as many do.

Ron

The fmx I put in my 66 leaks after sitting two or three days. Comes out the kick down even after putting new shifter and kick down seal. I've just accepted it and am one with the leak.

The fmx I put in my 66 leaks after sitting two or three days. Comes out the kick down even after putting new shifter and kick down seal. I've just accepted it and am one with the leak.

Click to expand...

I got an oldschool mechanic and he told me that our transmission are notorious for the orings to constantly leak tranny fluid from the kickdown linkage. Think of it this way, if it doesn't leak youre low on fluid if it leaks you're still good. I have the same problem. You're justgoing to have to keep trying to replace it. Its a huuuge pain in the ass. :/