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Old 09-28-2003, 08:36 AM
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Cross leaks in the 4L80 pump.

When I installed the new sonnax boost valve it gave a procedure for wet testing the pump for leaks. I did and it had cross leaks in the pump assembly, while adding pressure to the torque signal orifice it would leak out between the castings pretty good, the reverse boost orifice wasn't as bad but leaked also.
I had to find a piece of flat glass and used some 320 grit sand paper on it to flat sand the pump. It was a little difficult to work around the stator shaft. Sanded both pieces.
My ATSG manual says nothing about checking for cross leaks, how much can be tolerated? My home grown resurfacing made a pretty good difference but it still leaks very little.
The manual does not even mention it so that gives me the idea it's not critical. In the real world is it normal for it to leak a little or should it be air tight?

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Old 09-28-2003, 01:19 PM
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Some leakage is normal.

We machine the stator flat. Then we flat sand the pump body on a large 1.5 inch thick chunk of steel that was ground flat/smooth with a round sanding disc stuck on it.

Get them as flat as possible
Dont worry how old you are... it is the mileage on your body that adds up.
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Old 09-28-2003, 06:46 PM
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Cool, what I did sounds close to the procedure you use.
I just got back from a test drive, it runs great, strong reverse and manual first engine braking. All shifts are good. Went about 60 miles, about 25 city and the rest highway, the tcc only worked a few times at first. I'll change the solinoid. No trouble codes stored for the trans, it keeps getting a lean exhaust code, and come to think of it thats about when the lock up quit, oh yea somewhere between that and the brake light coming on, don't know if any will effect the tcc but I'll get it worked out.
Thanks for the help along the way.
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