You guys are awesome! Thanks for the education. I've learned more than I ever wanted to about planetary / ring gears and pump whines. Now if you can tell me how to stop the transmission fluid drips we would be in business! (I understand it's the nature of the beast with powerglides.)

 

Gotta find where the fluid is leaking from. No, it's not the nature of the PG. They don't leak anymore than most other GM automatics. You have many areas to check,
from front to rear of trans, front pump seal and bushing, torque converter hub, pump o'ring and gasket, pump bolts, if I remember correctly some take small o'rings and some take a flat type seal washer, cooler lines and fittings into the case, servo cover, filler tube and o'ring, sometimes the tube itself splits where the o'ring fits,

Some PG's had a switch by the cooler lines that leak, but early PG's don't have that switch, extension housing gasket, rear seal and bushing, worn driveshaft slip yoke, where bushing rides, speedo seals, inner and outer, or the speedo housing itself where the plastic gear wears out the center hole,

Shiftarm seal in case or the small inner o'ring on the detent rod that fits thru the main shift arm linkage, pan or pan gasket, vent tube on upper area of bell housing, fluid out the vent meaning trans is overfull or internal pressure build-up, band adjust nut/adjusting stud, modulator or modulator gasket to case, any of the small pressure taps on case.

That about sums up where any PG could leak from. Never all those areas at once but can be several at once.
Not trying to blow you away with all this, but these are actually the areas your PG can leak from. ...Thought of another, the cooler lines themselves, can be kinked, split, rubbed thru, joined with hose without flaring the ends of the lines, (should not use hose on cooler lines) anywhere from trans up to radiator. Have fun.. a good trans tech can diagnosis your leak in minutes.

Correct myself, extension housing takes a square rubber seal not a gasket.

 

You are a trans tech. And not because you said so, and you did, but because you supplied the same range of possibilities for a leaking glide as my urologist. Given my 20 year ownership tenure with one, I'm willing to bet $250 to your favorite charity that the OP's leaks are caused by converter drainback, an overwhelmed pan and subsequent leakage from pan gasket, selector shaft, dipstick tube or speedo cable drive.

Dan

 

I didn't say I was a trans tech, I said a good tech could diagnosis his leak in minutes. But I did learn the trans rebuilding business on alum Powerglides and ST 300's as a teenager. Drainback could very well be his leak. These old cars that sit more than they are driven can develop "odd" leaks.

I like to post information that I know to be true from experience and not from he said, she said forum jibberish. I don't mean to come on as a B-shytter but try to help folks here with info I know to be facts from my own experience fixing alot of my own early mistakes. If I don't know answers to questions I don't answer but read and learn instead.
I come in peace my friends...

 

This is a wee bit off-topic, but wasn't the ST300 equipped with a variable pitch torque converter? This feature was dubbed "Switch Pitch" back in the day.

The Buick Super Turbine 400's of '65-67 had this feature. Did Chevrolet ever install switch pitch in the THM-400 transmission, which I believe was derived from the Buick-developed ST400?

Switch Pitch is a neat performance feature, allowing the vanes of the torque converter to be angled in one of two positions depending on throttle position, further increasing torque multiplication off the line. It was almost like having an extra (low) gear in the transmission.

So, did the ST300's have Switch Pitch? During which years was it installed? In what car lines?

Chevrolet never bothered to put Switch Pitch in a Powerglide as this was GM's lower cost division, after all. But, Switch Pitch would have been a great addition to the two-speed Powerglide, which suffered from having a 1.76 first gear, a limitation of this automatic in a street driven car.

 

Variable vain, aka switch pitch was standard on the ST300 used on Buick and Olds, 64-67. Not sure about Poncho, have to look it up. Buick had a lot of experience with that arrangement having used it for years on the Dynaflow as kickdown, since the Dyna didn't flow down a cog like the rest. Buick designed the ST300 and the Turbo 400 as well. Hydramatic put their name on it and the rest is history. The 64-67 THM400 were switch pitch in all versions, I could be off by one year, someone say so if so. I don't like to be wrong. Switch pitch is complicated and expensive. The Powerglide cheap and simple. The two don't go together.

Dan