ST300 Inspection Cover Full of ATF...HOW??

Discussion in 'The "Juice Box"' started by online170, May 9, 2024.

  1. online170

    online170 Well-Known Member

    I have a 1965 Skylark with stock 300 and ST 300 trans. I have a transmission leak after doing a couple of maintenance items that I cannot explain. I think the leak has stopped (to be verified this afternoon) but want to understand what happened so it doesn’t re-occur.

    What I did:
    • Replaced the waterpump
    • Replaced the transmission cooler lines

    • After buttoning everything back up and topping up the radiator, I started the car and transmission fluid started gushing onto the ground. Very high rate of flow, as if I had forgotten to hook up the pressure trans cooler line. A closer look revealed that the transmission fluid was spraying out of the STARTER! Yes the starter!
    • I removed the inspection cover and noted that it was full of fluid. So when the engine was running, the ring gear was churning up the ATF and ejecting it out of the lowest openings in the starter hole, which made it seem like a pressurized line.
    • But how did the ATF fill up in the first place???
    • The fluid on the ground is indeed ATF (bright red) and not motor oil
    • The center of the torque converter is dry, and so is the pump seal. But the bottom of the TC is oily with ATF. Makes sense as that was submerged in the inspection cover.

    Some more details of EXACTLY what I did;
    1. Jacked up the front and put it on stands/ramps several times.
    2. Drained the coolant, removed the radiator. One waterpump bolt was stuck, so had to apply heat to the front cover.
    3. Damaged the rusty old trans lines, but I had to drive the car back into the garage, so bypassed the radiator by putting a hose from one line to the other. It may have had a kink in it. Drove it back in to the garage from the driveway, running for maybe 10 seconds.
    4. Removed the rusty old lines by unbolting them from the trans, and also the dipstick.
    5. The trans fittings were removed and the car was lowered off jacks and stayed that way maybe 2 days.
    6. Came back with the correct fittings, bolted them up, connected the trans lines to new external cooler.
    7. Removed and installed new water pump. Reinstalled fan, shroud, radiator.

    I have been driving the car for a few weeks and it was running OK and did not have a huge puddle of ATF on the ground. The inspection cover has dirt in it, so its possible the drain hole is plugged, but it would still drip a bit I would think. When I checked the ATF it was over-full a bit. The only things that changed are what I described above.

    At first when I saw the leak I was sure I had blown the pump seal. I didn’t flow test the new cooler circuit so maybe I forgot a plug in there? Or maybe the kinked bypass line backed up the flow? But then I saw that the seal was dry, as was the center of the TC.

    The only other thing I can think was maybe the jacking up/down the front of the car, and the open fittings and dipstick hole somehow created a leak that then flowed around the front of the bellhousing and into the inspection cover. This makes zero sense to me as the car is on relatively level ground.

    So then? How do you think my inspection cover became a pool of ATF all of a sudden? Any help appreciated. I would like to know what the cause was, otherwise im going to be nervous about this problem repeating itself when I least want it to, like on a long ass drive!
  2. online170

    online170 Well-Known Member

    Some not so clear pics.

    1) before inspection cover removal. We ran the car for a few seconds and I watched the cooler fittings but the starter was spraying ATF. You can see the one silver boss where it was coming from

    2) inspection cover removed and drained

    3)pump seal dry

    Attached Files:

  3. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    I am afraid you'll need to get the car in the air, clean everything really well, and then have someone start the engine while you look. That big a leak should be very obvious. Maybe you cracked the case where the lines go in.
  4. online170

    online170 Well-Known Member

    I still don't have an explanation, but happy to report no leaks.

    I degreased everything and ran the engine for about 10-15 mins with the inspection cover off and no puddles or drops on the road surface formed. I was worried there was a vent or something in the bellhousing that was the culprit. I think the fluid found its way into the inspection cover from the dipstick tube opening, with the tube removed and just filled it gradually overnight.

    Been on a couple 30+ minute drives with it. Fluid levels are unchanged, and no drips (except for gasoline). Carb rebuild is next on the list!
    12lives and knucklebusted like this.

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