ZF Transmission fluid leaking from filter cap

peterkvs

peterkvs

Active Member
Nov 11, 2012
511
Guntersville, Alabama
Boat Info
400 Sundancer 1999
Engines
3116 Cats, 1000 hours
I recently changed the transmission fluid in my 99 400 sundancer with 3116 and ZF 800 IV V drives. After a short cruise I noticed about a pint of transmission fluid in the bilge. Then after another short cruise I figured out that it was coming out of the filter cap on Starboardv drive.

The filter cap is a two piece arrangement that when tightened squeezes an O ring out radially so that it tightens against the housing of the transmission. However in my case the cap does not seem very tight and is quite easy to move and wiggle around. I was able to put two wraps of teflon tape around the oring on the cap and get the leak to stop for now, but really need to address the problem correctly.

Questions...

1) When the screw in the cap is tightened, compressing the oring, should you still be able to easily move the cap?

2) The torque spec for the screw in the cap is something is 4-6 ft/lbs, but I hardly get any resistance to the screw until the top and bottom halves of the cap come in contact with each other.

3) The oring seems supple, can they shrink over time? The outer perimeter seems a bit scuffed.

3) I believe that new orings come with a new filter, but nothing is wrong with my filter. Does anyone know where I can get the o rings for the filter cap separately. Anyone know the oring sizes?

Thanks,

Pete
 
Pete,

I wonder if you are seating the filter assembly all the way. It should be flush with the housing around it when it is seated.

Could a previous owner have swelled the filter when it was serviced previously? Try swapping ends with the filter itself.

Yes, the O rings should be available locally. They are probably metric in size, however.


That is all I can think of........this is a new one for me.
 
Frank, thanks for the advice. As far as I can remember the cap was all the way down and the tab on the edge of the cap was flush with the top of the housing. Even then, the cap was easy to rotate and I would have thought that there would be more pressure between the cap and the side of the housing when the oring was compressed by squeezing the caps halves together with the center screw. I guess I'll just order new filters with orings and see if they are tighter.

Pete
 
You are right. When the o-rings are compressed, you cannot rotate the filter cap. The new filtr assy will probably answer the question in that you can see t he correct o-ring size and filter shape.
 
I replaced the filter and O rings. No leaks. I can still rotate the cap, but there is much more resistance now. Thanks Frank for the help. Pete
 
So I checked down in the bilge again and noticed that it is still leaking, just slower. So I took out the lid and wrapped it with Teflon tape and put it back in and now it does not leak. Crazy. I think in order to fix it properly I would have to machine down one of the plates to make it squeeze the o-ring out more.
 
The leak should be fixed before you run that gear again. The filter housing operates at a negative pressure; the gear-rotor oil pump draws oil through the filter from the filter's center through the filter's media to the outside of the filter. If there is a leak in that O-ring the oil will mix with air and will be detrimental to the pump pressure, clutch plates, and valve body. If you do not have the service manual for the gear do an internet search for Reparaturanleitung u Ersatzteilliste ZF63IV bis ZF85IV.PDF and get it. There is not only the filter assembly diagram but also a fluid schematic in the manual.
 
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Thanks for the input. I am really confused now as I don't understand how the fluid would be leaking past the Oring if it is on the suction side, which it clearly shows in the manual. Just to reiterate.

1) No sign of leakage before I changed the transmission fluid and cleaned the filter
2) After changing oil and cleaning filter on both transmissions, the starboard side leaked out about a qt of transmission fluid through the filter cap in about 2 hours of operation.
3) Initial wrapping of Teflon tape around the oring on the cap stopped the leak.
4) Because I hate patching things up like that I bought new filters and gaskets and fitted them.
5) I did not observe leaks the first couple of hours of operation, then noticed it was leaking slightly.
6) Once again applied Teflon tape and it stopped the leak.

Observation of the parts show that even with the top and bottom clamshells tightened completely, and the oring squished out, the filter cap can still be rotated by hand, I would expect it to be tight enough that you could not turn it. I have not observed the fluid appearing foamy. The one transmission that does not leak always has a slight suction sound when removing the cap, the one that leaks does not.

it looks like I could machine the filter cap parts so the would close a little tighter and squish out the o-ring a little more, perhaps tightening it up a bit, but I really hate to do that. I guess I could try and find a place to buy a new filter cap assy. Is it possible that the gasket below the filter needs to be replaced so that it holds the filter and cap a little higher up and more against the lip of the case?

