904 Leaking. What to check first?

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Mako21

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I’m in the process of “resurrecting” a 1976 Dart. I’m quite comfortable with the engine at this point( fixed an overheating issue, plugs, timing).

Attached are pictures of what I want to tackle next. It’s leaking transmission fluid really bad. I was thinking of starting at the transmission pan gasket, lowering it, cleaning all the fluid off, a Felpro gasket and reattaching and torquing to spec. I also think the plug where the neutral safety switch (I think that’s what it is via the diagrams) is leaking.

I believe the other leak at the front is an easy fix. Someone put three clamps on a rubber hose running into the transmission cooler inside the radiator.

Where could you offer advice to start? Thanks.

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I think you have a sound plan.

You might want to pressure wash the thing clean and drive for a bit and see if you can pinpoint a leak. That way you are not throwing parts at it.
 
The first thing to check is the trans fluid level so you don't run it dry...
 
Bad plan. Just guessing and trying to get lucky? Some people aren't patient when trying to pin down leaks. So they start replacing stuff and end up taking it to a shop because they get frustrated. I had a guy tell me his transmission was leaking and sent me a pic of a puddle under his truck. Haha. Real helpful. It was a loose line that he didn't get tightened up all the way when he installed it. Another one was a torn dip stick tube o-ring. Everybody wants to yank off the pan and plaster it with silicone...but pans are extremely difficult to learn how to straighten and tighten properly; providing you use the right gasket. Most pans leak if they're installed by beginners.
 
Bad plan. Just guessing and trying to get lucky? Some people aren't patient when trying to pin down leaks. So they start replacing stuff and end up taking it to a shop because they get frustrated. I had a guy tell me his transmission was leaking and sent me a pic of a puddle under his truck. Haha. Real helpful. It was a loose line that he didn't get tightened up all the way when he installed it. Another one was a torn dip stick tube o-ring. Everybody wants to yank off the pan and plaster it with silicone...but pans are extremely difficult to learn how to straighten and tighten properly; providing you use the right gasket. Most pans leak if they're installed by beginners.
I agree with starting with the small obvious stuff. That transmission line with the hose and clamps is just asking for trouble. You should buy or make a new metal line with proper connections on both ends. Maybe replace the o ring on the neutral safety when you are fixing the line as it's small money and effort. Once you fix that, wipe down/clean everything else and then look for other leaks.
 
Agreed on selector shaft. Your backup light / neutral safety switch is soaked, which tells me its coming from there. Seal can be replaced in car but it can be a real chore. Also check your dipstick tube, a simple 3/4" (?) plumbing o-ring will fix that right up.

Couple other places to check are speedo and there is a small cover plate beneath the cross member that can weep. Its for accessing the snap ring to pull the yoke.
 
Middle pic shows selector shaft seal leaking. Fluid flows down from there to NSS and pan rail and floor. Carquest/Warever brand part cleaner is least expensive most of the time. Wash it all good and pin point the leak. When a metal line or fitting has a bulge for clamp to sit behind, 1 clamp. Smooth pipe should get 2 clamps. Longer piece of hose covering more of the pipe would help. There isn't a lot of pressure there. If the clamps are tight it shouldn't leak. You might could replace hose and clamps with a compression union rather than replace the entire line.
I dropped pan and valve body of my 904 and replaced selector shaft seal. Less than 90 days later the front seal started leaking. Should have known. They are all the same age after all. Good luck with yours.
 
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To me, it looks like it's time to get dirty. Get the car up on stands, get some good rubber gloves, some eye protection, some Gunk degreaser & brake clean. Clean all of the heavy grease & grime with the degreaser & a brush. Wipe it all down & clean the light stuff left with brake clean & a brush. Replace the cheesy rubber hose & clamps with a couple of compression fittings & a short length of the correct tubing. As stated, take a look at the shift shaft seal & replace if needed, along with the o ring for the NSS. Top off the fluid, drive it a bit before putting it back on stands to inspect & fix any other leaks.
 
Thanks fellas. I’ll be buying a pack of paper towels and start cleaning everything off to find the source and go from there. Hopefully it’s not the pan and just a couple seals.
 
I cleaned the bellhousing, sides and rear of the transmission. Squeaky clean. I’ve let the car sit 3 weeks and it looks like the leak is sourcing two places: from the very front of the pan and the rear of the trans pan. I’ve included pictures.

It finally just about stopped leaking. There’s probably no fluid left in there!

Before I drop the pan and replace with a new gasket, should I try retorquing all the pan bolts to factory spec, replace trans fluid and see if the leak seals? Or just commit to dropping the pan and doing the gasket?

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I cleaned the bellhousing, sides and rear of the transmission. Squeaky clean. I’ve let the car sit 3 weeks and it looks like the leak is sourcing two places: from the very front of the pan and the rear of the trans pan. I’ve included pictures.

