HELP...Leaky Ass 350 Trans Pan/Gasket

Ok, I have tried just about everything now, still have a leaker. I have a 350 turbo trans, got everything all bolted up and filled with fluid, had a small leak. figured the old gasket was shot so pulled off the old stock steel pan. They are thin and fairly flimsy, so I figured get a nice thick finned aluminum walled one and a nice thick cork gasket to seal it up. A small bead of RTV on top and bottom of cork (maybe thats the problem) got it all buttoned up, followed the pattern, not over tightened or under tightened, it has alan heads, so just hand torqued it. It sits in my garage for a couple weeks, seems to be sealed, I am gone for vacation for a week, come back, nice puddle below. So what now? Any ideas, I hear the 350s all leak, but this is nuts. Try a felpro rubber gasket? I have one,but ist is fairly thin, seems cork would have been better. Or do I have another problem? Its definitely at the seal, nothing from in front or above. Thoughts?

 

Check around the dipstick tube sometimes seepage there trickles down to the pan and "tricks" you,very common.

 

Also check the shift linkage seal. They are famous for leaking.
KD tools makes a nice simple tool for changing the seal. Just remove the linkage and pull the seal.



The number is KD 2393 ...
About 10 or 12 dollars for the tool.

 

Mine doesn't leak, so don't buy into that.
Is there a rubber gasket available like the newer style valve cover gaskets? I started buying those and made leaking valve covers a thing of the past.

 

The shifter shaft is right above the panrail, which looks like a pan leak. Look reeeeal close and you can spot it. MAKE NO ATTEMPT to change the shaft seal without the KD tool...if you scratch the case or the shaft trying to get it out any other way, you are fucked.

Ask me how I know....


Good luck, -Abone.

 

Leaking like that after sitting a while is not the pan gasket, it's something higher.

Shift linkage
Kickdown Cable
Speedometer Drive
Governor cover
Pump O ring
Rear seal

are all likely suspects

 

I have the same problem, went with the alum pan,but you need to put a coating on the pan as its porous. I did and it stopped that leak, now its the shifter seal. Thanks for the tip on the tool D/R.

 

FYI, in case you decide to change the pan gasket.
http://www.summitracing.com/parts/MOR-93102/

 

If you're certain it's the pan gasket, Permatex makes a a special sealant for automatic transmissions.

http://www.permatex.com/documents/tds/Automotive/81180.pdf

 

What he said ,just happened to my dads 56 changed the o-ring at dip stick tube and fixed it we thought it was a pan gasket at first would leak after sitting a few days

 

..
Is there a system ck valve for the convertor? I have a 350 trans that has an intermittent 3-5 qt leak if not driven weekly, otherwise dry. It sure makes a mess. Been chasing it for years, dose have a cheap chrome filler tube with new o-ring. Acts like the convertor is leaking back into the pan thus overfilled leak. Any one have a diagnosis?

 

If it is leaking around the dipstick seal and it's an o-ring, you might want to try using the later "boot" style or multi-lip seal.

 

Blue RTV isn't compatible with tranny fluid. Bill

 

The factory doesn't use rtv, so whats up with that? I agree with these fellas, you need to carefully identify the source of the leak. There are much better gaskets available other than cork. Clean, clean, clean equals no leak. look for wetness around the seals above the pan gasket.

 

Early dipstick tubes ('77-back?) had a "groove" rolled around the end of the tube to locate the o-ring. Later tubes ('78-up?) did not. If I remember correctly you can use the multi-lip seal on either style. But don't try using the o-ring on the later style tube.

Seal GM# 1259475 should be less than $4.00 at most GM dealers.

 

went to O'rileys after looking up seal, @ .79cents and it is pioneer part no 760014-5

 

if someone told you all TH350's leak they are a LIER!

i see you have many replies as to where to look for the issue, hope you find it and prove to have a th350 that doesnt leak

 

May want to pull the flywheel cover and make sure the front pump o ring is not leaking.

 

He might have done it over a year ago when the thread started?

 

Saltflats got bored this morning and started on the back page rather than the front.

 

Yeah and I haven't even been in the beer yet.

 

Well, Hey! I hadn't heard of that dipstick seal until now, either.
That's what happens when one devotes all his time to blacksmithing and fabbing brackets.

LOL Thanks for that tip!

 

NEVER use a cork gasket or sealer. Go to a good transmission shop and buy a black neoprean gasket. Clean parts and make sure the holes on the pan are not dimpled. Use hammer as necessary. Install gasket and pan ( no sealer ) and torque the bolts to 13 ft lbs. Torque twice. Use original bolts if you have them. If using allen head, place a good OD washer on the allen bolts.
Also, as mentioned above, the boot on the dipstick tube is much better than the o ring.

 

lol...... I always heard that the torque converter would drain down,push fluid out the front pump seal after setting for 3-4 weeks. any truth to this year old mystery????

 

Cork works fine. Just don't over torque and tighten the bolts in a pattern. Just like valve cover gaskets. Hey! It's traditional!

 

My theory on that is that the torque convertor seal will deform slightly and let a quart or two out when setting for long periods on some cars. Tolerances are probably borderline on the ones that do, a little tighter on the ones that don't. Usually top them off and fire them up and drive them and they won't leak a drop.

 

Old thread I know....but just an FYI.
I use to work at a transmission shop back in the late 80s. I have a lot of experience fixing leaks and fixed a lot of leaky Turbo 350s that nobody else could seem to fix. The shift shaft seal is a very common leak point and it does appear to be leaking from the pan gasket when it leaks. The steel pans are also a common leak point because the bolts usually get over tightened trying to stop a leaking pan gasket when its actually the shaft seal. Over tightening the pan bolts when using a cork gasket puckers the bolt hole until it makes contact with the trans case making it impossible to keep the pan from leaking. So now you have two leaks. Once I figured this out I started using the black paper gaskets and every steel pan I encountered I would flatten out the pucker around the bolt holes. When installing you just need to snug the bolts up. They don't need to be that tight. Never had another one leak after that.
When replacing the shaft seal its best to use the tool because the sharp edge on the shoulder of the shaft at the end of the threads will nick the new seal almost every time. Its very difficult to install a seal without damaging it without the tool.

 

The use of OE dip stick tubes help cure leaks also. You can cut the tube to fit. Put heat shrink on the cuts as you adjust to fit. When done cut holes in the heat shrink and tack weld. Remove the shrink and finish weld. Measure the tube before you start. When done remeasure and cut dip stick down the same amount as you removed.

 

mine does that, let it set for a month,it leaks about a quart. if I go out and start it up,about once a week, bring it up to operating temp, not a drop.

 

FARPAK..........love 'em!