Tips for ensuring best possible seal on transmission pan?

Common practice is to ensure a straight gasket surface that is also free of nicks/gouges (this includes the transmission case surface). If the trans was designed for a pan gasket (it was) then use a gasket. I'm partial to cork/rubber gaskets that are heavy on the rubber for trans pan applications. Some might call it neoprene specifically. Different brand filter kits will have different quality gaskets. While a new pan might be your best solution, attempting to straighten the corners and tapping the lipped bolt hole areas flat again could possibly yield a proper sealing pan. Torque spec is 12 ft/lbs from what I can gather (my info doesn't go back that far). Tighten the bolts in a few passes, starting at two middle bolts across from each other, then go to the next pair on either side, and so on, until the entire pan is snug. Then repeat a couple more times with increasing torque until you make the final pass at 12 ft/lbs. I'm not a fan of sealer if it isn't necessary on or around transmissions. A quality gasket, proper torque, and smooth flat surfaces will make it *not* necessary to use sealer.

Clean gasket surface. Main thing, don't over tighten!

It is common to see the bolt holes in the pan dished from being over-tightened. These can be repaired by careful reshaping with the ball end of a ball peen hammer. In 66, the factory installed gasket was cork.

I refuse to use silicon on an automatic transmission pan - however, if this is something you plan on doing anyway, avoid over application and allow a full day of cure time before putting the fluid in. silicon can "string" in oil - not a good thiung in any transmission.

Don't forget to check the trans vent to be sure it is clear.

This is one app where I dont think a torque wrench is a good thing. I always tighten with one finger on a 1/4 drive ratchet, and watch the gasket closely. As soon as the visible edges of the gasket begin to barely squish out a little bit, stop. HTH and good luck, Ben

How flat is flat enough? If I'm checking the contact surface of the pan with a metal straight edge, how close to machined flat - i.e. no gaps visible when checking with a backlight should I aspire to?

What about flattening the overall surface using a straight wood piece about as long as the pan (between the curves at the corners obviously) just narrow enough to fit under the lip of the pan on one side and another flat wood piece driven with a small sledge to work the surface? Is there a better way?

I've been lowering the raised bolt hole areas using a ball peen and a piece of wood on the other side of the lip as a dolly - is flush flat at the bolt holes ideal or would it be better to have them actually a bit lower, maybe to compensate for when the bolts are torqued?

On Thu, 2 Jul 2009 22:00:16 -0700 (PDT), muzician21 snipped-for-privacy@yahoo.com wrote:

You can only do so much with a pan, and it seems you've done it. If the pan lip is weakened so much that it flexes between the bolt holes under proper torquing and still leaks, you have to either use a dope, reinforce the lip, or get a new pan. to the point you still leak. You just might be worrying too much about "flatness." It's not a precision fit, and a good gasket and proper torquing should do it. I replaced a Grand Am pan gasket that was leaking about a month ago, and snugged it up to just squeeze the gasket a bit. Didn't bother with a torque wrench. It was seeping a few drops the next day after a test drive and I went over the bolts again and got about quarter to half a turn out of them to get to the first tightness, as the gasket had flattened a bit. Neoprene. Been dry since then. I'll check again that the bolts are snugged next time I jack it up. But I wouldn't hesitate to dope it if it gave me a problem. I'd use this:

Everything perfectly clean, l'd lay a bead on the pan lip about 1/4" wide and 1/8" deep, lay in the gasket then the same bead on the gasket. Snug the bolts up from the center of the pan out, alternating sides, in maybe 3 passes. Then I'd give it 24 hours to cure before refilling with trans fluid. That's always worked for me for beaten up trans/oil pans and valve covers. If it leaked after that I'd never touch a wrench again. Because that would mean my mojo is gone and a car will fall on me.

--Vic

The main thing is that if you put it on a flat surface the areas where the bolt holes are shouldn't be the where it is making contact. Typically if the pan bolts have been repeatedly tightened for 40 yrs or over tightened the areas around the holes will contact the flat surface. That is not good. You need to peen those areas to fix it. If the areas between the bolt holes are making contact that is good because it will flatten out when the bolts are tightens.

Doesn't need to be any closer than maybe .02" to flat just as long as the high spots (when inverted) are not at the bolt holes.

You can put the edge of a board on the side where the bolt heads go and lightly peen from the other side to knock down high spots.

bit lower is a good idea if it is just a tiny bit.

-jim

But a bit of FIPG never hurt...

I usually put a thin bead on both sides of the gasket. Just for the types of things you described (scratches, etc...)

Have you seen it get into the bore of a shift solenoid? I have, on a Toyota, FIPG used foolishly, and it caused a loss of several gears.

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Permatex #2... Best shit ever! Well, Hylomar is good stuff for hoses and water connections too.