Any help is greatly appreciated.

Pete
 
I supposed the question is, how much fluid did you put into the trans; too much and it will possibly do what is happening... Or, the clamping of the oring is inhibited due to bent or warped pieces. Might try to swap and see if the problem moves to the other gear. Also if the filter seal on the bottom is not allowing the element to seat all the way down. Just a couple of thoughts... You replaced both of the Orings when changing the filter,right? The filter kit comes with both.
 
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The transmissions were filled to the top mark. I measured just after running the engine and made the measurement without screwing the dipstick in. This is how they say to do it in the manual. The first time it leaked out the quart into the bilge it was down to the bottom line when I finally caught on, so I don't think it is a level issue. Let me ask you this, after you tighten the 6mm bolt on your oil filter cover, can you still turn the oil filter cover by hand? or with the allen wrench? My oil filter cover is pretty easy to turn. The filter cover does not look bent at all. I did replace bolt orings. I am not sure what the status is of the seal that the filer sits on. Perhaps if that was a bit taller/thicker, the filter cap would rest ride a bit higher which would push the oring up to where it is a little more narrow.

Pete
 
peterkvs said:
Let me ask you this, after you tighten the 6mm bolt on your oil filter cover, can you still turn the oil filter cover by hand? or with the allen wrench?
Click to expand...

Yes and that also bothered me the first time. Now I wipe everything down with solvent to remove oils and only put a very small amount of ATF on the O Rings. I also wedge/press the bolt down into the cavity as I tighten it to ensure the assembly seats firmly on top of the filter element and the O Ring is as low as possible in the groove. If I remember correctly the filter element has different size holes in the end covers so they will only go in and seat over the pickup tube and seals one way.

Again, you might want to swap the covers between the two transmissions to see if the problem follows or stays with that filter cover. If the problem does not follow to the other trans. You would have other issues.
 
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I have had six of these ZF transmissions and have never experienced a cap that would move after tightening the screw. I have also rebuilt two of these transmissions for a friend. Again, no movement of the cap. While reading this post I had a thought. Maybe you have an issue with the screw threads themselves. Perhaps the female thread has debris in it, maybe some stripped threads. Make sure both transmissions have the same length bolts. With all that you have gone through I would think you need to look at something else. The cap should not move.


Just a thought.
 
The screw pulls the two metal halves of the cap assembly together to where they are are in contact with each other (it's a hard mate); as you probably already know. With the cap halves fully pulled together it slightly squeezes the large O-Ring out from the cap assembly perimeter to enable a seal to the transmission housing. It is not a hard nor tight seal and if you should turn the screw beyond where it had drawn the metal halves together it will simply turn the cap assembly in the housing until the little tab contacts the housing and will not allow it to turn anymore. Originally, I could move mine by hand after tightening but now after fully cleaning the assembly and housing with solvent the O-Ring grips better; in all cases I can twist with the allen wrench and some minor force. Now, should the O-Ring not be the correct section thickness a suitable contact force to the housing will not be enabled; probably something to consider. I would doubt that the cap assembly is warped or bent as these are pretty hefty and when in full contact with each other the screw cannot be tightened any further.

AFT comming from the assembly can only be from either something blowing it out or the seal is completely ineffectual and splash is comming out; remember this area is operating at a negative pressure to draw ATF from the sump.

I still suggest that the caps be swapped between the two transmissions and isolate if it's the cap or something else.
 
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Thanks Guys,

The threads are fine and the bolt is not bottoming out.

I did notice that the holes in the filter are different sizes and that only one side press fits onto the oring on the cap. Interestingly, I recall that when I now remove the cap the filter comes with the cap and has to be pulled off, but when I took off the caps the first time, the filters did not come with the cap. I wonder if the doofuses at MM put the filters in upside down before? Now I am starting to wonder if maybe the bottom seal for the filter is no longer in the transmission or something like that. The orings I am using came with the replacement filters I bought, and were installed after I noticed the leak after the filter cleaning. Maybe there is a batch of bad/undersized orings? Who would think that. Is there a difference between metric and standard orings? I like the idea of swapping the caps. I will do that this weekend and see if I can see if the problem follows the cap. Being on the suction side of the pump I would think that the cap should be tight and not able to move, but most people say it moves. Interesting that Gary has seen them not move. What a PITA.

Thanks for your thoughts,

Pete
 
Pete,

I have had a thought on your leaking filter.............

