Tips for ensuring best possible seal on transmission pan?

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muzician21 - 01 Jul 2009 06:22 GMT

I've been trying to solve a leaking issue on a C-4 auto trans on a '66
Fairlane. I replaced the shift shaft seal, the bushings on the center
shaft, it's still leaking and as near as I can tell it's coming from
the mating surface of the transmission pan.

If the pan is sitting on a perfectly flat surface, ideally should the
gasket surface of the pan contact exactly flush all the way around? If
I place a steel ruler along the gasket surface and sight against a
light, there seems to be a very slight bending at a couple of the
corners. By slight I mean probably half the thickness of a matchbook
cover. Also I notice the area at the bolt holes is slightly raised.

Is an absolutely flush-flat all the way around configuration ideal or
should it be biased in a certain direction at certain points?

The guy at the parts house was talking up this "Right Stuff" silicone
in a Cheez-Whiz type can. Is a pre-cut gasket the best way to seal the
pan?

Thanks for all input.

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Toyota MDT in MO - 01 Jul 2009 06:38 GMT

> I've been trying to solve a leaking issue on a C-4 auto trans on a '66
> Fairlane. I replaced the shift shaft seal, the bushings on the center
[quoted text clipped - 17 lines]
> Thanks for all input.
>

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.

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Toyota MDT in MO

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twisted - 01 Jul 2009 13:12 GMT

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

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ben91932 - 02 Jul 2009 17:19 GMT

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

> Common practice is to ensure a straight gasket surface that is also free
> of nicks/gouges (this includes the transmission case surface). If the
[quoted text clipped - 15 lines]
> --
> Toyota MDT in MO

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muzician21 - 03 Jul 2009 06:00 GMT

> Common practice is to ensure a straight gasket surface that is also free
> of nicks/gouges (this includes the transmission case surface).

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?

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Vic Smith - 03 Jul 2009 07:08 GMT

>> Common practice is to ensure a straight gasket surface that is also free
>> of nicks/gouges (this includes the transmission case surface).
[quoted text clipped - 13 lines]
>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?

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:
http://www.permatex.com/products/Automotive/automotive_gasketing/gasket_sealants
/auto_Permatex_Form-A-Gasket_No_2_Sealant.htm

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

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Anumber1 - 06 Jul 2009 13:11 GMT

>>> Common practice is to ensure a straight gasket surface that is also free
>>> of nicks/gouges (this includes the transmission case surface).
[quoted text clipped - 48 lines]
>
>

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

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jim - 03 Jul 2009 17:22 GMT

> > Common practice is to ensure a straight gasket surface that is also free
> > of nicks/gouges (this includes the transmission case surface).

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.

> 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?

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.

> 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?

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.

> 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?

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

-jim

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hachiroku - 06 Jul 2009 04:00 GMT

> A quality gasket, proper torque, and smooth
> flat surfaces will make it *not* necessary to use sealer.

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...)

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Toyota MDT in MO - 06 Jul 2009 04:23 GMT

>
>> A quality gasket, proper torque, and smooth
[quoted text clipped - 7 lines]
>
>

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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Toyota MDT in MO

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Jim Warman - 01 Jul 2009 18:43 GMT

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.

> I've been trying to solve a leaking issue on a C-4 auto trans on a '66
> Fairlane. I replaced the shift shaft seal, the bushings on the center
[quoted text clipped - 16 lines]
>
> Thanks for all input.

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