Trans cooler lines- NO Flow. Aerated fluid...

[zjsheller]

Here's my problem. Trans wouldn't shift up in my 96 4.0 ZJ last week and upon pulling the dipstick I discovered aerated fluid in the trans. Fluid levels are OK. Fluid looked and smelled OK (it was changed less than 10k ago).
In doing some research I have seen others with a similar problem and the culprit was a blocked trans cooler. Thinking I was going this route, I pulled the cooler and it seems fine. No blockage. I can blow through it freely.
So I then decided to check for what kind of flow I had to the cooler. I started up the ZJ and let it run in neutral with the cooler taken off. I initially got what can best be described as a big burp, then nothing. Very slow trickle. I checked the flow in drive and same result.
Now my problem is I'm not confident in translating my test results into a solution to the problem!
Is there supposed to be regular, steady flow with the trans in P or N or D?
If so, how much? It certainly doesn't seem like a cooler would be too effective with this slow of flow.
If there is some kind of blockage, is it most probably in the line?
Is there a chance thats is some sort of pump in the transmission?
Filter was changed with fluid change. Any chance thats clogged already?
What should my next step be?
Thanks in advance!!

 

[shortbus4x4]

When exactly did this start? Right after the filter change or did you get a few miles on it? My first thought on reading your description would be to check the filter, not for a blockage but a leak. The filter is on the suction side of the trans pump, if it doesn't seal where it bolts to the throttle body and the sealing surface is above the ATF level then it will be sucking air. This will cause your ATF to aerate, low flow through the pump, and your transmission to do nothing when its in gear. Another thing is if the trans filter is held on with bolts I have seen them over torqued which then creates problem in the valve body, basically fluid going where its not supposed too. This is where I would start my diagnosis.
Does the 4.0 ZJ have a AW4 trans or is it a Chrysler product? Chrysler trans usually have a one way flow valve in the cooler lines that sometimes will become messed up and allow no flow. Its easy to check for though. Take the cooler lines off at the trans and see if you can blow through them.

 

[zjsheller]

When exactly did this start? Right after the filter change or did you get a few miles on it? My first thought on reading your description would be to check the filter, not for a blockage but a leak. The filter is on the suction side of the trans pump, if it doesn't seal where it bolts to the throttle body and the sealing surface is above the ATF level then it will be sucking air. This will cause your ATF to aerate, low flow through the pump, and your transmission to do nothing when its in gear. Another thing is if the trans filter is held on with bolts I have seen them over torqued which then creates problem in the valve body, basically fluid going where its not supposed too. This is where I would start my diagnosis.
Does the 4.0 ZJ have a AW4 trans or is it a Chrysler product? Chrysler trans usually have a one way flow valve in the cooler lines that sometimes will become messed up and allow no flow. Its easy to check for though. Take the cooler lines off at the trans and see if you can blow through them.

Nothing has changed since the fluid change. Ive put lots of miles trouble free.
Is it possible the bolt holding the filter had loosened?
Is it fair to say I should have a steady regular flow while in neutral? Or is park or drive the correct gear to test this?
Thanks for your advice.


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[shortbus4x4]

Look at the dipstick or owners manual and put the trans in whatever gear it says to check your ATF level in when checking for flow, your pump will be working when its in this gear. Make sure you check your trans using the proper procedure, you could be low but think your not if you don't. Your correct to think that your filter could have loosened since your trans was serviced, I have seen that happen before.
One way you could check for flow and aeration is to disconnect your trans cooler line and hook a clear plastic hose inline. You can find the hose, clamps and fittings(if required) at a hardware store.

 

[zjsheller]

Thanks folks!
Sounds like the next step is to pull the pan and check the filter.
I'll try to get to it in the next couple days and keep you posted.
Thanks again for your input.

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[zjsheller]

Well, pulled the pan and checked the filter. Seems ok IMO.
Any ideas on what the next step should be? How do I check the pump? Heck, where is the pump?
Here's the filter for your opinion: