Trans Pan Sealing

FENDERFAB

FENDERFAB

Well-known member
Joined
Apr 14, 2022
Messages
219
Hey Guys,

Looking for some insight here i can not get the trans pan to seal on my TH400.

I had my trans rebuilt at Maximum earlier this year. Originally we kept the oem pan and a new cork gasket. Right when i installed the pan and put the trans in the truck it started leaking. Next we went to a New moroso pan- figured the oem pan was bent/worn and not sealing properly. Installed a new BLUE moroso gasket. Still leaking. Thought possibly the gasket was bad. Tried another new BLUE moroso gasket, still leaking.... Next cleaned the blue gasket and installed it with The right stuff Black rtv on both sides and it again leaked. Last try was no trans pan gasket and a thick layer of the right stuff rtv on both sides. Installed it with the bolts just tight enough to hold the pan on, i let the sealant dry for 3 days and then snugged up the bolts. Lasted for 1 trip and its leaking again.

Any of you have any insight? I am so tired of this thing leaking, its leaking a good amount. I have a small puddle every day i have to wipe up. If it means anything i am running the B&M trick shift fluid.
 
I've never had an issue sealing up trans pans. I never use any type of RTV as is usually gets broken down by atf.

Personally I'd go with a reusable gasket like the lubelocker, ATP, or factory GM. I've never used that moroso gasket but most everything I've even seen from them is junk.

You've probably already done these things but put the pan on without a gasket and make sure something isn't stopping it from seating all the way.

Make sure the surface for the gasket has no burs.

Make sure your bolts are not bottoming out in blind holes or have a shoulder stopping them from clamping down on the pan.

Check the speedo hole, dipstick tube, modulator, cooler line fittings, and below the converter for leaks. I've had people claim a pan was leaking when it was one of those.

Cooler line fittings are straight pipe, not taper. Getting tapered fittings to seal without damaging the case is difficult.

Use a UV dye (gm makes a good one) and a ultraviolet light to see if the atf is leaking from a crack in the case. It does happen.

Also, if you have a huge trans cooler mounted really high up, you may be getting train back filling the case and coming out the vent. If the vent doesn't have a piece of hose on it add one so you can see if it's coming out of there. This is also good to keep atf away from the exhaust when the trans gets really hot.
 
Philo this is all great info! Thank you!

For the cooler, i have the -6an adapter fittings, running back to my cooler is mounted in the back window. I am running the large CBR cooler. I do have a vent on the trans that runs all the way to the back of the rear bumper and have not seen any fluid leaking out of that.

I will review more this evening and get some more pics and info!
 
I'm curious what works too. Mine has always been black RTV'd on but eventually leaks closest to the exhaust which runs a little too close. Tried a cork gasket from a rebuild kit that didn't ever seal, a few different pans, even bought the expensive Toyota black RTV but eventually starts to leak from what looks like the entire perimeter. I have seen pans sealed with orange RTV and was wondering if the chemical resistance has something to do with it?
 
Motiracer38 said:
I'm curious what works too. Mine has always been black RTV'd on but eventually leaks closest to the exhaust which runs a little too close. Tried a cork gasket from a rebuild kit that didn't ever seal, a few different pans, even bought the expensive Toyota black RTV but eventually starts to leak from what looks like the entire perimeter. I have seen pans sealed with orange RTV and was wondering if the chemical resistance has something to do with it?
Click to expand...
It says the orange is for higher temp applications so that may work for your problem where its getting hot.
 
I have the best kind of gasket. What trans pan do you have? If you're close I probably have one in stock.
 
Shit! You shouldn't have any issue with an aluminum pan. IF.....you use the right gasket and don't overtighten. Let me know if you need a gasket man.
 
Permatex 81180 is what I use to seal 4L80, 4L60E, and Alison connectors from leaking.

It's the only sealant that I know of that stands up to ATF.

If the seals are getting hot enough to fail you need a stainless heat shield or exhaust wrap because it's also cooking your fluid.
 
Motiracer38 said:
I'm curious what works too. Mine has always been black RTV'd on but eventually leaks closest to the exhaust which runs a little too close. Tried a cork gasket from a rebuild kit that didn't ever seal, a few different pans, even bought the expensive Toyota black RTV but eventually starts to leak from what looks like the entire perimeter. I have seen pans sealed with orange RTV and was wondering if the chemical resistance has something to do with it?
Click to expand...
The Toyota black isn’t compatible with ATF, the orange is ATF compatible according to Toyota.


