I have a Caterpillar 972M XE serial AN3 7800hrs Operator complaint was when he puts his foot on the service brake the whole machine pulsates/surges, in forward and reverse, No codes, No failed oil samples, no metal in filters. Service brake pressures are in spec, Transmission charge pressure in spec The clutch Fill calibration failed, 103 out of range, Anyone have any idea what to check out next or Ever heard of something like this
Has anyone checked the precharge pressure of both brake accumulators.?
Yes both are within spec 1950psi
Sorry but somebody isn’t testing them the right way. At 21 DegC ambient the nitrogen precharge pressure of the accumulators should be 800psi. Note this is not brake system pressure but the nitrogen gas pressure in the accumulators.
Do a quick and dirty test. Machine stopped, park brake on. Start the engine and let it run for a couple of minutes until the charging valve cuts out. Stop the engine then turn the key back ON. Press the brake pedal full stroke and release it. Repeat that process until the low brake pressure alarm sounds. How many pumps of the brake pedal does it take.? It should be three cycles of the pedal as an absolute minimum. See attached.
Yes did that test, it was 8 times before the light came on, Also checked the brake accumulator it's at 1960psi at 15 degrees C Way to high
Update Brake accumulators are 820psi at 10 degrees C
I bet the accumulators were not fully discharged before testing to get that reading. Have to press the brake pedal until it goes hard to get a true precharge pressure reading. Out of interest how many presses of the pedal does it take to put the low brake pressure light on.?
Those loaders have a neutralizing feature, when you apply the brakes. Is it possible, the pedal sensor is failing, or out of adjustment, and the operator is feeling the transmission coming in and out of gear? If you can, turn off the pedal neutralizer feature, and try it.
Have you checked the operation of the accumulator charging valve.? That's a bit on the high side. Should be 770psi. Has anyone messed with the charge pressures recently.?
They all have that feature. The worst part is that it can't be disabled and what makes it worse is that there is no right pedal on your machine that operates the brakes without transmission neutralization. Bugger. Are there any Diagnostic Codes for the left pedal position sensor.? If you have access to ET then I would suggest doing a recalibration of the left pedal position sensor if there are no Diagnostic Codes present. Another quick check. Is there any accumulation of material under the back side of the left brake pedal.?
Hasn't been any codes for anything, Nothing under the pedal, Yes I have done a pedal calibration, no change
I had another mechanic with me this morning, Had him look at the transmission with it was pulsating, The whole trany is vibrating and pulsating, looks like something on the top of the transmission is pulsating, Almost like it's clutch slipping, But no fibres have been in the oil samples or nothing in the filters, Failed a transmission fill calibration test, saying out of range, Is there an adjustment for this or is the transmission on the way out
How many total hours on the transmission.? Do your transmission oil analysis results include ISO Cleanliness Codes.? If so what results are you getting.? Do you happen to have a screen shot of the error message.? Try running a Datalogger for 10 minutes or so while the machine is working. Look at the parameters for anything out of the ordinary or for numbers that, while genuine, don't seem within the "normal" range. e.g. converter out, trans intermediate speed, and trans output speed don't rise and fall EXACTLY the same way.
Transmission is original, 7859hrs All I got from the office is yellow reading, I will find out more info from the service department
Try swapping the solenoid modulating valve for Clutch #1 with any of the others EXCEPT clutch #2 and repeat the transmission calibration test.? If the problem moves with the solenoid valve you have a simple solution. If it doesn't the solution may be more expensive. With less than 8k hours I wouldn't expect the transmission to be even close to the end of its life, but I guess a lot depends on how it has been treated. If you can get a copy of the last few oil analysis results (at least more than one) so much the better. If you don't want to post them up here you're welcome to send them to me on a PM.
There is an accumulator on the transmission to aid in smooth shifting. Has anybody checked the precharge.?
At step 6 observe the pressure drop after been shut off, There's no pressure there after shutting off the machine and getting everything up to temp.
That doesn't sound good. From the Parts Manual drawing it looks like a small bladder accumulator. IIRC they are supplied pre-charged and no test/recharge is possible. Take a look at it. Does it have a charging valve that you can hook up your nitrogen charging kit to.? If it does try putting a whiff of gas into it but don't be surprised if the precharge pressure stays at zero.
I've been asked to change the two accumulators 392-6348,they are pre charged with 0psi But reading a service report, it's saying that it should have 247 +- 14psi
Check the precharge pressure of the replacements before installation is all I can suggest. The 392-6348 accumulator is listed as being uncharged and "Field Replacement for" the OEM installation P/N 392-6347 which is shown as being Charged - probably the original factory-fit.
Try ordering the 392-6347 and see if the dealer can supply it. Pre-charged accumulators are subject to transport restrictions in many areas because they are classed as an "explosive device", but in other areas they are available. Otherwise you will have to order the 392-6348 and then charge them once they have been installed. You are correct that the precharge pressure is 247±15 psi. Before installing each accumulator carefully pour transmission oil into the fitting at the end that screws into the transmission oil lines until it fills up. Easy to do because the accumulators are installed with that port facing upwards. This will lubricate the bladder where it contacts the inside of the accumulator "sphere" when it is charged.
Does anybody know if changing or charging these accumulators fixed the surging problem? I just bought a second hand one of these loaders that seems to do the same. (972M XE EDW412)
Have you checked the precharge pressure on those two accumulators.?
No, I haven't checked anything yet. Only drove it off the float & noticed it doing the surging. I've got to fix the bonnet so that I can lift it & get a bit more access at things before I do any diagnosis. I just saw the thread & wondered if the accumulators were the fix.
Hopefully the OP responds but meantime I would suggest that you break your nitrogen testing kit out.
No it wasn't the issue, I'll get all the info of what got repaired, and get back to you as soon as I can
I changed the two variator solenoids that are located in the right hand side of the transmission just near the frame, Was able to do a transmission clutch calibration and which stopped the surging
Can you pick them out on this illustration, or from the attachment.?
This is what info I go from the tech who did the repairs
Gotcha. #1 & #3 in the illustration below in that case.
My problem was the same. One transmission accumulator was empty and leaking. Replaced it but made no difference to the hydrostatic torque calibration - kept failing on out of range. Replaced the seals on the tubes from the valve body to the variator & cleaned/inspected the A & B solenoid valves - still the same. Replaced the solenoid valves one at a time & only got a successful calibration after the second solenoid was changed. Can't see anything wrong with the old ones, but the new ones work. I'm a bit tight when it comes to spending up on parts that I'm not certain that I need, but I think the $1200 for solenoids is quite a bit cheaper than a trans. overhaul. Thanks Aussietech & Nige.