TH350 Transmission leak

Hi, I've got 1973 Malibu with auto TH350 and I got leak that I can't find solution for it. On the driver side there is a shaft (linkage) that comes into transmission which shifts gears (from P do D etc.). I've got oil dripping out of that spot. It’s probably something easy to fix but I can’t find solution to stop the leak. Did anyone have this problem? Any help is appreciated.
Thanks

I dont know, but I have a feeling you will have to tear down the whole transmisson to put in a 10 cent rubber seal. JB

JB2wheeler wrote:I dont know, but I have a feeling you will have to tear down the whole transmisson to put in a 10 cent rubber seal. JB

yeah, that just might be the case. if im not mistaken, that shaft can only be removed from the inside of the housing

Man, I hoped to avoid that but sounds like thats the only solution.
Thanks for help

You don't have to remove the shaft to change the seal, but you do have to have a specialized tool for removal (looks like a socket with threads on the outside). I haven't seen the tool at regular places. It shouldn't cost very much to have that seal changed at a tranny shop. If you do do it yourself be very careful... one tiny nick on the seal and it will continue to leak.

Thanks, I will try tranny shop first just because I don't have that specialized tool and it's probably not easy to find either.

Just get an oil & filter change, and tell them "oh, by the way, change the selector shaft seal while you are in there" The TH350 is easy to work on actually, and I've rebuilt a few, but it does require some special tools.

Up to now my sweet Malibu never had a trans leak except a minor one with the pan and gasket solved with the third pan replacement. But it looks like a front seal leak which dribbles out a thimbleful daily.

Since I am a newbie with trans leaks I have questions. As background I have carefully listened for any sounds however faint in the trans and engine but hear nothing out of the ordinary whether idling or driving level or up hills. Is it possible for the torque converter to leak oil silently in this kind of situation? If it is only the front seal is it it possible to mitigate with the trans stop leaks. If so what is the best way to do that in terms of amount and frequency? As background I have had good success with the engine stop leaks concerning the engine rear seal but the trans is a different animal.

If it becomes necessary to remove the transmission to install new seal and o rings or horror a new torque converter, is it advisable to replace both the trans and engine rear seals at the same time or is there some reason not to do that?

If you’re doing the trans seal leave the engine alone.  Engine seal is an entirely different animal than a trans seal.  Once the trans is out, the input seal is easily visible.  The engine seal requires pulling the pan off which usually requires lifting the engine, and then removing the rear main cap.  Sometimes it requires loosening the other main caps to let the crank hang.

OK so engine seal no no. But you didn't say anything negative about the trans rear seal so I assume that would be OK to do at the same time.

76Chevelle2Tone wrote:Is it possible for the torque converter to leak oil silently in this kind of situation?

Highly unlikely. The torque converter has no seals. It's essentially a can with an impeller inside. Since you've isolated the leak to be emanating from the front of the transmission, it's either the front seal (most likely), the front cover gasket (probable but not likely), or both.

To better understand the anatomy of your transmission, I very much encourage you to study the transmission section of your car's service manual; if you don't have one, get one.

76Chevelle2Tone wrote:If it is only the front seal is it it possible to mitigate with the trans stop leaks.

Only as a stopgap measure. You're merely postponing the inevitable; taking the trans out and replacing the front seal (and maybe the front cover gasket)

76Chevelle2Tone wrote:If so what is the best way to do that in terms of amount and frequency?

Follow the manufacturer's instructions.

76Chevelle2Tone wrote:If it becomes necessary to remove the transmission to install new seal and o rings or horror a new torque converter, is it advisable to replace both the trans and engine rear seals at the same time or  is there some reason not to do that?

No matter how you look at it, leaks suck. I have a love-hate relationship regarding leaks. As long as there aren't any, I love it. Once one manifests itself, I hate it. As for dealing with leaks, to each his own. Ultimately, there's only one permanent solution to leaks; repairing it correctly. That almost always involves a fairly inexpensive part and several hours of labor. Accordingly, I empathize with your trepidation at the thought of having to remove the transmission in order to address this leak.

