TH400 Fluid Leak.

[eightbanger]

I had a pig of a day on Sunday, when I took the trans pan off to fit the new gasket, found the filter was hanging loose so I thought it was broke. I posted a video on here... http://67-72chevytrucks.com/vboard/s...t=296601...and the replies I got said it should be like that and not to worry...cool. I wished I had known there was a filter in there though I would have replaced it, so put it back together and one of the bolts kept spinning as I was tightening...yep! striped the thread on the case so now im posting to find out what kinda Tap & Die set to buy for American cars. Today I let the truck run on the drive for a while to test it at that striped thread point and no fluid leak, so took it on a run and when I got back I left it running an crawled underneath for another look while it was hot and idling it started leaking fluid...but not from the gasket from somewhere up above the two trans fluid cooling lines and running down and dripping off the pan where I thought the leak was to begin with. Very long story short, gasket was fine all along and looks like I got a crack in the Trans case looks like it might be on one of the seams when it gets formed in the mould. So this is the same leak i've had all along and it only happens when the truck has been on a run and then you leave it idiling in park..don't know why it choses that time to leak?.
My chances of finding someone to repair my Trans case here in the UK are slim and none. Im done moaning.

[PanelDeland]

If it is a crack in the trans case,it probably doesn't leak until it gets warm/hot and the crack expands.
I don't know what to tell you on repairing the case,a good weldor may be able to weld up the crack but you would need to tear it down and rebuild it afterward.My suggestion is to just replace the trans.This would be a good time to upgrade to OD.

[jayharrell]

The reason it leakes from the top after running it and when its been sitting along time is because the tranny has spun all of the fluid into the body of the trans and left it locked up there when in park. Kinda like pumping alot of water into barrel on top of your house then pluging the hose. *bad reference, but it might do.* When its left set for a long time the trans has slowly released all the fluid back into the pan.

So if the crack is at the top of the trans, thats the time it'll leak. If thats the case, its time for a new case. I'm unsure about the UK and how avalible a used t400 case is. But here in TX they are pretty easy to come by. a few hundred dollars will get a good case, and an other hundred or so will get a stock rebuild kit.

I agree with Panel, if you have the cash, and are going to have someone find and rebuild a t400 for you, for just a little more you could get a 700r. you'll have to get a new drive line, but hey, when it breaks, fix it with better stuff if you can afford it.

[jayharrell]

Or just jam some weld putty into the crack and run it for a while. Thats the $15 fix. Probably what i would do. LOL its alot easier when its someone elses money and truck. LOL

[JimKshortstep4x4]

If the leak is in the case itself and not under pressure you may want to try using silicone sealant to repair the leak. Just clean the area real well and apply the silicone over the crack.
If the case is smooth at the crack then roughen it with some sand paper before applying the sealant.

I repaired a transmission this way and it has lasted well over two hundred thousand miles with no leaks.

Jim

[eightbanger]

Man I don't know what I would do without you guys and this forum, just talking to someone who knows makes me feel better and not feel like all is lost. I'll go the plug the leak point route for now and see if that works, so thanks for that Jay & Jim but your right PanelDeland I was looking at OD for sometime soon if the finances allow problem is I want to keep my TH400 and add a Gear vendors unit. I'll start Googleing the length and breadth of Britain to see if there is anyone here who knows how to repair and rebuild these Transmisions.
Thanks again for your help you guys.

[eightbanger]

Well I sanded and cleaned the seam on the trans case were I think ithe crack is and spread a lot of Bondo over it, when I was in there I noticed what looked like a sheared off bolt near the top of the case, could not get my head any closer to see properly so put the camera up there and took these pics to get a better look. And there was trans fluid weeping out...so this was the source of my leak all along not the gasket, and not a cracked case...phew! so I have gunked it with Bondo also.
So can anyone tell from the pics what should be there? the second pic is to give you an idea of where this thing is.

[jayharrell]

I don't know what goes there, maybe a temp sensor, but all 3 of my t400s just have a bolt in that hole just like yours, but its not broken of course.