It finally just about stopped leaking. There’s probably no fluid left in there!

Before I drop the pan and replace with a new gasket, should I try retorquing all the pan bolts to factory spec, replace trans fluid and see if the leak seals? Or just commit to dropping the pan and doing the gasket?

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I've had more than one car with loose tranny pan bolts. Doesn't cost a thing to tighten them up and cross your fingers. Just don't over tighten them.
 
Use a Duprene gasket; and hammer down the pan rail where the bolts have pulled it up, Go a little down past flush. No sealer. Pan bolts just tight enough to not shear the threads out of the case.
 
Well, upon further research on this sight Ive come to learn much about the offices and common leak points on the 904. Before I disassembled anything, I decided to take a culmination of y’alls advice.
I filled the tranny to full line with it hot after driving an hour around town to make sure it’s at capacity.
I then cleaned the tranny as best I could.
Let it all dry.
I placed thin tissue paper around every possible leak area. I let the car sit 48 hours.
The leak is solely and certainly coming from the shift shaft. Not the pan! So I just ordered the tool and seal and will have at it this or next weekend. Planning on leaving the tranny in the car and the pan on and having a go with it with some patience, clamps, pry bar.
Photos below.
Thank you all.

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Well, upon further research on this sight Ive come to learn much about the offices and common leak points on the 904. Before I disassembled anything, I decided to take a culmination of y’alls advice.
I filled the tranny to full line with it hot after driving an hour around town to make sure it’s at capacity.
I then cleaned the tranny as best I could.
Let it all dry.
I placed thin tissue paper around every possible leak area. I let the car sit 48 hours.
The leak is solely and certainly coming from the shift shaft. Not the pan! So I just ordered the tool and seal and will have at it this or next weekend. Planning on leaving the tranny in the car and the pan on and having a go with it with some patience, clamps, pry bar.
Photos below.
Thank you all.

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Damn good sleuthing. Congrats on figuring out the problem.
 
Well, upon further research on this sight Ive come to learn much about the offices and common leak points on the 904. Before I disassembled anything, I decided to take a culmination of y’alls advice.
I filled the tranny to full line with it hot after driving an hour around town to make sure it’s at capacity.
I then cleaned the tranny as best I could.
Let it all dry.
I placed thin tissue paper around every possible leak area. I let the car sit 48 hours.
The leak is solely and certainly coming from the shift shaft. Not the pan! So I just ordered the tool and seal and will have at it this or next weekend. Planning on leaving the tranny in the car and the pan on and having a go with it with some patience, clamps, pry bar.
Photos below.
Thank you all.

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Good job using the towel trick. Heard of flower/powder. That's slick.
I didn't know there was a tool for the shaft selector. can you post it up.
 
I uploaded the screen shot for the tool. Pricey at $50 but I’d rather pay it and try to take the seal out as opposed to removing the pan, drain fluid and remove valvebody.

Here is the link:
https://www.amazon.com/dp/B011SBJSHA/?tag=fabo03-20

Also the screen shot for the seal I purchased. From my research it was Mopar # 3878447, however, has been replaced by new #4505098.

Hope it works.

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The trick is getting clearance to operate the tool from above.

I put a bottle jack under the tailshaft, dropped the crossmember and let the tailshaft drop down slowly to get some extra clearance to work. I've seen some cut a hole in the floor and get it from inside the cab.

I pulled the pan and used a socket, washers and some threaded rod to press the seal in.
 
I also suggest getting rid of all the rubber hose on those cooler lines. They were not part of the original equation from Chrysler and they don't need to be on there now. Needs to be hard line all the way. Rubber will always break down and leak at some point in time.
 
Hi Rob! Yes I was able to fix that with some 5/16 steel tuning and brass compression fittings. All dry no leaks.

Again, thanks to the help from those on this sight to guide me in replacing those rubber hoses spliced onto the tranny cooler lines. Still learning more everyday and am have a ton of fun with the Dart!

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I uploaded the screen shot for the tool. Pricey at $50 but I’d rather pay it and try to take the seal out as opposed to removing the pan, drain fluid and remove valvebody.

Here is the link:
https://www.amazon.com/dp/B011SBJSHA/?tag=fabo03-20

Also the screen shot for the seal I purchased. From my research it was Mopar # 3878447, however, has been replaced by new #4505098.

Hope it works.

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I have that tool already. It’s on loan to somebody to fix their car. It’s really easy to change the seal. I have all the pictures necessary if you need them.

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Hi CarNut, I tried to message you but no luck. I’d greatly appreciate pictures and insight for the job. I did find some videos on YouTube, but on Jeeps and pickup trucks. I can send me email if it helps. Thanks.
 
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