I have recently purchased a Cat 943 with about 10200 hrs on it - or so the meter tells me. It's a hydrostat drive system. I use it for pushing dirt in the West Australian goldfields. I've added only 100 hours to it since I bought it. It has now developed a problem that becomes apparent only after 2 hours or so of operation. It was first apparent in reverse but is now obvious in forward. I only just managed to get it out from the bush onto a low-loader the other day to get it back to the nearest town. Even back when I bought him and first used him, I was never able to run the engine speed lever in the “rabbit” fast position – in the detent position, without the machine slowing a lot. If I put the engine speed lever into the detent, which is where it should be when operating, the machine would barely move. I’ve always had to run at about 3/4s of the way to detent. The previous owner said that where he always ran it as well. At first I thought it was me not knowing how to drive it, but it seems that the problem may have always been there. Whilst I strongly suspect the Hydrostat drive pump (motor), here are the symptoms and my observations. I’ve had a bit to do with oils and hydro pumps many years ago – but I’m no expert. As above, reverse speed drops to near stop after a few hours of working. Forward speed now drops in a similar manner - now, but didn't at first. I’d expect some very slight drop in speed if the oil was hot due a the slight drop in oil viscosity at higher temperatures. But nothing like this problem. The problem manifests itself after the trans oil temperature hits about 60 to 65C. This takes about one to two hours of driving but less time when pushing hard. Hydrostat oil tank level is within the correct range The “forward – park-reverse” linkage appears to be correctly adjusted. No adjustment to the above linkage has ever been attempted by me. I just removed the clevis pins and checked the lever movement versus the selector arm at the hydrostat selector (under the bonnet) The hydrostat oil is “bubbly” when checked with the engine at idle speed. Caterpillar service manager tells me this is normal with these hydrostatics. Engine speed and power are both OK. The revs are there, the power is there but the power to the the tracks isn’t. It just drops away as the day goes on. I don’t know where the hydrostat filter sits in the hydro drive line – suction filter or discharge filter?? The oil would be colder and thus more viscous in the mornings so it would have greater difficulty getting through that filter if it was dirty. BUT – the drive is OK with cold oil. So I doubt it’s the filter. The oil looks a bit bubbly or foamy, could be the oil is breaking down when hot? The oil’s viscosity is breaking down when hot?? My first suspect is “tired” hydro drive pump – oil is hot, pump pistons or swash plate are worn, slippage through the pump? If it is the hydro drive, I expect that to be massive dollars and I’m not convinced the rest of the machine is worth such a major job. It’s a workshop job from what I can see and I couldn’t fit a new drive myself as it’s far too big a job for the bush. Any ideas for a simple fix or is this terminal?? Thanks
Hello, Aussie Gold, Remember all things contract when cold execpt water, I just got a small loader and the last oil change was in 2008 and who knows about the transmission. If i were you i would change the filter and clean the screen, if you have one, as the screen gets hot and the build up could be the problem. Also another thing is the detent can sometime get off a bracket, bent, loose bracket. or get out of ajustment. Do you have any books with your loader??
Thanks Wozza. First thing I'm gonna check is the trans oil filter. But to do that I gotta get the cab up first and thosed bolts are 600 ft/lbs. A tacho would be good to check engine RPM at various points on the throttle slide. However, I reckon these ideas, whilst worth trying, will be "clutching at straws",,,,,,,,,,,I hope not. I was told by the former owner's mechanic that "he DID change the trans filter,,,,,,,,but not the trans oil"!!!! Very strange that one. He was a bit "vague". I got the feeling that he'd charged the previous owner for 120 litres of trans oil but didn't actually change it. It was a wierd phone call. I may get the oil analysed and open up the trans oil filter for inspection. It can only help,,,,,,,,before we go ripping the transmission apart. My gut feeling is "very tired and worn" hydrostat pump. But keep 'em coming and thanks from "Down Under" Aussie
The hydrostat transmissions do have a filter relief valve instead of a filter by-pass valve like other transmissions, with a filter relief valve if the filter becomes restricted to much it opens the relief valves and actually dumps the oil back into the case, and when it opens it drops the charge pressure that is used to operate these transmission which will cut back or de-stroke the pumps thus slowing down the machine so you want to make sure the filter is good. be sure and drain the filter housing with the drain valve for the filter hosuing so as not to let any unfilter oil get by. good luck
Thanks KB. All good info and I will bear that in mind. I've bought a used Cat 943/953 repair manual form the USA on eBay. I'm still awaiting it's arrival here in "Oz". Thanks again, mate.
