904 Pump Housing Leaking Between Ports

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T56MaxTorq

T56MaxTorq

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Hey guys, have a '76-78 904 that I'm rebuilding for my Duster. I have 5 clutch front clutch and pump (it's tapered on one end) Problem is that when air checking the clutches I have air and fluid leaking from the front clutch port to the rear clutch port. It's leaking at the pump split line halves. With 20psi I can actually actuate both clutches simultaneously. I assembled the pump halves by putting the pump in the transmission housing and torquing the bolts. I even did it twice and and tried lightly sanding any burrs on the surface where the two pump halves meet. Is my pump garbage or am I doing something wrong??
 
Never saw one leak there before. Are you sure you don't have a parts mismatch somewhere? I'd pull the pump and front clutch packs and bench test them as an assy. and see what happens.
 
fishy68 said:
Never saw one leak there before. Are you sure you don't have a parts mismatch somewhere? I'd pull the pump and front clutch packs and bench test them as an assy. and see what happens.
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WTH? I have never seen that before either.

You are putting the halves together without anything between them right?
Check for burrs?
Are you sure there isn't a broken ring on the stator or input shaft?
 
I checked for burrs and gave a light sand to both halves. No there is nothing in between the two halves. No broken rings. I have the front and rear packs assembled on the bench with the pump and I'm air checking it that way. The clutches are actuating properly when air is applied. It's just leaking over from front to rear clutch. I put my thumb over the port I'm not applying air to and there is enough air leakage to actuate it.

When I first assembled the pump, I installed a used gerotor from the trans shop that pressed my bushings, I'm going to remove it and see if that helps. And torque the two bolts nearest to the pumps ports first.
 

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It is normal for some bleedover in automatics, but how much is the question.
Have you tried putting bolts and nuts in those two bolt holes and checking it?
It might make you feel better about it if you can see it clamped.

Since there is no gasket between the pump halves I would expect bleedover in those places especially without all the bolts in it.

Just snug them a little, and not as tight as you would put the actual bolts in.

If the front drum fits the stator and rings well, and the direct drum input shaft rings and bushing fits good I'd be ok with putting it together.

One thing you might try is to put it in and when you air chk the direct drum see if you can turn the forward drum while the direct is engaged.
If you can turn it, I would feel fine about it.
 
I will try nuts and bolts and see if that helps! I didn't think of that. It might help since the bolt holes are adjacent to the those fluid ports.
 
I also learned it's best to just give a quick "blip" with the compressed air. If left on longer it will bleed out & I've thought there was a problem when there wasn't. I changed a set of piston seals about 4 times before someone cleared that up for me.
 
T56MaxTorq said:
I will try nuts and bolts and see if that helps! I didn't think of that. It might help since the bolt holes are adjacent to the those fluid ports.
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Of course it will only make you feel better about it, but that couldn't be a bad thing.
Once bolted in it should seal as well or better.



80fbody said:
I also learned it's best to just give a quick "blip" with the compressed air. If left on longer it will bleed out & I've thought there was a problem when there wasn't. I changed a set of piston seals about 4 times before someone cleared that up for me.
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About one second at 30 lbs or so is what I have always used.
After awhile you get used to the sound it makes when it is good, but that does'nt do any good for someone who has never heard it. :)
 
Someone posted a quick video of them air checking an assembly on the bench. Also explained that the 727 front drum is a little lazy when checking with added springs. That's the one I thought was no good.
 
Using the bolts and nuts really helped, it still leaks a little but not nearly as bad and only slightly actuates the rear clutch but not enough to push the clutches and steels against the snap ring. I feel good about it. Thanks for the help!

I still get a good air leak sound and I found it to be the front clutch rings which are installed on the pump. The front clutch drum is new and I changed the rings out for a different set but no change. With just the front clutch installed, some air bubbles and fluid leak by but not much. Should I be concerned? The rear clutch doesn't sound this way.
 
T56MaxTorq said:
Using the bolts and nuts really helped, it still leaks a little but not nearly as bad and only slightly actuates the rear clutch but not enough to push the clutches and steels against the snap ring. I feel good about it. Thanks for the help!

I still get a good air leak sound and I found it to be the front clutch rings which are installed on the pump. The front clutch drum is new and I changed the rings out for a different set but no change. With just the front clutch installed, some air bubbles and fluid leak by but not much. Should I be concerned? The rear clutch doesn't sound this way.
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Think about this and it'll make total sense to you.

Air leaks out a TON faster than fluid, so you should be good to go now.
Air can cross over into other things a lot easier also, and that is why I wasn't to worried about it as long as the sealing rings were ok.
 
Awesome! Makes total sense. I've only built a 727 but that was over a year ago and it didn't have any hard parts replaced unlike this 904 which trashed the front clutch drum. Hence why I'm so uneasy about it. Thanks again for your help, guys!
 
TrailBeast said:
Think about this and it'll make total sense to you.

Air leaks out a TON faster than fluid, so you should be good to go now.
Air can cross over into other things a lot easier also, and that is why I wasn't to worried about it as long as the sealing rings were ok.
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Just what I was going to say. Every time I air test them I get enough air leaking you'd think there's a problem but fluid is so much thicker it'll seal up and not leak past.
 
fishy68 said:
Just what I was going to say. Every time I air test them I get enough air leaking you'd think there's a problem but fluid is so much thicker it'll seal up and not leak past.
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I still remember some of the stuff I learned :-D
 
Hey T56 how did this work out for ya? I just ran into the same problem on a 904 I'm building. It's leaking real bad and for the life of me I can't see anything wrong laying a good straight edge on it.
 
I normally squirt a bit of ATF into the holes with a syringe before I do an air pressure check. It usually seals things up good, where air would just whistle out.
 
fishy68 said:
Hey T56 how did this work out for ya? I just ran into the same problem on a 904 I'm building. It's leaking real bad and for the life of me I can't see anything wrong laying a good straight edge on it.
Click to expand...

I know you know this but the bolted in pump won't leak anywhere near as bad as one sitting on the bench without the perimiter bolted down in the case.
 
KickDown said:
I normally squirt a bit of ATF into the holes with a syringe before I do an air pressure check. It usually seals things up good, where air would just whistle out.
Click to expand...

that usually does the trick..especially if the seals are dry.......

and use some good old vasoline on the seal..
 
TrailBeast said:
I know you know this but the bolted in pump won't leak anywhere near as bad as one sitting on the bench without the perimiter bolted down in the case.
Click to expand...

I haven't tried bolting it into the case but I did install bolts and nuts through the mounting holes around the perimeter and it still leaks real bad. The bolts help a little but I don't think it's nearly enough. Air just pours out. The crazy part is laying a good straight edge on it I can't even get a .001 feeler gauge under it nor can I see any daylight under the straight edge. I may try pouring some atf in it and see if that slows it down any.
 
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