TH350 aftermarket oil pan will not stop leaking bad

[mtnmankev]

On one hand I sorta like the idea of an all aluminum finned transmission oil pan to dissipate heat, but this leak is out of hand.
To be clear, I did NOT buy the oil pan, it came on the truck when I bought it.
It leaked when I bought the truck, so I serviced the trans, filter, helicoiled several stripped out bolt holes, and reinstalled the pan with a new gasket.
It leaked at the pan to trans body interface.
I got a tad upset, removed the pan again, cleaned everything up nicely, new gasket again (this time with a thin bead of RTV black on both sides.
I'm positive it will stop leaking now.
Guess what ?? I was wrong.
Time for the aluminum pan to go in the recycling scrap pile.
Anybody got a spare steel TH350 pan they want to donate?

 

[Dutch Rutter]

Before you throw anything away try a lubelocker gasket. Best sealing gasket ive ever used, goes on dry, and can be carefully reused, if it is a problem with the pan itself.

Here's a summit racing link.

https://www.summitracing.com/parts/...BPQFdTmixStv3trFZ1SxxZTfq15h-HjUaAjVvEALw_wcB

 

[mtnmankev]

Thanks, that sounds like it's worth a try.
Seeing as how the aftermarket aluminum pan was cast, not machined, there's a good chance it has a fair amount of built in warpage.
Only other thing I can think of is to have the pan machined smooth as long as the edges don't end up too thin.

 

[Dutch Rutter]

Sounds like a good plan. Definately worth checking out. If your interested in a good pan for cooling and have the space but also dont mind paying a bit more I put a derale cooling pan on my 700r4 with one of those gaskets and its been fantastic.

 

[Matt69olds]

Take a file around the perimeter of the pan. See if there is any obvious low or high spots. I’d be willing to bet your going to find a leaking dipstick tube, kick down cable leak, or converter seal leak

Go to a parts store, get a small bottle of the fluorescent air conditioning oil. Add a little to the trans pan, run it for a while. The dye will highlight the leak good enough for Ray Charles to see.

 

[JoeR Jr]

Any chance it's the shifter seal, or maybe pass-thru for the lockup converter, if it has one?
Joe

 

[mtnmankev]

Thanks for those suggestions, it's not a 350C so no lockup to deal with.
There is a chance it's the dipstick tube O ring leaking and the fluid is working its way all around the perimeter of the pan.
Somehow that had slipped my mind, but then again old age IS setting in.
Since I have to yank the engine out to replace the rod and main bearings, the dipstick tube will be free of the rear of the block and I can put a new O ring on it, clean everything up good, and see if the leak continues.
May end up having to sell the truck and I want it 100%.
The only things the truck needs (other than the trans leak) is the engine bearings and front end alignment and somebody will get a nice truck to drive.

 

[HotRodPC]

For sure, check all the seals on the top that can be running down making you think it's a pan leak. Try that other gasket if you want.

In the mean time, if I get to my shop, I'm fairly certain I probably have an OEM Th350 pan.

 

[QBuff02]

I had a similar leak driving me nuts, thinking that g-darn pan gasket was the culprit. It was the itty bitty shifter shaft seal that is the problem. with the shifter linkage in place, it appears its the gasket, when the reality is it drips out of the seal and runs the pan rail around and makes it appear its leaking in multiple spots. I bought the remover/installer tool from NAPA to remedy the problem, but the shift shaft is galded just enough I feel I'm going to do damage trying to remove the seal from outside the case. I am going to drop the pan and service the trans once I get the truck out this spring and run it around a little, and I figure i'll address it from the inside with the shaft removed. You mentioned that you had to heli-coil bolt holes on the trans case? Sounds to me like someone went he-man and over tightened the bolts at some point in it's life. You could very well have a case that is no longer true, and a pan that is also no longer true. Have you held a straight edge to either of them yet? You might be a candidate for a leak from those areas given the trouble you have with the bolt holes.

 

[mtnmankev]

I don't know who the idiot was who rebuilt the transmission for the previous owner, but I ended up installing helicoils in FOUR pan bolt holes and two for the tailshaft housing bolts.
When I bought the truck, it was missing the two bolts that come up through the crossmember to secure the rear mount to the trans.
They also used a hard setting silicone to glue the cover for the governor, the clip was too much hassle to replace I suppose.
It does make me question the integrity of the rest of the rebuild too ............

 

[HotRodPC]

I don't know who the idiot was who rebuilt the transmission for the previous owner, but I ended up installing helicoils in FOUR pan bolt holes and two for the tailshaft housing bolts.
They also used a hard setting silicone to glue the cover for the governor, the clip was too much hassle to replace I suppose.
It does make me question the integrity of the rest of the rebuild too ............

You don't even need the clip. The O ring itself is plenty. Obviously an idiot did it. I use an inch pound bar type torque wrench building transmisison. Most of those torque specs are only 12 foot lbs. so with an inch lb, I go 150 inch pounds and call them good. I just don't see how a foot pound wrench up to 150-300 foot lbs is accurate for 12lbs.

 

[Backfoot100]

Hearing horror stories like this is exactly why I make sure to start every pan bolt with my fingers before ever putting a wrench on them.
Clean the bolts beforehand too. Always takes a few a few extra minutes but soooooo worth it in the long run.
I learned my lesson way too many times before I got it through my thick skull.

 

[mtnmankev]

I was very fortunate in high school auto shop (1971 thru 1973) and I had the best teacher one could ask for.
He taught us "start all bolts by hand before tightening any" along with tons of automotive and laws of physics theory.
It has stuck with me to this day, I don't trust ANY auto repair shop.
I do all my own repairs if I am able, and if I'm not, I find somebody I can trust and I teach them myself.

 

[QBuff02]

when I was a kid, I remember helping my dad put the fender deck back on the riding lawn mower, I was so excited to help and I started putting the bolts in and gunned the first couple up when my dad stopped and started staring at me.. I remember looking at him and asking "what?" and he told me to come around to the other side because he wanted to show me something, needless to say not all the bolts would line up because I'd already started tightening it down albeit crooked, and he told me two very valuable things that day that have stuck with me. One being no matter the size of the hardware, if you can't start them and screw them in with your fingers there's something wrong. And two, always get all the hardware started before tightening anything. And as I've gotten older and followed into the career path of being a mechanic, I can't tell you how many times I've gotten pissed off because of some previous hackjob someone else did that I have to take apart and/or redo. because that was probably lesson #267- You gotta fix what you find wrong, even if it isn't the original problem you went in for. Case in point, how your little project turned into multiple repairs. Stories like this really grind my gears. LOL

 

[Backfoot100]

Yeah, I have a totally new appreciation for cleaning out threads too. Running a tap into every head bolt hole before I put my headers on made it a most pleasurable experience.
At the very least a shot of compressed air or a quick shot of brakeleen into a threaded bolt hole can be a life saver that I never overlook now.