New to me, as posted in the newbie, 72 88 convertible, 455, 400, Car has been off the road a long time, however been started regularly, I have been servicing everything, tune up,oil, grease ect. Now got it up in the air to check trans and rear, had to add 2 qts. trans to get it to move, but seems fine now,( only driven a few short distance's) PO said it had some trans leaks, so after 4 hours pulling seized pan bolts, (2 broke) got pan off, no big pieces! just some glitter (140k miles) what other things should be done to trans? shifter seal, speedo seal, what has to be done while pan is off? plan is to refill with fluid and pump out thru return line, and possibly change again. After some rotted fuel line leaks are fixed (possibly new tank) I can take it on the road,

 

On a transmission with time and miles behind it flushing or changing all the fluid can make problems...your call. Consider replacing the filter putting the pan on and refilling.

As far as other things to do, nothing unless you see leaks to address.

Good luck!!!
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I think the stories of people flushing/fluid change and then having transmission issues are questionable. Most people don’t change the fluid or filter until they think something is wrong. If the transmission is on its last few miles, changing the fluid is like putting a bandaid on a gunshot wound. Of course routine maintenance won’t FIX anything. Routine maintenance is intended to keep things in good working order. Nobody in their right mind would suggest not changing the oil and filter on a neglected engine, why are transmissions any different?

With the pan off, it’s easy to replace the shifter shaft seal. The dipstick o-ring is always a suspect, especially if the leak develops after the car sits a few days.

 

Transmissions are different in that some of the worn friction plate material is in suspension in the fluid keeping the transmission alive. Flushing can get debris in valves and make them hang-up. I'm not saying it will never help but if the transmission is marginal flushing can hasten the complete failure. After saying that, I've had servicing transmissions make them work properly again. I think it's a coin toss with some favor toward changing the fluid and filter helping.

If the fluid is changed regularly this is a non-issue
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My point exactly. If the trans is so neglected that the only thing keeping it going is the grit floating in the fluid, then it’s been on borrowed time for a while. And unless your changing the filter in a sandstorm, or replacing the filter with something like a window screen media, then nothing should be able to get thru the filter to jam up a shift valve. The purpose of the filter is to catch particles big enough to cause problems. Unless the filter is cracked, filter media torn, or just top course to catch debis,


Somewhere out there is a mid 70s cutlass that would not move until the trans warmed up. When I dropped the pan, there was a perfect imprint of the filter embedded in clutch debris. The guy that owned the car couldn’t run 2 quarters together, to say he was broke would be an understatement. New filter, fluid, cleaned out the trans cooler in the radiator, and it worked just fine for the next 2 years, until he sold it. For all I know, it may still be on the road. I would have never believed it if I didn’t see it myself. I would never believe that a trans would work with that much friction and thrust washer shrapnel in the pan, how much could really be left on the clutch plates??

 

T400 in my experience will leak around pan gasket if they sit unused any length of time. If my 73 88 sat for 2 weeks you would see drips under it. Driven every few days everything stayed dry. Apparently ALL the fluid will drain back to the pan and overfill it enough to seep past the pan gasket. The 76 98 does this too but not as bad as the Delta did. Even after new gaskets on a known true gasket surface it would do this.