Mower slows down

[SeniorCitizen]

Well shame on you for mowing wet grass.:laughing:

Bout fall outta my chair laughing every time I read that, just like everyone lives in the hi desert of Nevada. When the over night lo temp might be 78 with a dew point temperature of 77 the grass may only be dry for an hour between 3 and 4 pm. have those folks ever wondered what commercial mowers do?

At least you have gained 1 notch in the solution and we hope that was the fix.

 

[rigoletto]

Sheesh- here I am again, belts slipping/mower slowing down just as it did last year. Now, Mower is clean, and I checked the slackness in the variable speed belt and it is slack when clutch is released (like as in running/mowing), and right mower height lever is on position #1 (the highest mow height, which I usually prefer). It this slack normal? Spring seems OK on the variable speed pulley. Feedback appreciated.

 

[tom3]

Or damp belts that needed to dry out? Best fix there is though.

 

[bertsmobile1]

It seem like only yesterday you had that licked
In drive mode both belts should be tight .
If one is not tight then either the spring has broken or fallen off .

 

[rigoletto]

Good points- there is some fairly decent "spring force", at least when I push the spring loaded pulley back/forth. Now, Bert, when you say "in drive mode", is that as I described (clutch positioned in drive mode, all the way back, and mower deck engaged in one of the mowing height "slots")?

If yes, then I do have either a stretched belt, or something.......

 

[bertsmobile1]

First the easy bit.
Aramid mower belts do not stretch, they get thin on the V sides so go sloppy

Vari-Drive 101
You need to understand how this puppy barks in order to fix it
Below are two images of what you should have

When you change the speed the rod # 6 ( pic 1 ) restricts just how far the brake / clutch pedal can move.
The slot on the bottom of the speed controller # 10 allows you to push down the pedal to stop the mower.
IT matters not weather the speed controller # 10 is in the mudguard, on the floor between your legs or on the dash , they all work exactly the same .
Now on to picture 2
Spring # 66 applies a fixed tension to the top belt # 79 and that works against the tension of the lower belt # 25 .
Which ever belt has the most tension will run on the smaller diameter of the variable drive pulley # 82 by forcing the sliding member away from it.
This changes the ratio of the upper & lower sections of the variable speed pulley # 82

Now here is the tricky bit.
The tension on the lower belt is applied via the spring # 34.
SO ultimately your speed is a tug of war between the two springs # 66 wins & you go slow # 34 wins & you go fast .
Exactly just how much the much spring # 34 can pull is limited by the position of the clutch / brake lever # 44 which in turn as mentioned previously by the position of the speed controller .

Because MTD love to make things complicated the spring # 34 moves the mounting plate # 67 that the variable pulley runs on # 82 via the rod # 71

When the brake is on the rod # 71 pushes the mounting plate # 67 BACKWARDS ( because it is on the end of a lever which reverses the direction ) which pushes the varidrive pulley # 82 forward and that takes tension off the lower belt so it can slip on the engine pulley # 25

In a nutshell if you are going slow then something is preventing the lower belt # 25 getting as tight as it should.
That can be a broken or missing spring, a spring that has worn a deep groove in it's mounting point, a spring that is in the wrong mounting point or any one of the pivot holes worn oval .
Checking all of them should gie you some thing to do while your are isolated for Covid-19 prevention.

Now the one dark horse that is almost unrelated.
Some where that I can not see in either diagram is a bracket that prevents the whole tranny rolling forward which of course changes the tension in both belts because pulleys # 75 & # 21 will get closer together.

Without being there drinking your beer while I look at your mower I can not do much more than to arm you with this knowledge.
I will take payment in dunny paper

 

[rigoletto]

So much good info, Bert, which is almost unavailable anywhere else! I need to study this very closely, while Im at the same time at the mower. I think I should remove the battery while i do this, for better visibility. Rod #71 and the springs might be the key. THANKS SO MUCH FOR THIS! I will get back to you with results!!

And dont drink weak beer.

 

[bertsmobile1]

From an engineering point of view, vari drives are work of beauty , so simple .
From a repairing point of view they are the opposite.
The ones with a tension arm working directly on the lower belt are so much more easy to to work on.
and yes you need to be there looking a it or nothing makes sense.
MTD put out some legacy manuals called "The Must Have manual of Outdoor Power Equipment "
Troll around the web for a copy .
You are looking for book 2 rear engine riders & lawn tractors .
Down side is the book covers about a dozen varaitions on the theme so can get confusing .

 

[rigoletto]

OK, just went out there and gave it only a quick look as the sun is setting, and mosquitoes are biting hard, Maybe I am mentally stuck on the idea that the problem is that the slacky feeling belt #79 when engaged, not #25, Bert. #25 goes back to drive the rear wheels, right? Belt #25 is really tight. Engine transfers force to #25, then that transfers to #79 to powwer the rear wheels, which slow down if belt #25 is too slackish. Maybe lets start with that- Im either on the right track and will continue here, or let me know if you suspect Im on the wrong path.

If #25 is tight, then the power from engine has to be transfered to the back to belt #79, to power the wheels via belt #79(?). This may take some back/forth, Bert. Your patience is appreciated in advance.

 

[bertsmobile1]

Yep,
you are heading in the right direction,
Belt #79 should always be tight .
If not it will slip rather than drive the input pulley
So spring # 66 is the next place to look but wait till sunlight & the mozzies have gone to bed .
Not sure on that particular model but you might need to access it via the battery hole.