Hello all, I am experiencing some troubles with the diff lock on my machine 140h, first thing I noticed was a fuse blown on my diff lock switch, which never happened before, when I backed out of the shop and slightly turned, the rear of the machine started to skip jump on loose gravel like it was locked up and you were trying to turn on pavement, no diff lock light on , so this is when I noticed the fuse gone on the switch, replaced the fuse every thing seemed fine then the fuse blew again and it acted like it was locked up on pavement again, the rear pass side really jumping, pulled back into the shop, this machine never acted like this ever even when locked up on gravel or hard packed road, our mechanic replaced the diff solenoid and also took a pressure test at that port its at 220 at idle he feels that's to low, its also leaking oil out the back of the trans by the 3 bolt plate( lower one), replaced o ring, still pushing oil out, also checked tandems all is fine there, any idea's what's going on? thanks :Banghead
Your diff lock solenoid is junk...crawl under the right side of the machine and look up. You will see it up there. Not too bad to change. Only one wire going to it if memory serve's me correct.
Thanks, we installed a new one and still the same, voltage at the solenoid is fine, there is voltage there when the diff switch is off, none when its turned on, I think that's how it works, any more idea's? thanks
You should be measuring the pressure at High Idle with the transmisison in 1st speed forward (needs the wheels off the ground or the drive shaft removed) - the minimum pressure you should see is 380psi. The solenoid is referred to as the "Diff Unlock solenoid" so I agree with you that it should be powered to unlock the diff. There is a diode wired in parallel to that solenoid, it might be worthwhile checking to just make sure it's OK, but I really think your problem appears to be a lack of pressure to the hydraulic side in order to unlock the diff, at least on the face of it.
Thank you, I will have the our mobile mech check the diode to see if that's allright to rule it out, I think its in the works that she's going to Cat to get fixed $$$$$$, if you can think of anything else let me know, thanks so much
I think if it was me and it was confirmed the pressure at the diff unlock valve was low, I'd effectively follow the system backwards to where the oil comes from, plus maybe think about doing a complete recalibration of all the transmission clutches.
Thanks, The Cat guy was out today and did a pressure test, 220 at high idle, he also said min pressure should be at 380 just like you said, he figured it was a blown internal o ring not building the pressure up for the diff lock to fully engage causing it to jump on the end of the spider gears under the pressure when turning, the extra oil that is by passing is being pushed out two little orifices outside the o ring on the 3 hole plate on the back of the lower trans, the trans and diff has to come apart to fix, does this make sense to you? thanks
Sounds logical to me, especially with the oil leak you describe that appeared at the same time, but I'd be interested to hear what others on here with grader experience think.
The diff lock is hydraulically applied and the default position is for the diff to be locked. In other words with no power to the solenoid the diff will be locked. This is why when you had the blown fuse, the diff was locked. Are you saying you now have the electrical problems fixed and the diff locks and unlocks OK?, but you have low pressure? Don't jump straight into pulling the diff out. There's a couple of things to check first; The diff lock circuit takes its pressure from the main transmission feed. Check main pump pressure at the tranny filter. If that's at 220psi then the problem isn't in the diff lock. If you have good pressure at the filter then you can be losing pressure either through the diff lock valve, the diff lock or the centreshift lock system. Eliminate the centreshift lock by disconnecting the hose to it and installing a blanking plug. Eliminate the diff lock valve by unscrewing the valve cartridge and checking the O rings on it. Even if the O rings look good, I personally would consider installing a new valve cartridge. It's a lot cheaper than pulling the diff out. If you still have low pressure when you've done all that, you're looking at an internal leak in the diff. The leak on the plate at the back of the tranny is probably just a leak. I don't think it's related to your problem.
Thanks, yes the oil leak started a month or two earlier, a drip now and again nothing to serious or to get to alarmed about but was reported to my supervisor, than it got worse over time, our mechanic replaced the o ring on the back plate hoping this was just the case of a bad o ring, It started to leak more out the back making our mechanic take a harder look, than the blown fuse in the diff switch and the jumping of the diff, pressure tested low, called Cat, it would be interesting to hear from some other grader operators on this issue, thanks so much Nige.
I'd suggest to try Cmark's suggestions before pulling the trans/diff.
Thanks, I believe this is what the Cat man did, he plugged one line off and connected to another by the diff lock solenoid pressure port and used some sort of a hand pump to try and build pressure and the pressure would not build, I did not see him check the pressure at the filter, what are your thoughts on this? thanks
When the diff is unlocked, the pressure drains away through the valve then internally into the diff housing. If you connect a hand pump straight to the diff lock valve and can't build pressure, this doesn't eliminate the possibility that pressure may be bypassing the valve cartridge and dumping into the housing.
yes that makes sense, I will bring this up to our mechanic first thing in the morning and try what you told me to check first, hopefully we can get it done before float shows up for it, thanks so much Cmark I appreciate it.
I'd be a little hesitant about pulling the guts out of it just yet too. I'm still asking why did the fuse blow for the diff lock to start with?
thanks, I have no idea why the fuse blew, it did it twice we replaced the solenoid and valve and it has not blown sense, we tested the switch and it seemed fine,
Hello, well I tried everything you suggested and still around 220psi at the diff lock solenoid test port, around 400psi at the trans filter test port at high idle, also checked the diode to, its looking like a internal leak, there's another grader 140h a year older than mine at the other base that is having the same problem with the diff lock, any other suggestions? thanks so much
I stand corrected, this morning in one last effort, while the float truck was waiting to take my grader to Cat to be taken apart, I installed a new diode from Cat and by golly the pressure returned, I could not believe my eye's what the gauge was reading, tested and retested everything was fine, the float truck went home empty, Thankyou Nige and Cmack and grandpa
Just for info, the diode (aka arc suppressor) he's referring to is the one that's wired in parallel across the terminals of the coil in the diff unlock solenoid valve. see below.
Glade to see you got it fixed before you sent it off to cat.
Yes indeed, and it would have gone to Cat if it wasn't for the help from this forum, thanks
We like to hear success stories!!