706 MCV issues

Red48M · Mar 18, 2014

I recently purchased a 67 Farmall 706 German diesel. The tractor starts and runs great, yet doesn"t like to move. If its cool out it will drive just fine Direct drive and TA until the hyd oil warms up a little bit. Then the tractor wont move at all and the oil light stays on. The steering and brakes always work good.

I pressure checked the MCV, when cold It is around 245psi in Direct, but bounces up and down quite a bit. In TA the reading is much more steady and about 240psi. As the tractor warms up the pressure drops. After the tractor runs for about 20 minutes the pressure in direct is about 210 and still a little jumpy. In TA it is about 230 and pretty jumpy.

I"m guessing the problem is in the MCV, but is it in the valve body or the pump? Can someone help me out here? Thanks!

Owen Aaland · Mar 18, 2014

What does the pressure reading do when the steering wheel turned in either direction as far as it will go?

That will cause the steering to open the pressure relief valve. If the pressure on the MCV readings drop off the pump is not able to provide enough pressure to maintain proper flow. The flow through the opened relief valve goes to provide oil to the MCV so the pressure and flow to the TA should not change when the steering pressure is increased.

Red48M · Mar 19, 2014

Owen, When the tractor is cold the pressure will spike to about the 270 with the steering held all the way. When it warms up the pressure will go back up to about 235, but the quickly falls back to 215 or so with the wheel held. Thanks.

gbs · Mar 19, 2014

not an expert on mcv's but I've run into the pressure bouncing,it can be caused by cavitation add about 5 gallons of fluid more than it holds full and see if that helps the pressure bouncing, check the dump valve to make sure it's seating,also remove the bottom plug in the mcv valve then remove the pressure relief valve that is above the plug the o-ring will go bad and lose pressure,it is non serviceable look it over to see if the spring is damaged or valve is stuck open,it would pay to pressure and flow check the mvc pump,don't want to tell you wrong but if I remember correct the pump should produce around 9 gpm at 1300# psi new, don't know what the minimum is ,roughly 4.5 to 5 gal is priority to the steering & brakes rest is for TA and lube

Red48M · Mar 20, 2014

Gbs, The rear end is at least 5 gallons over on the dip stick. Last owner must have tried that. The dump valve seats against the snap ring. I'll pull the relief valve when I get a chance. How do i check direct pump pressure? I don't have access to a flow meter. Thanks

706 MCV issues

Red48M

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Owen Aaland

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Red48M

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gbs

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Red48M

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