I have a 4YS serial number 938G. The trans sometimes will not come out of forward, I can put the shifter into N or R and the loader will drive and shift forward. There are no fault codes on ET. I wiggled the steering column and the fault would appear and disappear for a time but would eventually stick in forward, the same with the parking brake if I moved it up and down the fault would come and go so I changed the switch on the back of the parking brake and it made no difference. So I am back to this intermittent fault, when the trans is working as it should it shifts strong in every gear. I thought it might be the spoolsticking in the tranny but that seems unlikely due to the wiggle and parkbrake scenario. Any one come across this before, I don't really want to start tearing a loom apart. Thanks Gary.
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CAT 938G, transmission
- Thread starter steed6557
- Start date
Nige
Senior Member
I would need to dig a little deeper into the system to be sure (no internet right now) but from the symptoms you are describing my first thought would be a harness fault in or around the steering column - especially in view of your comment that wiggling the column makes ther problem go away temporarily. I'll have a closer look when I get back on line and post with more info. Meantime if you want an electrical schematic then send me a PM with your exact Serial Number and your e-mail address and I'll fire one off to you.
Just a couple of thoughts to get the discussion going. First of all this is an ECPC controlled transmission. Simply, it is controlled by the PCM depending on inputs from you. Obviously if it is staying in gear (forward) then it is not receiving your input from the switch in the F-N-R handle and it is maintaining forward clutch pressure (typically clutch #2 in this machine) through the proportional solenoid that controls this pressure. My guess is consistent with Niges assessment, you have an open or intermittent in the harness or switch in the FNR handle. Because the switch is on the input side (correct me if Im wrong Nige) the PCM will not see an open, it does not send a pull up voltage to the input side to check circuits, only sensor side.
Nige
Senior Member
Would you like a copy of the Electrical Schematic..? If so send me a PM with the machine Serial Number and an e-mail address. I can send one to you right now because I'm working today.
Nige
Senior Member
Maybe take a look at any/all the harness connectors to the shifter control loacted around the steering column and inspect for corrosion/contamination in the pins/sockets would be a first step. Next would be a "Wiggle/Pull Test" to check the resistance of each wire in the harness related to directional shifting while attempting to forcibly separate the harness into its component parts (2-man job).
I don't know if it's relevant but depending on the Date of Manufacture of your machine there was a Service Program "FOR REPLACING THE TRANSMISSION SHIFTER IN CERTAIN IT28G, IT38G, AND IT62G INTEGRATED TOOL CARRIERS; AND 924G, 928G, 938G, 950G, 962G, 966G, AND 972G WHEEL LOADERS" dated 19/07/2002. I can't see too many details but I'd bet it was a Before or After Failure Program that may well not have been applied on your machine if the originally-installed shifter did not fail before the Program Expiry Date. There are 3 generations of Part Number for the shifter control - 130-6260 -> 201-0211 -> 299-5839. Which Part Number do you have installed..? If it's a 130-6260 it should be considered as "potentially dodgy". The 202- number was introduced in late-2001 and the 299- number in late-2008.
I don't know if it's relevant but depending on the Date of Manufacture of your machine there was a Service Program "FOR REPLACING THE TRANSMISSION SHIFTER IN CERTAIN IT28G, IT38G, AND IT62G INTEGRATED TOOL CARRIERS; AND 924G, 928G, 938G, 950G, 962G, 966G, AND 972G WHEEL LOADERS" dated 19/07/2002. I can't see too many details but I'd bet it was a Before or After Failure Program that may well not have been applied on your machine if the originally-installed shifter did not fail before the Program Expiry Date. There are 3 generations of Part Number for the shifter control - 130-6260 -> 201-0211 -> 299-5839. Which Part Number do you have installed..? If it's a 130-6260 it should be considered as "potentially dodgy". The 202- number was introduced in late-2001 and the 299- number in late-2008.
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Ashton Cooke
Active Member
Nige**** I have Hey similar problem my cat 938G with a 6W serial number, goes forward in both forward and reverse. If I put the SNR switch in reverse the machine still goes forward when put in neutral the machine does not move as should and forward it goes forward. Please help
Nige
Senior Member
I assume you mean 6WS-prefix for the Serial Number.?
You're going to need the electrical schematic for a kickoff. There are two so to get the correct one we need to know if the Serial Number is above or below 2578.
You're going to need the electrical schematic for a kickoff. There are two so to get the correct one we need to know if the Serial Number is above or below 2578.
Nige
Senior Member
Also I suggest that you take a look at the F->N->R control and try to find a Part Number on it.
See post #7 above for three possible Part Numbers, at least one of which should be considered as "potentially dodgy" reliability-wise.
See post #7 above for three possible Part Numbers, at least one of which should be considered as "potentially dodgy" reliability-wise.
Ashton Cooke
Active Member
6ws00902 938G . Serial number and model
Ashton Cooke
Active Member
Also I noticed that my forward solenoid top left of control valve . Has 4.5 volts ign on in neutral same with reverse 4.5 volts ignition on in neutral .
Nige
Senior Member
Should be dead either way.
Are you measuring the voltage with the solenoid valve connected to the machine harness.? If you had it disconnected then you will need to reconnect it and back-probe the connector to read the applied voltage.
When you finish that, pull the electrical connector from that same solenoid valve and measure the resistance of the coil. It should be 31 +/-3 ohms. Post back with your findings.
Also dig into the transmission speed/direction control and get the Part Number.
Ashton Cooke
Active Member
Nige thank you so much !!! can you email in to me I am having trouble opening your file .. uptospeedgarage@gmail.com . TiA
Nige
Senior Member
It's nothing special, only a pdf file. Try opening it on a PC. A smart phone won't show it worth a damn.
Ashton Cooke
Active Member
okay nige so the previous owner told me that he had the valve body off because it was engaging hard and when he put it back together , the machine now travels foward in both foward and reverse. im thinking he may have gotten a selector backwards. are there any good diagrams as to how reverse selector spool sits in the valve body .? please and thank you.
Nige
Senior Member
Penny just dropped............We now have two threads going for the same machine - not good. Here is the other one.
https://www.heavyequipmentforums.com/threads/cat-938g-6y-ser-no-reverse.87832/#post-955003
First up, get the P1 & P2 pressures and see what the results are, then we can talk further.
https://www.heavyequipmentforums.com/threads/cat-938g-6y-ser-no-reverse.87832/#post-955003
First up, get the P1 & P2 pressures and see what the results are, then we can talk further.
Ashton Cooke
Active Member
Okay so I pulled pressure P2 = 0 psi when machine is started also when put in reverse and cycled through all speeds .
P1 has 50psi then when shifted into forward it drops slightly then returns
P1 has 50psi then when shifted into forward it drops slightly then returns
Nige
Senior Member
If those pressures are correct that machine will not move anywhere. P2 is the direction clutch pressure.
Based on that I cannot reconcile your statement that the machine moves forwards whichever way you shift the direction control. It should not move at all.
Based on that I cannot reconcile your statement that the machine moves forwards whichever way you shift the direction control. It should not move at all.