cat 938g series 2 brakes

[mobile-tech]

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

 

[Nige]

IIRC the neutralizer can be deactivated using a switch on the dash. Have you checked that possibility.?

 

[Nige]

Here's another thought. Does the Action Lamp (Fault Indicator) lamp #6 stay lit permanently after the initial panel self-test.

 

[mobile-tech]

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

 

[Nige]

Post a Serial Number please. There are plenty of options, just want to make sure to get the right one.

 

[Nige]

Have you checked that both of the brake system accumulators are functioning correctly.?

 

[mobile-tech]

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

 

[Nige]

0938gkcrd0185 is the full number off id plate

Your S/N is missing a digit. There should be five numbers at the end after "CRD", not four.

i have not checked accumulators , what is the procedure for that ?

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.?

 

[mobile-tech]

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

 

[Nige]

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.

 

[Nige]

By chance did you check the operation of the transmission neutralizer override switch #27 on the illustration below.?

 

[mobile-tech]

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

 

[Nige]

in 3rd it stats to push threw service brakes at 1500 rpm

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.?

 

[mobile-tech]

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

 

[John C.]

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.

 

[mobile-tech]

oil looks good , these axles dont have coolers on them, single hose to each axle , oil smells ok

 

[mobile-tech]

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

 

[Nige]

oil looks good , these axles dont have coolers on them, single hose to each axle , oil smells ok

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.

 

[mobile-tech]

so i just checked presssure at both test ports at the pedal valve engine idle man on the brakes 400 psi

 

[Nige]

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.