Noise from the filter relief??? KB, Have you experienced any type of noise from the releif dump valve when a filter is blocked as you stated above? It'd be another clue to look and listen for. Thanks, Aussie
Aussie, Any chance of getting a serial No.? I have access to Cat SIS and might be able to email you some trouble shooting info on this unit. you can email me direct at [email protected]
Serial number is - 31Y 01431,,,,,,,,,,,,,,,,,,,,,,,,,and a very big thank you. I have a full Cat repar manual coming from the USA but that's still ten days away. I'll email you. Aussie Gold
Don't be afraid to tilt the cab. Be sure to disconnect the control linkages before jacking. The six big bolts will yield easily to a 3/4" drive ratchet. There is an early and a late style transmission filter. Regards, Clark
Thanks SL. We've managed to crack the 6 cab bolts OK and the jack seems to be working. Had to use a 3/4 drive socket 'n tee bar with a piece of pipe on it. But we haven't actually tilted the cab yet. I still have "experts" wanting to drive the machine and then offer me thier opinion! First I have to pressure clean the machine (his name is "Henry BTW) as the last thing I want is to have soil and sand dropping in to the hydro filter housing. He's lot dirty at the moment. I have the Operating Manual (the repair manual is still in transit from the USA) and it does give a instructions on how get the cab up. I would say that the bolts on my cab, whilst tight, were NOT at the 600 ft/lbs torque specified in the Ops Manual. This is a good thing!! Aussie
Aussie, I have saved three files as PDF's on Systems Operation, Testing and Adjusting, and Troubleshooting for you serial number range. I tired to attach them here but they are too big for the forum. If you want them sent direct to you let me know, and to what address. Ken
Ken, check your email. Les
OK. You sound to be in a bit of strife so I'll bite First, check you are getting full engine RPM with the throttle wide open. Check the governor lever on the fuel injection pump is hard against it's stop then check the RPM. It should be 2550+-60rpm. Don't guess. Beg/borrow/steal a good phototach to be sure. Second, as the machine is new-to-you, change the transmission oil and filter. Don't cut corners. Put in genuine Cat HYDO10W and a genuine filter. These hydrostats sense engine rpm by measuring transmission oil flow , not pressure. Correct oil viscosity and filter is vital. Install the genuine article and it removes all doubt. If you do this and are still having problems, let us know. Good luck. PS. And if you do this and stop having problems, let us know as well, thanks.
Cmark's remarks are spot on. It is good to see another who insists on naming all of their vehicles and machinery. We have not settled on a name for our 943, but the two finalists are "Grubby", and "Digger". Regards, Clark
Thanks Cmark, I'm in the process of doing just as you said above. My biggest problem is that the nearest Cat dealer is 300 kms away (150 miles), there's not a workshop within a bulls roar of the paddock in which I'm working and I'm not carrying much in the way of "heavy spanners". So at present it's more of a logistics excercise than a repair job at present. Cat dealer is not being very helpful, doesn't return phone calls or emails and communication by phone or laptop is hopeless where I am right now. But the job has gotta be done. I've seen the full extent of the Cat Pressure Test diagnostic - it's about 38 pages long and very "heavy reading". The cab is up at the low angle but I can see I'm gonna have to get a crane in to tilt the cab the whole 90 degrees if I'm gonna do any more serious work on him. This whole job could end up in Cat dealer yet! BTW - Sealark, my mate calls his Cat D5,,,,,,, "Plugga" which, having seen the little devil working is very appropriate! Thanks to you all and more soon, Aussie
no aussie i do not think you would be able to hear any noise from the filter relief valve if it was dumping your charge pressure oil.
