Th400 leak locations

[blazerbones]

Hi all,

Could someone please summarize the likely leak points in a th400 other than the lines, pan, input/output seal?

 

[owenst7]

Dipstick shroud and the shifter. Also any of the caps on the side of the case such as the governor, think there's at least one accumulator with an external seal on the 400.

Dipstick shroud seal even has a Dorman Help! part i believe that fits a 400. I've bought them for 350s before off the shelf. Looks like a tophat, and they're a pain in the ass to do.

 

[DokWatson]

Well, I can tell you where mine leaks

T-case adapter on mine weeps. I've had the vacuum modulator leak too, it has an o-ring that can go bad.

 

[blazerbones]

Thanks guys. I've gotthe leaky adapter... I think that's the output shaft seal right?

The modulator oring is no good and the dip stick shroud is wet... Those'll get replaced.

One more thing though. There's a wire plug on the driver side rear of the case. The plastic fitting going into the trans is leaking. Looks like just a press fit piece of plastic to me.

Any idea how to change it out? I'm guessing there's a bad Oring there. Thing is, it doesn't seem to screw in so I'm afraid trying to pull it out with pliers may shatter it... And not sure what it's connected to on the inside of the case...

 

[DokWatson]

Sounds like the kickdown solenoid, I think you have to drop the pan and pull it out from the inside... I don't remember.

 

[76zimmer]

The t/c adapter has to be sealed with a gasket or RTV...no seal in there, the trans case is open up to the adapter plate.
The solenoid switch has two ears on it that need to be compressed from inside the pan area, it has an O ring on it to seal it to the case.
Also watch for a plugged vent on top of the case causing pressure inside the trans, and get a lock down dipstick from Hughes, and a triple lip dipstick to case seal.

 

[Amtek]

Mine leaks at the selector shaft, replaced the seal only to find out the shaft has been fubar'd when the PO tried to remove it with a chisel.

Anyone know where to pick up a new selector shaft from?

 

[blazerbones]

Zimmer - I've looked at at the dipstick shroud seals online... Haven't seen the "triple lip" version specified. Do you get that from Hughes or online/parts dealer?

 

[76zimmer]

I got my dipstick from Coan, its a Hughes with the triple inner lip design seal....you need to put the seal in the trans case, then the dipstick tube....no leaks on either of my T400's with that setup.

http://www.coanracing.com/Catalog.asp?ProductDetail=655

 

[bigjimmy82]

The t/c adapter has to be sealed with a gasket or RTV...no seal in there, the trans case is open up to the adapter plate.

Bumping this up to confirm NO rear seal on 4wd TH400? I am seeing leakage from the adapter (np208). Does it strictly rely on the RTV and paper gasket?

see attached photo, starting the engine, fluid begins to fill the rear tail shaft area.

Aside from the leak, I am concerned because I have removed the transfer case several times and never had so much ATF leak as yesterday. Just pulling the bottom adapter bolt was like a drain plug. Could there be an issue with the drain from this area back to the pan? ‍

 

[bigjimmy82]

Here are the pictures, 1st is after t case removal, 2nd is with engine running, you can see fluid pumping(Leaking?) into this area.

edit:not sure why they are sideways, the plastic gear is the bottom for reference.

 

[76zimmer]

Im not sure about a 208, my doubler is made from a T400/203 combo.
Dont worry about the fluid running past that rear bushing/speedo gear.
On the adapter there should be a square Oring that goes in a groove., that seals the adapter to the T400 case.
On the tranfer case side of that adapter, I use a thin smear of rtv, on both sides of the paper gasket where it mates to the machined surfaces of the adapter and transfer case.
On the transfer case itself, there should be a shaft seal housing that bolts onto the front of the transfer case.
Check your transfer case to see if any of the attaching bolt holes are open to the inside of the case. Also be careful not to use to long of a bolt where it might hit the gears inside
Pics of a T400/203 adapter

 

[bigjimmy82]

Thanks for the reply, so looks like on a 203 even, there is nothing to stop transmission fluid from contacting the front of the transfer case. Meaning the tail shaft is sealed by RTV?

 

[76zimmer]

The tail-shaft isn't really sealed, i.e. it doesnt have a specific seal.
the seal retainer on the front of the transfer case keeps fluid from exchanging
Make sure both vents are clear so the cases don't build pressure.

 

[bigjimmy82]

the seal retainer on the front of the transfer case keeps fluid from exchanging
Make sure both vents are clear so the cases don't build pressure.

that’s what I was looking for, essentially the “transmissions” ATF can travel/flow all the way to the front seal of the transfer case under normal operation, hence the RTV and gasket. BUT if vents are clear then it won’t build pressure and find its way out.

Thanks Zimmer!

 

[imiceman44]

that’s what I was looking for, essentially the “transmissions” ATF can travel/flow all the way to the front seal of the transfer case under normal operation, hence the RTV and gasket. BUT if vents are clear then it won’t build pressure and find its way out.

Thanks Zimmer!

If you notice the groove on the first picture of the adapter that @76zimmer posted between the bolts and the inner ring,that's where the square O ring goes and seals the 2 pieces so no need for gasket or silicone.

 

[bigjimmy82]

The 208 adapter is just a piloted flange, no o-ring. I reassembled yesterday with the paper gasket and gray rtv. Test drove 60miles today, so far so good. I think the atf had just gotten to the old rtv and it was starting to leak.

 

[imiceman44]

The 208 adapter is just a piloted flange, no o-ring. I reassembled yesterday with the paper gasket and gray rtv. Test drove 60miles today, so far so good. I think the atf had just gotten to the old rtv and it was starting to leak.

I am sorry I thought we were talking about a 203

 

[76zimmer]

203/205’s are the only ones I have to work on! So that was the only example I could use with any experience.

 

[bigjimmy82]

No worries guys, the answer was the same, the transfer case front seal basically doubles as the rear trans seal. I was thinking there should be something to keep transmission atf from getting to the front of the t-case, but nope.