Combines 750 drive belt slip

[ski_whiz]

Check top and bottom pulley closely, as the angled sides of the pulleys lose thier straightness as belts slip in them over time. The sides become cup shaped and are unable to properly grip the belt. Once belts are worn so narrow, they may contact the center hub of the pulley as well. Once they do they no longer grip on the sides and slip easily. I had an MF 750 slip the belts before and the problem was the transmission was flexing in its mounts (Bolts backed out slightly). Realigning and tightening repaired problem. Also, verify condition of center sheave in variator. Should have almost no play.

 

[ski_whiz]

Be sure both bolts are bottomed on the spring adjustments and that the linkage is able to travel freely to take up the slack in the arm. Would consider having a spacer machined to increase spring preload if you're sure they're sacked, not more than 1 inch. Suspect it may be your clutch slipping, not belts. Pulley cupping usually most severe on clutch pulley. Be sure belts aren't bottomed and driving on hub of pulley - must be clearance between belt and hub when tight. Feed a piece of wire through to be sure. Have you cleaned your clutch lately, as dust buildup can prevent proper clamping of disks. Remember to give lots of freeplay at release bearing. If you need to overhaul clutch, have surfaces machined to correct dimensions.

 

[ski_whiz]

Forgot to tell you to check the condition of the sliding sheave in the variator pulley. With belts out of pulley, there should be no play in sliding sheave - meaning it should not rock. This play can cause belt slippage in variator and accelerated belt wear.

 

[dav11]

Just had to answer this one-- ski- whiz is right-- must be someone who has worked on these -- I would quess clutch disk is bad or packed full of dirt - I clean mine every year, if the center hub variator pully is bad usually you will ruin the top drive belt in a very short period of time. On my 860 I have had the pulling problem when the top pulley gets worn, the one on the engine output shaft, I have had to change that pulley twice on mine, if the top pulley is shiny in the middle when running it-- it shouldnt be--that means belt is running in the middle and traction belt should be running on the side of pulley.

 

[cookie_jar]

Thanks very much for the suggestion to look at the clutch. It should be a no-brainer, but I guess I missed the forest for the trees.

 

[Doc_Holiday]

I'd check my pulleys very carefully. I've run into this before on MF combines. I would venture a bet your pulleys are wore just enough to cause you this problem. If you see a shiny area anywhere near the bottom of the pulley groove your in trouble. It takes a lot of time and fiddling around to measure a pulley accurately. Best thing might be to take a drive belt and cut a 6" section out of it (the belt doesn't have to be brand new...as long as it's not totally ruined it will work, your just using it to make a comparison),place the belt in the groove of the pulley on your combine and note how deep the belt fits. Now head off and check a new pulley (if possible) with your same chunk of belt. If you can't check a new pulley head to your local salvage yard and start checking the machines they have on hand. I'd be betting you'll see a major difference. Good luck Doc