HST owners - Don't let this happen to you

[beowulf]

Well, I doubt this is the issue but I hope it is because if it is it is easy to fix. Twice on my HST3410 I could not shift - it seemed as if it was always in neutral - tho I could go in reverse - just not forward. The first time it happened was many years ago and from this forum I learned that the mechanism which pops in and out of the range lever simply popped out of place. After examining it I tapped it a few times with a 2x4, and it popped back in. All was fine. A few months ago the same thing happened and I used a crow bar to tap it back in and again all is fine.

When this happens - no gears- always seems like in neutral - it appears as if it is a major issue, but perhaps not. Anyway, it is worth trying that. If you can take off the range lever cover it is easier and you can actually see what is wrong - the "U" groove there needs to be repositioned.

Hope that is it.

 

[Oldpath05]

I don't think this should necessarily be a warning only to hst owners. What do you think the result would be if the tractor had been a gear drive, with the transmission in gear, the bakes on, and then the rear wheels hit the road like yours did. It would be just as catastrophic to that drive train, especially if it were in 4 wd.

I started reading this thread because I thought there was something wrong with HST, I've always assume that HST was the safest tractor there is, I can see this happening to any tractor. Short cuts, yea I've gone on a few short cuts, only because the GPS in my head doesn't always see the sharp curve down the the road, but my hind sight is 20/20.

 

[Jim in ICT]

Good thing no one was behind you, could have been real bad. The oilfield crews around here used to run from job to job without booming down their equipment. A friend of ours met a lowboy trailer with a D9 Cat on a curve. The truck turned, the dozer didn't. The last thing he saw was the D9's blade in front of him. Folded up his pickup like an accordian.

 

[snoracer]

Part 3 - splitting rear section from the tunnel

As I mentioned in part 2, I could see metal chips in the tunnel section. There is an inspection window in the side of the tunnel. I removed the cover and took a look inside by sticking my smart phone through the window (window is only about 2" x3") and using the camera to snap a few shots of the inside. The gears on the front end of the range trans are undamaged. Notice the metal chips along the bottom of the tunnel. They appear to be aluminum and brass.



I realized that the damage must be further forward. I feared that the hydro motor could be damaged. So, on with the split. I supported the front of the tractor with jack stands positioned under each of the FEL mount pedestals. I used my cherry picker/engine hoist and a sling to lift the rear section.
After splitting I was able to get a better look inside the tunnel. What a mess. Metal chips and chunks were scattered along the bottom of the tunnel.
I looked forward at the Hydro motor and I didn't see any damage. Now I'm really puzzled. Where are all those metal chunks coming from? I used an
inspection mirror to get a better look at the motor, and that's when I found a nickel size hole on the bottom side of the hydro motor housing - my worst fears are confirmed.



OH CRAP, THIS IS GOING TO BE EXPENSIVE !!

So now I have to split the tunnel from the front section in order to access the hydro unit. Once it was split, I removed the hydro unit and tore it down.
The hydro unit is made up of three parts. The hydro pump, a backing plate, and the hydro motor. The pump mounts on the front side of the backing plate, and the motor on the backside. The backing plate is about 2 inches thick and contains several pressure relief valves, oil passages, and pressure test ports. First I removed the motor. As soon as it was loosened, parts fell out all over the bench. Now I know where the metal chunks came from.
It appears that the motor experienced a catastrophic hydro lock. When the tractors rear wheels hit the ground and tried to roll, all of that force went through the gears and tried to turn the hydro motor which was idle and full of oil. Oil doesn't compress and it had to go somewhere. It couldn't go backwards into the backing plate and pump, so, it blew a hole through the side of the motor housing to relieve the pressure. The housing was the weakest link. Everything inside of the motor housing was totally destroyed. Can you imagine the amount of pressure that must have built up in that split second!



I made a list of parts needed and began searching. I couldn't find a complete hydro motor, either new or rebuilt, so I had to order every piece individually. I also ordered a few seals and bearings that weren't damaged or leaking, but I felt that since the tractor has 17xx hours, and as long as I was in there, I might as well be pro-active for a change, and replace them. All together, I ended up ordering a little over $2000.00 worth.

The parts have arrived, and in part 4 I'll start the re-assembly.

 

[TemporaryKubotaOwnerMark]

One of our local contractors did not chain down a dozer he was moving for a short trip. It slid sideways off the trailer and decapitated a man in an oncoming car. Don't take short cuts it is just too dangerous.

I don't know if I could live with myself if I had been responsible for that. I might manage to keep going for the sake of wife and kids, but it would certainly leave me a broken man.


Well, big kudos to you, snoracer, for diving in to this major repair, and thank you for sharing it with us. :drink:

 

[Toyboy]

Make sure it's squeaky clean when you put it back together flush everything and anything out of the housing. Hopefully you've ordered a new wear plate for the slippers to ride on. If you get any scrubbing/debris between those two you'll be back to square one again. Make sure the barrel and port plate look good and mate well.That's the other trouble spot (bronze & steel)with a Axial Piston Motor / Pump. They're a great design but are susceptible to foreign debris getting between those two ares. Cleanliness cannot be overstated.
Change the hydraulic filters and hope none of the debris travels upstream to the pump when you light it up.
Good luck.

 

[countrybumpkin]

Make sure it's squeaky clean when you put it back together flush everything and anything out of the housing. Hopefully you've ordered a new wear plate for the slippers to ride on. If you get any scrubbing/debris between those two you'll be back to square one again. Make sure the barrel and port plate look good and mate well.That's the other trouble spot (bronze & steel)with a Axial Piston Motor / Pump. They're a great design but are susceptible to foreign debris getting between those two ares. Cleanliness cannot be overstated. Change the hydraulic filters and hope none of the debris travels upstream to the pump when you light it up. Good luck.

He actually already has it back together and been using it for several hours, according to his earlier post before even starting this thread.

 

[Looking4new]

Expensive lesson. Good thing someone wasn't killed. That would have been more expensive.

 

[k0ua]

A hydro grenade!

 

[Toyboy]

You cannot believe how careful/clean you have to be with axial piston pumps & motors. The slippers in both have to ride on a thin film of pressurized oil on the wear plate to keep from scrubbing. The cylinder barrel and port plate mating surfaces are the same. You loose that microscopic film of oil and start metal to metal contact, and it's just a matter of time before it's toast again.

When those units are assembled, they'll be run on a test stand going through the different pressures etc, the end of the test there will be an oil sample taken while its running and do a particle count, to see if anything is breaking down (scrubbing). If the sample is within acceptable specs, the unit is passed on to assembly. If its not, its rejected, tore down, faulty parts replaced and back to test.

Gear type units are more tolerable to debris then the axial piston type. You can get the high pressures with the axial piston pumps/motors that you cannot get with any other style. But the main culprit in them is foreign particles.

If he's already up and running I wish him well, and would advise changing out the hyd filter a couple times just in case. If any debris has found it's way to the pump it's already too late.