Is there a way I can better seal my transmission modulator on my TH400? The oring doesn't seem to be cutting it. For reference, this is a new modulator and oring from Inline. I have another new one from B&M sitting on the bench, but if the issue is the seal, I'll just need to correct that instead.

Thanks.

 

Odd a new modulator valve O-Ring would not seal. No offense, but are you 100% there isn't an old O-Ring, or parts of one, still stuck inside the transmission opening? Hard to look directly inside, a mirror & flashlight would assist. Sometimes using a finger you can't catch an O-Ring inside the opening and a dental cleaning tool pick can grab better.

 

The previous Oring came right out. When the trans was rebuilt, he put a new modulator/Oring in it, but it got kinda beat up when everything was being installed in the car..so I went ahead and replaced it. I do know that when I changed it, fluid was coming out of the hole..but I wouldn't expect that to have created sealing issues.

 

I had this same problem with my '69 4-4-2. The bottom line - the installed o-ring was the wrong size. When I got the correct size o-ring (I wish I could recall the size description but I just don't remember other than it looked smaller in diameter than the originally installed one) the leaking stopped. It didn't leak that much with the wrong size o-ring but it was enough to leave a small pool of red fluid on my garage floor pan in a month or so. But the correct size o-ring completely stopped the leaking.

Randy C.

 

Maybe I'll get an assortment and try to find one a step smaller in that case.

Thanks.

 

Go to your nearest transmission shop, chances are they have a box full of them.

Other option, go to your nearest autozone, ask for a MV100. That’s the part number for a replacement adjustable modulator, with the proper Oring. Last time I bought one it was under 20 bucks.

 

I have a replacement modulator on the bench, but the one in there is also a replacement (different vendor) and it's leaking

 

Does the Oring have a snug fit? It should take a little effort to install.

Any chance the leak is coming from the cooler lines? Case cracked? Some other flaw preventing a good seal?

Go to your nearest part store and buy a small bottle of A/C oil with the fluorescent dye. Add a little to the transmission, run it for a while. Use a black light, the dye will outline the leak bright enough for Stevie wonder to see it.

 

I've found that many of the replacement o-rings for TH400 parts (dipstick tube, governor, etc) have too small a cross section to seal properly. I've ended up buying o-rings from McMaster Carr with a larger cross section to get my dipstick tube to seal properly.

 

Got under it and did some inspecting. First, the pan bolts were about a half a turn loose, some of them maybe even more. So I went ahead and snugged them up (not going full pull for fear of warpage). I was able to get maybe an eighth of a turn on one cooler line, but the other was solid. I pulled the modulator out and reseat the oring, making sure not only did it "pop" in, but I held pressure while tightening the bolt rather than using the hold down to draw it in. I did notice I can see the rib of the dipstick tube, and just barely below it. It doesn't seem to be easy to move, but I'll keep my eye on it for sure. I gave everything a wipe down and moved it out of the garage for a few minutes while I cleaned my mess up and put a towel down to check for more leaks. Tomorrow if the weather is nice, I'll drive it around a bit and bring it back to verify. The frustrating thing is that the more I think about it, the leak wasn't there until I drove the car in stupid cold weather (literally just to flip it around in the garage) and now Im fighting it.

I'm not beyond going ahead and getting better Orings, but hopefully this is at least a step in the right direction

 

Meant to update this after driving it around and noticed its still dripping a bit. Not sure from where yet as I've not been back underneath it, but just add that to the list of annoyances right now, ha!

 

Could be weeping out of the vent hole. Chance you overfilled when cold now it’s seeping out the went?

 

Not sure, and honestly that's one thing I hadn't checked.

That being said, everything was full initially..and once I changed the modulator I noticed a few drips here and there, but then they stopped..so I figured that was residual from when I changed it. Then one day as I was flipping the car around I noticed a decent trail everywhere the car was, but figured I'd get that sorted once the intake was back on (the reason I was flipping the car around the begin with). When I finally got the car started after the intake gasket change (long story) it was pouring out of the top of the dipstick tube. All in all, I probably lost close to a Quart if I had to guess.

I put not even a half quart in the other day, and noticed it was still leaking. So is it possible itd been overfull-yes. I can't imagine that'd be the issue though hence why I'd not checked it.

 

I am not certain I am completely following. You state above you changed the intake (manifold I guess) gasket and it (what is it? engine oil, transmission fluid?) was pouring out of the top of the dipstick tube. Not following. Please be a little more specific about what "it" is and what a "Quart" is. Again, transmission fluid, engine oil? Not following.

"If" any transmission fluid was pouring out of the top of the transmission fluid dipstick , you are far, far, far, far over transmission fluid capacity. And tons of transmission fluid will be leaking from your transmission. "If" that is the case, you need to very carefully evaluate the transmission dipstick tube and pay careful attention to the COLD & HOT fluid level markings at the bottom of the transmission dipstick tube. Do not fill the transmission above the COLD marking when the transmission has not been brought to operating temperature or you will be in an overfilled condition and transmission fluid will weep from the transmission vent hole.

 

When I changed the intake gasket, I also reset the distributor (it was installed 180 out) and had one heck of a time getting it back in time due to a separate issue. Once I finally got the car to fire, I shut it down to check for leaks and heard something pouring out. That something was transmission fluid that had run up the dipstick tube and out the top. When everything was all said and done (when I could finally move the car out of the garage to clean up my mess) I had about a quart of transmission fluid laying on the ground. The odd thing with that was, nothing had been added to create an "overfull" condition to the point where the trans fluid would come out of the top of the dipstick tube.

