L2900D with a (very) slow engaging GST

Spectramac · Jul 25, 2011

Hi guys!
I've been working on this tractor for a while now. I was thinking the hydraulic clutch was going out so I pulled the tractor in half and checked it all out. Not for the faint of heart! Only a couple small issues were inside, nothing that would make it slip or engage slowly. Now that it's back together I've gone back to testing pressures on the side of the valve body. First plug I checked had no pressure in any gear, so I tried the next plug back. That one seems to be the clutch pressure. It gets around 25-30 lbs right off the bat and slowly climbs (like a psi a second). Once it gets to about 75 lbs the clutch locks up pretty good. After around 30 secs it pops and burries my 300 lb gauge. So maybe I have 2 issues?? Slow to build pressure, but eventually too much??

Does anyone have a diagram or location of the valves that control the clutch or what pressures I should have?? Tomorrow, I start pulling plugs and seeing what I can find.

Thanks,
Malcolm

KennyV · Jul 26, 2011

WOW you need a WSM ...bad.

The GST uses the Power Steering pump for operation... The pressures you should see will be 356 psi.
There is a reducing valve that checks it at 356 psi, and a pressure relief valve set at 427 psi..
There are several pages describing the Clutch and shifting operation... pages 3-M20 through page 3-M30...

Do you know the history of this tractor? What caused this problem? Was there any problems with the steering?

I can scan & post the pages, .... How many hours are on this tractor? KennyV

KennyV · Jul 26, 2011

Actually you likely don't need the operating principals ...
Here are the pages on GST valves- checking & adjusting...
Good luck... and post back with what you find...
Take some pictures as you go... I'm sure they could be interesting... KennyV

Spectramac · Jul 26, 2011

Thanks a lot Kenny!
This tractor get's used like a D-8 cat, almost always in the mud. We had to take it all apart just to get it cleaned up enough to see the parts.

It had broken the hydraulic filter base off the side of the trans and the pipes were pretty bent up from hitting bottom. When I had it split, the only thing were found bad in the clutch pack was the snap ring end was broken. We couldn't find the missing piece anywhere! Maybe if we ever find it we'll figure out the problem.

So it looks like the valve on top of the pump is the brains in the system. I'll see what I can find in there!

KennyV · Jul 26, 2011

Spectramac said:
... So it looks like the valve on top of the pump is the brains in the system.

The pressure regulating valve at the right hand side, rear of the engine...(See the center two pictures of the second attachment)... That is where the GST system gets the 412 to 427 PSI operating pressure to start with...

And the Reducing valve on the Trans, that is where it is reduced to 356 to 370 PSI...KennyV

Spectramac · Jul 26, 2011

I checked the pilot pressure and it seems fine. Winds the gauge right around in every gear, but the clutch pressure just doesn't want to wind up. I pulled the valve that sticks out the bottom of the GST and found the orifice and screen in the bottom. It was pretty muddy, I was hoping I'd found the problem. I cleaned it up and put it all back in. The clutch pressure seemed to work good for a few minutes but then just hung around 40-50 lbs... I think I need more than one gauge so I can check both ports at the same time.

Do you have a pic that shows what valves are what on the GST?

Thanks

KennyV · Jul 26, 2011

It will be tomorrow before I can scan anything in & get back to you... KennyV

Spectramac · Jul 26, 2011

I went to a bigger gauge so I could see what pressure I'm getting up to. Looks like right at 400 at the pump and around 380 at the pilot port. I still can't get the pressure to pop up at the clutch though... It hangs up around 50 lbs or so. Once in a while it will pop and go up, but I can't tell where it's hanging up? I'm guessing it has to be in the GST.

Texas Fella · Jul 26, 2011

First thing that I would do is make sure it has SUPER UDT in it. I am familiar with GST (in Kubotas) and often times a rough or slow shift is due to the wrong hydraulic oil. I have personally seen several units that shift so poorly that you can not drive them. We drained the hydraulic oil and installed Super UDT and the unit shifted fine. It is my experience that some of these units are more "picky" than others when it comes to the type of hydro oil. I have seen some that just do not like Hi-Tran (Case Tractor's hydraulic oil, and not bad (cheap) stuff either) at all, drive like crap with it. May not make any differance in yours, but I would try it.

Texas Fella · Jul 26, 2011

Oh, one more thing, if you already took it apart, check the "bango" fittings for the pto and the trans. hydro supply line. They look the same, but the PTO has an oriface in it, and the trans does not. I have seen many techs put the wrong one in the wrong place and get a symptom much like (if not just like) what you are discribing. The easiest way to tell which is which is to just take them both off and inspect them. Like I said, I have seen many a tech mix them up during re-assembly. Let us know what happens.