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Discussion Starter · #1 ·
Rubbing under my butt
Over 12 months ago I posted a query to my problem.
When the machine is more than half full and the cab is on the downhill side a bad scrapping or rubbing sound comes.
I finally got it to do it with the machine pulled up and got out to find the noise.
Found one of the Hydrostatic drive belts jumping and bouncing.
I am yet to look into it but believe that either the belts were not replaced in pairs or the bearings in the countershaft sheave are sick or maybe the sheave is out of line as it is adjustable.
The bit that worries me is it only does it when its half or more full and leaning to that side and it doesn't have to be traveling , which I hope is not a sign of body flex putting things out of whack.
has anyone else experienced a similar situation ??
 

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Not sure if I can help you with the noise, but if there is chassis flex check the frame uprights behind the cylinder drives. There is an idler there that was notorious for breaking the frame upright... I had to rebuild it with heavier angle irons on our 7721.
 

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Discussion Starter · #3 ·
Not sure if I can help you with the noise, but if there is chassis flex check the frame uprights behind the cylinder drives. There is an idler there that was notorious for breaking the frame upright... I had to rebuild it with heavier angle irons on our 7721.
Thanks will investigate that this morning.:)
 

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I also had the splines go out of the countershaft on the cylinder drive side. It seems to me that I built a puller to get it apart. When it got bad it let the top variable speed pulley wobble enough to start breaking the little hydraulic lines.
 

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Discussion Starter · #6 ·
searched for cracks on both sides. found nothing ,one upright support had been rewelded to the chassis rail but looked to be true. found the idler for the feeder house drive belt to be welded back on but seemed straight also.
had the cylinder drive all off last winter when I sped the beater up and didn't see any signs of cracks.
the hydrostatic belt jumps about when the threshing gear is disengaged or engaged. which tells me its diffidently in the drive line. But I don't understand why it only does it with weight in the tank and sloping to the left.
I know the previous owner replaced the engine but the mounts appear to be done up and straight.

the bearings in the propulsion drive sheave seem good but I did tighten the shaft nut up to reduce play in the taper bearings.

the two top belts are diffidently a pair and are probably original as they both have the same green overspray on them, but one does seem to be stretched a bit more than the other. so I now believe this to be my cause . Does anyone think the difference in the belts would cause my noise ?? and why only when loaded ?
 

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Discussion Starter · #7 ·
Check for a broken 'star' in the cylinder
I will do, but the noise is there when the cylinder is disengaged .
The belt that is jumping in time to the thumping sound is on the propulsion drive . from the engine down to the hydrostatic drive on the gearbox.
 

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Discussion Starter · #9 ·
Check the engine power-shaft bearing(nobody ever greases that bad boy)..check and make sure the ground drive belt pully is tight on the engine power-shaft...
I know tha rascal you speak of and there is a knocking when rocked back and forth. do you think that matches my expert description .lol.:D
 

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The engine power-shaft splines into a coupler bolted to the engine crankshaft with same bolts that hold the flywheel on. Yes..it can 'tonk' back and forth a bit and be normal.

Might also check all the belt-guides under the seat cover. These can get bent and rub when the engine is running.

So when does it make these noises...just when the engine(and ground drive belts) is running?...Or the separator running..or separator and feederhouse running?
 

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Might sound like a dumb question, but have you checked your oil levels in the final drives lately? Maybe jack the wheels up and check for play at the wheels as well. Although...you did say it keeps making the noise even when you aren't moving...
 

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the two top belts are diffidently a pair and are probably original as they both have the same green overspray on them, but one does seem to be stretched a bit more than the other. so I now believe this to be my cause . Does anyone think the difference in the belts would cause my noise ?? and why only when loaded ?
Our 7720 was on its fourth set of ground drive belts at 3,500 hours. Are you sure that your machine hasn't been painted at some stage?

The pulley grooves were quite worn on our machine, they were not worn exactly the same, and so getting the tension right was impossible. One would always be slacker than its pair and would jump around a bit. But never enough to cause any noise or any problem for us.
 

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I replaced a set of drive belts on an 8820 titan ll. The next season after some hours had been put on we started getting that thumping your talking about. We checked everything and the belts looked perfect. The mechanic went back and got another set of belts and the problem disappeared. But that doesn't explain why it does it in just certain conditions. It sounds interesting keep us posted
 

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Don't know if it will help but our old 7720 had a crapping sound like that.
It turned out to be a broken front axle.
I'll have to ask dad where it actually was crapping as I was away when he repaired it.
 

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Discussion Starter · #15 ·
The engine power-shaft splines into a coupler bolted to the engine crankshaft with same bolts that hold the flywheel on. Yes..it can 'tonk' back and forth a bit and be normal.

Might also check all the belt-guides under the seat cover. These can get bent and rub when the engine is running.

So when does it make these noises...just when the engine(and ground drive belts) is running?...Or the separator running..or separator and feederhouse running?
With just the engine running. can be moving or pulled up. Has to be more than half full of grain and the cab on the downhill slope.
 

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Discussion Starter · #17 ·
I replaced a set of drive belts on an 8820 titan ll. The next season after some hours had been put on we started getting that thumping your talking about. We checked everything and the belts looked perfect. The mechanic went back and got another set of belts and the problem disappeared. But that doesn't explain why it does it in just certain conditions. It sounds interesting keep us posted
its interesting all right. sounds like it could be a big gear rubbing on a cast housing. makes me clench me butt cheeks.
Pulled the final drive off last year found no marks and replaced bearings just to be shore.
The belts jumping in time with the thumping makes me think they are the cause. Only cost a few hundred bucks to find out .lol:D
 

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Discussion Starter · #19 ·
Might sound like a dumb question, but have you checked your oil levels in the final drives lately? Maybe jack the wheels up and check for play at the wheels as well. Although...you did say it keeps making the noise even when you aren't moving...
Yep thought I was going to cure it last year when I pulled the final drive off and into pieces. Fun job that for no result.
 

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Interesting problem. Our 8820 used to give enough trouble on its drive train as well.

The belts may have both been painted the same green, but are you sure they are a pair? The bottom pair is not the same length as the top.

Perhaps when she is loaded and leaning the longer of the two develops a whip. I had to replace those belts close too every other season so sounds you could be close enough to due for a new set. Have your top and bottom pulleys worn? (Is your belt bottoming in them?) Then any diff in length will cause a whip.

Sheaves and bushes on the electric header clutch also make auwfull noise when they start going.

Hope you find the rascal!
 
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