So I put all new seals in my TH350 a few years ago. After running it for a while it developed a pretty good leak. The only seal I didn't replace was the pump seal, and I think that is where the leak is coming from. I really don't want to pull the tranny anytime soon. I was thinking about trying some stop leak, but have never used it. Anyone ever used tranny stop leak and did it help?
I've done a few pump gaskets on th350s, as in the pump housing to the case. Stop leak is typically snake oil, but probably worth a shot.
I would not. It is designed to "soften and swell seals" chemically. One is supposed to use it and then service the transmission (fluid/filter change) and not leve it in. Most do not do a flush/purge using new fluid and disconnecting the coolant line to catch all the contamitad fluid and endure the full tranny, cooler, lines and converter are flushed. The seals often fail, and if the lip seals fail, you will burn clutches and steels. If you use it, you will likely see yourself pulling the transmission sooner than letting the front seal leak and dealing with that. (if it is a small leak and you keep an eye on it)
Did you replace the shifter seal and dipstick tube 'O' ring. Stop leak worked in my wifes 04 Sienna with 197K mi.
Replaced shifter seal, dipstick o-ring, front and rear seals, modulator o-ring, speedo cable seal, and pan gasket. Didn't replace pump seal since you have to tear the front end of the trans apart. Pretty sure that is where its leaking. I've used radiator stop leak for dozens of vehicles and it usually fixed the problem for a while. Just wondering if the trans stuff works any good. I'll have to pull the trans again eventually and replace the pump seal and o-ring, but that is something I don't look forward to.
Cooling system stop leak forms a solution and the active component reacts with air as it leaks out and forms a solid, plugging the leak. As stated earlier, the transmission stop leak, causes the seals to soften and swell and stop the leak, but if it is not flushed after the specified time, seals will soften too much and lose "body". Lip seals in the clutch pistons, accumulators and such start leaking (bypassing) internally and the clutches will not hold apply pressure and you will burn up clutches. The new seals you have installed as well as most rubber parts are going to be degraded. Not sure of the mileage of your transmission, but it is likely a rebuild is needed as you have already At this point you can try the stop leak, but plan on a rebuild. Rebuilding a "good operating" transmission is better than pushing it to failure and then replacing hard parts as a result. Finding cores for parts is getting harder.
Found out where my leak was coming from (not the pump seal). Pulled off the pressure switch and put an air hose to it and fluid/air rushed out around the plastic part. It was squirting out fluid and covering the front of the transmission so it looked like the pump seal. Went ahead and got a new one and no more leak.
