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Discussion Starter #21
No.

The main regulator creates line pressure. It is controlled by the EPC (Electronic Pressure Control) solenoid. Line pressure is used to actuate the clutches, but not through the shift solenoids. The shift solenoids use a pressure tapped off of line, but also limited. All the shift solenoids do is move the shift valves in the valve body. The shift valves send line pressure to the clutches.

Yes, that's how it works.


Not necessarily. The converter doesn't see line pressure, it sees a pressure that is limited to 120 PSI. Line pressure can exceed 300 PSI.


One gallon per minute is the spec. I like to measure one quart in 15 seconds. That way you won't run the pan out of fluid.


Maybe that will help while the clutch is applying. Maybe.
WOW! School is defiantly in session!
I think I see it now.
Pump to main Regulator Valve (which limits Converter feed to 120 psi but will reduce flow to converter in an attempt to maintain line pressure.) From there flow is divided to the converter, and Line pressure which is controlled by the EPC. Control circuit is fed from reduced port off Line pressure. Electric Solenoids use the control fluid to operate the valves which send line pressure to the desired clutches.
Therefore, if i am correct in my new thinking:
A flow check would help determine position of the Regulator valve.
a) Low line pressure and high flow thru the converter, then the valve is possibly stuck open?
b) Little to no flow and low line pressure, Regulator valve is closed attempting to maintain line pressure. faulty pump? Internal leak?
c) EPC is programmed low which would give high flow and low line pressure

Does the EPC ramp up Line pressure depending on gear and engine load demands?
I am thinking the ECM has no way of monitoring the Line Pressure?

I have a live tune chip on the truck and could adjust the EPC, once I locate that feature in the tune. The tune came from a friend and I have only adjusted shift points according to my needs. So I don't know what adjustments he may have made to the line pressure. I have had no reason to think programmed line pressure was low. Shifts are always firm. I will contact him to see what was programmed.

For the flow test;
Which cooler port do you use?
I am thinking once I know which port to use, secure the hose in a bucket. Run truck for 15 seconds.
I have an old cooler bypass line. I could use it to make a valved test port and even check pressure? I could just drill and tap the head of the Banjo bolt and make a test port.
Better yet. What size are the threads in the case that the banjo bolt threads into? Possible oring boss?
I could put some fittings on with valves and look professional. Lol!

Thanks
 

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A flow check would help determine position of the Regulator valve.
Maybe. I've never considered that.
a) Low line pressure and high flow thru the converter, then the valve is possibly stuck open?
There is a fixed orifice that controls the flow through the converter. The check valve only prevents the converter from draining when the pump isn't running. Even if it is stuck open it will not cause a pressure issue.
b) Little to no flow and low line pressure, Regulator valve is closed attempting to maintain line pressure. faulty pump? Internal leak?
Yes, either the pump or an internal leak.
c) EPC is programmed low which would give high flow and low line pressure
It would give low flow and low line.

Does the EPC ramp up Line pressure depending on gear and engine load demands?
I am thinking the ECM has no way of monitoring the Line Pressure?
The ECM adjusts pressure every few milleseconds. It looks at gear, load, speed, and many other variables.

The PCM does not monitor any pressures.

For the flow test;
Which cooler port do you use?
I use the port on the rear of the trans. If you get a spray of fluid out of the trans either the cooler circuit is restricted, or if your trans has a cooler bypass (I forget what years had one) is bad. A few drips while it is running is normal, but not a good size flow.
I am thinking once I know which port to use, secure the hose in a bucket. Run truck for 15 seconds.
Use two buckets and a helper. Start with the line in one bucket and watch the flow. After a few seconds it will become steady. Now move the hose to the second bucket for exactly 15 seconds, then back to the first bucket, and have your helper shut the engine off.
I have an old cooler bypass line. I could use it to make a valved test port and even check pressure? I could just drill and tap the head of the Banjo bolt and make a test port.
I don't have a spec for cooler line pressure.
Better yet. What size are the threads in the case that the banjo bolt threads into? Possible oring boss?
I don't know.
 

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Discussion Starter #23
Could 5 psi of fluid pumped into the out going port that goes to the cooler be away of testing the converter circut back to the drain down check valve?
 

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No, that won't prove if it works or it doesn't.

To diagnose the check valve check the transmission fluid level after the truck has sat for at least 8 hours. Check it before starting the engine. If the level is way above the full mark the check valve is not working.

The ONLY problem the check valve can cause if it doesn't work is that the converter will drain down when the engine is off. Within the first minute after starting the engine there will be NO effect from the check valve. It cannot cause low pressure, poor cooling, etc. It has NO effect when the engine is running.
 

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Discussion Starter #25
This week I have been chasing down another issue with the truck. For the last several weeks I have been getting a sound very similar to all terrain tire noise when I let off the pedal slowing down, torque converter locked or unlock all decelerating speeds. Braking or not braking. I first thought my transfer case was engaged it was the running noise of the front axle. Hubs are unlocked and both spin free. Front drive shaft spins freely also. I then inspected the rear axle gears and found excess back lash. I re-shimed the ring gear carrier to specs and expected the sound to go away. Much to my surprise there was no change. It sounds like it is coming from the front axle or front of tranny. I thought perhaps needle bearings in the hubs. I decided to shift to neutral when decelerating and if was the axle then the sound would still be there. But the sound stopped. Every time I shift to N when decelerating. Is there anything with my low line pressure issue that can be causing this in the tranny. Torque converter?
Thanks
 

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Discussion Starter #26
Hello Mark,
An update. Turns out that the digital pressure gauge have been using is defective, giving false readings. I hooked up a mechanical gauge and at Idle I have the following pressures:
P-65 psi
R-90 psi
N,D,2,1-65 psi
Stall:
R-225 psi
D-125 psi
That's much better.

When I shift to R, I have learned to pat the accelerator a couple of times to get the pressure to spike for a moment and the transmission will not bind when I back up. Like their is a stuck valve or something like a valve that the moves at the higher pressure.
 
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