Cat 943 hydrostatic drive problem

[Aussie Gold]

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

 

[wosama931b]

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??

 

[Aussie Gold]

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

 

[kbeen]

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

 

[Aussie Gold]

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.

 

[Aussie Gold]

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

 

[kshansen]

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 ken.hansen@lehighhanson.com

 

[Aussie Gold]

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

 

[sealark37]

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

 

[Aussie Gold]

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

 

[kshansen]

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

 

[Aussie Gold]

Ken, check your email.

Les

 

[Cmark]

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.

 

[sealark37]

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

 

[Aussie Gold]

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

 

[kbeen]

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.

 

[Cmark]

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

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

 

[kbeen]

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 ?

 

[Aussie Gold]

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

 

[Cmark]

I am the kinda guy that reads until I really, really understand it.

I like your style. God helps those that help themselves, as my granny used to say