Get some gas tank repair putty. It comes in a little log/ tube looking thing, most places have it on the counter. You nead it together and then seal that bolt up.

That would be a monster to pull the trany just to pull that broken bolt out.

[eightbanger]

Yeah I know the stuff you mean Jay, I know you said you have 3 Transmissions and they all have bolts there, but is there a breather tube on these case's you don't think thats what could have been there?. I agree big time on pulling that thing just to get a tiny bolt out, it can stay there with my blessing.
Thanks mate.

[jayharrell]

Well there should be an overflow/ breather tube on the other side of the trany. about 1/4 inch tube. I'll get a picture of a core i have laying around just to make sure wheni get home.

[jayharrell]

well as i always figured, i don't know what I'm talking about. Mine is an overflow hole there, but then again my t400 is a Buick housing. the bolt i was talking about is lower one near the bottom in the center of the pic right under the cooling line holes. Not sure what its for. just stuck in my mind that i had a bolt in the trans i didn't know where it went.

You might have too much fluid in the trany.. Check the level while the motor is running, and after you've sifted it through all the gears while standing still at idle to make sure the trans has spun up all it can handle. If its leaking out that hole after that, then theres too much fluid in it.

You would have been better off not even considering my opinion in the first place. LOL. something my wife has already learned. LOL

[Classic Heartbeat]

I would remove what is left of that bolt in the case. That is supposed to be the vent tube. Without the vent tube your transmission builds up pressure and has no place to go, so it eventually makes a new place. Usually by blowing a seal or gasket. Here are pictures of the tube. WES

[kelsfine69]

I agree with Wes dont plug the breather hole/tube. It will just start other problems like he said. I think the only way to replace it is to pull the front pump out. Why it is leaking to start with is the big question. Might be overfull, or something internal. Ther was a GM recall late 80s-90s that you slide a hose over the tube and run it down the side of the tranny so that when or if it got really hot it would puke the trans oil on the ground not on the tranny or exhaust and start a fire.

[eightbanger]

Originally Posted by jayharrell

well as i always figured, i don't know what I'm talking about. Mine is an overflow hole there, but then again my t400 is a Buick housing. the bolt i was talking about is lower one near the bottom in the center of the pic right under the cooling line holes. Not sure what its for. just stuck in my mind that i had a bolt in the trans i didn't know where it went.
You might have too much fluid in the trany.. Check the level while the motor is running, and after you've sifted it through all the gears while standing still at idle to make sure the trans has spun up all it can handle. If its leaking out that hole after that, then theres too much fluid in it.
You would have been better off not even considering my opinion in the first place. LOL. something my wife has already learned. LOL

Well Jay at least it was advice of a sort...just the wrong sort
Thanks mate for taking the time.

Originally Posted by Classic Heartbeat

I would remove what is left of that bolt in the case. That is supposed to be the vent tube. Without the vent tube your transmission builds up pressure and has no place to go, so it eventually makes a new place. Usually by blowing a seal or gasket. Here are pictures of the tube. WES

Wes can those breather tubes be bought, and re-installed? Those pics really show clearly what part has been lost on mine, I don't know what the PO was up to but all I keep doing is finding stuff thats missing on my Truck.

Originally Posted by kelsfine69

I agree with Wes dont plug the breather hole/tube. It will just start other problems like he said. I think the only way to replace it is to pull the front pump out. Why it is leaking to start with is the big question. Might be overfull, or something internal. Ther was a GM recall late 80s-90s that you slide a hose over the tube and run it down the side of the tranny so that when or if it got really hot it would puke the trans oil on the ground not on the tranny or exhaust and start a fire.

Overfull may well be the reason, im a bit heavy handed with amounts of anything..especially that stuff that Mr Daniels makes interesting on the recall though and makes sense to extend that tube. Just wish I had one to extend.

[kelsfine69]

I did see years ago that a trans case cracked and the owner used Bondo. It worked for the life of the truck. Even when we rebuilt the tranny we had to use a blaster to take it off to see the crack. Then we found a used case.