Help, can't get C4 trans pan to seal

[66coupe351]

I would appreciate any pointers anyone can give on how to get the pan on my C4 transmission to seal up. I think I've now redone it 6 times, and it is still leaking.

Has anyone else had anywhere near this much trouble getting the pan to seal up and no leak?

My technique:
1) Using a new gasket(tried both cork and a black rubber) and the gray gasket sealer.
2) Clean the pan and trans surfaces thoroughly - first with degreaser, then with soap, then with just a wet rag. Let dry.
3) Put a layer of gasket sealer on the pan, lay down the gasket, put a layer of gasket sealer on top of the gasket. I've been using a fair amount of sealer - enough that it presses out a little when I install the pan.
4) Install the pan with all bolts making snug contact, but not really tightened down.
5) Wait 24 hours, snug down the bolts, add trans fluid.
6) Look under the car an hour or a day later and see that some fluid drips are collecting in a couple of different places and slowly dripping onto the floor.

The last time or two I've also used a new trans pan. This one is much thicker and stiffer than my old one. I thought that would allow it to seal better, but it didn't make a difference.

I also made one attempt WITHOUT a gasket, just the sealer, and that leaked even worse.

 

[biggyfan1]

what weird is that i have a brand new c4 from TCI and it is not even installed on the car and mine is doing the same thing. i see that it is wet with fluid between the pan and trans. i wipe it off real good then go back out a day later and it is wet and even drips a little. and whats even weirder about mine is that the only fluid thats it in is the stuff they put in it to test it. so its really empty with just a little fluid here and there in pockets that couldnt be drained. i hope its not going to get worse when i install it but i bet it will need a diaper. im looking for the same answers guys thanks.

 

[68keyblr]

Me 3

 

[shhak]

I had a c4 that leaked like that. I finally put a bead of the blue RTV silicone about 1/2" wide and fairly thick on the pan, set the gasket on the sealer and took some thread and used it to tie the gasket in place on all 4 corners. Then I put another thick bead of silicone on top of the gasket and put it into place. I tightened the bolts as tight as I thought I could possibly get by with. And let it set of about 2 days before adding fluid. It did seal, but if you ever have to pull the pan off again, it makes for a heck of a time cleaning things up before you can put the pan back on.

 

[chromedog]

has the pan at sometime been overtightened, and distorted the boltholes? you can look closely at the holes,and see if the rail is no longer perfectly flat. if so, you need to either take a ball pein hammer, and flatten the rail back out, or get a new pan.

 

[66coupe351]

OK, so sounds like having problems getting a C4 pan to seal up nicely might be somewhat normal. I'm a little happy it's not just me, but concerned that I'm not ever going to get the pan to seal.

chromedog: My previous pan was a little wavy along the gasket surface area - the area where the bolt holes were was a little high and in between was a little low. I've used a new - thicker, perfectly flat - pan the last couple of times and am still having just as much trouble getting it to seal properly.

I can't imagine what it would be, but I was hoping that someone would have some 'trick' to get this work seal up properly.

 

[dennis112]

You may want to look at other possible leak locations, such as the dipstick O-ring, shifter rod, or high pressure lines. Wash the whole tranny down until it is all dry, put the car up on jack stands, and then see if it leaks. Let gravity take over and do a careful inspection. Mine ended up being a leaky O ring used on the front pump.

From the school of hard knocks--I caution anyone who uses silicone to be careful. The stuff can break loose and cause havoc with the various parts of the valve body.

 

[GoinBroke]

As Dennis said degrease and inspect carefully. It may be leaking past the shifter arm as the convertor drains while it sits. Good luck!

 

[66coupe351]

Thanks for the replies, but I'm fairly certain it is leaking from the pan seal area. I don't know for certain that it is, but that is where the fluid is visible, and I've tried inspecting above the pan seal - as well as I could - to try and find a higher leak. So far it really appears to be the pan seal.

Also, I am not driving, or even starting the car between when I replace the pan and when I see the leak - it is up on jack stands.

I suppose it could be leaking at the fill tube. What other seals or leak points are below the fluid level?

 

[Great68]

I am having the same problem as well. My pan started leaking, I replaced the gasket 3 times, the last time I bought a new B&M cast aluminum pan which is really thick and will not warp, but still get leaking.

I am now certain the fluid it is coming from my front pump, dripping down and appearing as though the pan has a leak.

 

[jadesville]

Add me to the list too as well.

I'm actually trying to solve this problem as I speak too as well. I thought it might have been the gasket, changed the gasket, leaked worse. I first had issues with the pan rail being warped, tried to flatten it, it stopped leaking for a day, then it started leaking at 2 corners. Bought another pan, finished leaking but now my dipstick tube o-ring is leaking.

Now i'm afraid if I fix the dipstick tube o-ring that the pan is going to start leaking again.

 

[guevara42]

Alrighty fellas, here's the cure. I replaced mine not too long ago and it is drip free, dry as a bone. Remove the pan and clean the contact points, let drain for two days, put a cork gasket with hi temp sealer(fair amount) on the pan. spray a rag with lots of wd40, this stuff works great as a degreaser and dries quick. Once dry put some hi temp sealer on the tranny contact point. Then put the cover on and tighten to approx. 12 ftlbs. let sit for another 24hrs. add fluid next day and you're golden. It worked for me, hope it works for you.