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Hi guys,
This problem was raised in a post last year but the issue was not resolved as the poster went off topic very quickly with other questions.
The dozer is a 2001 YCT306-6 transmission compartment fed shuttle shift with an accumulator. It was bought almost new (11hrs) from a dealer and has now done approx 380hrs. From delivery day it has emitted a loud hydraulic squeal when reverse is selected. The sound is difficult to pin-point. The shuttle will not engage reverse if there is much load on it, for example when trying to reverse up a slight incline in which case it is necessary to select a lower gear. Once the shuttle engages there is no problem with movement although the hydraulic squeal remains. Forward travel has no engagement issues or noise.
I suspected some debris left over from the manufacture process has lodged somewhere restricting the flow of oil to the reverse selector so I opened the rotating valve at the control lever and also checked associated hoses for blockage but found nothing. I figure the next logical step would be to remove the shuttle clutch and look for a damaged seal but I'm not willing to do that until I have exhausted all other ideas. Scott White from Midway Sales suggested opening the transmission cover and pressurising the system with air might help identify if the shuttle pack is leaking somewhere.
Suggestions anyone?
Dozer YCT306S shuttle shift - root rake, tree-pusher, backhoe
Excavator Hyundai 17 tonQLD, Australia
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Ooh, very interesting Bob. That's what I needed to hear. Would you please go into detail on steps you would take to investigate the problem? My hydraulic trouble shooting skills are very limited, not much experience in that field. Multiple issues….. hope not!
Cheers.
Dozer YCT306S shuttle shift - root rake, tree-pusher, backhoe
Excavator Hyundai 17 tonQLD, Australia
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The relief valve for the shuttle clutch hydraulic circuit is attached to the direction selector (rotate) valve by U-bolts. I suggest you disassemble and thoroughly clean it (rotate valve also), and replace all the O-rings. Before you do that, make sure there is no pressure stored in the accumulator. You will have to reset the relief pressure, so accurately mark the number of turns it takes to remove the spring screw, and reassemble in reverse order.
Do you have any idea what oil was being used in the shuttle clutch?
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Bob, your suggestion gave me an idea; a temporary swap on the forward/reverse hoses at the rotating valve to determine if the problem was at direction control or inside the transmission. After doing so and running the dozer I still had the same symptoms when travelling in reverse (with the direction control lever at forward position). This was to be expected as I have previously dismantled the rotating valve looking for issues but found none. I haven't touched the PRV but since the machine works fine in forward I can't see any reason to mess with it.
Oil is whatever the manufacturer filled it with. I don't see anything in my logbook to indicate it has ever been changed and the service interval is 1000 hrs anyhow. All I did to the shuttle system was open the drain to check for contamination and install an external filter but the problem was current long before that.
Dozer YCT306S shuttle shift - root rake, tree-pusher, backhoe
Excavator Hyundai 17 tonQLD, Australia
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Ok, then that takes the direction control valve out of the equation. The next step, as your mechanic suggested, is to remove the clutch top cover and try to observe the reverse servo operation with compressed air. It should only require about 40 psig to overcome the clutch pack spring pressure to release the reverse clutch. Now it sounds like there is a restriction somewhere in the reverse servo oil passages, but that still doesn't explain the relief valve unseating, if that's what it is in fact.
It's my guess also that you also have the wrong type of oil in it. It's been a long proven fact that the lubricants shipped in the Chinese tractors (dozers included) is not to be trusted for correct type and quality. The reputable dealers will change all lubricants to domestic brands and types, and flush and treat the cooling systems as part of the pre-delivery service. The shuttle clutch should be using an AW ISO 220 Machine Oil. This oil has an AGMA rating of 5 and is recommended for geared friction drives. You can also use Caterpillar T0-4 torque fluid. You can get by temporarily using AW ISO 46 hydraulic oil. Do not use ATF, UTF, THF, engine oil, gear oil, etc. Oils are formulated for specific purposes.
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Thanks for the info Bob. I probably won't be able to give the dozer much attention until next week as I have a 16 ton excavator on it's side about 30m down a jungle covered hill. Another digger arrives tomorrow to get some stumps out of the way and make a pad so I can use rigging gear to pull it back over. Fun and games!
Why do you say a restriction in the reverse servo passages wouldn't cause the relief valve to unseat?
Dozer YCT306S shuttle shift - root rake, tree-pusher, backhoe
Excavator Hyundai 17 tonQLD, Australia
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Ok now that the excavator is back on the flat where it belongs I had a chance this afternoon to remove the cover plate and presurize the shuttle clutch. Forward disks engage with minimal air leakage. The reverse pack engages also but a loud gurgling noise indicates a lot of air escaping under the oil.
Dozer YCT306S shuttle shift - root rake, tree-pusher, backhoe
Excavator Hyundai 17 tonQLD, Australia
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On page eleven of your parts manual, it gives you exploded views of your forward and reverse clutch packs and servos. My guess is that there was no pre-delivery service work done and some debris cut up a servo or shaft O-ring seal. Not an expensive fix, but since you'll be dismantling the whole shuttle clutch you may as well replace them all, and check your clutch discs and plates as while you're in there.
This would also account for the hydraulic squeal. Oil being forced through an orifice at pressure. The orifice in this case is a damaged seal.
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So now we know. Thanks for all your help Bob. It's a wet season job so I won't be getting into it until early next year. Too much work to do on the farm at present. By then the dozer will be about due for a dulux overhaul. It has to root rake all the country the excavator cleared before it gets any love care and attention.
Dozer YCT306S shuttle shift - root rake, tree-pusher, backhoe
Excavator Hyundai 17 tonQLD, Australia
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Well I cut out the steel about 4 years ago but never got around to completing it. Now most of the steel has been used up in other projects so I will have to buy more. Using tines from the box blade plus 3 taller ones which extend above the dozer blade to stop branches dropping over the top when windrowing. Can you post a pic of yours?
Dozer YCT306S shuttle shift - root rake, tree-pusher, backhoe
Excavator Hyundai 17 tonQLD, Australia
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It’s been a while but the time has come to deal with this shuttle clutch malfunction. The dozer has been stripped down for a complete overhaul and the shuttle clutch removed. Yesterday I dismantled the clutch looking for an explanation for the hydraulic squeal when it drives in reverse. I found one piston ring joint has some damage and does not fully close. This would explain the squeal and also the reluctance for the clutch to engage reverse.
Dozer YCT306S shuttle shift - root rake, tree-pusher, backhoe
Excavator Hyundai 17 tonQLD, Australia
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