working on a 938g series 2 loader serial crd01895 , brakes work but at the bottom of the pedals also seems like neutralizer isnt engaging , any inforamtion i can get on this system would be greatly apeciated
IIRC the neutralizer can be deactivated using a switch on the dash. Have you checked that possibility.?
Here's another thought. Does the Action Lamp (Fault Indicator) lamp #6 stay lit permanently after the initial panel self-test.
i cant verify it seems like the pedal travel is very low , i dont have any fault lights on dash , seems theres no pressure on pedal until its down to the floor and machine will stop , i think next step is to remove pedals and check that brake valve , i see 2 pressure taps under the cab on brake valve , ill pull some pressures from them
Post a Serial Number please. There are plenty of options, just want to make sure to get the right one.
Have you checked that both of the brake system accumulators are functioning correctly.?
0938gkcrd0185 is the full number off id plate i have not checked accumulators , what is the procedure for that ? as per normal im shooting in the dark with limited resources and since are cat dealer got bought out and sis changed im very limted what i get thanks
Your S/N is missing a digit. There should be five numbers at the end after "CRD", not four. 1. Start the engine and let it run for a couple of minutes to allow the accumulators to fully charge. 2. Stop the engine, then turn the key back to the ON position. Let the panel do the self-test. 3. Press the brake pedal fully to the floor and then release. Do not hold the pedal on the floor. 4. Continue doing this until the low brake pressure warning light (#4 on the diagram I posted above) comes on and the alarm sounds. 5. How many pumps of the brake pedal did you make.?
sorry about that trying to type on my phone while i was in the crusher , CRD01895 i have 7 pumps before the light comes on
That's within specification. According to the O&M Manual it should take "at least 5 pumps" for the light to come on. That being the case I don’t think it’s the accumulators (FYI There was a case on HEF a couple of months ago when the light came on the first pump of the pedal) Do a test of the service brake holding ability. 1. With the engine running apply the service brake and release the park brake. 2. Put the transmission into 3rd speed forward. 3. Increase the engine RPM up to High Idle. The machine should not move.
By chance did you check the operation of the transmission neutralizer override switch #27 on the illustration below.?
in 3rd it stats to push threw service brakes at 1500 rpm . my neutrilizer switch is a self retuning switch , i have no dash illumation when switch is pushed and released or held into postion , the brakes dont engae until the pedal is at the end of travel
It looks like a brake overhaul is looming large on your immediate horizon then........ Failing that service brake test in many operations would be enough to put the loader out of service. By any chance have you taken a look at the magnetic plugs on the differentials/final drives and also at the colour and smell of the oil in both axles.?
no i'll pull the plugs and check that , yeah the operator was coming off a big pile of ca-6 and didnt want to stop
For reference, the service brakes should hold the wheels from turning in second and third gear ranges and turn through the brakes in first gear. I'm not familiar with your brake system but I'm always loath to take things apart without confirming the easy to check items. I would check brake supply pressure to and from the pedals before going forward on removing and checking the pedal valves.
oil looks good , these axles dont have coolers on them, single hose to each axle , oil smells ok
machines only got 3350hrs on it , guess it would vary from application but i kinda figured should get more hours on brakes than that , yea i have to get a spec for pressure there is 2 test ports up by pedal valve , ill also check pressure at each axle
If oil does not smell burned and with only 3550 hours on the machine the probability is that the brakes are OK. TBH 3550 hours changes the picture totally. I agree you would not expect the brakes to be worn out at those hours. Brakes are a twin-circuit system, one for the front axle, one for the rear. That's why there are 2 accumulators.
so i just checked presssure at both test ports at the pedal valve engine idle man on the brakes 400 psi
No difference at all between the two circuits.? Spec is 1250 ± 50 psi on the rear brake circuit and 50psi more than whatever you measure on the rear in the front circuit. Brake accumulator charging valve test would be the next step. See attached. Just a thought. If this loader is equipped with Secondary steering (the online system says not but pls check) that could be screwing up the braking system operation.
maybe 50 psi difference the presssure slowly creeped up to 400 plus both hit 300 the creeped up ill get everything together and preform the test you posted and report back , thnks
Make sure you do both of the test procedures and then compare the results. It would be especially interesting to see the brake accumulator precharge pressure even though the number you get from the test is only approximate.
