Yuchai Dozer Shuttle Clutch Pressure

Hi Mark.  I have my dozer stripped down and the shuttle clutch in pieces at the moment. The dozer was very slow to engage reverse and once engaged emitted a hydraulic squeal. I found the problem to be a damaged o-ring on the piston.

Need more information. Is the knocking sound the only issue or does your dozer have difficulty engaging forward and/or reverse? If it engages ok then I wouldn’t expect hydraulic pressure to be the problem.

Does it knock just once upon engagement or is it a continuous knocking? Did the knocking start after or before you changed the oil in the shuttle compartment? What oil did you fill it with?

Mark, a consistant knocking sound is not good. Means something has come loose and is bashing against something else. Could even be your flywheel getting ready to fall off. Attached are some photos to help you see what might be going on inside since you don’t have a manual. Close to the oil dipstick is a small coverplate which holds the tachometer sensor. You might be able to remove it and insert a screwdriver to check for wobble in the flywheel. Check that it’s not the tacho sensor coming loose and rubbing on the ring gear.

As you can see there is not a lot between the flywheel and the transmission compartment that could account for the consistant sound you describe. Could be a bearing collapsed on one of the idler gears. Only other thing comes to mind is a problem in the engine bottom end and the knock sound simply amplifying through the bell housing thus disguising the location of your real problem.

I have the same machine and can help you out with parts manual. Hopefully we can get some better minds on this before you resort to pulling out the engine. Wait till the Americans wake up – it’s only 4am over there right now.

The gentleman that wrote a “manual” on the shuttle clutch initially had a problem with his in that the splined input shaft was machined slightly too short, so that might account for the knocking sound you hear (hopefully not).

There are no service manuals available for these machines, but the owner’s and parts manuals cover most of the basic stuff. If you will PM me your email address I will send you the manuals plus the shuttle clutch supplement.

I think the oil you selected is a bit heavy and slightly off target for this application. You have what is essentially a geared friction drive, similar to a marine or forklift transmission, and not unlike an automotive automatic transmission. The oil I recommend for these clutches is ISO AW 150 Machine Oil. ISO AW 46 hydraulic oil may also be used. Both of these oils will have an AGMA rating.

An afterthought on the knocking noise. I would check the tang drive on the shuttle clutch’s hydraulic pump. These have been known to give problems on the tractor’s pump, but not aware of any issues with the clutch pump. Just a thought.

If I remember correctly the operating pressure for the servos is around 40 – 60 psig.

I’m almost positive that’s not a normally stocked part. Your best bet, I think, would be to have a dealer order one for you (Eastwind?), or you may be able to order directly from Yuchai.

Man, that’s a bummer but glad you found it before it got worse.

If you have no luck with Eastwind let me know. There is an excavator dealer in Brissy who has sourced some heavy parts for me direct from the factory in China. Only parts he couldn’t get were the seals for the shuttle clutch. I’ve ordered those from Circle G Tractors in USA. Check out their website. You will find the special seals for the cylinder on page 8; https://www.circlegtractorparts.com/yuchai-bulldozer-parts?p=8

Word of warning, when you strip the shuttle clutch there is a spring-loaded seated collar retainer which requires clamps and jigs or a shop press to remove.

Excellent. Some progress pics would be great too.

Actually, 60 psi would be ok since it actuates the opposite servo (releases the reverse servo so the forward planetary is engaged, and likewise for reverse). The springs in the clutch packs are what actually engage and hold the engagement. The servos collapse the springs, allowing the planetary turn free. I know it sounds as clear as mud, but that’s how it works.

The gauge is a good idea but should be a 100 psi gauge. It will tell you when the strainer is plugged when the neutral pressure drops.

Back to front on the spring function Bob. It’s probably a different set-up to what you’re used to. As opposed to a manual clutch on a car, the dozer shuttle springs act to maintain separation of the clutch plates, not hold them together. In neutral there is about 3mm clearance between both pistons and their clutch plates. When F or R is selected oil flow is diverted through one of two galleries that run lengthways through the shuttle shaft exiting a port behind a piston. Hydraulic pressure then overcomes the force of the spring and the piston clamps the clutch plates together directing drive (in the selected direction) to the transmission.

Today I had the “pleasure” of reassembling my shuttle with new seals. For the benefit of anyone else having to do this job I will explain how it was done. Understand that it is necessary to compress and hold a strong spring while fitting a split collar retainer on one end and a circlip retainer on the other. It had me scratching my head for a while until I noticed that the shaft would slip through the 40mm bore on my lathe. To fit the split collar I held the shaft tight in the 3 jaw chuck and compressed the spring using the tool post on one side and a g-clamp on the other. This allowed enough wriggle room to fit the split collar into it’s grove on the shaft.  The circlip was easier. I first set it in position against the spring then slipped the long shaft through the bore (leaving the chuck loose). The tailstock was used to push the shaft deeper into the bore until the circlip snapped into place.

After assembly I tested the shuttle function with compressed air.

There is another earlier version of the shuttle clutch that incorporates the use of two external hydraulic cylinders to engage and hold the clutch plates. You are right, I stand corrected. The steering clutches however, do work that way.

Hi – I am having issues with my forward motion on my DH326ST with a shuttle clutch.  It will work for about 20 min and then loses power to move forward.  Hydraulics continue to work and usually have some luck with reverse.  In this state, only low range low gears will power the machine.  Once cooled off, it’s back to working as it should for another 20 min.

Any direction or assistance would be appreciated!

what poking around on that machine I found is that the clutch/brake/steering box must by dry if a oil seal has failed and oils have contaminated the discs a power to the tracks problem will happen. I have never worked on these shuttle machines.