With that said, permit me to share with you my experiences. First off, the stop leak products contain some penetrants and glycol amines which are designed to soften and swell rubber and silicon, the most common materials used to make seals. What they don't tell you is this weakens the seals. When I discover a leak, I evaluate the hassle to repair it vis-a-vis how much it bugs me. If I had a 100 point show car with an immaculate chassis, any leak, even seepage, would be unacceptable. My standards are much lower for my daily driver but that also depends on what's leaking. For instance, a cooling system leak gets addressed immediately whereas power steering can wait. If the transmission on my daily driver had a thimble sized leak, I could live with that for quite a while. If I had to top-off the trans fluid more frequently than I change the oil in my engine, I would probably see about fixing the leak(s). The same philosophy applies to the rear engine seal; to each his own.

As for properly addressing the leak at the front of your transmission, you will need to remove the trans. Once it's out, examine the torque converter shaft that engages the transmission pump. It should be smooth and uniform. If there's a groove where it mates with the seal, you'll need a sleeve kit or you'll have to replace the torque converter along with the seal. By the way, while you have the transmission out, you may as well replace all the other seals and gaskets; they make kits for that. After all, it's only a matter of time before one or more of the other seals start leaking.

As for the rear engine seal, the best way to deal with it is, you guessed it, to pull the engine.

Good luck and keep us informed.

76Chevelle2Tone wrote:OK so engine seal no no. But you didn't say anything negative  about the trans rear seal so I assume that would be OK to do at the same time.

Rear trans seal you can do with the trans in the car.

The trans leak slowed down with slightly warmer weather so I put in a small amount of stop leak and it seems even better today. I hear no noises at all even going up steep hills. I get it that this is a temporary stopgap no pun intended but I want to finish with the renovation of the engine mechanical, electrical and vacuum apart from the engine block and transmission if at all possible. Since it is a daily driver I can only fix problems sporadically and piecemeal. I just have the fuel pump, alternator, valve cover gaskets /tune up stuff plus a few switches to do. Replacing the engine and trans vacuum thingies made an amazing difference BTW. So hopefully the leak will be slow enough for the next several months to be able to deal with the trans in the summer. I also have to worry about the timing chain as the mileage is nearing 150k. (It was very low mileage when I bought it many years ago). Thanks again.

76Chevelle2Tone wrote:I also have to worry about the timing chain as the mileage is nearing 150k.

Rightly so. If the engine is still factory stock, the timing gear on the cam is aluminum with nylon teeth. With advanced age, those teeth will shear/break off and you risk the chain jumping one or more teeth thus throwing off valve timing and risking bending/breaking valves and/or pistons. That job can be done with the engine in the car but you'll need to drop the oil pan in order to correctly seal everything up.

As for replacement, I've had good experience with all steel double roller chain and sprockets. Cloys used to be THE go to for those chains back in the 1970's and 80's. You can find them at SpeedwayMotors. I've been recently informed that pretty much all names are made with the same quality nowadays, your mileage may vary.

OK so the timing chain seems like a top priority. Are there any consistent symptoms that the timing chain is about to go? I was well aware of the potentially catastrophic consequences of a timing chain failure but it seemed that there were some telltale prior symptoms but maybe not always. Now I really hope that I can manage the transmission for the time being as the timing chain seems even more urgent to get done.

Also quite frankly I don't find the service manuals very helpful or informative except for some technical specs. I've learned far more from online videos and this site and a few others.

Before we go further, this is how it should look from the factory…

76Chevelle2Tone wrote:Are there any consistent symptoms that the timing chain is about to go?

I have never witnessed a catastrophic failure like the one described above but I have seen my fair share of worn timing cam sprockets. They'll usually start with one or more of the nylon teeth shearing off.


As more of the teeth shear off, the chain-to-sprocket fit loosens. If the gods of automotive maintenance and repair favor you, it will loosen to the point where you can hear an odd knock at the front of the engine caused by the chain slapping against the side of the timing chain cover.

I'm definitely going to push this up the priority list. Thanks for your pictures. Since the timing chain is off topic for the thread, if I have further thoughts or developments I'll start a new thread.

Cloyes C-3023K was always good for mild small blocks.

rogal_tx wrote:Thanks, I will try tranny shop first just because I don't have that specialized tool and it's probably not easy to find either.

Link to the Napa removal tool that I have used on my TH350 and also a 4L80E:
https://www.napaonline.com/en/p/BK_7769250?cid=paidsearch_shopping_dcoe_google&campaign=GSC-Tools-Equipment&campaign_id=8553470562&adgroup_id=107047174069&adtype=pla_with_promotion&gclsrc=aw.ds&

The shift shaft seal would be nearly impossible to do without this, but is relatively easy with it.