938G brake pressure light comes on and brakes quit working. Kill the machine start it give it a few and brakes go back to working. Not sure where to start
A Serial Number is always the best start.......... I see a dozen different flavours of 938G.
Last 8 is RTB02312
OK, so you have a Series II machine. Do a test. Start up the engine and run it until the brake warning light goes out then let it run for at least a couple of minutes more. Shut off the engine then immediately turn the key back on. Let the panel do the self-test. Press the brake pedal fully to the floor and then release it. Wait 1 second or so. Repeat that process until the low brake warning alarm sounds. How many cycles of the pedal does it take.?
Low brake light stays on constantly. The brakes will get pressure for a bit and then it gets to where you have to stand on the pedal to stop. I’m thinking a valve is sticking somewhere
Does it not go off at all after after engine startup before the machine is moved.?
Correct. This morning the machine had brakes and by lunch they barely catch
So the machine is being operated with the low brake pressure warning permanently sounding.? That's not exactly safe. Was the light going out this morning when the machine was first started.?
No
Do you have pressure gauges for testing.? You will need one that goes to maximum 6000psi and another that goes to 2000psi.
Max I have is 3500 psi
Seeing as you have low/no pressure that might probably work. First step is to check the operation of the accumulator charging valve. See attached. Post back with your results. I would suspect you're not going to see the pressure reaching cutout. Do you have any equipment for checking accumulator precharge pressures.?
No equipment for accumulation charge. No pressure with gauge hooked to brake valve
Even with a defective accumulator charging valve it ought to generate a bit of pressure. Now you know you have very little pressure maybe put a smaller gauge (1-200psi maybe.?) on it if you have one.? Take a look at the brake pump maybe.? Also did the brakes disappear suddenly or have they been getting worse for a while.?
Replaced brake pump and still brakes are intermittent. Pressure up for about a minute then lose all brakes
Did you test the accumulator charging valve operation again after replacing the brake pump.? What did the old pump look like inside.?
On start up pressure goes to about 1200-1300psi and then drops out. Old pump doesn’t look trashy just spins pretty freely
When I said "Take a look at the brake pump maybe.?" I wasn't suggesting that you change it, more tak a look inside it. Having zero pressure could have been something obvious such as a sheared pump shaft. The other obvious candidate is the accumularo charging valve, but to make it clear I'm not suggesting that you replace it. Simply pull it apart and take a look inside for anything obviously wrong. I'll try to find a parts breakdown for it.