TH350 leak
 

Driving home on the freeway last night I noticed light smoke trailing behind my truck, crawled under to look at the issue and it seems my transmission has sprayed fluid all over the place! The smoke was from ATF landing on the hot exhaust. Where is it coming from? I've attached a pic looking at the back of the transmission from the passenger rear tire. You can notice ATF dripping off some cables and parts. Also attached a pic of the exhaust.
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Re: TH350 leak
 

Driver side exhaust is clean, so the spraying ATF is coming from the passenger side.
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Re: TH350 leak
 

I would degrease it. It could be a few places on the passenger side. The pan, the vacuum modulator, the dipstick tube o-ring and the kick down cable. All these are on the passenger side.

Re: TH350 leak
 

That oil is spraying which suggest it is under pressure. The first place I would look is the cooler lines. One might be cracked

Re: TH350 leak
 

I experienced the same issue, ATF all over the place on the passenger-side only. Turned-out that my secondary modulator cover, o-ring was toast, and in removing it I found the spring inside broken. Glad I pulled that cover...I replaced the spring and now it shifts like new. The o-ring is about 3" in diameter.

Tom

Thanks for the suggestions, guys. Is the modulator the same thing as the accumulator? That has been the main suspect while tracking down this leak, but I never imagined it was bad enough to be spewing fluid under load. I have a spare o-ring and spring for that. I'll check the cooler lines and other fittings as well.

It doesn't leak much while parked, a few drops on the driveway is the worst it's done. That could be from the fluid that was sprayed onto the underside of the truck while driving.
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Re: TH350 leak
 

If it turns out to be the dipstick o-ring, it's a #113.... 3/4" OD, 9/16" ID, and 3/32" thickness.

Re: TH350 leak
 

Looks like it was a fairly easy fix and the cleanup will probably take longer than the repair.

Re: TH350 leak
 

I had a bad leak that was difficult to track down, it ended up being the ignition control switch on the pass side under the cooler lines. The sending unit itself was shooting fluid under pressure between the steel body and plastic center. A brass plug cured that major leak but still working on a few others. Did I mention I HATE automatics!!!

Re: TH350 leak
 

Once degreased, take a good look at the cooler lines, if they are touching each other they can wear a hole into each other...Also if someone cut the hard cooler lines and put in rubber lines...replace the rubber with hard lines...never use rubber in your cooler lines...asking for trouble...

The accumulator servo cover o-ring could be leaking as well... GM designed two type of servo covers, be careful on how you install the O-ring... either in the case or on the servo cover while installing the servo cover. If the spring is broke, no big deal...install the cover without the spring if you do not have another spring...its OK.

Check to see if you have a electrical plug near the dipstick, those electrical plugs seem to leak as well. (Trans Spark) wired back to a relay either on firewall or under the dash by the steering column... Just replace with a threaded fitting...if you can not find the electrical plug.

detent cable O-ring is on that side as well...again, once degreased look for the possible leak or leaks.

Have fun degreasing and try not to get to wet and dirty...Good Luck!!

Re: TH350 leak
 

The detent cable is not under pressure and usually leaks when parked.

Re: TH350 leak
 

I finally had a chance to inspect the transmission, although I didn't do a very thorough check. At first glance, it was easy to spot a leak around the switch that RedRoad described.

This may not be the only source of my leak, but once I get this resolved I can rule it out during future leak checks along with the pan gasket.

A bit of research leads me to believe this is a Transmission Controlled Spark switch, and the general consensus on the internet is that I can just remove it and plug the hole. Has anybody else done this to their TH350? What size plug will I need?

Thanks in advance!

Re: TH350 leak
 

sub'd.

Re: TH350 leak
 

I just plugged mine. Got an assortment of brass plugs from the local auto parts that came in a package and one fit fine.

Re: TH350 leak
 

I spent about 20 minutes under the truck turning the switch to pull it out, but the thing wouldn't come loose. I didn't have time to put the truck on a jack, so I was in an awkward spot and couldn't see the switch easily. The plug pops off easily, leaving a 3-prong electrical connector, which seems to rotate separately from the threaded body of the switch. Do I need a special tool to remove it? I'll try again this weekend when I have time to get the truck on ramps or on jackstands.

Re: TH350 leak
 

It was a ***** to get out. I needed a deep multi point socket to get mine out

Re: TH350 leak
 

Thanks for the info, RedRoad. I got the switch out using a 1 1/16" deep multi-point socket. Cleaned up all the grime and gunk around the threads and plugged the hole with a 1/8" NPT Brass Plug that I got from the local autoparts store. I'll be driving the truck to and from work today, and I'll check for any signs of more leaks. From a quick inspection this morning, I couldn't see the usual red drops hanging off the edge of the transmission pan, so that is a good sign! :bo2:

Here is a pic of the switch, for anyone else who might be suffering a similar misfortune. The three prongs at the front rotate loosely around a rivet, so to get it out you need to get a socket around the widest part of the switch. I left the electrical connector in the engine bay for now... add that to the long list of wires I need to tidy up (another day, when it's not so hot outside:lol:)!
http://s24.postimg.org/9fst3gokh/Pho...7_03_56_PM.jpg

Re: TH350 leak
 

Four days of driving and I haven't lost any noticeable amount of ATF, so I think the TCS switch was the main culprit of the leak. Now I am wondering how to clean the exhaust tube that is caked in burnt ATF, as seen in my first post in this thread. I tried a couple of degreasers (Simple Green and Formula88) with a wire brush, but that didn't do much. Can anyone suggest a method of getting the exhaust pipe clean?

Re: TH350 leak
 

Wire wheel on a small grinder might work