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Having to backtrack. I had my 400 Trans rebuilt and after 3 times going back for a leak the guy is telling me it's the pan. He swapped with a trans. He had at his shop no luck. Anyone had issues or luck with a aftermarket pan. It's worse now then ever. Underneath is embarrassing.
Only a couple of dozen places for a TH400 to leak....
But as far as your question on aftermarket pans.
I've been running a TCI-228011 pan for several years now with no issues. Nice and heavy quage (thicker than the factory pan) steel pan. (chrome but a can of paint could fix that)
Other than that most of the ones I looked at were pretty flimsy
I'm personally not crazy about aluminum pans as I'd rather have a dent than a hole.
I had a very strange issue with a th400 . The top of the case developed a hairline crack. When the transmission got hot the crack would open up and leak . You couldn't see it unless you got under it when it was hot. I finally found it with a mirror.
It sounds like you're not totally convinced its the pan that's leaking. A couple of years back I bought one of those UV lights where you put the dye in the fluid and use the light to look for the leak. It wasn't terribly expensive and it works great when you're trying to track down a leak. You would pour a bottle of the dye in your trans fluid and use the light to follow the leaking fluid back to the source. If its the pan, it should be an easy fix with a new pan.
I had it rebuilt and it was leaking same as before the rebuild. At first we thought it was shift arm. He redid that now he says pan. I've been busy at work so I've took his word. I guess I'll crawl under it tomorrow. The guys been doing trans forever.
From: At my Bar drinking and wrenching in Lafayette Colorado
Here's a crude but effective way to find the source of the leak: Wipe all the leaky fluid off the tranny. Then, wrap every gasket and penetration with white paper towels. Wrap paper towels around the pan gasket area. Tape it in place if you need to. Put paper towel around the accumulator cover. Put it around the dipstick penetration. Speedo cable cover. Wrap everything in paper towel and wait to see which towel location starts bleeding red first. It works...
They used to make a product called "Baker's Secret" which was finely ground flour with some light vegetable oil in a spray can. It was GREAT for spraying on surfaces to identify leaks (after those areas were thoroughly cleaned and dried). Spray on and fire it up. Any leakage would show up immediately. (as it would with paper towels or toilet paper)
It was just a bit less time consuming and messy. But I don't know if that is stlll being sold.
(find the leak) If any of the upper connections are leaking they run down to the pan gasket and then seem to run around everywhere
A couple of install items I've run into...
The cooling lines are sometimes a B**** to get tightened enough to seal, (a crowsfoot wrench on a couple of long extension works) and they'll leak down onto the area around the fill-tube and then onto the edge of the pan and around it goes...
I have a fill tube with the two rings so I do run a bead of "right-stuff" between them as the top one rests right on the edge of the hole chamfer.
You didn't say if the car has been sitting for a length of time or not, but this is a common issue in the winter. RodNok is right. Its the dipstick tube "O" Ring.
In storage, the convertor drains, all the orfices in the valvebody drain and the fluid overfills the pan so to speak. The seal on the dipstick is overwhelmed with the extra capacity and will leak. And I mean lots. Those cheap-little "O" Rings can't handle that much pressure behind it. The fluid level in the pan is at its highest when sitting for months.
Because of that, in the winter, I now start & run my TH350 every 4-6 weeks after seeing what appeared to be a gallon on the garage floor ten yrs ago.
I have heard stories of past dealerships complaining of tranny fluid under brand new models sitting on the lot years ago. Corp Hdqtr told them:
"start, run, move the damn thing once in awhile". Problem solved.
Last edited by HeadsU.P.; Feb 27, 2018 at 04:29 PM.
Or, GM could have installed a much BETTER O-ring. But, that would have cost them 2-3 cents. It's much better for them to have the dealers/owners start their cars more often....
P.S. The cheap O-rings used will take a "set" after some time due to heat cycling, etc. O-rings of better synthetic rubber would have lasted (and sealed) forever.
Last edited by 7T1vette; Feb 27, 2018 at 01:16 PM.
Unless you park your car on a slant, its not the dipstick "O" Ring which of course is on the other side. I assume all pan bolts are snug.
It might be the seal under the shift linkage. I believe that is replaceable when the cable & bracket are removed, but thats another issue.
Last edited by HeadsU.P.; Feb 27, 2018 at 06:04 PM.
Transmission headache
(find the leak) If any of the upper connections are leaking they run down to the pan gasket and then seem to run around everywhere
