Guys ive got an issue it seems as though my trans is leaking (TH400 Chevy). I dont know what to do about it. I have looked at it time and time again and cannot pin point where the leak is coming from. My guess would be the cable modulator position on the passenger side but i cant tell there is trans fluid all over the place. I didnt notice it the other day but yesterday it was raining as i was going into wal mart and i noticed all through the parking lot were oil stains. so i was like what the hell i looked at it and there was trans fluid all over the place. prolly like half a quart low. i do have a deeper pan bigger pan from summit. would this be part of the culprit to why the dipstic reads low but really is only like 1 pint low? when i add fluid i believe it gets overfull and leaks everwhere or am i missing something thanks guys.

 

A TH-400 uses an electrical signal for the kickdown. There should be a plug on the drivers side.

The vaccum modulator is on the pass. side.

What kind of dipstick do you have? It could just be overfilled and leaking out the vent, which is right on top of the case above the modulator. I have had this problem on the chrome Mr. Gasket ones. Actually I have never bought an aftermarket dipstick for a TH-400 that works. The factory ones from a 67-72 chevy p/u are nice. Not too long.

No matter how deep the pan is the fluid still has to be filled to the same level, thats how the deeper pan adds capacity.

Do you have a trans temp gauge? I am sure the Cummins is making lots of heat in the TC. If its overfilled and gets hot the fluid will start to puke out.

 

makes sense no i do not have a gauge. Mine has a cable modulator because that is how you get them to work with a cummins (no vaccum pump) i blocked my ports on the power steering pump for this. anyway the thing shifts great nice and firm, i have a shift kit installed. even with the added power that ive been giving it lately it still rips. i know these trans are good for a lot of hp. Right now i have the trans lines running from the trans to the radiator to a trans cooler and back to the trans. i imagine the fluid isnt getting over 180 degrees but i could be wrong. i have a 2 qt extra pan. The thing has always leaked thats why i got a new pan it didnt leak right away but now it does. i tighten the bolts everynow and then. I wonder if the dipstick seal is junk now that i think about it. i did have it out at one time and the think never sealed right. So ill check for a vent tonight to see if it is there what does it look like? is it a little rubber nipple or something else. thanks for the reply

 

I guess I didn't know you could get a modulator like that.

The dipstick can be a pain to get sealed. Does it have an O-ring? Or does it take the rubber sleeve? If it's the o-ring one I would put a generous amount of silicone on it and re-install. If that would be to butch for you, the newer style seals up nicely. The end of the dipstick tube is necked down for the rubber seal.

 

No that wouldnt be to butch for me and it does have the o ring. i bet that is where it is leaking from. I cant really tell because there is oil all over the place which means its coming from a high point like the dipstick. The cable modulator uses a cable not vaccum to adjust shift points. They are used alot on supercharged cars where low vaccum is an issue. thanks for the response

 

The overflow is right above the modulator, where the bellhousing meets the round part of the case. When new it has a little plastic tube aiming the fliud at the ground. Not too hard to break that off. The hole in the case will be facing towards the rear of the truck.

 

i dont think i have one come to think of it so that might be the missing link maybe it is gone but i am gonna jam some silicone in the dipstick for sure. i dont like leaks especially when there is fluid all over the place.

 

I hear ya, it's very annoying, and getting pretty expensive to boot.

 

mine doesnt have an overflow but it does have a dipstick right above the modulator. i siliconed it ot the max

 

it may have been a little overfull but not much i siliconed the holes and no leak now!!!!! hopefully it stays like this. the truck rips now thanks guys