Mate. Don't despair. The service manual is heavy going. That's why most people throw in the towel at 'seven systems' and give it to a dealer, but guess what? dealers are staffed by humans as well, who might read beyond 'seven systems' but then throw in the towel at round about 'underspeed override' and start repairing it with lots of new parts and blind faith. From what you've described, I don't think you should book a lowloader yet
no aussie i do not think you would hear any unusual noise from the filter relief valve if it was opening and causing the problem. have you had any luck so far ?
cmark and kbeen, No, no luck thus far. The transmission filter etc should be here tomorrow and I spent today pressure cleaning "Henry" off ready to lift the lid on the filter housing. Spent the weekend reading up on the Cat hydrostatic drive system "System Description", "Troubleshooting Guide" and some other stuff. I'm getting a pretty good understanding of it all - after reading it again & again. I reckon with the right guages etc, I could diagnose this fault. Maybe not repair it, but depending on what the diagnosis is, I may just give it a go. On the othere hand,,,,,,if it all gets a bit too heavy, I'll get a Cat mobile field mech in. It's a gamble of about $1500.00 (AUD) to get him in for day or float it to Kalgoorlie for the same price. Thanks for the reassurance cmark. I am the kinda guy that reads until I really, really understand it. "underspeed override",,,,,,,,,,,,,,hmmmm,,,,,,,,,,,see, I know how that one works already!! And the charge oil system,,,,,,,and the swash plate system,,,,,,,,,so I'm getting there!:yup
I like your style. God helps those that help themselves, as my granny used to say
Cab up 'n trans filter done Thus far, the cab has been up and I've changed the transmission filter to no avail. It's still a problem. I've also "jacked up" the machine with the tracks off the ground (using the rippers and the bucket as jacks), put the machine into "Forward" and pulled the throttle gradually from "slow" to "fast" - right back into the detent. Even with no load on the tracks (being off the ground), as soon as the throttle passes 3/4 the tracks just stop dead. This is quite amazing when one considers the tracks are "free running" at the time. Progress has been very slow as the lines of communications and logistics here in the West Australian "desert" are a very poor and everything takes three times longer than it should! On Sunday (tomorrow) I finally have a Cat mechanic coming out to carry out diagnostic pressure testing. We shall see if he knows what he's doing or whether he'll just give me some waffle and tell me that it has to go into the Cat workshop. I've been down this road before with "experts"! Now that trans filter is ruled out, my next suspects are the Main Control Valve venturi. Apparently there is a known failure with these where the venturi throat develops a hairline split. More soon. PS - "Cmark" I just realised you'e located in "Oz", on the Gold Coast!! I thought you were in the USA!! Les
Well, the Cat guy finally arrived and we spent almost fours hours carrying out the test proecedures. He was no hydrstat expert but smart enough to "decode" the testing etc. Between us we made a good team!! THe engine RPMs are OK at 2523 RPM at full throttle. The charge pump discharge pressure was OK. The pressure drop across the trans filter was Ok at 10 PSI. There was no sign of the filter relief valve lifting either. We drove "Henry" around with the test gauges attached and watched the indicators as we went from low idle to high idle. There was no sudden pressure drop in any part of the charge oil system. So it was all OK in that department. Then we moved on to the Main Control Valve venturi, which senses the engine speed by using oil flow and thus acts a "controller" for the whole Main Control System. Here we had a minor departure from spec where the differential pressure (pressure drop) across the venturi was on the low side at only 160 PSI. The spec says it should be 165 PSI or greater. So there's a minor issue there that would indicate the seals are leaking slightly or the venturi insert has a crack in it. The latter is a known weakness. Next we moved on to the Underspeed Valve. This is another area where I reckoned there could be a problem as it's never seemed to work the way it should do in order to prevent the engine from slowing or stalling. I can stall "Henry" quite easily. Sure enough there was an big out of spec pressure drop from the venturi outlet to the inlet of the underspeed valve. According to manual, this is caused by leakage of the "O" ring seals on the small pipes from the venturi to the underspeed valve. This fault would be the equivalent of a slowing engine speed that would reduce the oil pressure from the venturi to the underspeed valve - and the underspeed valve reacts by opening and dropping the flow to the track motors in order to get the engine speed back up to correct high idle (max RPM) so the engine doesn't labour (lug) too much. This sounds like it could be IT!~! I'm ordering parts today and getting the crane in to throw the cab right over some time this week. More soon, Les
Aussie Gold thank you for the up-date. good luck with all.