 

OK. I have some things to attend to, thanks for clarifying. If transmission fluid was pouring out of the top of the transmission fluid dipstick tube, the transmission has far exceeded capacity. At this point, I suggest removing the transmission pan, drain all the fluid - maybe even let it sit overnight. Once you're completely satisfied the transmission fluid has been emptied, refill the transmission fluid paying careful attention to the COLD & HOT markings on the transmission fluid dipstick. NOTE: You know you cannot empty the torque converter correct? Fluid will always remain w/in the torque converter. Again, after a complete draining of the transmission fluid, fill the transmission fluid and DO NOT exceed the COLD or HOT markings - best to be just a tad below the marking than over the marking. That's the best I can offer. Good Luck.

 

A more or less final thought. In an overfilled capacity scenario since you’ve already puked out the majority of the overfilled fluid, the transmission will EVENTUALLY stop puking from the vent hole somewhere 5-6 months down the road with significant driving. During that period of time you can place a drip pan under the car to catch the fluid.

 

I guess I'd not paid much attention to the dipstick, but I didn't realize there was a "cold" mark. I'm used to only being able to check it with everything up to temp and in gear. If there's a "cold" then I'll just check it when I get to the house as its not moved since Saturday.

 

The best procedure is to evaluate transmission fluid level when engine & transmission are at operating temperature with the engine running & NOT in gear. Read the transmission section in the CSM.

 

Please take the vehicle for a ride of at least 20’ to 30’ minimum. The transmission fluid will not heat up to operating temperature while it sits stationary at idle. The torque converter is NOT under load while idling. The fan blades inside the torque converter and the transmission itself must be ‘run” under load as in ‘driving’. Go for a ride, keep it running when you return & check level while engine running.

 

I checked my spare original modulator for my '69 4-4-2 and found another o-ring for it that is the correct size. I measured that o-ring against the pics in my Auveco catalog and here's what I came up with. This should be correct for that modulator.

Auveco part number: 4317 (for a bag of 50)
Industrial Standard: 115
11/16" ID X 7/8" OD

Don't know if that will help or not but I just wanted to get that correct size out there. It made all the difference in the world for my '69.

Randy C.

 

I may go ahead and run it around the block when I get off work, and check it before putting it away..because now I'm curious. The other thought I had was could a misreading be related to the auxiliary trans cooler I'd added.

 

Only if you recently installed a spoiler wing on the trunk deck.

 

Lol..exactly. I may not know a lot, but I know enough to know the cooler would require more fluid, but wouldn't change the reading on the stick (or be an overfull issue)

 

Alright, got home and took the car up and down the main drag for about 20 minutes. Checked fluid in the driveway and couldn't get a reading. Drove over to the church as the parking lot there is not on an incline, and still couldn't get a reading.

When I'm looking for a reading, am I correct in assuming it'd be a reading similar to oil on the engine dipstick (a clear line and color difference)?

I did however notice in the garage that some of the drips on the pad I had under kt seem to be in a familiar pattern..

 

Yes, similar to oil dipstick but obviously red in color. I erred earlier your dipstick says FULL on the top. It's specifically stated in your CSM (I believe Chapter 7) how to read the dipstick. You need to follow Post #8:

You can buy a small penlight UV flashlight to visualize the dye, as well.

 

Went out this morning and verified, I do have the dyed AC oil..so I'll give that a whirl. Also for good measure I checked the dipstick after it sat overnight (did not fire it up) and it reads about a half inch above the full line..so at least I'm reassured there's some in there.

I'll throw some of that dye in there and cycle it at some point over the weekend hopefully. I've gotta change the hoses from the hard line to cooler anyway (don't like how they're routed) so it'll give me another reason to address the fluid.

 

update on this...I never did make it out to put the dye in the fluid and check it before the car went into the shop. However while at the shop I asked them to look into this, which I was told "it has a cork pan gasket so we'll tighten that up and keep an eye out"

*so reassuring*

With that being said, I suppose we'll see how things shake out over the next few days.

 

Your update isn't really an update pertaining to a fluid leak. I originally suspected you overfilled the transmission and it puked out the vent & I feel rather confident that's the source of your leak. Do NOT tighten those transmission bolts above the specified torque values - unless you want to create additional leaks, irrespective of poly or cork transmission gasket.

 

Overtightened pan bolts, especially with compressible cork gaskets, is the leading cause of pan leaks. Beware of clueless gorillas.

 

Just drove it into work, sure enough another puddle.

At this rate, I'm strongly leaning toward looking into different gaskets..if thats truly the problem. I'm not sure what'd cause it from the start, but I know I've had way more luck with the rubber gaskets than I have with cork.

This way too, I can monitor the fluid level better.

 

You REALLY need to add some fluorescent dye and visualize the location of the leak(s).

 

When you pull the pan, check the mating surface of the pan with a straightedge. Use a hammer and dolly to repair any distortions. I've found the Lube Locker brand neoprene/metal core pan gaskets to be the best. And USE AN INCH-LB TORQUE WRENCH!!!!!

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

 

Thanks for the heads up, though the inch lb torque wrench is a trigger for me for other reasons..ha!