Ashton Cooke
Active Member
i will check once more and report back. thanks
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CAT 938G, transmission
- Thread starter steed6557
- Start date
Nige
Senior Member
Did you follow the procedure I posted (post #8) on your other thread.?
Are you sure you got the gauges on the correct test ports.?
Also can you see now why having two threads for the same problem is confusing.?
Are you sure you got the gauges on the correct test ports.?
Also can you see now why having two threads for the same problem is confusing.?
Last edited:
Ashton Cooke
Active Member
Yes I see this now . And I’m 100% sure that my guage is on the right test port . It’s too right of valve body (p2) . P(1) is on the bottom of valve body . I checked again today I have 0 psi at test port p2 and it goes forward . Previous owner said they had valve body off
Nige
Senior Member
Refer back to the test procedure page 5. Put a test gauge on port marked G that is located on the transmission filter housing and measures pump pressure. See what that gives you. Note all these readings should be done with the oil warm.
Ashton Cooke
Active Member
test port g = give or take 390 psi close to 400..... i understand that p2 is the direction clutch . but i **** you not i have 0 psi but the machine moves foward.
Nige
Senior Member
Spec's 400+/-25psi so you are on target with that.
Ok, so based on what you said before regarding the previous owner removing the trans control valve (and disassembling it) for whatever reason.
clutching at straws a bit but what do you have to lose.? Take a close look at the valve body. Take photos and post them here. Are there any other plugs in the valve body that could have been swapped when the valve was disassembled and the test points installed in the wrong locations..?
Ok, so based on what you said before regarding the previous owner removing the trans control valve (and disassembling it) for whatever reason.
clutching at straws a bit but what do you have to lose.? Take a close look at the valve body. Take photos and post them here. Are there any other plugs in the valve body that could have been swapped when the valve was disassembled and the test points installed in the wrong locations..?
Ashton Cooke
Active Member
i will remove the valve body flip it over and take multiple pics he said he replaced the reverse spool and slug . i know zf transmissions worked on kawasaki loaders for years now working for kobelco dealer. but i bought this cat to clear my land thinking i could solve reverse easily but seems like i found myself an abortion the guy didnt mention any of these bogus repairs until after i was knee deep.
Nige
Senior Member
Before removing the valve body I would take a close look to see whether or not it is possible for the test points to be installed in a wrong location.
See my suggestions two posts up - need photos of the valve body so that we can see what you are seeing.
See my suggestions two posts up - need photos of the valve body so that we can see what you are seeing.
Ashton Cooke
Active Member
Okay here is the valve body also when I went out to take this picture I started the machine with guage in test port g . This time guage reads 50- 80 psi . No clue why I got over 300 psi before . But now machine Has been running for an hour and Gage won’t go above 80 psi
Attachments
Nige
Senior Member
Maybe start by draining the oil and remove the suction screen to check it.? That is if you haven’t been in there already.
Nige
Senior Member
Before getting in too deep. Would you like to try the pressure readings with another gauge..?
Ashton Cooke
Active Member
i have a break through .... was looking at the control valve pdf you gave me ... so i took the valve body off ands he had the plastic modulating valve on the wrong side of the control valve and the spring on opposite side . i put back together per the pictures provided, and now i have substanial pump pressure 400+ and on p2 port i have 235 psi or so and when put into reverse it drops for a second then returns to normal prssure same with the speeds it drops and returns ... so now i am lostt.........
Nige
Senior Member
At least you are moving forward. I was thinking a bit about your isues earlier today and what came to my mind was "I wouldn't mind betting that this is more than one problem, and the root causes could well be in completely different parts of the machine". So take what you've got so far as a plus - you've found and corrected one issue but a few details need confirming before it can be classed as "sorted". Now read on ..........
P1 & P2 pressures will always dip for a split second when you engage any gear forward or reverse. It's the pressure drop caused by the cavity behind the clutch piston filling as the piston moves. In fact if you had two identical gauges you could put one on test point A & the other on test point B and watch the pressures dip & recover together.
Your P2 numbers seem a bit on the low side, it should be no less than 250psi because the spec is 275 ± 25 psi. See comments below.
What do you have for P1 pressure now.? You never mentioned that.
Remember from the spec that P1 should be 42 ± 10 psi higher than P2.
Also please do the pressure tests (Pump, P1, & P2) at both Low Idle & High Idle RPM and observe if the results are at all different, even if only slightly. Post up all your numbers.
What is the max pressure of the gauge that you are using for your measurements.?
Ideally it should be no more than 500psi, and more important still a gauge that is known to be accurate. A gauge of 1000psi max or even higher can lose accuracy at lower pressures.
