Hi guys we have a problem with a 740 series 2 (b1p) dump truck. start it cold in the morning no brace pressure you have to rev it up for about 3 mins then you can hear the pump cavitating and then it builds pressure and works fine. basically the pump and suction hose runs dry over night because 1 morning i went to it disconnected the hoses on the pump and wer all dry. i replaced all the hoses to the tank and the o-rings the hose going down through the tank is steel and is not cracked. it has me baffeled now as i taught if anything the pressure side of the tank was at fault it would leak. Any suggestions? :Banghead
Check the breather on the tank. It incorporates a check valve that allows air in through the breather but won't allow air out, thus pressurising the tank. If it's blocked, a vacuum will form in the tank overnight causing cavitation. Hoist/brake tank is on the left, steering tank is on the right, from memory. For some reason the 740s are always a bugger to prime the hydraulic pumps. If you do a 2000hr on them (ie drain/refill hyd oils) the pumps take ages to prime and make you cringe at the graunchy noises they make doing it.
I wondered too if you were checking BOTH tank levels
Both steering & hydraulic tanks are pressurized in exactly the same way. The 157-7911 Breather provides up to 7psi of positive pressure in the tank to try to avoid cavitation in the respective pumps.
Correct its the brake tank on the left. I will check the breather next week and let you know i might just go order a new 1 now to try
Has the machine been regularly/correctly serviced? The breathers and check valves should be replaced on a 2000hr and will come in the PM kit if ordered from the dealer.
When we bought them they wer supposed to have just recieved a 2000h service diffs trans etc. i carried out 1000h last week they have 1000 put up since we got them. Cant be sure if it was done before we got it though so itl be no harm replace them
Changed the breather and it helped a lot now when you start up pump makes noise for maybe 10 seconds and then comes good which is a big improvment. Im guessing the 10 second delay now is down to pump wear from driving it for so long with it not being right
You should probably also check the brake accumulators. Do you have the procedure? It's just connecting a gauge to the circuit and counting the number of pedal presses it takes to deplete the pressure. Let us know if you need more info. Aus is a big old paddock y'know. Where abouts are you Paddy?
Haha it sure is a big paddock. Im not far from you im just in Brisbane. I would probably get the procedure on sis? Machine is out west working at the minute so im only near it now and then
Yes, the procedure's in SIS. Just don't be surprised if at first you get zero pressure anywhere. The remote hyd test points are/were connected by (someone correct me if I'm wrong, Parker, maybe Gates) microbore hoses. They proved to be very unreliable and a constant source of leaks. Cat's answer was not to change the test hoses for a more reliable type but to disconnect them at their source and then if you needed to test pressures, instruct you to to lift the cab, or whatever, bugger around in the bowels of the machine, reconnect the test hoses and then commence to check the pressures. Kind of makes the remote test points redundant.
@Cmark Beentheredonethat....
LOL, ***** Cat and their remote lines. I had a 725 that didn't want to dump so I checked the pressure at the remote port, 0psi. I said hell it must be plugged off like the others so I tipped the cab and checked at the pump, still 0psi. Turns out the hoist pump really had **** the bed.
Don't talk to me about remote pressure test lines ................ every 994 I assemble gets them removed and thrown in the scrap bin when we're putting it together. If I was young enough and stupid enough to climb into the bowels of a machine to connect a test line 20 years ago then today I have enough minions that I can employ to do the same thing. It's called not keeping a dog and barking yourself.