Hey, good info. Also check the underspeed override valve for internal leakage. That's the one on the left of the HPCU that's moved by the throttle control linkage. BTW, you don't need to lift the cab all the way over to do what you plan to do. Good luck.
Cmark, From what I've exprienced so far with this cab up in the low position, I don't fancy mesing about in such a small, constrained place, trying to get the "lid" off the trans as well undoing those pipes on the underspeed valve. It took me all my time to get the quick-connects on for the pressure test. I'm only a small guy and I was struggling to get my arms in there occasionally. I'll flip the cab right over and give myself a better view of things and "stand up" access. It's only an another hours work including starting my mates old crane!! I'm retired so my time is my own. I'm not sure how I'd check the underspeed valve for internal leakage. I'll have to read the manual a bit more and figure out how it can be done. I recall a test procedure for that. Thanks, Les
I hear what you're saying about poor access with the cab half raised, however the advantage with working like this is that you can take the lid off the HPCU and run the engine to look for your leaks and carry out the adjustments. Access improves a lot if you remove the fenders. If you raise the cab all the way, you can still run the engine but you must be very, very careful that you don't accidentally move the bucket control linkages and send the cab crashing back to earth. Also you lose the ability to move the machine in a test, as the cab is very finely balanced up there and the same thing can happen. As far as the underspeed override valve goes, just remove, strip and inspect. It's not hard to get out. It joins the internal pipework with a nipple which you will need to remove from the valve body before the valve can be removed from the outside. Good luck. Edit. Don't confuse the underspeed valve with the underspeed override valve. Two different things...
Cmark, I've discovered that as of 1983, there's a revised seal arrangement for the pipes that lead to the underspeed etc. I've ordered a whole new set (6) at about 20 bucks each plus freight ex-Melbourne. I'll throw the old ones out completely and fit a whole new set of pipe seals. I'd prefer the cab right over as one of the flare nuts is tight against the side of the HPCU and about half way down. I reckon it'll be a bitch to undo etc. The top seals are bad enough without full access. I don't reckon it can be done without flipping the cab right over. Being an ex-truck mechanic, I'm aware of the hazards of the cab etc and I won't be trying any "Caterpillar Aerobatics" with the cab over!! I've read the manual about the dangers of operating when the foot brake pedal is disconnected as well as the buckets etc. I'll just put the cab down again to try it - 'cos if this latest plan doesn't work, I'll box him up, leave him until next prospecting season next year and think about whether I'm gonna let Westrac have a go at it. There is one issue that sprung to mind yesterday after reading the manual AGAIN!! The spec for the charge pump (low pressure pump), as I recall, was 1000 psi at high idle (max RPM). But we only had 470 psi at the charge pump discharge at high idle. The low spec is, as I recall, 100 psi at low idle RPM. I need to check these specs again - if I can find it once more - but if I'm right, we may have a charge pump problem as well. The pressure was enough to give satisfactory (but low) readings at the venturi but,,,,,,,,,,,,,,,,,I'm starting to feel that this machine has a lot of cumulative issues. I need to get my own pressure test kit. Paying out 170 bucks an hour to Westrac is painful when I seem to understand the system more than they do!! It's gonna be a long week!! Les
Remove the fenders?? What fenders?? Les
The sheet metal panels that go between the tracks and the side doors.
