My brother in law just got one of nine brand new Cat 742 haul truck at the mine he works for. It turned 200 hrs on the night shift last night and the dump quit working. The Local CAT mechanic spent all day on site and on the phone today and has no clue what is going on. It was his first look at the 742. They determined that it has no bed lock like the larger trucks. Brother in law voluntary swept floors in the shop all day today waiting for the truck. He says help!!! Any ideas?
Do you mean 740b? Never heard of a 742?
Is it loaded? I have found on several Cat trucks that they do not have enough lift to dump ther bed if it is slightly overloaded. With damp sand I can overload my 735 to where it won't dump.
He to He told me 742 over the phone. I have never seen it.
Update, they pulled part of the load out with a backhoe. It dumped the load after that. They put the box down and it will not go up. He says it goes up to where there is about an inch of clearance under the front of the box and acts like it has a hold down lock on it. They can not find a bed lock or where it might be binding and the CAT godfathers are telling the CAT service tech that there is no bed lock on that machine. Will keep you posted when I find out what they find. They were hauling very wet fine sand as they had 3 inches of rain in 24 hours.
Need more info. "742" as a model does not exist. A 740 maybe, if it's brand new it will be a 740B..? Try to get at least a Serial Number Prefix (most likely L4E or T4R) because there are 4 versions of the 740B truck in existence........... The machine worked fine for the first 200 hours I take it..? Was he on it all of those 200 hours..? Any issues at all relating to dumping..? I know it's simple but if the body raises about 1" with no load and then won't go any further then "acts like it has a hold down lock on it", has someone checked the relief valve pressure in the hoist system..? Any "screaming" hydraulic noises when it gets to the point where it doesn't lift any more..? My first thought on hearing the symptoms is something has broken inside one of the dump body hoist cylinders. If that was the case then when the body raises the 1" and stops it ought to be possible to see one cylinder still trying to push and the other one stop. However that's just a WAG from left field. Another thought is that it appears that the pump for the hoist system in the 740B (I'm looking at L4E prefix) also supplies brake cooling oil like on the big trucks and it relies on a changeover when you go from "brake cooling" mode to "hoist" mode. I wonder if the relief valve inside the main control valve that is designed to protect the brake cooling system isn't working properly..? Below is a cut & paste from the Systems Operation for the Hoist System on the L4E-prefix 740B ADT. When the hoist control is moved to the RAISE position, a pulse width modulated (PWM) signal is sent to the ECM. The PWM signal is sent by a position sensor which is connected to the hoist control lever. The ECM sends a current to the pilot control actuator. The current is proportional to the displacement of the hoist control lever in the cab. The pilot control actuator relieves some of the pilot pressure to the tank. The stem of the hoist control valve is moved to the RAISE position by the pilot pressure inside pilot control actuator. The hoist control valve directs oil from the gear pump to the piston side of hoist cylinders. The hoist control valve directs oil from the rod side of the hoist cylinders to the cooling system for the service brake. The oil changes direction of flow in the valve body. The valve body contains relief valve which protects the cooling system for the service brake. The hoist cylinders extend and the body is raised. The maximum system pressure is controlled by a relief valve. Oil pressure from the piston side of the hoist cylinders is transmitted to the relief valve. The oil transmitted to the relief valve increases the relief pressure of the relief valve. Greater system pressure when the hoist cylinders are extending is due to the above action. Refer to Systems Operation, Testing and Adjusting, "Hoist Control Valve" for further information on the relief valve. The lower control valve is used to open up a line between the piston side of hoist cylinders and hoist tank. The line is opened when lowering the body with a dead engine. The accumulator reduces pressure spikes in the brake cooling system when the hoist control valve changes operation
Hi Nige, It must be a 740B. I went by what the brother in law told me over the phone. It was late when he called, I may have got it wrong. He was not on the truck when it quit dumping. They are running 2 ten hour shifts per day, 7 days a week, so there may be even more than two operators on it. It happened near the end of the night shift and was at the shop when he went to work in the morning. He had no previous issues with it. He liked the truck. He is pretty sharp mechanically, having owned/repaired non electronic driven equipment most of his life, so there would be a pretty good chance he would pick up on any weird stuff going on. He is going to call me later this evening when he gets home. I will get an update then if CAT figured it out today. Until the influx of all the fraq sand plants in the last year there was no call for big new equipment in that area. I think the dealer service department is still in a learning curve. I'll keep you posted.
Surely they must have put a gauge on it and check the pressure for hoist?
You would assume so, but remember this is a Cat dealer we're talking about..............
I tend to think most of the dealers gauges are hooked up by a wire these days.
Cat spent all day Friday on site. Sounds like they pretty much ruled out cylinders failure. Don't know nothing else. It poured cats and dogs there and the crews got sent home. Brother in law had called in late in the day to see if it was fixed. He was telling me that management has got them running the trucks in soupy mud with hard bottom. Said the crap is up to the bottom of the radiators at the load site. Makes one wonder how long any of them will hold up.
