. C4 transmission pan sealing

[66hcs-conv]

How can I get the C4 pan to stop leaking?

I have purchased a new pan & gasket, got everything torqued to specs, but a couple of the rear bolts on the pan continue to leak.

What am I missing here?

Would appreciate any help - thanks, Dave

 

[dalorzo_f]

Usually it is the pan lip, over-torqued in the past and the lip is deformed. Odd it would happen on a new one. If the case flange is not fully clean and scraped it may be a cause.

Pull it, gently hammer the lip flat if distorted and it should seal. I use a small piece of flat steel bar as a mandrel and hammer against a large flat of a bench vise to limit thinning/distortion.

A small amount of non hardening gasket sealer can be used in a pinch, just be sure to use it sparingly and only around the outer edge on the pan...

 

[robert campbell]

So I assume this in your 1966 Mustang? I just have been to this rodeo on a 1965 green dot cruise-o-matic.

First the easy stuff. I hope your new pan gasket is of the solid rubber type and not the paper ones. Most of the new kits have the new rubber ones. A trick to help is to take the pan to a vice with a 1 inch wide flat piece of steel camped in and hole the pan rail on it a use a hammer to "beat" the pan hole dimpling back to flat. Most of these pans have been over tightened through the years and the pan is not flat around the bolt holes. This will aid in sealing to the new gasket.

Second is to correctly identify the leak. If you were on my 4 post lift this is fairly easy. The dip stick tube has an o-ring and they are prone to leak. make sure this is not the leak. I tell you that ATF will travel all over the place.

Third is the shift shaft seal. This gets harder as you need to drop the valve body off to service it. It is on the left hand side of the tranny and you will need to lower the transmission to remove the shaft and replace the seal. This job is fairly easy, but not to the novice I am said to say.

Now the bad one. If your dip stick shows high fluid level when cold, you may have a stuck torque converter drain back valve. In the early C4 this valve is in the front pump. What happens is it does not seal and the torque converter which holds around 8 quarts drains back into the tranny. This fills the tranny above full and the fluid comes out the vent tube that is in the top of the tranny and drains out on the left side aft of the shift shaft area. It will leave a nice "pond" under your car. It is again easy to se on my lift and this is what was happening to my latest customer car. The fix in this case is basically a complete rebuild as you have the tranny out and down to parade rest a bit.

Get under you car and clean every area around the pan as best you can. Drive it and go under again. It is amazing how the fluid travels around. What you may thing is a pan gasket leak may be from somewhere else.

Rob

 

[Mosesatm]

If the leak is coming from the pan it may help to spread out the load with some valve cover washer thingies after flattening out the bolt holes.

 

[66hcs-conv]

THANKS for the replies, lotsa good info there.

The red transmission fluid is dripping off two of the rear pan bolts, and only two. It will leave about a 1/2 dollar size puddle on the floor in 2-3 days. I have checked the shifter rods and the fill tube & they appear well sealed. I have tried no sealer on the gasket, and using a blue silicone sealer - no help. The gasket I am using is the rubber type.

Will the valve cover "washers" that Mosesatm referred to work on the xmission pan, and where can I get those? I've thought of making a 1/2 inch wide piece of steel with 3 correctly spaced holes for the rear of the pan, and use that to distribute the tightening of the pan bolts.

Thanks, Dave

 

[Mosesatm]

I think they are a standard big block Chevrolet item so any auto parts store should carry them.

 

[robert campbell]

I would still try to flatten out the dimpling around the pan bolt holes. Yep, that means dropping that pan a 4 quarts of fluid once again.....

But you can try what Arlie shows. Or go to you local hardware store and buy a piece of 1/2 by 1/8 thick flat stock. You will more than likely need a bit longer bolt. Remember the pan case is aluminum and if the bolt is to short you can strip out the first few threads and then hate yourself!!

And if the bolt is too long it beds down in the end of the hole and does not tighten. You can stick a pencil in the hole to check depth and mark it.

There are some aftermarket aluminum pans that increase your capacity a bit and seal much better. They do hang down a bit and can be hurt on a large speed bump with a low car.

I put a TCI Aluminum pan of this current car. Found out that there is a small change between the 64 to 66 C4 and the 1967 and later C4. You have to elongate one hole in the pan to make it work. But it seals much better. About $130 bucks.

Rob

 

[66hcs-conv]

gonna try this

I put a flat piece of metal on its edge and laid it along the back of the pan and it doesn't appear that the hole's have been dimpled.

I made this piece of metal & got it installed, so will give it a try.

If this doesn't work I will get one of the cast pans like Rob has suggested.

THANKS for all your help, Dave

 

[rvrtrash]

Just to throw it out there, we're sure it's not the tailshaft to housing seal that's leaking and just showing up on the rear of the pan, right?

Steve

 

[robert campbell]

If the convertor drain back has failed the fluid will show up on the back two bolts on the driver rear corner of the pan......

One sign of this is the fluid level with the car off after sitting for a day or two is about 4 inches above the normal full mark.....

Hope the pan thingee works!! Before you invest in a pan get a good eye on the vent tube on the top of the tranny on the left side. The automatic I have was "clean as whistle" just below that tube!! From quart after quart of leakage for a quite a few years.

Rob

 

[66hcs-conv]

With a cold engine & trans, I checked the fluid level this AM & it is about 3/8' above the "Full" mark on the dipstick. Nowhere near the level that Rob has described with a failed converter drain back.

After a 7-9 mile drive yesterday, the back of the pan (where it was leaking) & where I installed the metal piece, is dry. Given this cars history of being incontinent I'll take this small victory, and check it after a longer drive.

Again, thanks for all you help, I really appreciate it. Dave

 

[robert campbell]

GREAT!!! I am just putting in this failed (now rebuilt) C4 today. Nothing like a simple fix and cheap also!!! Bask in your victory!!!

Rob