938m Brake issue

Cat 938m P5K01390. Having a loud crunch chatter type noise in the front when applying the brakes with id say half pedal not a hard push of the pedal. You can almost see the wheel vibrating when you apply them. I figured i would Check my pressures with et the max cutout was 2460 ish, cut in was 1680 ish, and with koeo it started to fall fast at 700 ish. Precharge of accumulators call for 800+- 50psi so i set them at 825psi this morning as they were just below spec. I also tested both outputs of the brake control valve and those were both in spec at around 790psi ish spec is 825+- 50psi. Also took plug out of the out finals to check brake disc wear min level is 4mm when actuated i had 4.5-4.6mm new is 4.7. Fluid has been changed every 2000hr in both axles with MTO. You can use tdto-4 but have to add additive. I stuck with the mto. I guess one of my questions during all my testing before i haul the brake groups off to check internaly has anyone ran into this possibly a glazed brake disc. I will perform a brake purge before i do that to rule out any air. Also i did notice when my brake pressure reached the max cutout on et it dropped steady without touching the brake pedal. Looking at the trouble shooting pressure in accumulators dropping without brake application would be the check valve in the brake and fan drive pump is not working correctly or the brake control valve is leaking. Kind of getting ahead of my self before blocking off the inlet lines to the brake valve to see if the drop stops is the check valve a serviceable part in the brake/fan drive pump. The pump on sis says sometimes its on the engine but its not so im assuming its on the end of the pump stack just before the lube pump.

Check your parts drawing to see if there are three release pistons and springs that push on the plates to release. I haven't worked on this model but have seen the symptoms you are describing when one of the springs breaks and causes the piston to get wedged in the cylinder bore.

John C. said: Check your parts drawing to see if there are three release pistons and springs that push on the plates to release. I haven't worked on this model but have seen the symptoms you are describing when one of the springs breaks and causes the piston to get wedged in the cylinder bore. Click to expand... Yes I looked this morning it does have the 3 springs and dowels

Well I took it out and hauled it apart today I really don’t see anything out of the ordinary. Maybe a couple weird looking spots on the first and last clutch disc #4 in the diagram 364-4378 DISC-CLUTCH I hate to throw a set of friction discs and plates at it as Im not a parts cannon but with all my tests seem to come out fine Im at a loss as to where to go next and I know it’s in the brakes. I could see if the differentials were not changed at the regular interval and the wrong fluid was used but every 2000hrs and mto oil used I can’t see the friction discs to be contaminated. The noise is like a scrunching rumbling noise when applying half pedal pressure coming to a dead stop and it only does it when your just about stopped. Anyone have any ideas they could throw out

How many hours on the machine.? I’m assuming the brakes have never been overhauled before.? Have you taken a look at all the magnetic plugs in the axle that’s making the noises.? If it was mine it would get SAE30 TO-4 oil plus the 1U-9891 Cat anti-rattle additive. I note the ZF-branded axle oil is factory-fill and according to Note [3] can be replaced with TDTO/TO-4. How do the friction discs and plates compare to specifications.? Have you checked each one for flatness.? The usual way is to place each disc on a sheet of plate glass and look for daylight.

Nige said: How many hours on the machine.? I’m assuming the brakes have never been overhauled before.? Have you taken a look at all the magnetic plugs in the axle that’s making the noises.? If it was mine it would get SAE30 TO-4 oil plus the 1U-9891 Cat anti-rattle additive. I note the ZF-branded axle oil is factory-fill and according to Note [3] can be replaced with TDTO/TO-4. View attachment 366007 How do the friction discs and plates compare to specifications.? Have you checked each one for flatness.? The usual way is to place each disc on a sheet of plate glass and look for daylight. Click to expand... 8200hrs on the clock. Brakes have never been overhauled before. I always just used the mto oil as when cat was down for the service warranty period thats what they used and the 1u-9891 wasn’t needed I believe that part number has been since updated for the additive. But I have no problem switching to 30w to-4 if you think thats a better option than the mto. I have checked the plugs at every drain and they look normal no chunks and a little bit of material but not much. I measured the friction linings today when I got it apart and they were at 4.54mm give or take new is 4.7 but that doesn’t mean anything other than there not beyond minimum spec. Tomorrow I will check out the flatness of the discs when I get back in the morning.

The brakes shouldn’t be worn out at 8200 hours unless they have been hammered, but in that case the separator plates would likely be blue and twisted. Plummer194 said: Tomorrow I will check out the flatness of the discs when I get back in the morning. Click to expand... If you find nothing out of the ordinary in that regard I would suggest to throw it all back together with TO-4 oil plus additive and see how it goes

Nige said: The brakes shouldn’t be worn out at 8200 hours unless they have been hammered, but in that case the separator plates would likely be blue and twisted. If you find nothing out of the ordinary in that regard I would suggest to throw it all back together with TO-4 oil plus additive and see how it goes Click to expand... I agree 100% the operators seem to treat the machine pretty well for a landfill machine as far as that goes. I will post back with how it all works out! Thanks

Just thought I’d share the end result so the thread doesn’t end without a result. Got back to the machine today and put the final/brake groups back on. They all checked out good internally and all the discs and plates measured like new. When I put the groups back together i mixed up some tdto 30w and additive in a clean bucket and coated the plates and discs during reassembly. In the pictures the top disc you see faces the piston the pictures make it look weird and spotty but they were fine. After I installed them back on the machine i filled with tdto 30 and additive as nige suggested and within 20 minutes of a test drive the noise disappeared completely. I will go back next week and drain the rear differential and refill with the same oil. I appreciate all the help this forum is when you need it. I took a roll in the municipal government as a mechanic 6 years ago as I have red seal automotive and red seal truck and transport tickets but I have really enjoyed working in the field on yellow iron so it’s nice to be able to come here when you need the extra help.

Glad it worked out for you.