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806 Sudden loss of lube pressure


AmateurHobbyFarmer
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I recently installed a new TA and the pressures were 300psi for the TA pressures and 20 lube psi.  I have about an hour of use on the new TA.
 
Hopped on the tractor today and my power steering started to get really noisy and harder to steer.  Seems like the noise is mainly coming from the steering column area and the MCV seems to be making a little noise too.
 
Checked TA pressures and those checked out good at 300psi.  
 
Checked lube pressure and I barely have anything.  I get maybe 1-2PSI with wheels straight and I completely lose pressure when the steering is maxed. I get around 18 or so when I hit the brakes.  
 
Any ideas on what might be wrong? Only thing I can think of is that my sump check valve is bad?
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7 minutes ago, snoshoe said:

Sump check would not cause hard steering. Blown oring in mcv would. Steering return is  regulated flow. Lube is left over regulated. If steering is low. Lube is where you see it first. Yes a bad sump check dumps regulated causing loss of lube but not steering.

Why does lube pressure increase when brakes are applied?  Could it be a leak in the brake valve causing regulated to drop? 

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4 minutes ago, snoshoe said:

There is a steady flow through brakes that is shut off when applied.

Ok.  That's right.  Fed by the orifice in the regulated circuit, correct? I'm rusty....

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This isn't right.  I went and looked it up.  Brake valve is closed center like I thought.  Only bleeds the 1 GPM supply while brakes are applied.  

Check valve in the MCV, orifice in the brake valve.... so the answer is "Yes", lol.

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5 minutes ago, snoshoe said:

I would like to see that chart. That one gallon flow should be constant to keep reservoir on top of valve full for manual braking. I have been wrong before. Will be again.

Book said that some leak by happens to keep reservoir full, but it is a closed center. I'd grab a pic, but I already put the book up and I'm headed to bed.  Plus, it was in the valve operation description, so it's all reading.  I can try to grab a pic in the A.M.  As I recall, a leak in the seat circuit also causes loss of steering pressure, and therefore no oil left for lube. 

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7 hours ago, J-Mech said:

Book said that some leak by happens to keep reservoir full, but it is a closed center. I'd grab a pic, but I already put the book up and I'm headed to bed.  Plus, it was in the valve operation description, so it's all reading.  I can try to grab a pic in the A.M.  As I recall, a leak in the seat circuit also causes loss of steering pressure, and therefore no oil left for lube. 

Don't trouble yourself with the pictures. I've got a pretty good handle on it. Lube is not the problem. It is the result. Check points.

Oil level

Filter

Mcv

Pump

If problem was beyond mcv there would be oil on ground. It happened all at once. Makes me focus on the orings. Could also be diaphram in pump.

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12 minutes ago, J-Mech said:

You lost me on this....

I don't imagine many trw pumps exist anymore. It used to be good business. Remove pump. Stuff in seal kit. Put it back in. The diaphram(a seal that put pressure on thrust plates)would blow and pump would lose flow and pressure. Cessna can do the same thing but usualy wear out first. Have no idea what is used now.

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47 minutes ago, AmateurHobbyFarmer said:

Thanks guys.   Oil level and filter are good.  I put a new pump in when I replaced the TA.  I think I'll check the oring on the upper end of the steering safety relief valve first before I start digging into the mcv.

Relief dumps into regulated.

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Figured I'd post the numbers on here too see if this helps identify anything before I begin tearing into it.  These were the results I got tonight.  I uploaded a pic of what I found in the service manual - its the closest scenario I could find compared to what my pressures are reading.  I think they reference lower TA/DD pressures since factory pressures were much lower than what the Hy-Capacity TAs need.  (I had to add an inner spring to the pressure regulator to bump the pressure up)
 
Wheels straight, no brakes - 
TA psi - cold 170 / warm 300
Middle psi - cold 170 / warm 280
DD psi - cold 170 / warm 280
Lube psi in all TA lever positions - cold 0 / warm 1-2
 
Wheels at stops, no brakes - 
TA psi - cold 120 / warm 300
Middle psi - cold 120 / warm 280
DD psi - cold 120 / warm 280
Lube psi - cold 0 / warm 0
 
Brakes pressed, wheels straight -
TA psi - cold 300 / warm 305
Middle psi - cold 280 / warm 280
DD psi - cold 280 / warm 280
Lube psi - cold 0 / warm 18-20
 

20201014_194132.jpg

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  • 3 weeks later...

Well guys.. finally got around to actually addressing this today.  I went and replaced the transmission filter again and it did the trick.  Got all my pressures back, no more noise and steering is good.   

I did replace the fluids and filter shortly before the TA job.  But it appears that there was enough gunk to clog the filter and the filter bypass valve screen was pretty clogged with fine particles. 

I'm kind of wondering if some of the crap came from when I worked on the range cover - I had to scrape the old gasket off.  I used a rags to prevent the old gasket material from falling down below, but maybe it didn't catch it all.   Not sure.  I did re-filter all of my used transmission oil before putting it back in the tractor, too.

But it's good now!  I appreciate all your help! 

   

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1 hour ago, AmateurHobbyFarmer said:

Well guys.. finally got around to actually addressing this today.  I went and replaced the transmission filter again and it did the trick.  Got all my pressures back, no more noise and steering is good.   

I did replace the fluids and filter shortly before the TA job.  But it appears that there was enough gunk to clog the filter and the filter bypass valve screen was pretty clogged with fine particles. 

I'm kind of wondering if some of the crap came from when I worked on the range cover - I had to scrape the old gasket off.  I used a rags to prevent the old gasket material from falling down below, but maybe it didn't catch it all.   Not sure.  I did re-filter all of my used transmission oil before putting it back in the tractor, too.

But it's good now!  I appreciate all your help! 

   

Just noticed this post and the low pressures cold/high warmed up screamed a suction issue.  

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and on my 806 i loose lube pressure once warmed up. cold 20 lbs. and then once warm it drops to about 8 lbs. no one has given me an answer as to why this is happening. all they say is ta goin bad. dont seam right to me. the ta works good till the pressure drops.  the ta pressure was around 220 lbs. i kept the guages on it while working it and was watching them. filter was replaced as old one was plugged. checked new filter after 8 hrs. work and clean as can be. so not a filter problem. also did the 5 gal over fill thing did not make any difference. so is here some o rings bypassing  in mcv or is it inside the housing at ta?

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11 hours ago, rustred said:

and on my 806 i loose lube pressure once warmed up. cold 20 lbs. and then once warm it drops to about 8 lbs. no one has given me an answer as to why this is happening. all they say is ta goin bad. dont seam right to me. the ta works good till the pressure drops.  the ta pressure was around 220 lbs. i kept the guages on it while working it and was watching them. filter was replaced as old one was plugged. checked new filter after 8 hrs. work and clean as can be. so not a filter problem. also did the 5 gal over fill thing did not make any difference. so is here some o rings bypassing  in mcv or is it inside the housing at ta?

I have to guess at what you are not saying. Iube pressure loss does not cause the ta to act up. Loss of regulated pressure does and causes loss of lube pressure. If this is whats happening. Then I need to know regulated pressure in the 3 lever positions when lube is lost. Direct drive ta and in the middle. If pressure is low in all 3 and steering is good. You can look in the mcv. First the sump check. If pressure was good in the middle but low in either dd or ta or both. They were right. Ta going bad. Exception being orings on jumper tubes. I've only seen that on misinstallation.

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