ok test 1 : start engine aand idle pressue comes up then falls alittle to 1750 cuts in runs til 2050-2100 psi cuts out 7 pumps down til i hit 1350psi brake light turns on , countinune pumping down til gauge drops suddenly 16 additional pumps text 2: start and run at high idle the slight pause in pressure before quick rise 700-1000psi its raises prettty fast to cut out pressure 2100psi and holds aply brakes 3 to 4 pumps hits 1750 psi cuts in , repeatedly apply the brakes cuts in ans out per spec
What was the pressure on the gauge at the time it dropped like a stone.? That is (give or take) the accumulator precharge pressure. See Step 9 of Test #1. From the way you say it is behaving it sounds to me as though the Accumulator Charging Valve is working OK.
Have you checked that there is no debris under the pedals or that the floor mat is not interfering? Do the pedals hang down from a mount above or are they mounted on the floor?
nige , sorry per step 1 900psi and then drops like a stone , the pedals are floor pivot mounted i checked them out i can see the brake valve pluger and watch the movemnt looks to be bottoming out whever i work the pedal with my foot or hand , thanks
So that should be approximately the acumulator precharge pressure, which is around 950psi depending on ambient temperature. Double confirmation that the accumulators do not appear to be the root cause of the problem. I think that somehow you have to make sure that the pressure you measured in the system from the test point is actually reaching the brake valve. This might involve making some sort of temporary connection where one or other of the lines from the accumulators supply the brake valve. I can't see any reason why you should not be getting full system pressure there but it's worth a check. Please ensure that nothing is messed up in the floor linkage (the left pedal is connected by a link to the right pedal). If it's all good then it seems as though you are going to have to go into the brake valve. See attached which is how it operates. Not the easiest thing in the world to get at unfortunately. And I've saved the worst part for last - there are no service repair parts for it so it's a new replacement valve or nothing. It seems as though this is typical because I looked at a couple of other models that use a similar design of valve (but different Part Numbers) and they are not serviceable either. The Part Number for the valve illustrated below is 215-3687.
yes i agreee im going to tee into service brake valve where accumulator pressure is coming in and verify i have correct pressure , i know i had a brake problem on our 815f brakes are simalar and the valve was serviceable but thats been a few years ago and that one the plunger would stick so it was a dragging issue , i will check it out and report back, thnaks brandon
Once you have verified the inlet pressure there is nothing to stop you tearing the brake valve apart for a look. Simply if you do find anything worn or damaged there are no spare parts available to repair it. At least not in Caterpillar’s system anyway.
The 815F Service Brake valve is a different Part Number 106-1774 and there is still a repair kit available for it. It looks to be significantly different to the one on the 938G. 257-7676 Kit-Repair (INCLUDES BOOT, SEALS, RETAINING, DETENT BALLS & SPRINGS)
t into inlet of service brake valve 2000 psi at idle , step on brakes til 1750 psi cuts in runs up to 2100 psi cuts outs \ looks like the valve is next
is there a way to check the percent left of brakes without diassembly ? thnks
im wrapping up for the day here , ill pull and disassemble valve if there are no crisis monday mournng and report back thanks
Here's a thought. Re-connect the inlet lines from both accumulators to the service brake valve. Then try plugging the outlet side of both brake circuits at the brake valve, re-test and see how the pressure behaves. Then reconnect one axle circuit and re-test. Plug that one again, re-connect the other, and test again. Do you see any difference in behaviour between the front and rear brake circuits.? Yes there is. See attached. The problem will be getting into the ECM to see the initial measurements when the machine was new. I assume you don't have ET.?
ok so i finally got back on this ordered the service brake valve and installed it today , i now have 1250 psi and 1300 psi at outlet test ports of service valve ( theres my 50psi diff between fron to rear ) i havent disassembled old valve yet , i dont have cat E.T , im gonna install side pannels and take it for a run , thanks
i did block off lines and test pressure it was stile low 300-400 psi , i belive that valve was bleeding to tank
That's probably why you couldn't get any decent pressure to the brakes.
pulled that valve apart today the spool valves where scored , machines stop excellent and has been back in service , thank you !!!!