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Farmall & IHC Tractors Discussion Forum

806 MCV hydraulic problem

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Author  [Modern View]

08-28-2016 19:42:50

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1965 farmall 806

New fluids and filter

Worked good for first 25 hours

MCV pump started to whine, then steering and TA stopped working, but brakes work fine

Replaced MCV pump with new 9 GPM hy-cap unit

Replaced all gaskets and seals on MCV

Installed new filter and everything worked

25 hours later, same problem

Overfilled by 4 gallons of hytran

Replaced all springs in MCV and safety valve 2000 PSI one at a time, no change

At less than 1000 RPMs, steering, brakes and TA work fine, installed gauge in lube port for low side pressure, all reads good, at under 1000 RPMs, no pressure over 1000 RPMs, except when brakes are pushed.


Can it be the oil filter is plugged and I'm not getting any suction at higher RPMs?

Can the filter bypass be stuck, it seemed fine when I took it apart?

Tractor was stored outside 5 years prior to my acquiring, now has been stored inside. Have been getting a lot of water out of the hytran, could this be somehow involved in my issue?

Didn't connect high pressure gauge into safety valve. Didn't know what snubber was. Do I need one to do this check?
Any suggestions would be helpful.

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09-08-2016 14:03:09

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 Re: 806 MCV hydraulic problem in reply to afewacres, 08-28-2016 19:42:50  
Found the problem!! Plugged hydro filter and bypass valve.. Still had water in the Hy-Tran. Probably didn't need the new pump or rebuilding the MCV. Sometimes it is the obvious fix that I miss.

Thanks all for the help

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08-29-2016 12:20:35

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 Re: 806 MCV hydraulic problem in reply to afewacres, 08-28-2016 19:42:50  
Thanks all!! I have removed the plug next to the pressure sensor switch and cranked engine got fluid no problem out of port so i dont think its a priming problem. I did miss replacing the spring behind the tell light sensor so here is to hoping its that or the filter

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caterpillar guy

08-29-2016 11:45:51

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 Re: 806 MCV hydraulic problem in reply to afewacres, 08-28-2016 19:42:50  
there is a plug on the back side of the MCV if you loosen it up and things work fine you are losing prime. I take that out and have somebody either bump the starter or you do it. The other has to catch the spring that comes out. As soon as it starts it needs to be shut down or pump all the oil out. then stuff it back in and see if things work. Like said if they then work it is loosing prime. Could be a blown gasket bad o-ring or eeven have a bad valve in the MCV. I would also check the filter. If you have that much water you need to change the oil or loosen the plug on the bottom and see how much comes out before oil does.

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08-29-2016 08:02:37

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 Re: 806 MCV hydraulic problem in reply to afewacres, 08-28-2016 19:42:50  
At low speed, under 1000 RPM the TA shifts and the tractor moves fine in low or high. Brakes are great no matter what RPM, steering great below 1000 RPM but when I wind up the throttle only the brakes work well, steering gets hard and gauge in lube port drops to 0. MVC pump whines a high pitch when I turn up the speed. Shouldn't the bypass valve with screen let fluid fluid pass if the filter is plugged. Why would higher RPM affect the gauge negatively?

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09-01-2016 09:57:51

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 Re: 806 MCV hydraulic problem in reply to afewacres, 08-29-2016 08:02:37  
Was searching for something and found interesting thread on RedPowerMagazine genersl IH forum. Dated Nov 2014. Excellent info on MCV operation. Title was MCV Pump question.

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08-29-2016 07:29:14

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 Re: 806 MCV hydraulic problem in reply to afewacres, 08-28-2016 19:42:50  
The water can plug a filter pretty fast. Water molecules are bigger than oil molecules. Had a 560 once that would do that.Replace the filter and find out.Odd though,the steering is the first thing served by the MCV.If I remember correctly,and have been told,Steering gets 3gpm;brakes get 3gpm;TA gets 1 1/2 gpm;what is left lubricates transmission.If this is not correct,I'm sure TractorVet or someone will correct me...LOL

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08-29-2016 07:40:05

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 Re: 806 MCV hydraulic problem in reply to DeltaRed, 08-29-2016 07:29:14  
Right now I would be going through the flow chart and trouble shooting in the service manual. When you say TA doesn't work am assuming you mean high side?

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