Yesterday was cab right over with my mates BHB crane. I reckon it's easier to tilt the cab all the way than it is to remove the side fenders. After gettting the cab to "24 degrees" with the cab jack, it's only a couple of clips and the brake pedal yoke and it's "up 'n over"!! Much better access if one is doing the stuff that I was doing under the tranny cover. Be careful of the throttle linkage to the fuel pump governor and underspeed override valve. Once the tranny cover was off - and it's heavier than it looks - the pipeworks from the Main Control Valve to the Underspeed Valve and Underspeed Override Valve are readily apparent. Of the six flare nuts, three were less than finger tight, a baby could have undone 'em and the others were hardly spanner tight. Upon removal every flare nut seal was ripped, distorted or falling in bits. The control pressure oil musta been spewing out everywhere!! Things I noticed: Make sure the area at the back of the tranny cover, between the Main Control Valve and the cover is cleaned out before you take the cover off. The "valley" there was choked with hardened, decades old grease and grit. The gasket broke and stuck to the trans casing right at that spot - the worst place it could have stuck - so I stuffed clean rags into the trans top before scraping the old gasket off. Use a small air blower to blow away the bits before they go into the trans casing. I used a piece of gardeen hose and just blew down it. The flare nut size is a British spanner size - 7/16ths BSW or about 21 mm. You have to remove two big pipe clips to get the pipes off and the bottom flare nut on the top of the Main Control Valve is one awkward ***** of a thing to get a spanner on. Best bet is to grind down the sides of a old spanner to get better access to this one. Anyway, I'll be surprised if today doesn't reveal a much better Cat 943 hydrostatic drive on "Henry". Cab right down and test in about an hour's time. More soon. Les
The cab is back down and all is well. Henry now moves like a thirteen tonne bobcat. He's so quick it's dangerous driving him! At full throttle, back in the detent, he's off like a whore's kecks when the fleet's in!! No more slowing down and damn near stopping. He's pushing about 20% better and high speed ground travel is almost exhilarating - backwards and forwards. The operating temps are back UP where they should be and he just keeps on keep keeping on!! He's been in bad way for some time I reckon as the flare nuts to the underspeed and overspeed valves were very loose and the seals were totally ripped to shreds and that doesn't happen in a short time. He was losing control oil pressure like water through a colander. Now, he's scary to drive he's so quick!! The whole exercise has cost us $200.00 in parts, $450.00 for a Cat manual, lotsa skin, lotsa washing powder and three dollar coins for the van park washing machine, but a lot in lost gold prospecting time. But still a darn sight better than the mobile telephone number quotes that Westrac throw around like I was Gina Rhinehart! If you ever throw the cab over on one of these, make sure, doubly sure that the hexagonal cross shaft to the fuel pump rack and the underspeed override valve are in the correct relationship - the same as they were before the cab was tilted. We made an error here and dismantling that cross shaft throttle link with the cab down and the fenders is less fun than pulling out yer own fingernails!! Thanks to all contributors for your help and support. Les
Well done.
Hey Aussie Gold, Great job and thanks for keeping us informed, Hope you fined that big strike, You must be proud of your work and your loader. wosama
Wozza, I am a bit "taken with myself" to be honest!! I sorta get a perverse pleasure out of solving this type of thing. It was certainly a trip down memory lane for me and took me back to my days as "the breakdown mechanic" on big truck and tankers about 40 years ago!! Mind you, I'll be sore for days after this lot - not getting any younger! Stay safe, good luck and thanks to all of you, Les
You were luckey to get a poor running machine and fix it so cheap.Those hystats usually go the other way on you. If speed scares you only pull travel part way back, it has an adjustable friction joint. Later Bob
Attached are some pics of "Henry" under repair. The two flare nuts that are in focus are sitting on top of the "Underspeed Valve". The other four are out of focus. They weren't even finger tight and I'm surprised the Cat was even moving at all.
Hi Aussie Gold, Good photo, did you torque the nuts ro just put a good wrench to it. You know that song , when i'am 64. Time for a cold one, sam
Wosama, Not sure what ya mean about, "When I'm 64"???? I didn't torque 'em up. Being an old mechanic, I'm rarely far out in "how tight a nut should be" just by using a spanner. Besides which, it's bloody difficult (nigh on impossible) applying a torque wrench to an open-ender spanner! Out in the Australian Bush, sophisticated gear is non-existent so "bush mechanic's sense" has to fill the void. The two flare nuts that you can see in the photo are merely the ones that are easy to get to. The others ya can hardly get a spanner on 'em,,,,,,,,,,,,no way ya can a torque setting on 'em. She'll be apples mate, no wukkas!! I'll post some pics of the damaged seals when we've unpacked from being 5 months in the bush!!!. We only got back home last Friday. More soon. Les