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Tractor transmissions: fixing synchros, common problems – Inside Machines

We have come a long way from a straight gear-to-gear shifting system to a transmission that shifts by itself as the load and the speed changes.

The original tractor transmission could be shifted only when you stopped. The gears would mesh with each other only when they were both running at the same speed or both stopped.

From there we developed synchronized, constant mesh, power shift and now, continuously variable transmissions. A lot of tractors have synchronizers in them. They are subject to abuse and are easy to check.

The synchronizer’s job is to make it easier to get the gears to run at the same speed. When you move your gearshift, instead of moving the gear, it moves a spring-loaded cone that is part of the gear you are using at the moment. The synchronizer slides it into a cone that is part of the gear you want to shift into. These two cones might be travelling at different speeds but as you push them into each other, they want to turn at the same speed.

The pressure is controlled by springs and by pressure on the lever. When the two gears turn the same speed, you can push the gears together without grinding. You could push hard enough that you overcome the strength of the springs and you would still grind the gears.

Here’s a simple test.

With the tractor in neutral, engine running full speed and the clutch engaged, put your foot on the clutch and see how long it takes before you can shift into a gear. It should take less than two seconds. With no synchronizer, it will take about 10 seconds. If you are on smooth pavement or hard ground, you will notice that the tractor wants to roll ahead. That’s normal.

However, if your clutch is dragging, this test means nothing. Then you will have trouble getting the tractor out of gear and all the times will be longer. Set the freeplay on the clutch before you do this test.

If the test takes longer than two seconds, wear is taking its toll on the synchros. They are durable, but they do have a life span. The more you use them, the sooner they wear out. If you have a habit of getting impatient, they wear that much faster.

There are common combine issues, not related to the synchros, on older Massey combines, including the 750, 760, 850 and 860 models.

The gears were cut so that when the linkage was set properly, the gears pulled together once loaded.

When fully engaged, there should be adjustment left on the linkage cable, with no load on the cable itself. When set tight, the cable causes gear wear that can make it impossible for the transmission to remain engaged.

Over-tightening of the lock nuts at the bottom of the cable could have caused distortion of the cable and resulted in it becoming unable to be set loosely. Replace the damaged parts and set it properly with the nuts snug against each other.

If you are inside the transmission, check for a bent shifter fork caused by pulling hard to get or keep the machine in reverse.

Hot oil treatment

Transmission oil can get so hot that it melts the solder on the intake tube. Usually it’s from too high a level caused by a poorly located level plug. Drain and fill with the recommended amount in the manual. It should then run at 100 F above ambient temperatures.

Q: We have an 860 Massey Ferguson combine and two problems.: excessive straw accumulating on the sieves and a low back-beater speed of 690,which is supposed to be 740. – M.K.

A: I am going to answer the second question first because getting your combine up to speed could solve the first problem.

The speed of the rear beater is totally a product of the speed of the engine.

Hold the throttle lever on the pump right against the pump’s stop. You might have to disconnect the cable to do that. Run the engine. If the beater runs at 740, you have found the problem. It is quite common for the cable to stretch over time and you need to reset it.

If that didn’t solve the trouble, you have a problem with your engine.

Ideally, the engine should lug down to 710 under load because that’s the ideal speed of all the parts including the shoe and the walkers. The higher speed should clear up some of that straw.

If the engine is working right, it should try to hold the speed at 760 when unloaded. If you start pushing it too hard and it lugs to 690 or 680, you are getting close to plugging it.

To further solve the straw problem, go through the basic setting of the shoe. Start with the sieves open, so the threshing job you are doing can be seen in the grain tank.

Always set your concave to do the best job possible. You might have to put in concave blanks.

Now set the shoe. It is important that you leave the front part of the top sieve about three quarters open. That’s why you must do your threshing the first time around. If you have the front part of the top sieve closed, it deflects the air so it travels along the shoe instead of through the shoe. Then there isn’t enough air to lift the straw.

Correct speed and air through the shoe should solve that problem.

I will try to answer as many questions as possible in the newspaper or on the website at If you leave me your phone number, I will call collect and answers will also be sent via e-mail.

Got a question for Henry? Send it to

Henry Guenter is a former service manager for Massey Ferguson.

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