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MCV Troubles on 1981 1086 ?


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#1 RED KEV

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Posted 05 June 2012 - 06:53 PM

I put a new mcv pump in. Had a local dealer put kit in the mcv valve , and polish valves. Now i'm having same low pressure as before , my lube psi. light on dash comes on at idle or after oil gets hot. My psi. at switch is 18psi. clutch it goes to 0 , let clutch pedal out back to 18 psi. touch brake pedal goes to 0 let off on pedal back to 13 psi.. I checked psi. at safety relief valve it was 312 psi.. Torque
is new and works fine. I might add some one has changed the pfc. hydraulics back to gear style pump through hy cap.kit. Any idea where im leaking hyd. oil past to cause low pressures?

Thanks Kevin

#2 pete 23

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Posted 05 June 2012 - 08:58 PM

You need to do a more complete pressure test on the mcv. You have to compare regulated pressures in direct drive, TA, and middle position of the ta lever where you reach the lowest pressure. Then with brakes applied and then steer to stops and hold wheel against stop. At the same time be recording lube pressures in each position. That way you can pin the problem if it is in only one area. You could take the fitting off the brake valve and make sure the screwed in orfice is in the valve under the fitting and also, do the brakes work first time every time or do you have to hold them on. It could be as simple as a leaking sump check valve, that little plastic valve down in right lower corner when you have mcv off or as serious as broken rings on ta input shaft. . Service manual explains how to do the tests. Also, I don't like to see regulated pressures that high. Two hundred seventy is plenty for any of those tractors and more pressure just creates more heat and more blown gaskets and o-rings. I believe the 15 series mcv increased the pressures to help TA clutch life but all I ever saw it do was rip more things apart instead of slip.

#3 Red Tech

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Posted 06 June 2012 - 09:32 AM

I would suggest unhooking, and capping, the line to the brake master cylinder so that you could eliminate that as a cause, OR pinpoint it as the cause. Also years ago, on a 1066 with a clutch booster, I found leakage through the clutch booster cylinder to sump; this would cause the light to come on. I've never had that problem with an 86 clutch booster cylinder, but it is something to consider.

As Pete 23 said, the regulated pressure is way too high. I normally set them at 245 psi; sometimes 275# on the higher horsepower tractors.

If you have the TA lever in the mid-point position when testing, you can eliminate any potential problems with the slip rings on the TA shaft.

Good luck, keep us informed so that we can all learn from your experience.

#4 Ktp460

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Posted 06 June 2012 - 04:57 PM

I had a 986 do the same thing last month it was the ta

#5 1967806

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Posted 06 June 2012 - 05:58 PM

Got an 806 doing the same thing. Push the brake down and lube light comes on.
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#6 Followme1086

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Posted 06 June 2012 - 09:29 PM

You could also check the flow divder orfice plug, I had one partialy plugged once so even tho there was a new pump installed, it would not flow 5GPM across the flow divder to the steering then brake, TA and libe circuits. Orfice should be 9/64 I beleive????? Maybe some one can verify. Thanks

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#7 RED KEV

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Posted 11 June 2012 - 05:55 PM

It has brakes as soon as you start it. Checked pressures again with a new guage this time. Old guage was bad.
Oil warm at idle TA forward or back 250 psi
same test at 2000 rpm 263 psi

Oil warm TA in half way point at idle 225 psi

TA halfway steered left and right, and held against stops while pushing lite on brakes at 750 rpm 130 psi

Same test at 2000 rpm 250 psi

What do these pressures mean!

#8 Followme1086

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Posted 11 June 2012 - 06:27 PM

Steering releif may be leaking. Releif valve is behind plug that points toward ground on bottom of MCV valve. The supercharge line hooks to a 90 degree fitting coming out of the bottom of MCV next to releif plug. Could also be a blown gasket or oring.

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#9 Owen Aaland

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Posted 11 June 2012 - 07:11 PM

Since you should have a priority 5 gpm through the orifice the pressures you are checking should not vary from low idle to high idle. Some change in pressure is to be expected as the temperature of the oil changes but it should be slight.

The changed in pressure readings at different speeds are somewhat consistent of a pump problem where there is not enough flow. Is there any difference in the steering between low idle and high idle? A change in steering between high and low idle would indicate pump flow problems where it can not maintain at least 5 gpm under pressure. A leaking or defective steering relief pressure valve may affect the steering but should not affect the rest of the MCV since the bypassed oil is returned to the 5 gpm flow in the MCV.

Any chance that you installed a 9 gpm pump rather than a 12 gpm pump? Older tractors used a smaller pump since the orifice used in them was only 3 gpm. The extra 2 gpm in the 86 series tractors is used to lubricate the brakes. There is a one gpm orifice in the elbow in the lube line at the brake housings. As Pete already mentioned there is another one gpm orifice in the brake valve. The brake, clutch, and hydraulic seat all used closed center valves so there should be flow through them only as they are being used.

Using a 3 gpm orifice rather than a 5 gpm orifice in the MCV can cause problems since the brake lube uses 2 gpm all the time. A leaking steering check valve (the little plastic valve in the center section behind the MCV) will also bleed off some of the 5 gpm flow.

#10 RED KEV

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Posted 06 November 2012 - 05:36 PM

Well, finally found the internal leak!!!!!! It ended up being the power steering hand pump on the fire wall. Took one off a 1981 986 that a buddy has to try and bingo fixed the problem! Now have to locate one to put back on, part #1263446c91.




Thanks, Kevin



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