TC Orifice Screen behind the pipe plug.

[havoc1482]

So, I've always had this issue with the system building air pressure in the reservoir of my Super A. I remember years ago when I got the tractor a previous owner had put a vent hole on the TC fill cap, I can only assume to mitigate this. I rebuilt the unit a few years ago and it works... okay. I'll make a list to break this down:

• I had a pump that kept losing its seal into the crank case and after multiple seal replacements I just got a new pump. I don't think it leaks anymore, but.. I don't work it that hard anymore.
• The pump itself gets warm to the touch before the engine block in that area is warm.
• The unit builds air pressure behind the fill cap (if I take it off during or after running I get a *pop hiss* of air)
• The reaction time of the working rockshafts when lever input is made seems sluggish/delayed
• I can hear the engine bog down during rockshaft movement, but return to normal once the cycle is complete

I was doing some research and I've found that the orifice screen behind the brass screw behind the pipe plug can cause weird stuff to happen if its blocked. So I removed the pipe plug, and unscrewed the slotted brass part and... there was no screen attached to it? According to my I&T Shop Manual, the brass fitting and the screen appear to be one single item. I can't for the life of me remember if there was a screen in there when I rebuilt the TC years ago, but is it possible that the screen is missing or detached itself from the brass screw and is wedged in the hole? Or maybe blew itself to pieces? I would think if it was the latter (blown up) there would be bigger control issues with the hydraulics.

Hypothetically, if everything is clean and no crud is in the system, would this missing screen cause problems? Does part of the design engineering take into account the restrictive nature of a screen? Am I chasing a red-herring?

 

[havoc1482]

Im thinking I might just drain the block and take the head off to get a better view of the inside of that area. It's hard to get a good look down there with the dash board obstructing a good viewing angle.

 

[havoc1482]

Does anyone know where I could source one of these screens/plugs? The only thing I could find was a used one for $50! You'd think an apparently critical part wouldn't be so difficult to find!

Also, does anyone have a recommendation for a pressure gauge to go into the test port of the TC manifold? Would any old cheapo gauge work as long as its the right thread?

 

[Jim Becker]

Any cheapo gauge with a pipe thread and that can measure 1,100 to 1,500 PSI. The system runs 75# or so when it is idle at low pressure.

 

[havoc1482]

I took the hydraulic lines off and removed the pump and confirmed the seal for the gear shaft is leaking into the timing cover. Would cavitation and air in the pump cause it to fail? Or would a bad seal allow air into the pump leading to cavitation?

Also, the inlet and outlet ports on the pump are both large diameter, while my old pump had a smaller diameter on the outlet (high pressure) side. Given that the hydraulic line itself steps down into the smaller diameter, would this difference in diameter between the pump outlet and the tubing cause any issues?

Below are pictures of the two pumps. The one with the smaller hole on top is the original that came on the tractor when I bought it, and the other (with the blue orings) is the "newer" one I got a few years ago.

I've had the gear shaft seal go on both of these, so I always assumed it had to be a symptom of something else going on.