Gehl HL2500 Transmission - No movement after repair

Moved this to a new thread from "Gehlk HL2500 Transmission" because I have a new problem now...

From the last thread, bought a broken skidsteer, left hydrostatic transmission drives fine, right side no drive at all. Took it all apart and found a broken input shaft on the right side. Replaced the shaft and here we are.

After reassembly. started machine, and neither side drives. Figured I needed to bleed air from line, so I disconnected lines from just as they exit the spin on filter and filled the lines manually with a syringe. Started machine and still nothing.

Next step, I removed the covers from the mechanical drive side of transmission and saw the tanks were almost empty. The way this hyd system works is it sucks hyd through the filter @ 5" hg, uses whatever fluid it needs and dumps the return fluid into the mechanical drive tank. Once the tank gets about 6 inches up, there is a big return port the fluid spills into and gravity feeds back to the main reservoir.

With the mech drive tanks empty, I figured it couldn't hurt to fill them up to the gravity return level. After that, I pulled the bleed screws on the hyd trans until I got flow, then put them back on. Took a 30 min lunch break, then fired up the machine and the left side began functioning as it should. Right side still did not function.

Continued troubleshooting and saw that with the engine running, the right side mech tank empties out back through the pressure side. My only explanation is the left side must be pulling fluid from the right side instead of through the filter - probably because there is less resistance. Thinking this must be a check valve issue, and not having any spare parts on hand, I swapped the check valves from left to right, and right to left. Bled the air out and started the machine again. Same condition, left side works fine, right side not.

While I had the hydrostatic unit apart, I inspected the charge pump and it seemed fine. And I should mention I was an aircraft hydraulic/pneudraulics specialist in the Air Force for a couple decades. I am rusty, but I understand most of the concepts still.

I am going to order a new filter, but right now I think it will not make a difference. I suspect I have a faulty Charge Pump. What are your thoughts? Thanks!

This post was edited by mongoosetoo on 07/07/2022 at 09:48 am.
 
Did you get the little drive pin that passes through the shaft and drives the charge pump in place as you installed the charge pump?

Also, it is easy to break the pin or pump gear if things don't do together properly or if the gears are jammed for some reason (possibly a bit of debris) and the engine is cranked.
 

I would love to say that I did, but cannot be 100% certain. I guess, the hydrdostat unit is gonna have to come off anyway. I'll double check it when I get it back off.


This post was edited by mongoosetoo on 07/07/2022 at 10:22 am.
 

Good news/bad news....
The good news is I am getting pretty quick at removing this transmission. The bad news is, the pin is in place on the charge pump. I don't see any metal shavings, and the shaft spins all the way through to the other side (not broken).

I guess while I am waiting for some guidance, I'll look for a spec and measure the pump parts.

Thanks
 

The make a right and a left rotation charge pump, any chance something got swapped around there.

On some hydros the charge pump can be installed two different ways by (IIRC) on this type the bolts won't line up if it is flipped.
 
I may have found something. I don't recall which way I had the charge pump housing installed, but I just read a note in the service manual about indexing the charge pump housing so the "flat" side faces the control lever. Page 60, step 5:
[i:6da2b670c4]
5. Install charge pump housing with FLAT side toward control lever. This MUST be done for proper indexing of charge pump, to establish correct direction of oil flow from charge pump. [/i:6da2b670c4]

I can't remember which way I had it installed, but I'll reassemble per spec and give it a try. More to follow...
 

Put this one in the memory files...The charge pump housing on my particular Sunstrand 5 Series Type U can indeed be installed upside down.

There are two eyelets that 5/8" head bolts go through to secure the charge pump housing. One of the eyelets is rounded, the other is flat. Once I put the flat side pointed towards the control lever it came back to life!

Thank you so much "wore out", that was a great tip looking into the charge pump. It makes total sense now why one gear box would empty out - it was flowing in the wrong direction!

5.5 gold stars for you! Thank you much!
 
(quoted from post at 12:32:42 07/07/22)
Put this one in the memory files...The charge pump housing on my particular Sunstrand 5 Series Type U can indeed be installed upside down.

There are two eyelets that 5/8" head bolts go through to secure the charge pump housing. One of the eyelets is rounded, the other is flat. Once I put the flat side pointed towards the control lever it came back to life!

Thank you so much "wore out", that was a great tip looking into the charge pump. It makes total sense now why one gear box would empty out - it was flowing in the wrong direction!

5.5 gold stars for you! Thank you much!

You are most welcome! Glad you got it going, and with minimal work and $$$$ vs. having a special hub made or buying a $$$$ new shaft.
 

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