MF506 Ground Speed Variator problem

[GmB]

As usual, last minute rush to service the old combine ready for a smooth harvest, only to have an issue with the ground speed variator.
This will be my 3rd season with it and have suffered with belt slip for the last 2 harvests when trying to speed up, thought I had better sort it out.
Both belts are the correct ones and in good condition, but I can’t get the belt from the variator to the gearbox to stay tight when I push the lever forward to increase ground speed.
It becomes so slack that it looks like it might jump out of the variator pulley. Try to tension it up and it makes a nasty noise, but still goes slack when trying to increase speed. The belt from the engine to the variator seems to stay the same tension at all times.
Have tried adjusting using the thread on the bottom of the ram, no better.
Could it be a problem with the variator itself? Have no idea what is inside it, is it something that can be easily stripped?
Would like it sorted, not an issue in the field, but driving the 3 miles from home to the fields is a SLOW job.

 

[MF-ANDY]

The 2 outside sheaves are fixed and the middle one should slide. It maybe not sliding as it should.

 

[GmB]

How easily should it slide?
I’ll slacken the belts off and make sure it does move, the combine was unused and barn stored for a fair few years before I was offered it so there is every chance you could be on the right track, ta.

 

[MF-ANDY]

Fairly freely. Other models were greaseable not sure about the 506

 

[GmB]

There is a grease nipple, just about able get to it through the tension adjustment slot

 

[GmB]

Slackened and removed both belts this morning, the middle part did slide side to side but there was congealed grease on the sliding surfaces. Cleaned it all off, gave it a squirt of WD40 and slid it from side to side for a good 10 minutes, put it all back together, ran it up........ just the same as before

 

[MF-ANDY]

Not familiar with the 506. Is the only adjustment on middle the variator pulleys and not on the gearbox?
Have you touched the ram adjustment. I'm guessing it should be adjusted so that both belts sit an even amount below the top of the sheaves in low and high.

 

[GmB]

The ram had been removed by the previous owner and used for something else. He re fitted the ram when I bought the combine, so I can’t say for certain if it has been re fitted correctly. The handbook is a little vague when it comes to belt adjustment, the threaded part on the ram tightens or slackens the belt to the gearbox and once this belt is at the same tension as the belt from the engine, you can further adjust both belts together, using the threaded turn buckle on the variator.

 

[Exfarmer]

You have probably got worn belts. You need to check the width of the belts against new ones. Only 2 or 3 mm will make a huge difference to performance.
The two belts work against each other as the variator moves it tensions one belt which makes it dig deeper into the double pulley this pushes the central divider across tensioning the other belt. Provided the divider moves freely it is a belt issue

 

[Andy Nash]

Exfarmer might well be right, but I would experiment with the turnbuckle arrangement.
I would try putting it in the fast position, slacken the main pulley bolt and adjust the turnbuckle until you have a bit more tension on the bottom belt.
Tighten up and get an assistant to operate the variator lever gently while you watch the belts for any tendency to overtighten as it goes through it’s range.
I think that’s what I did with my 440 when I had the same issue. Even when the belts are new you don’t get a great deal of drive in 3rd gear without a lot of squealing.

 

[Tractortech]

Now Then..
It looks the same as the John Deere version as used on many combines.
The centre section should always have clearance in the centre when the ram is at each end of its stroke..
Maybe new belts would help. See if you can get a measurement of a new belt to check yours first.

 

[GmB]

Raining yet again, so the workshop it is.
Ran her up, put the variator into the fast position, turned it off and the belt to the gearbox was so loose there is no way there is enough adjustment to tighten it up. The belt from the engine on the other hand was as tight as tight.
Have just ordered a new pair of belts, soon to be unavailable apparently, so will be interesting to see the width of them. Being in France, there is no way of checking measurements without buying On a 2 day delivery, so won’t see them until next week. £175 and £145 didn’t seem out of the way, at least they were available, so fingers crossed.

 

[Andy Nash]

Did you try slackening the through bolt on the pulley and adjusting the turnbuckle?
If one of the belts is bar tight and the other is totally slack it seems to me that something is not set right somewhere.
Having said that, your belts do look a bit thin and may be too worn to be any good.

 

[GmB]

Did you try slackening the through bolt on the pulley and adjusting the turnbuckle?
If one of the belts is bar tight and the other is totally slack it seems to me that something is not set right somewhere.
Having said that, your belts do look a bit thin and may be too worn to be any good.

Yes, that adjusts the tension on both belts at the same time though, the thread adjustment on the ram adjusts the belt to the gearbox only, this is to allow for tolerance in the manufacturing of the belts when fitting new ones.
The ram can only fit one way, and goes in and out, the variator is free, see above post, so that leaves the belts as the only remaining unknown. They may well be original, 1978 machine so I can’t complain too much.
As I said, she runs fine as she is, apart for the slow road pace and you don’t touch the ’go faster lever’

 

[Andy Nash]

Yes, that does make sense.
Good luck with the new belts.

 

[Exfarmer]

If you suspect they are original, they will be a D or E section belt, which is given away by the depth which does not ususlly chsngethat much.
.75 , 3/4’s for D or .91 15/16ths for E.
I suspect they are slightly smaller

 

[GmB]

If you suspect they are original, they will be a D or E section belt, which is given away by the depth which does not ususlly chsngethat much.
.75 , 3/4’s for D or .91 15/16ths for E.
I suspect they are slightly smaller

The numbers on the belts that are on the combine correspond with the numbers in the parts book. Interestingly, there is a lot of surface corrosion on parts of the variator surfaces which would accelerate belt wear I’m sure

 

[Exfarmer]

The numbers on the belts that are on the combine correspond with the numbers in the parts book. Interestingly, there is a lot of surface corrosion on parts of the variator surfaces which would accelerate belt wear I’m sure

It is too late as you have ordered new, but I suspect there are cross checking lists. Most of those belts were bog standard, but sadly times have moved on and belt manufacturing has changed

 

[GmB]

It is too late as you have ordered new, but I suspect there are cross checking lists. Most of those belts were bog standard, but sadly times have moved on and belt manufacturing has changed

I tried another source for the belts before I ordered from MF, they couldn’t match the spec.

 

[glasshouse]

I tried another source for the belts before I ordered from MF, they couldn’t match the spec.

Is there a fault in your hydraulic lever in the cab? A stuck plunger?
I had that once with a dominator