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It could actually be leaking from that bolt. The drill/tap into the bottom rail of the trans main case can open porosity in the aluminum casting to the sump area and allow oil to seep into those threads. You might try removing that bolt, cleaning the bolt and the main case threads, then applying some Permatex gasket sealer or Ultra-Black Permatex RTV sealant to the threads of the bolt and reinstalling it.
I suggest that you let it set and cure overnight before you fire it up. But, a short drive at normal operating temps should tell you if the leak was fixed.
P.S. Aluminum castings are especially prone to porosity problems which can open-up following machining operations.
FWIW, chrome pans have a propensity to leak from my experience....too smooth perhaps.
Use a cork/neoprene gasket dry on a flatten pan rail. Ball peen hammer the holes flat. Tighten to 12 ft lbs in two passes, re-tighten again after several heat cycles. It might be leaking from kick down connector in case...takes an o-ring. That's right above the area that showed up as a leak.
Last edited by jimvette999; Mar 2, 2018 at 08:45 AM.
Right above the area you show in your picture is your shifter shaft. A leak in that location will look just like a leaking pan gasket as it will run out of the opening and down to the pan. I rebuilt the TH400 on my 1974 and replaced that seal during the rebuild, but if you're not super careful you can nick the seal and it will leak like a sieve....I know this to be true, it happened to me. The good news is that it's easy to find with a mirror when you know where to look, and it can be replaced on the car.
You need a special tool to install it, the best place to get that tool (and the cheapest) for me was my local NAPA. Beware though -- if you are buying online, some online sellers jack the price of that tool up immensely.
Right above the area you show in your picture is your shifter shaft. A leak in that location will look just like a leaking pan gasket as it will run out of the opening and down to the pan. I rebuilt the TH400 on my 1974 and replaced that seal during the rebuild, but if you're not super careful you can nick the seal and it will leak like a sieve....I know this to be true, it happened to me. The good news is that it's easy to find with a mirror when you know where to look, and it can be replaced on the car.
You need a special tool to install it, the best place to get that tool (and the cheapest) for me was my local NAPA. Beware though -- if you are buying online, some online sellers jack the price of that tool up immensely.
That's where we thought it was coming from. He changed it twice and then said it was the pan instead. Pans in so I just have to get with him to change.