P1 & P2 pressures will always dip for a split second when you engage any gear forward or reverse. It's the pressure drop caused by the cavity behind the clutch piston filling as the piston moves. In fact if you had two identical gauges you could put one on test point A & the other on test point B and watch the pressures dip & recover together.
Your P2 numbers seem a bit on the low side, it should be no less than 250psi because the spec is 275 ± 25 psi. See comments below.
What do you have for P1 pressure now.? You never mentioned that.
Remember from the spec that P1 should be 42 ± 10 psi higher than P2.
Also please do the pressure tests (Pump, P1, & P2) at both Low Idle & High Idle RPM and observe if the results are at all different, even if only slightly. Post up all your numbers.
What is the max pressure of the gauge that you are using for your measurements.?
Ideally it should be no more than 500psi, and more important still a gauge that is known to be accurate. A gauge of 1000psi max or even higher can lose accuracy at lower pressures.
Ashton Cooke
Active Member
yeah my guage is 1000psi let me see if i have a 500 max guage ill post back with p1 and accurate readings on p2
Ashton Cooke
Active Member
ok so found 2 500psi guages... plumbed p1 and p2.... p1 is running around 320-325psi and p2 is 275-280 when engaged to reverese they cycle together nd return to their original pressures ...the pressure doesnt seem to move at all when idled up high
Nige
Senior Member
Well that's all within spec. P2 - 275 ± 25 psi, P1 - 42 ± 10 psi higher than P2.
So what's the transmission doing now regarding gear selection.?
Has anything changed in respect of engaging forward speeds even when the transmission control in the cab is moved to reverse.?
Another question. When you select reverse in the cab does the backup alarm sound.?
So what's the transmission doing now regarding gear selection.?
Has anything changed in respect of engaging forward speeds even when the transmission control in the cab is moved to reverse.?
Another question. When you select reverse in the cab does the backup alarm sound.?
Ashton Cooke
Active Member
the machine no longer moves fowrard in reverse . when selected to fowrard the machine will drive in any gear . when put in reverse you feel the torque converter engage with a thud then nothing happens . the back up alarm does sound when put in reverse and when shifted through the speeds in reverse you can feel the gears changing in trans .
Nige
Senior Member
Put the gauge back on P2 again.
With the engine at Low Idle note P2. Engage 1st forward. Observe the pressure dip and especially note the lowest value it reaches before recovering. You'll need quick eyes or maybe have to repeat the test a few times.
Then do the same test in 1st reverse. Is there any difference at all in the pressures you see compared to 1st forward.?
Have you ever removed the suction screen on the bottom of the transfer case to inspect for particles.?
With the engine at Low Idle note P2. Engage 1st forward. Observe the pressure dip and especially note the lowest value it reaches before recovering. You'll need quick eyes or maybe have to repeat the test a few times.
Then do the same test in 1st reverse. Is there any difference at all in the pressures you see compared to 1st forward.?
Have you ever removed the suction screen on the bottom of the transfer case to inspect for particles.?
Ashton Cooke
Active Member
the screen was completely clean of particles ... i will go out and pull p2 again to compare forward 1 and reverse 1. i did notice that it take a few cycles of the f-n-r switch to engage the transmission in foward and same exact symptom with reverse the back up alarm comes on every time you move the fnr switch to reverse but i will only feel the torque coverter if i move it back and forth from N to R a couple times. figured its just getting worn out and prolly not my issue for no rverse cause i do have my solenoid power and torque converter engaging,
Nige
Senior Member
While you are into it, do you have DMM lead attachments that will enable you to back-probe the wires to the solenoids.?
Try taking the voltage readings on the FWD (#3), REV (#2), & 1ST speed (#4) solenoids, but as above it will only give you good results if the solenoids are connected to the machine harness while you are doing it. Measure the resistance of the three solenoid coils while you are at it. The specifications are in a table somewhere on the electrical schematic.
My thoughts - If the F-N-R control does not engage a gear in the transmission immediately that it is moved from N to F or N to R it has to be considered to be somewhat suspect. You might jib at the cost of a new one though, IIRC they are somewhere around $1400.
Try taking the voltage readings on the FWD (#3), REV (#2), & 1ST speed (#4) solenoids, but as above it will only give you good results if the solenoids are connected to the machine harness while you are doing it. Measure the resistance of the three solenoid coils while you are at it. The specifications are in a table somewhere on the electrical schematic.
My thoughts - If the F-N-R control does not engage a gear in the transmission immediately that it is moved from N to F or N to R it has to be considered to be somewhat suspect. You might jib at the cost of a new one though, IIRC they are somewhere around $1400.