First, open the repair and parts list:

http://www.bukh-bremen.de/files/346...itung u Ersatzteilliste ZF63IV bis ZF85IV.pdf


The torque spec for the filter is low.....like 4-6 ft lbs........... page 27. The o-ring should expand enough on the taper to contain the fluid very easily since only 6 ft-lbs are required to seat it.

Now look at page 32. This shows the fluid flow in the transmission. The pump sucks the fluid from the transmission sump thru filter which is the only component the fluid passes thru on its way to the pump. I think that means the filter should have a vacuum on it when the transmission is operating. So it shouldn't leak from the filter housing when the boat is running. If this is correct, then there are only 2 ways I see where there would be enough pressure to force fluid out of the filter:

The transmission case breather is stopped up............page 70-71, item #2, and the "lube pressure relief valve". If it doesn't seal, then pressurized fluid is returned to the sump and the filter would be under pressure rather than a vacuum during operation. Unfortunately, I am not as conversant in Italian as I am in Southern red-neck so I can't find the location in the parts break down for the the pressure relief valve, but I suspect it is going to be nothing more than a ball and spring held in place by a retaining ring of some sort.


Hope that helps............
 
Follow up. I went down to the boat and pulled the airvents. I could kind of blow through them if I wiggled the cap. So I cleaned them with brakeparts cleaner and lubed them with ACF-50. Then reinstalled. I sucked about a pint of fluid out of the port transmission as it seemed a bit over full, the starboard trans was fine. I really cleaned and prepped the oring areas on the caps and in the transmissions and reinstalled the caps. I also swapped them from one transmission to the other. So far no sign of leaks. The damn caps still seem loose to me and I can't imagine that they are not allowing some air to be sucked into the transmission. However, after a long run I pulled the dipsticks and the fluid is not foamy. When I was cleaning the mating surface on the transmission I noticed that where the oring sits agains the wall of the transmission housing that there is a slight indentation there. I wonder if that is supposed to be there or if over time the oring has worn a groove which is why it seems a bit loose.

Pete
 
Follow up on the follow up.... Drove the boat for a couple weeks with no sign of leakage and thought the problem was fixed. Then drove the boat for a couple hour ride up river at about 1350 rpm. Just cruising and enjoying the trip. The next day I topped up with fuel and climbed down into the bilge to check on everything. Damn starboard transmission covered in fluid. About a pint had leaked out through the filter cap and ran down the bow end of the tranny. I had switched the caps and apparently that did not fix or move the problem. The oring is just not tight enough to seal against the worn sealing surface of the transmission housing. So I wrapped three layers of Teflon tape around the cap and the oring and replaced it. Now no leaks again. I'm not sure what the heck is going on. Perhaps it is spilling over after I stop and heat expands the air and pushes up the fluid. I have no idea. it is supposed to be the suction side of the transmission. How can it be getting past the damn oring and cap if it is on the suction side. Perhaps after I shut down the transmission cooler drains back into the tranny and causes the overflow somehow. It is very annoying.

Thoughts?

Pete
 
Pete - so the problem did not follow the cap; that eliminates 5 out of 300 parts (levity)....
I just cant believe the housing is worn out. Next thing to check is the running temperature and as Mr. Webster earlier stated is the case vent. I will note that every time I check the oil there is a "hiss" as I unscrew the dip stick when cold; it's slightly under vacuum, both transmissions and every time. The only other thing is an erratic pressure regulator causing suction side pulsations (wild thinking). I believe the regulator is easily accessible from the forward end of the unit.
 
When I feel the housing, there is a fairly rough indentation where the oring in the cap sits. I thought at first it was an indentation for the oring to expand into when it was compressed, but its a bit irregular and could be showing some signs of wear. I'll take my IR thermostat down and make some comparative measurements under way and see what I am getting. The vents were cleaned when I swapped the caps. With the Teflon tape wrapped on the cap I get a suction hiss sound when I remove the dipstick, I don't get that sound without the tape on the cap. The other tranny always has the suction sound when removing the dipstick. Keep in mind there was no sign of leakage until I changed the trans fluid and cleaned the filters. I wish they made orings with a slightly larger cross section as that would be more elegant than Teflon tape. I also wish I had some pressure gauges and knew exactly where to hook them up.

Thanks for the help

Pete
 
Peter
Can you get a decent measurement on the o-ring and check McMaster-Carr's website for something a bit thicker? Maybe order a few sizes and try them in to see what works.
 
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