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People,

MTD mower, 1998, 13 HP tecumseh engine. Mows well, except when mower travels up a slight hill, it slows down until the ground levels off again, after which it picks up velocity again. Engine rpm's do not seem to change. Is it a slipping belt? If so, know which one?

Thanks, people.

Could be the belt but we need a little more information
Like the numbers from the tag under the seat.
When you find them search partstree using the model number .

I would think belts are slipping. Most if not all MTD’s use a variable drive system with 2 drive belts.

Thanks. I will get back to yous asap on this.

Sorry for delay in replying. Model # is 13A4667 F118. Havnt fixed it yet. Belts are not that old. 1 or 2 are less than 1 yr. But if they are slipping are they tightened by the levers/springs system down there?

When traveling up the incline and the ground speed slows, turn the ignition switch to off without touching anything else. Get off the tractor and check the slack in the 2 belts of the variable speed system. The slack should be equal or nearly equal. Report back and tell us which one is loose.

SeniorCitizen said:

When traveling up the incline and the ground speed slows, turn the ignition switch to off without touching anything else. Get off the tractor and check the slack in the 2 belts of the variable speed system. The slack should be equal or nearly equal. Report back and tell us which one is loose.

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That’s good advice, I never thought of that. I learn something new all the time here.

Ok, will try that, Senior. Next mow, will be tomorrow if it doesnt rain.......

Also make certain it isn't just the wheels spinning some from loss of traction on the slope.

I was prepared to do that while mowing, but just before mowing I noticed the deck was packed full of debris. I cleaned it all up. Then started mowing. It moved up those slopes easily. I think we figured it out, people. I never would have thought. But otherwise, that was a good tip to beware of. Thanks, people.

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.

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.

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

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 .

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.......

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

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.

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 .

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.

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.

OK, Bert, Im happy to know you agree with my direction on solving this mystery that I bet no one will hear about on CNN. So, we have a wishy washy loose belt #79, and I just double checked that the variable pulley lever #67, which I believe is the limiting factor as to how far the spring action can affect, meaning that lever is maxed out, no matter how strong the spring #66 is, if the lever "plate bottoms out, that is how far the variable pulley can push belt #79. Right?? The pulley is maxed out, despite how good/worn the spring is. A stronger spring/new spring will still be limited to the distance that plate #67 can travel to place the pulley closer to tighten belt #79.

If you concur with my convoluted logic I think a new belt should be ordered.

Before you do that pull all of the pivot plates off.
If I was a betting man I would bet that the hole in plate # 30 is flogged out oval.
They are supposed to be lubed regularly but no one ever does apart from better techs.
A can of white spay gears does about 1/2 a mower service to give you an idea of how much I use .
A very small amount of ovality can make a massive difference at the pulley and there are 3 so you can add the all together.
In reality they all should have a replacable bush in there.
Most times I build up the holes then recut them round with a Dremmel as getting those parts down here is usually 6 to 8 weeks as they have to come from the USA or Canada via the dealer via the local warehouse .
After than I weld up the anchor points for the springs as the spring has usually just about cut through them .
As litlle as 1/8" either end makes a difference.
I have seen some where the spring anchors on the frame cut a groove near 1" long

Big thanks, Bert. I got some homework for tomorrow!! I will let you know what happens!!

Try to get the mower up really high cause you need a bit of space.
I have truck stands so can get them up about 2' which makes thigs real easy , ok less difficult as you have space to swing spannars

bertsmobile1 said:

Try to get the mower up really high cause you need a bit of space.
I have truck stands so can get them up about 2' which makes thigs real easy , ok less difficult as you have space to swing spannars

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That is the only thing I cant do, Bert. Floor jack is it. So, I did remove battery, looked down there and as you know it is almost impossible to view that area. But I placed my fingers down there (a dangerous thing) and felt around as I moved the clutch pedal down.up, and that plate felt like it is OK, but no way to tel 100%. Heres an idea- I spend $9 or so, get a new belt on and see what happens. Cheap risk. Also, seems like every 2 years I have to buy a new belt here, which seems bad.

Not as good because you are working the full length of the mower you can always sling it up over tree branch , balcony rail etc .
If you have a pair of trucks you can have it straddle the tail gates or sit it on a pair of ramps.
All of these are after you remove the deck of course.
A "techie" test is to get the wheels off the ground set up your phone under the mower, turn the video on the film each of the pivots as you move the drive to se if any of them are flogged out.
While the springs & belts are connected you will not feel the play created from a flogged out hole.