856 mcv problem

[cjrpr]

Our 856 was on auger Duty during Corn Harvest. It's sat in one spot running the auger for about 2 weeks. Not constant. The MCV pump lost its prime. This tractor did the same thing last year. The pump will not prime up when I remove the 5/8 plug on the backside of the MCV. In fact if you put your finger over the plug hole that actually has a slight suction. The hitch pump works fine. This tractor did the same thing last year and I took the MCV apart and checked all gaskets and the pump and replace filter. Put it all back together and for some reason it worked. It worked great all this year up until now when it's set on the auger again. The tractor sits level on the auger. Also I have a 5 gallons over full on hydraulic fluid to rule out a bad o-ring in the split area. Anybody have any ideas what's going on? Why would it have a suction where the 5/8 plug goes?

 

[caterpillar guy]

Not sure which plug exactly you mean. I do know if you pull the plug on the rear side about half way up it will spray oil all over when it starts. That will prime it. It sounds like you have a bad placed o-ring on the filter plate with the screen or the pump is close to shot. Would need to flow rate the pump for better diagnostics. Or just replace the pump. Does the plastic check valve for steering when dead seat good in the bottom and did it fall out when you had the MCV off last time. That deal is what is supposed to hold the oil in for steering without the engine running. Have you tried driving it slowly turnig the wheel as much as you can till it picks up oil? The steering ,brakes,trans lubrication,TA all work off that pump.
Do the brakes work ok? If so your pump is priming. IS there oil leaking from under the steering wheel or down on the top of the trans case by the starter if so you might be loosing oil enough to let air in while setting not using the steering even though the pump is not failing.
The lift on the 3 point,and remotes work on a different pump located farther back behind the cover over the reverse fork.

 

[cjrpr]

Yes we are talking about the same plug halfway up the back of the valve. That's where I have always blood other tractors if needed. I actually repair farm tractors for a living. I know I have the MCV valve together correctly. Nine times out of 10 it's the pump that is bad. But the pump is in good condition on this one. I took it apart and examined it. Nothing works no steering no brakes the tractor will not move. Even ones worth worn-out poems I can still get them to bleed out by taking the plug out. This one just will not do it no matter how many RPMs I run the tractor. And I don't quite understand why it has a suction where it should be squirting oil out where the plug is

 

[cuby]

Take a squirt oil can and put oil in that hole until it runs out and then start the tractor. just for squirts and giggles it might come around.

 

[cjrpr]

You know what. I was thinking the same thing a little over an hour ago and that is what I did. And it primed it right up. I'm not sure what's going on with it that it had a suction there. But now at least I was able to park it in the shed until I get time to work on it this winter. Thanks for your help

 

[caterpillar guy]

I know we had that same problem with our 856 wound up changing the pump and no more problem since. Was doing the same not priming . Didn't notice a suction though.

 

[the tractor vet]

Really not sure on this myself and with out more testing to see what the MCV pump is doing when it is working can't say . Now by chance you did not loose the sump check plug and spring when you did have it off did ya qand you did replace all seals gskt. and do a test on all the springs making sure all valves FLOAT in there bores smoothly , you do have the quad ring on the tin filter cup that goes behind the hyd filter and you are replacing the filter gskt each time you replace the HYD filter ever 250 hours or sooner , next is the filter cover bolt holes all flat making for a PERFECTly FLAT because they may not show outside leakage BUT can suck air . Keep in mind here the hitch pump if good will do 10-13 GPM and the MCV at best will do 9 so what pump get more and could stave a weak pump as the both get fluid from the same filter . Now say someone put the 15-17 GPM pump on the hitch , i have thought about this a lot as the filter is only good for say 14 GPM and to get more thru the filter ya have to stack two . I have only been working on I H tractors full time since 83 so i am still learning .

 

[cuby]

There are times when we bypass the simple things. Glad you got it going and you might not have to do any more to it..