# 67 GTO with leaking transmission; automatic



## jimmy328 (Oct 12, 2011)

I have leaking auto transmission; model turbo 400. I’m starting with the basics; oil pan gasket. There is a 4 inch plastic tube which connects to the filter with a rubber gasket then travels to an orifice within the trans. This end does not have any kind of gasket. Does anyone know if a gasket belongs here?

Also; is there an aftermarket tranny pan for this vehicle that has a drain plug? The original does not; therefore, tranny fluid spills everywhere.

Thank you,
Jim

I tried to insert a picture but received a script error…whatever that means. No time to trouble shoot this error; time is valuable; I’d rather get my Goat running.


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## geeteeohguy (Feb 2, 2008)

There is an "O" ring that goes around the plastic tube and holds it in place in the trans. Try the aftermarket for a drain-plug pan....


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## jimmy328 (Oct 12, 2011)

Continuing research I’m now realizing there are other areas of potential leak…rear seal, front seal, speedo cable, and modulator o-ring. What is a modulator o-ring? Where do I find it? Is that the plastic tube I referred to?


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## geeteeohguy (Feb 2, 2008)

The modulator is that canister looking thing the size of a spool of thread on the right side of the trans with the vacuum line going to it. The most common place for a TH400 to leak, in my experience, is the fill tube that attaches to the back of the right cylinder head and leads into the transmission. Very common for the O ring to dry up and let fluid slosh out and work its way down the trans around the pan (looks like a pan gasket leak). Be sure to straighten the pan rails so they don't dip between the holes (use a ball peen hammer and a solid backing for a dolly) and be sure that the pan rails are straight and clean. Do NOT over tighten the pan bolts (I use a nut driver a lot of times), clean, and re-check.


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## jimmy328 (Oct 12, 2011)

Thanks so much GTOTEE. I now know exactly what the modulator is and will replace this gasket. 

I notice a rail that encircles the pan and it looks fine; however, I am buying a new one with a drain plug. Perhaps from Summit; don’t know yet.

As for the fill tube removal; I disconnected the bolt near the back right cylinder. Should I use a rubber mallet from beneath the car to tap it out?

Your help is greatly appreciated.
Jim


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## geeteeohguy (Feb 2, 2008)

The tube should pull right out. A twist should do it. If a rubber mallet or a wood drift is needed, there you go. It sounds to me like this is new to you, but you have the good sense not to go in blind and seem to have the common sense not to force things. Excellent. Go slow, ask questions, and also, I'd recommend getting a reproduction '67 GM service manual, or a '67 Motors manual. That'll be a huge help. Also, don't get a chromed pan....they tend to leak prone. I would leave the shift shaft seal alone at this time. It can be a real chore to get it replaced, and if it does need replacing, it can be done when it's all back together due to its location with minimal fluid loss. Good luck.


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## pontiac (Mar 6, 2011)

a better approach is to put a clean cardboard down underneath the trans and figure out where the leak appears to be coming from. that would help narrow down the area to look at. However, if your trans after a road trip and has been sitting for awhile then is leaking, that happens to a lot of them. that actually is not a leak requiring a fix, that is due to inactivity and seals will stop leaking once the trans gets hot and is run for a time.


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