Stock TH350 Pan

[geunther]

From what I understand no TH 350 came with a drain plug from the factory. The confusing part about this pan is that it has a date stamp consistent with GM date stamps. Also the date would be consistent with coming on the truck originally but I guess that cannot be accurate.

Anyway, I cannot get the thing to seal no matter what. When I tighten it enough to seal (about 14 foot points), it pushes the gasket out as you can see in the pic. The pan has a ridge about half way on the flange between each bolt. I am wondering if it is splitting the gasket. I am considering ordering another pan without the ridge but wanted to get your input first.

I had both surfaces spotless.
Rubber gasket

[geezer#99]

Keep that pan.
Use a ballpeen hammer and tap the bolt holes on the top side back downwards. Don't make the holes flat, move them downward.
Then install it.
Looks like the gasket is squeezed out at the bolts only.

[Gromit]

I had a similar problem - for me it turned out to be scratches in the (steel) pan sealing surface (from the previous owner of course).

The pan has a very tight fit between it and the transmission; and depending on the condition of the transmission rubber mount to cross member...

As that trans mount wears, it permits the transmission pan / cross member clearance to go less than zero (if that makes sense). So in other words, if the mount is worn in order to get the transmission pan off you have to loosen the trans mount bolts or nuts and then lift up on the tail shaft when you remove the pan (to get the back edge of the pan out from between the cross member and the aluminum of the transmission housing.

If someone is not aware of this interference, they may try to force that side or edge of the pan out from between the cross member, and this will create gouges in the gasket mounting surface of the pan. The gouges don't need to be very deep to let trans fluid leak out... if you have a good 5x jeweler's loupe look at the pan sealing surface on that side again...

I sanded my pan with 400 grit to clean up the gouges and then RTV's the gasket to the pan (not to the trans of course)...

Hope that helps..

[Gromit]

I should have wrote "tight fit between it and the transmission cross-member"

[kwmech]

Follow instructions above for the pan flange, ditch the rubber gasket and get a quality cork one and don't use any type of sealer or silicone. Install and torque pan to 100 INCH pounds.


And yes the pans did come with a drain plug for quite a few years until some number cruncher decided they could save .02 per car without it

[geunther]

I did loosen the crossmember bolts and lift the tail shaft up a couple of inches. The surface looked in great shapes, not scratches etc. I will try bringing the area around the bolt holes down a bit and install a new gasket. I did check the pan for flatness and it seemed true.

This cannot be a stock pan though, correct?

[kwmech]

It's a stock pan. If the pan is that close to the x-member, what shape is the mount in? When they are that close, the mount is usually squashed down and needing replacement

[Gromit]

KWMech is right on about no sealers - I only used the thinnest possible RTV coat to fill the gouges in the steel pan sealing surface that could not be sanded out. Normally you don't use RTV or sealers on the gasket and especially not on the trans side of the gasket. You'll have a mess if that RTV oozes out inside the trans pan and chunks of it manage to get past the filter and into your valve body.

[hugger6933]

14 Foot pounds of torque in itself is enough to make a rubber gasket fail that is more than what I would even call German torque[goodentight]. Yes that is a factory type 350 pan. I would bet that a hammer and dollie and a few light taps will fix this problem. Jim

[geunther]

The mount seemed ok, though I am sure it is somewhat compressed after 43 years. Am I understanding correctly that if the mount is in good shape there is room to get the pan out without lifting on the tail shaft?

I did even have a hard time getting a socket in there for the back two bolts. I had to go to 1/4 drive with a universal ( wobbly). Once I got the bolts off I still could not get the pan out until I lifted on the tail shaft.

While I got you here, should the oil level be above the gasket area? I believe the dip stick is a replacements and it was too long. It would hit the pan and spring up about 1/2 inch. I trimmed the bottom a bit to clear the pan but I don't trust the markings. I know where the bottom of the dip stick is and can measure up from there and place a mark. I just need to know how high from the bottom of the pan should the oil level be.

[Gromit]

Actually I don't know if a new mount will correct the interference with the cross member - I did buy a new mount but it is not installed quite yet.

If your current transmission mount is really the original 1972 and this is 43 years old I would definitely suggest a new one; it is Anchor Industries (Korea) #2378 for my TH350 and 1970 Chevy C10 Longbed - and the price is... are you ready? $4.97

Yep; less than $5 from Summit - and they really get on it you place an order IMO.. for me it is here the next business day from Nevada..

[fp1967]

In your original post, you mentioned that you didn't think stock pans came with drain plugs. From what I've seen, every TH350 from 72 and older came with drain plugs. This applies to both cars and trucks. Back in the 80's and early 90's, when you would buy a filter kit from the local parts stores around here, the kit came with a new drain plug gasket.

[Gromit]

I don't know about the history; but my 1970 C10 and TH350 had no drain plug.

There is a provision for a drain plug on the metal pan press die forming though. It is a flat spot visible in the photo of the pan at the beginning of this thread.

I ordered a Dorman #65128 Drain Plug Kit for $6.97 from Summit (to whom I have no connection other than buying stuff once in a while). It is a simple hollow bolt and thin hex nut and two nylon washers that make it a lot les messy to change your AT fluid.

Also the 1/8" pipe thread plug in that Dorman part will permit the connection of a trans fluid temp gauge if you are the nervous type like me.

[geunther]

Just wanted to thank all for the recommendations on sealing the pan up. I was able to straighten all the sides and worked the bolt holes down a bit. Installed a cork gasket with only a little copper to tack the gasket in a few spots.

Unfortunately it did not cure all the leaks. The spark control switch was leaking too, but I got that fixed now and so far, leak free. Thanks!

BTW maybe next time I won't use my wife's counter top's flat surface to check for trueness.

I tightened to 90" pounds