Th350 atf leak

iamtherealJayy

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So I just got my first automatic squarebody, 1976 Chevrolet k10 custom deluxe with a 350/350/np203(yikes) I noticed the trans drips a little atf I was just wondering what some common spots are for them to leak. I have no idea what any part of it is called as this is the first automatic I’ve ever touched. It has recently been pressure washed underneath so I can get some half way decent photos of maybe where it’s coming from
 

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Dipstick tube, kickdown cable, vacuum modulator, shifter, speedometer and pan. Then you have front and rear main seals.
 
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Matt69olds

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Go to your nearest auto parts store. Get a bottle of A/C oil with the fluorescent dye. Add a little to the transmission and drive it. Shine a black light around the transmission. The dye will make the leak obvious enough for Stevie wonder to see it.

As mentioned, the most likely leaks are the dipstick tube o-ring and kickdown cable grommet. If it turns out to be the dipstick tube, be sure to closely inspect the area the O-ring sits. It’s pretty common to find them cracked.

If the tube needs to be replaced, get a aftermarket replacement that uses the later model boot style seal. They are a much better design.
 

iamtherealJayy

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No idea what the vacuum modulator is but,
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Dipstick tube?
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Shift linkage has a drop from it? I’m assuming that’s the shift linkage
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last photo is just oil but I don’t know how to remove a photo
 

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Dipstick tube, kickdown cable, vacuum modulator, shifter, speedometer and pan. Then you have front and rear main seals.
Nailed it. I am doing this as we speak. My son, my brother and I pulled the transmission out of our 80 Z28 because it leaked from EVERY place possible. Should be finishing up tomorrow. Just waiting to get an American made front pump seal. Not the Chinesium trash. Bought a whole kit off of the internet for 65 bucks. All of it is China trash. Had to piece an American kit. Still trying to get all American seals. Anyone know a good AMERICAN MADE place to get all the seals and o rings from? Really TIRED of the idiots on Capitol Hill selling out our country so those traitors can make extra cash. I want our country to start manufacturing our own stuff agin. I will pay the extra cost for our American people to make our products. Below aver I.Q. MORONS make laws that kill our American manufacturing just so those corrupt bastards can pocket extra money. In a truly honest society, that wouldn’t happen. I’ve had it with this crap. Seriously.
 

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Vacuum Modulator is on the passenger side. Kinda looks like your distributors' vacuum advance. There's a steel tube running from the manifold, behind the engine, and down to the modulator. Then there's a short piece of rubber tube from the steel tube to the modulator. This usually deteriorates and if the modulator is leaking internally, you wind up with ATF all over.
 

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I understand it can be difficult, but first clean everything you can, the dye is also a good idea, but a clean canvas to identify the origination of the leak is key.
 

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The shift shaft seal is definitely leaking, no question. I’m betting the dipstick and kickdown cable seals are also leaking, you can see how the fluid leaking has washed away the dirt and grime around those areas.

Go to your nearest transmission shop. If the builder has been in the business long chances are he will have a container full of the O-rings and seals. If not, he can order them. TransStar at one time sold a external reseal kit, basically every external seal in one package. I’m at work now, my TransStar catalog is at home.

Drop the oil pan first, that will make the repair much easier and cleaner. Disconnect the kickdown cable from the carb, that will give you the extra slack you need to disconnect the cable from the trans. There are several videos on how to replace the seal on the shifter shaft. Replace all the o-rings and grommets, make sure you lube everything with clean ATF or Vasoline. It’s easy to cut the seals installing them dry. Replace the filter, reinstall the pan, refill and your done.
 

QBuff02

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NAPA makes a tool that facilitates both the removal of the failed seal and installation of the new seal without having to remove from the vehicle. I used it on my th400 and it was pretty slick.
 

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Good luck. I'll be honest, I rarely see a TH350/400 that doesn't leak. Thankfully, most leak points are somewhat easy to address.
 

Matt69olds

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NAPA makes a tool that facilitates both the removal of the failed seal and installation of the new seal without having to remove from the vehicle. I used it on my th400 and it was pretty slick.


I have that tool as well, it works great. In this case, removing the pan is needed to fix the other leaks. If the pan didn’t need to come off it might be worth investing in the tool.
 

Matt69olds

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I just looked, the tool for replacing the seal is only 10 bucks. I thought it was more than that. It’s definitely worth spending the money!!

Just make sure you remove any burrs from the shifter linkage before installing the new seal.

 

Rusty Nail

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No idea what the vacuum modulator is but,
You must be registered for see images attach

Dipstick tube?
You must be registered for see images attach

Shift linkage has a drop from it? I’m assuming that’s the shift linkage
You must be registered for see images attach
You must be registered for see images attach
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last photo is just oil but I don’t know how to remove a photo

Looks to me like it's that pan bolt.
 

iamtherealJayy

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I don’t have a transmission shop local nor a Napa, but I’ll definitely clean everything up and see how bad it’s really leaking and order seals and weigh my options. I’ve never touched an automatic so this is all a learning experience.
 

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