Farmall 756 MCV/TA questions

Gentlemen,

First off, I'd like to say thanks for sharing your knowledge on this forum, this is my very first posting; however, I've referenced this forum many times over the past couple of years to answer various questions and have always been very impressed with the amount of experience and knowledge that you all posses. Recently, I've acquired a 756 diesel with a koyker loader mounted to it that I plan to use this fall/winter to hay cattle with and have an IT manual and parts catalog for it. I've researched this forum enough to know that the T/A and MCV system seem to give quite a few problems with these tractors. I feel that my tractor is slipping when I am in one of the higher gears and going up an incline--hitting the bottom of the hill at 2ooo rpm, the rpm's will drop by about 500 and if I don't downshift to a lower gear, the tractor will stop all forward movement, but the engine will still run 1500rpms…the engine won’t stall at all. Today, I put the bucket against a tree to see if I could make the tractor stall….with the T/A in low, the wheel (no diff lock) spun in L1, L2, and L3. In L4-H4, the rpm dropped by 500 and no movement. With the T/A in direct (handle forward), the wheel spun only in L1 and L2; rpm dropped by 500 in the 6 other gears and no movement. As this tractor is showing 9000 hours on the tach and I don't know the past history of it, I assumed the MCV pump would be the first place to look. I checked the pressure at the orifice plug and got 240-250psi at high idle. After holding the steering wheel against the locks, I got 1750-1775 in each direction. The gentleman that I purchased the tractor from had issues with the steering in the winter and I got the orifice plug bleed procedure (from you guys) and shared it with him last winter. So I think the MCV valve is weak or it’s sucking air, but my pressure check today doesn’t show it. I’ve hooked up the red tell-tale light and it is working as it should…..comes on with the key, goes out immediately after startup, comes on when depressing the clutch, comes on after killing the engine. I’ve never seen this light come on any other time. I inspected the T/A plunger in the top of the MCV and its going down all the way against the snap ring and after disconnecting the linkage, found that its extending all the way up when throwing the T/A lever. The fluid level is halfway between the marks and I don’t know when the filter was last changed (I’m going to change it out this weekend and top the fluid off…..I’d add an extra 5 gals if I thought I wasn’t going to have to replace the MCV pump). When throwing the T/A lever, there’s no grinding or noise and it definitely works (although sometimes it seems like it shifts more firmer than other times). This is my first T/A tractor, do you guys think there’s something slipping somewhere or am I just being paranoid? If there is something wrong, I want to get anything fixed before its time to hay the cattle, and I don’t want to use it and take the chance on damaging it farther. Does it need a pump or the MCV valve gone through and spring lengths checked/replaced? Please let me know what you think or where you would look next as your opinions are highly respected. Sorry this is so long winded, but I wanted to give you all the information that I knew. Thanks

T/A is cooked. Overhaul the MCV while she is apart.

You have done a pretty good job of checking the TA and MCV system. Everything there is working as it should. You did not mention any steering problems at low RPM so the pump should be good.

The problems you describe all indicate a slipping engine clutch. If the adjustment has the required free travel the problem is with the clutch itself.

When you are ready to replace the t/a shoot me an email. I have them on hand and all of the other parts along with it. OEM, Heavy Duty, and super.
Kevin Meier

Your going to have to replace your engine clutch. Since it slips in both TA and direct drive this means your TA may be good. Its your call if you want to replace the TA when your replacing the clutch but the TA may be OK. There is just no way to tell until you can put full power to it.

Ok guys, thanks for the input. I originally thought about the engine clutch; however when I could spin the tire in the lower gears, I thought that pretty much ruled out any engine clutch problems. Now I'm going to look into seeing how much clutch adjustment I have left and trying that before going deeper. I'd much rather do a clutch job than a T/A replacement. One more question.......suppose the adjustment doesn't do anything for me and I find myself splitting the tractor, is there any way to get a visual on the T/A while it is still in place, or does a guy have to remove it completely to inspect it? If it is inspectable in place, what should I look for? Again, thanks for any info you can share.

Nothing that has been posted indicates that.

Same tractor with same indications; TA was cooked.

The t/a would need to be completley removed to see what is exactly wrong with it. My guess is bad seal rings on the shaft and the sprag and carrier is worn. You may have some signs of the discs that have been slipping due to bad seal rings and ring glands on the shaft. When you pull it apart and replace it. Buy a heavy duty t/a and stay away from the diodes which are junk. If you have questions why feel free to email me.
Kevin

The problem is in the main clutch. In order for it to be in the TA both the high side and the low side would have had to fail equally. That is not going to happen since the low side is mechanical and the high side is hydraulically applied. Once the low side fails it takes very little torque to get it to slip. If you do not have problems with steering at low idle and your hydraulic pressures are OK the high sides disks would have to worn out. An indication of that would be slow shifting when going from low TA to high TA. During the shift the tractor would stop if the low side sprague was out. Leakage in the TA assembly severe enough to cause slippage should also cause the TA lube light to come on.

The higher the gear you use the more lbs/ft of torque is requires by the transmission input shaft. Your slippage is directly related to to the amount of torque required which points directly to the engine clutch, not the TA.

If you really want to verify the slippage, take the cover off to access the clutch. Let the clutch slip for about a minute. That should be enough to things red hot. It will probably destroy the flywheel in the process but you would now for sure.

Thank you all again for the help. Owen Aaland and MN Scott, you guys were absolutely correct, the clutch had no free travel and needed adjusting badly. I adjusted the clutch, dump valve and trans. brake.......... tractor runs great now....lots of power and the T/A shifts nice and firmly. I guess with this being a new tractor to me and all, I got a little carried away with troubleshooting the what-ifs and didn't concentrate enough on the obvious. Thanks for setting me straight.