TH350 Transmission Leaking from everywhere!

[hotwls13]

My new to me 70 GMC LWB TH350 is leaking a LOT. It is also an ugly mess that has evidently been leaking for YEARS. So far I have found what appears to be leaks from:

- Speedo Bullet
- Vacuum Modulator
- Pan
- Shift Selector

I have picked up the following:

- New Speedo Bullet (with seal and O-ring)
- New Redline Vacuum Modulator (with hose)
- New Shift Selector seal
- New Pan Gasket and Filter kit (filter is the metal type, gasket the rubber type)

ANything I'm not thinking of? Maybe Filler O-ring?? The rear seal is NOT leaking surprisingly.

Should I try to get a replacement Pan Gasket (either Fel-Pro or Cork with metal inner part)??

I also may need a new "Driven Gear" as it may have a groove worn in it. They are hard to find around town so I will have to order one once I pull it and find what color/size I need.

[demian5]

Replace the filler tube o-ring and the tv cable o ring may be leaking. I would clean it off and pinpoint the leaks before doing anything.

[Stocker]

Originally Posted by hotwls13

ANything I'm not thinking of? Maybe Filler O-ring??

That was my first thought, since I had a leaky o-ring that drove me crazy trying to find the leak. They're cheap, might as well do it along with everything else.

[hotwls13]

Originally Posted by demian5

Replace the filler tube o-ring and the tv cable o ring may be leaking. I would clean it off and pinpoint the leaks before doing anything.

Easier said than done. This thing is a mess. And lately I've had some horrible Vertigo. With the 105 temps it is slow going.

I KNOW it's leaking from speedo/vacuum/pan. I figure do everything I can now (or as I can get to it) before filling with fluid.

[hotwls13]

Thinking of picking this up instead of the rubber one that came with the filter kit:

https://www.autozone.com/drivetrain/...306_26641_6156

[hotwls13]

Been a while (life got in the way). Got back to messing with the trans. Swapped filter and pan gasket, put new speedo bullet in and also a new vacuum modulator. Put about 4 quarts back in. Still leaking from front of pan.

The pan itself looks a little roughed up in the front corner (where it appears to be leaking).

Any recommendations on a replacement pan?? Don’t need fancy just functional. I’ve read the aluminum ones seal better??

[Barnfind46]

Replace the pan. If the factory pan has been over tightened in the past it will tend to want to leak after the new gasket has been installed. An aluminum pan is nice but a new steel pan will do. Good quality gasket and you should be good.Be persistent. You will get it done!

[AussieinNC]

Originally Posted by hotwls13

Been a while (life got in the way). Got back to messing with the trans. Swapped filter and pan gasket, put new speedo bullet in and also a new vacuum modulator. Put about 4 quarts back in. Still leaking from front of pan.

The pan itself looks a little roughed up in the front corner (where it appears to be leaking).

Any recommendations on a replacement pan?? Don’t need fancy just functional. I’ve read the aluminum ones seal better??

I have had great success with these aluminum pans and bolts....

https://www.amazon.com/Assault-Racin...0+aluminum+pan

$39.60 incl shipping on the A-Z

[hotwls13]

Originally Posted by AussieinNC

I have had great success with these aluminum pans and bolts....

https://www.amazon.com/Assault-Racin...0+aluminum+pan

$39.60 incl shipping on the A-Z

This is the one I was planning to get. Already had it in my Amazon cart.

Thanks for the positive input on it. Makes me feel better. Ordering.

[geezer#99]

Is the vent clean?
If not you’ll be fixing leaks forever.

[kwmech]

Originally Posted by hotwls13

Been a while (life got in the way). Got back to messing with the trans. Swapped filter and pan gasket, put new speedo bullet in and also a new vacuum modulator. Put about 4 quarts back in. Still leaking from front of pan.

The pan itself looks a little roughed up in the front corner (where it appears to be leaking).

Any recommendations on a replacement pan?? Don’t need fancy just functional. I’ve read the aluminum ones seal better??

More than likely leaking from the front pump or input/torque convertor seal

[57larry]

I'd power wash that tranny, then check for leaks

[hotwls13]

Originally Posted by geezer#99

Is the vent clean?
If not you’ll be fixing leaks forever.

No idea. I'm new to all of this, I probably just should have had a rebuilt transmission put in. Trying to to do all of this on the cheap. Just want to drive the truck. I honestly have no idea if this trans is even any good. I've only driven it about 3-5mph from a guys field onto a trailer, then up my driveway when home. It ran/drove, reverse and first gear worked but other than than, who knows.

At this point, I have about 20 days to do stuff to this truck, then life takes over again til February. SO many other things that need work on this truck (and a lot of it I WANT to do to the truck). Haha, don't know if it makes sense but I need to work on electrical issues, brakes, guages, oil leaks (oil Pan, filter both leaking). Not to mention it probably needs a new heater core, the AC stuff is torn apart, the electrical engine fans are wired wonky, I need to replace the trashed bench with some buckets I have etc.

I bought the replacement pan, but that's not going on til this thing is ready for the road.

But, as far as the vent leaking, the leak started after I filled the trans back up with 3.5 quarts, and I hadn't ran the engine yet. Let it sit overnight and I have a small leak on the front/passenger side of the pan (which is also the spot that the edge of the pan is chewed up a bit). SO my thinking is while it "may" have a clogged vent tube, it would only cause leaking from there is the truck had been run (creating pressure), correct??

[cleszkie]

Originally Posted by geezer#99

Is the vent clean?
If not you’ll be fixing leaks forever.

X2 on this. Its located on the top of the case just back from the belhousing section. Takes two minutes to remove, flush out, and reinstall.

[AussieinNC]

Seeing the trans was down 3-4 quarts the likely culprit is the vacuum modulator sucking trans fluid out and burning it in the engine...

I see you have a new modulator, great, follow the metal pipe in back of modulator up to the intake manifold and replace the short rubber tube that connects the metal tube to the intake....BUT...before you put new rubber hose on, grab a paper clip and probe the manifold fitting and ensure the vacuum source port is open...spray a little carb cleaner down it and blow it out with compressed air...

Then fit new rubber tube etc...

Have fun...

[hotwls13]

Originally Posted by AussieinNC

Seeing the trans was down 3-4 quarts the likely culprit is the vacuum modulator sucking trans fluid out and burning it in the engine...

It wasn't "down 3-4 quarts". I changed the trans filter and pan gasket (drained trans fluid before doing this). Once those were changed, I also replaced the vacuum modulator and speedo bullet which were both leaking previously. THEN I added 3.5 quarts back in.

[tdangle]

I fought with this for a long time also. Trans pretty much looked like yours. I hate to say it, but probably the best solution is to have a shop pull it, rebuild it and reinstall. You will never get it clean while in the truck, I tried. If the external seals are hard and bad, you probably have internal seals in the same condition. I ended up replacing it with a 4 speed overdrive unit.

[hotwls13]

Originally Posted by tdangle

I fought with this for a long time also. Trans pretty much looked like yours. I hate to say it, but probably the best solution is to have a shop pull it, rebuild it and reinstall. You will never get it clean while in the truck, I tried. If the external seals are hard and bad, you probably have internal seals in the same condition. I ended up replacing it with a 4 speed overdrive unit.

Yep, I'm definitely leaning that way (eventually). The plan for this truck was to get it driving (road worthy) and clean up the visuals a bit.

No $$ in the budget right now to replace trans. I still have a few months til I plan on registering it (it's on Non-Op right now and Mar 31st is renewal date which I'm waiting for so I don't get dinged for this Year). Plenty of other headaches to deal with on this thing between now and then.