Chuxter

I have a th400 transmission that I am having trouble getting the pan to stop leaking resealed twice. Thinking the pan may be warped. The question is if I install an aluminum pan is there any problem attaching the shifter cable bracket? The pans all look like they have an offset for reinforcement. Also is there any clearance problems with the deeper sump pans. It is in a 1970 Cutlass Supreme' stock ride height.

droldsmorland

IMO stick with the stock GM trans oil pan. Pull it, put it on a flat surface and look for the high/low spots. Chances are the bolt holes are proud of the gasket surface from years of over torquing. This can be fixed with proper hammer & drift techniques. Use a deep socket as a backer and gently finesse/rework the areas flat.

Or replace the pan with a genuine GM Delco TH400 pan. Do not use chineese junk....which ALL aftermarket is. A trans shop may be able to help find a true GM Delco. Lord knows my internet search produced nothin but aftermarket ocean freighter junk.

What gasket and sealer are you using? I have better luck with the black composite gasket or the high end rubber style. I use a thin coating of clear or "The Right Stuff" RTV on both sides. Let the RTV slightly skin up before laying down the gasket and bolting it to the trans.

Torque it to "just right". In other words not (re) warping the bolt holes. I have been doing this for 40 years and dont use a torque wrench. Its a feel just past snug. Let it sit dry over night or for at least a few hours before filling. You may need to go around the pan again after letting it sit then again after a few heat cycles.

Are you sure the pan is the leak culprit? Dont rule out the dipstick tube or speedometer seals. Clean the whole thing with brake cleaner then watch for the leak.

Olds64

I bought an aftermarket deep transmission pan from Summit Racing for the C6 in my classic Ford truck. It is the Summit brand and it is far superior to any OE pan (great build quality and it's not a cheapy).

If you decide to stick with the OE pan straighten the gasket surface as mentioned. I got the LubeLocker gasket for my C6. Here's one for a TH400. Per the instructions install it dry.

https://www.summitracing.com/parts/lub-llt-g400

Chuxter

I have been through the whole straightening it out on a flat surface. The leak was better but still there. I used the rubber gasket that came with the new filter and black rtv using the procedure called out on the rtv.Funger tight till it bulges. Wait an hour then torque and I did not fill for 2 days giving it plenty of time to cure. The leak is consistently near where the bracket for the shifter cable is.

matt69olds

I wouldn’t pay a dime for the cheap Chinese stamped steel pans, especially the chrome ones. As for the cast aluminum, I haven’t had any issues with them. I wouldn’t be surprised if they are all cast in the same foundry regardless of brand name stamped into them.

I have never had any luck with the rubber gaskets. Get a good cork or paper gasket. I recently did a 4L80 trans with a aftermarket cast aluminum pan and the shiny tan gasket, it took several hard hits with a rubber mallet to break it loose. They seal very well!

Before spending a lot of time on this, are you sure the pan is the issue? Make sure the case is dry around the shift shaft seal, the o ring on the dipstick tube, modulator seal, or the electrical connector for the kickdown solenoid. A leak around any of those is easy to mistake as pan gasket.

joe_padavano

https://www.lubelocker.com/products/...ssion-llt-g400

Chuxter

OK I have ordered the lube locker gasket. I will give it one more try. Don't you just love draining transmission fluid lol?

droldsmorland

Hopefully, you have the pan with the drain plug. If not a drain plug kit is available to install into the existing pan. Makes the job 50% easier & neater.
Now you can drain and fill in between filter changes to always keep the oil fresh.

Chuxter

No plug, factory pan. Where do you find this plug you can install? Also ordered a tool to change out the gear selector seal just to be safe

droldsmorland

Search the usual parts sites or get friendly with a local trans shop.
You can purchase the plug kit from any of the usual suspects. And as you know the aftermarket pans come with a plug (most).
I will TIG weld the bung into an existing GM pan(best practice). But they say the home-brew method of using the seals with the kit works too. Makes trans service a breeze.

oldcutlass

The pan has to be perfect to use this gasket.

matt69olds

droldsmorland

Jez-us I cant find an OEM TH400 smooth pan! Last time I bought one I didnt have a problem...early 2000s.

joe_padavano

Not particularly. It's a metal core neoprene gasket with silicone beads on it. I've found them to work quite well. I used one on the far less than perfect rear cover when I put the TruTrack in my truck and it never leaked a drop.

joe_padavano

You can pay Corvette restorer prices...

https://www.corvettecentral.com/c3-6...oil-pan-533064

or... $5 for a used one on C-list

https://losangeles.craigslist.org/sf...735008878.html