Hydrostat issue...with video

[finsruskw]

What he said.
Most phone pic's and vid's are a PITA to watch/see and figure out just what is going on.

[sawdustdad]

Originally Posted by R Bedell

What oil are you using ??

HyTrans equivalent--same as I use and have used in all my Cubs.

Originally Posted by Ambush

As far as the belt destruction: is it possible the rear trans returned to neutral which would essentially force your front trans pull it, putting a heavy sudden load on the belt?

Its also possible the two issues are unrelated and coincidental.

And a tip for anybody posting vids from a phone, hold the phone sideways.

I believe the belt broke because this hydro "locked up" momentarily and the engine spun the PTO pulley which smoked the belt, then it hung up a second time and the belt broke.

Let me emphasize, the hydro was working prior to this. So whatever happened, it happened before I took it apart. It may have developed over time, I'm not sure, or it could have been a sudden failure. Either way, it developed this behavior on it's own.

Yeah, sorry about the phone video. I'll dig out the GoPro next time.
I'll post some pics. I've got the hydro apart (for the third time) and perhaps post another video.

Thanks for all the thoughts and ideas. I'm stumped.

[Ambush]

Remove the springs from the piston blocks. You can depress the spring under a press ( or drill press even) to remove the retaining ring. The spring hole is a great cavity to hold contamination. Use a metal edge to scrap it then solvent on a white rag. That will give a clue as to past wear. I would also definitely remove the swash cradle spring pins on the trunnion shaft. It's usually two pins, so make sure to get the bottom one out of the way before driving the second one all the way through.

[sawdustdad]

I put another video up of the disassembled hydro, better this time I hope.

https://youtu.be/SVzFiva78mE

Could it possibly be that both relief valves have failed open and at some point after some seconds of fluid flow slam shut and suddenly cause the spinning pump's flow to be diverted to the motor? I bought both valves a year ago from MachTech. (Actually bought 4, put the other two in the front axle.

I did put a pair of used manual valves in and got the same result, so that is why I've not gone down that path.

I am trying to find a replacement locally, but the one source I've used before had just sold his entire stash of Cub stuff. He's going to try to see if the buyer will let me buy one of the hydro rear ends. Otherwise, I'll keep looking locally, call Scott Urschel or Ray Weaver.

I'd still like to understand the cause of the problem, so as you've suggested, I'll remove the piston block springs and the swash plate. I have most of the parts from another hydro in my spares inventory if I need something.

[Ambush]

Put your rotating groups in and set the case upright. Place the gasket on the case and the valve plates on the barrels (cylinder blocks). Put a straight edge across to be sure there is adequate spring pressure on both.

Removing the springs from the barrels and cleaning that bore is preventative maintenance. Usually lots of junk in there unless the system has never had any contaminates.

I would also clean the valve plates and give the backside a few circles on a flat plate with 400 grit paper and varsol. High spots will show up as shiny. With the valve plates clean and dry and same for the cover, put them in place on the cover, dry. Put (one) finger pressure on the edge of a plate and tap on the opposite side with one finger from the other hand. Do that in quarters for both plates. That will tell you if the plate is warped or there is a high spot.

If all good there, and the swash lever is indeed pinned to the swash cradle, then I would start to look hard at the charge pump circuit. Even though it was moving oil, the question is did it get to the main pump first.

Your drill may not be turning fast enough, as well, for a proper test. You may have to put a belt on it and run it with the engine. maybe un-belt the front trans? Put a gauge on the charge pump relief.

[sawdustdad]

What do you think would account for the violent action in the unit? Where it locks up for an instant?

I discovered this issue when I was testing my hydraulic drive system--the pump I mounted behind the engine and the motor I mounted behind the rear axle. The rear axles were off the ground on jack stands.

When running the two interconnected cub hydros with the hydraulic motor that I mounted behind this axle, at 3600 rpm (approx), (rather than the belt) the hydraulic motor driving the hydros would stall for an instant then continue (relief valve on the drive circuit would actuate) and it would do this every couple seconds. Meanwhile, the engine RPMs would drop (under the load) then recover. The front axle, attached by the common driveshaft, was driving forward and backwards as expected. So this behavior of stalling every few seconds was revealed while driving the hydros at close to 3600 rpms. This behavior is what got me digging into the situation as the rear axle was not operating like the front axle was.

[sawdustdad]

Looks like I've found a 1210 nearby for sale on CL. Same hydro per parts tree.
Will go get it next week. Unless there is a breakthrough before then.

[Ambush]

I’ll have to go back and look at your build better. Do you have your two hydro pump shafts coupled together. ie, rear of front pump shaft to front of rear pump shaft?

The “jamming” sounds mechanical to me. Possibly something in the diff assembly.

[Ambush]

Not sure I should say this, but I'd go back to the original belt drive idea, but with a good cog belt and pulleys. Its a very dangerous plan to run gear pumps and motors from the same reservoir as piston pump/motors.

It is very possible that under a sudden heavy load either your gear pump or motor will momentarily "seize" as the gear defects from pressure and gouges into the housing. This can happen also is initial break in procedures are not followed. And its particularly prevalent in the "cheap' components. Once the relief reacts the gear relaxes.

[sawdustdad]

Originally Posted by Ambush

I’ll have to go back and look at your build better. Do you have your two hydro pump shafts coupled together. ie, rear of front pump shaft to front of rear pump shaft?

The “jamming” sounds mechanical to me. Possibly something in the diff assembly.

Yes, there is a common shaft that joins the two hydros.

The "jamming" is definitely in this one hydro. I think the first video I posted demonstrates that.

Originally Posted by Ambush

Not sure I should say this, but I'd go back to the original belt drive idea, but with a good cog belt and pulleys. Its a very dangerous plan to run gear pumps and motors from the same reservoir as piston pump/motors.

It is very possible that under a sudden heavy load either your gear pump or motor will momentarily "seize" as the gear defects from pressure and gouges into the housing. This can happen also is initial break in procedures are not followed. And its particularly prevalent in the "cheap' components. Once the relief reacts the gear relaxes.

I figured the hydrostat is fed from the filter so that would prevent any contamination of the piston pump/motor from the gear pump/motor wear particles.

I originally was looking at a separate reservoir, cooler, etc, but space is tight and this looked like a simpler solution.

But you've pointed out a possible problem with this arrangement, and I appreciate that.

I looked at the cogged belt or chain drive as possible solutions but could not find a combination of pulleys or sprockets that would easily work. I'll look at that again. It's possible the belt arrangement I had would work fine and the belt failure I experienced was a fluke caused by the jamming hydro and once I fix that, the belt drive may be fine in the long term. Certainly simpler.