All the fancy electronics might not be happy with those conditions! Could be something like a pressure sensor lying to the computer saying pressure is too high so it shuts off something. We have a 769D that last fall was showing overheat of transmission when you could hold you hand on the case and it was not hardly warm. Then before I had time to try checking it it stopped showing the overheat. It did the same thing a couple weeks ago for a few minutes! I'm going to install a new sensor next chance I get but it may be months before I can be sure that solved the problem:Banghead
Yair . . . kshansen . But I thought these were 6x6 articulated dumpers designed to work in wet conditions? Cheers.
Scrub, As a general rule you would be correct. However trucks are not designed to be taken swimming, especially in mud holes which by the sound of it is what's happening here. We are still coming across issues on our rigid frame haul trucks that date back to a time when Mine Ops thought nothing of taking the trucks wading through mud holes (or swimming pools). It took us 9 months to convince them of the folly, and I as I said we're still paying for it now almost 2 years later.
Yair . . . Gotcha Nige . How things change. I wish I had pictures of how it used to be . . . new stiff hitch 627's pushing bow waves and Johnstone 621 egg-beaters with waves breaking over them picking blacksand off the beach. You didn't do it by choice but that was the job . . . excavating canals for rich folks houses and picking up the rich mineral sand off the beach after some rough weather. With a wash down and check for milky oil the machines could do it and they did it for years. I guess I have a warped opinion of what machines can do Cheers.
Oh they still can, don't you worry ................ but there are consequences, just as there were forty years ago. The thing is that the mud gets into little nooks and crannies where it shouldn't and you don't realize there's a problem until maybe a year later when everything goes for a ball of chalk. Wiring harnesses are one thing, muddy water under the insulation dries leaving the mud there, and our mud has high acidity because of what we're mining. Radiators are another thing, corners blocked up with mud lead to a decrease in radiator performance and that can have knock-on effects on total engine life. Just to give you an idea, some of the surface water at our place has a PH of just over 2 - so you can imagine what it does to metal parts.
Then there are the skid steer loaders at our plant. It took me close to 2 hours with a air chisel and water hose to dig down through the dirt under the floor of a Case 1845C to be able to remove the hoses to the drive motor. They think nothing of running them in knee deep mud cleaning up around the quarry. Then wonder why the wheel bearings fail. And how about running R-35 Euclids through a water hole that was waist deep? Went okay till a driver decided to enter from on end while the other driver was in the middle. If anyone recalls those old Euclids had their air filters mounted on the left front fender. Bow wave off one truck hit the intake of the other truck! The twin blowers on the 12V-71 sucked water right past the air filter and into the cylinders, bent rods big time!
Strange to say we have exactly the same issues with skid steer wheel bearings........... and for exactly the same reasons.
Finally got the update. Cat fiddled with it for 2.5 days checking things and doing diagnostic testing. Stated they could find no problem. Started it up after the last diagnostic check which had also came up clean and it dumped fine. It has continued to work for 3 days now. Cat speculated that because the trucks set at a 21 degree front to back angle( back lower) when dumping may have caused a safety sensor malfunction but admitted its only a guess. Time will tell. It's still a mystery. Every load is dumped the same with the other 8 trucks still performing well.
Scrub, You lived in the glory days of heavy equipment! Back in those days there was very little electrics on the machines to get wet or salty, in many ways far superior in terms of reliability to what we're seeing in the last twenty years. I spoke up many years ago at the CAT dealer I worked for, asking what was going to happen to these computerized machines when mother CAT decided to stop selling replacement computers or wire harnesses for them? Nothing to be done, we have to live with it now, and when it all works, it works great! When it takes a dump though, it can be a pretty foul and stinky one for sure.
Yair . . . lantraxco . Thanks for reply. . . and yes I do realize my working life was spent in the glory days of heavy equipment. What I can't get my head around is why the new systems are seen too be "better". . . I can see it with engines of course with less fuel consumption but why every thing else has to be electric/electronic is quite beyond me. Cheers.
Competition, pure and simple... if Hitachi puts it in their machines, CAT has to one up it, etc. Besides it gives the engineers a "gee-whiz" thrill. Electronics does allow some nice functions and options that are impossible, unreliable, or economically unfeasible if done mechanically, but as in all things there is a tradeoff. Don't know why the engine computer would care that I turn the lights or wipers on for instance, but in some machines the button you push just asks the computer "pretty please will you engage the relay and turn my wiper on?" Crazy.
One minor example of something I never understood. Back when 988B's were new the solenoid that activated the "full torque" valve on the converter was operated by a switch one the hydraulic control lever. Power from fuse panel went to the switch then one wire down to solenoid with the other terminal of solenoid grounded by short wire to to one of the valve body bolts. Simple and easy. Then the newer models came out. Same switch on control and same solenoid on valve on converter. Now however power from fuse panel goes to solenoid then back to switch on control then ground wire from switch goes to ground stud under dash. Better than double the amount of wire to activate the same solenoid by the same switch:beatsme Did someone get a bonus/kickback from the wire company?