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Where does a 904 leak from when shut off?
https://www.slantsix.org/forum/viewtopic.php?t=54634		 Page 1 of 2
Author:  Reed [ Sat Feb 15, 2014 10:03 pm ]
Post subject:  Where does a 904 leak from when shut off?
Trying to diagnose a delayed D and R engagement on the rebuilt 904 in my brother's project Duster.

I suspected the low/reverse band was adjusted wrong. When I dropped the pan only about a quart of fluid came out. The band adjustment was right on.

A while back the transmission leaked out a bunch of its fluid while the car was parked in my garage. So now I am fairly sure the engagement problem was a low fluid level issue.

However, why would the trans leak when the engine was shut off? The leak was from under the bellhousing. The front pump seal is new, the TC is new, there were no signs of leaking from the cooling line ports, the shifter, or the speedo cable. The dipstick tube doesn't appear to be leaking, but I will check closer tomorrow. The pan doesn't appear to have leaked either. I am hoping the problem is not something like a cracked case.

I guess the upside is I already have a rebuilt spare 904 under my workbench. :roll:
Author:  mattelderca [ Sun Feb 16, 2014 7:33 am ]
Post subject: 
What about the torque converter plug if it has one. Or maybe a loose front pump bolt?

These trannies do have a delay into gear by nature though. The torque only fills in gear or neutral, not park. Going right from park to drive, especially after a day or so, does give you a very noticeable delay. I usually go to neutral first for a second. Doesn't explain the leak though.
Author:  Reed [ Sun Feb 16, 2014 7:36 am ]
Post subject: 
This is more than the typical slight delay. This is me having to rev the engine up to about 200 RPM for several seconds before the gear would slowly engage. I am going to refill the trans today and crawl underneath the car and watch where the drips initiate. I really hope it isn't a front steal or TC issue. I don't believe the TC has a drain plug. It is a 1983 lock-up version.
Author:  Doctor Dodge [ Sun Feb 16, 2014 8:36 am ]
Post subject: 
A slow leak during long periods of sitting is usually thru the gear selector / kickdown seal.
Converter drainback, after shut-off, raises the fluid level past the seal and that is when it leaks.
The early "cable 904" seal is small so it needs to be in good condition to work.
Later units have 2 seals that both need to work.
DD
Author:  Reed [ Sun Feb 16, 2014 8:46 am ]
Post subject: 
Thanks Doc. I refilled the trans this morning and I am keeping a eye on it. No immediate leaks, but I am going to run it in neutral for a bit to try and find the leak.
Author:  wjajr [ Sun Feb 16, 2014 9:49 am ]
Post subject: 
The other seal to see fluid after drain-back while parked is filler/dip stick tube. Any fluid leaking past that O ring would work its way down to bottom of bell housing/ dust plate area mimicking a leak from torque converter/ air vent/ pump shaft seal.

Clean outer connection point of fill tube to transmission body & lower bell housing areas well, add fluid, and keep inspecting occasionally. That O ring must be fresh and supple as well as real clean when installed, a little dab of Vaseline will aid its installation.
Author:  Reed [ Sun Feb 16, 2014 10:06 am ]
Post subject: 
Hey, guess what! Automatic transmissions work better when they have fluid! After adding two quarts of ATF the trans drops right into both D and R like it should. I ran it for a bit in N to let the fluid circulate and then shut it down. Now I will watch all the leak points to see if and where it is leaking from.
Author:  Joshie225 [ Sun Feb 16, 2014 10:08 am ]
Post subject: 
The front pump bushing is rather narrow and can wear rather quickly if the crank and pump are not concentric. Therefore a new pump seal can leak rather quickly because the converter neck is not adequately supported. Converter drain-back is usually the first sign of a worn pump bushing as the stressed seal wont hold the small vacuum needed to keep the converter full.
Author:  Reed [ Sun Feb 16, 2014 10:20 am ]
Post subject: 
Hmmmmm. I will keep the pump bushing in mind. So far, no leaks. I will let it sit some more today and see how it does.
Author:  Reed [ Sun Feb 16, 2014 11:46 am ]
Post subject: 
Well, so far, so good. I ran it again and shifted it through all the gears. It has been sitting for about 45 minutes and no leak. Cool. THis means I can trailer it over to a body shop and get the bodywork done. Hooray. Then the project will really get moving.
Author:  wjajr [ Sun Feb 16, 2014 8:42 pm ]
Post subject: 
Yup, a yard driver is a big plus.
Author:  Reed [ Sun Feb 16, 2014 9:06 pm ]
Post subject: 
A yard driver definitely beats a garage sculpture for five years.
Author:  slantvaliant [ Mon Feb 17, 2014 6:17 am ]
Post subject: 
Intermittent leak points I had to deal with on a '64:

Dipstick tube O-ring
Hidden cracks at the dipstick tube bracket spot welds.
Author:  WagonsRcool [ Tue Feb 18, 2014 11:03 am ]
Post subject: 
+1 to worn front pump bushing. Even if trans case alignment is in spec. a worn bushing will let the converter neck "flop around" & allow drain-back. The trans will often seep from the vent hole in the bellhousing after the car sits for a week or more.
Author:  Reed [ Tue Feb 18, 2014 11:57 am ]
Post subject: 
Thanks. I will be pulling the engine and trans to prep the car for painting and I will inspect the front pump bushing when I have the teas out.

Now, I am off to load the car on the dolly to haul it over to the body shop to have the rear end bodywork finished.
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