On to the OPs question, you’re 100% sure it’s the pan leaking and not the front pump and running down the lip of the pan? I’ve never had a problem with th400 aluminum pans but I have had more than 1 pump leak that was initially thought to be a pan leak.
 
84Prerunner said:
The Toyota black isn’t compatible with ATF, the orange is ATF compatible according to Toyota.


On to the OPs question, you’re 100% sure it’s the pan leaking and not the front pump and running down the lip of the pan? I’ve never had a problem with th400 aluminum pans but I have had more than 1 pump leak that was initially thought to be a pan leak.
Click to expand...
Im going to check again but im 99% sure its leaking on the very back of the pan closest to the tail shaft.
 
the bodj said:
Was this ever resolved? I'm dealing with the same thing on my 4l80
Click to expand...
Its been ongoing.

So i sealed the pan without a "gasket" and used The right stuff on the pan and the trans side and bolted them together. This was prior to the last leak. It held together for about 2 months and developed a leak which has steadily gotten worse. It is leaking from the back of the pan.

I believe i have found the issue- Many RTV style sealants dont do well exposed to ATF. Apparently ATF has something in it that slowly degrades the rubber/gasket material thats in the rtv.

Currently i am trying to get the pan off and its been a nightmare. I cant get the pan to let go from the trans. I am currently using a gasket seperator tool but im having a really difficult time to get it between the pan and the trans case. I had this same exact issue when I had to remove my third member from my housing when i did my last gear change. Absolute nightmare.

Once i get it off, i am going to re seal it with Permatex orange Trans pan sealant and give that a try. First i gotta get this fuckin pan off though.
 
FENDERFAB said:
Its been ongoing.

So i sealed the pan without a "gasket" and used The right stuff on the pan and the trans side and bolted them together. This was prior to the last leak. It held together for about 2 months and developed a leak which has steadily gotten worse. It is leaking from the back of the pan.

I believe i have found the issue- Many RTV style sealants dont do well exposed to ATF. Apparently ATF has something in it that slowly degrades the rubber/gasket material thats in the rtv.

Currently i am trying to get the pan off and its been a nightmare. I cant get the pan to let go from the trans. I am currently using a gasket seperator tool but im having a really difficult time to get it between the pan and the trans case. I had this same exact issue when I had to remove my third member from my housing when i did my last gear change. Absolute nightmare.

Once i get it off, i am going to re seal it with Permatex orange Trans pan sealant and give that a try. First i gotta get this fuckin pan off though.
Click to expand...
Can't fit a chisel in between the pan and trans? A really sharp one, with the flat edge against the trans and slowly work your way around it
 
FENDERFAB said:
Its been ongoing.

So i sealed the pan without a "gasket" and used The right stuff on the pan and the trans side and bolted them together. This was prior to the last leak. It held together for about 2 months and developed a leak which has steadily gotten worse. It is leaking from the back of the pan.

I believe i have found the issue- Many RTV style sealants dont do well exposed to ATF. Apparently ATF has something in it that slowly degrades the rubber/gasket material thats in the rtv.

Currently i am trying to get the pan off and its been a nightmare. I cant get the pan to let go from the trans. I am currently using a gasket seperator tool but im having a really difficult time to get it between the pan and the trans case. I had this same exact issue when I had to remove my third member from my housing when i did my last gear change. Absolute nightmare.

Once i get it off, i am going to re seal it with Permatex orange Trans pan sealant and give that a try. First i gotta get this fuckin pan off though.
Click to expand...
Ha ha get a metal scraper; something like this: https://www.grainger.com/product/38...bwEwi4HH85SpuVNOXTBoCp_wQAvD_BwE&gclsrc=aw.ds

Also don't use any sealants...they suck and are a pain in the fuck to get off and make a mess (as you have experienced) lol.

Trust me. Use a fiber gasket.
 
Props goes to @Klever - The trans pan gasket you sent me has solved the issue!

I havent driven the truck yet, but i was able to remove all the rtv- i wire wheeled both the pan surface and the trans surface and it has sealed up well.

Thank you all for the help solving this issue! finally one less leak on my truck!
 
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