# MTD 603 sit-on-mower problem



## IslandLife68 (Jul 1, 2019)

Hi folks,
I wonder if you could help me with an issue I have with my Lawnfite (MTD) 603 sit-on-mower. 
Spring is here and this morning, I was planning to give the lawn it's first cut. The mower started fine, took it for a little run and I had the feeling it wasn't driving as fast as it should, especially downhill! Going back uphill, it gently slowed down and came to a stop (engine was still running as normal). I pressed the brake pedal and when I released it, it gave a little boost to the mower which drove for another 10ft or so and slowly ground to halt again... I managed to get the mower back to the garage where I checked the speed control and brake linkages. Took the mower out again and I thought I'd cracked it! I even hooked the basket and cut a couple of 25 yard strips at normal speed, until it slowed down and stopped moving again. I managed to take it back to the garage by playing with brake pedal, which seemed to keep the mower moving (???). 
Not sure if any of you guys have experienced this before...
In this period of Covid-19, I'd like to be able to sort out the problem myself otherwise not sure what our garden is going to look like in a few weeks...


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## LawnRat (Mar 22, 2019)

Sounds like the drive belt is going or gone, not adjusted correctly, or it's tensioner is stuck in the loose position. You'll probably have to remove the deck and crawl under to even see the belt or belts (many have two).

I don't even want to make a guess at how_ that_ drive belt system is designed, because MTD puts out many different horrible systems every year. I've worked on enough of them to maybe give you some pointers if you are going to replace it yourself. Some are a total PITA. I will never ever ever ever buy another MTD product.


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## IslandLife68 (Jul 1, 2019)

Hi Lawnrat,
Thank you very much for your reply. It is a two belt model right enough but the drive belt is in good nick, as I only changed it last year after it snapped when hitting a cable... After I changed the belt last summer, it worked lovely until October and now, it stubbornly doesn't want to go anywhere! To be more specific, the serial number is 13AC478C611, a 2002, 603 model Lawnflite. There's no problem with the engine, it revs up, stays on idle and does everything you want it to do, however, the variable speed lever is only tight when on PARK but completely loose on settings 1 to 7. I went through all the linkage checks and it's made no difference at all. When I drive the mower without engaging the blade, it doesn't pick up speed as it should, be it on the flat or even downhill and when it's a matter of going uphill, it pathetically slows down and stops. The strange thing is that if I brake and release the brake, the mower gets a wee boost and can cover a few yards before slowing down again. I managed to take it home uphill by very slightly pressing the brake which seems to have helped keeping "something" under tension to keep it going... That might make sense to some of you guys, but I'm baffled... Also, I mentioned earlier that the belt got cut by a cable... The 10 or 15 in. long cable actually snapped from the mower and was attached to the body at the front. I was unable to find what it was attached to and didn't bother with it. I had posted last year regarding that cable but it didn't seem to inspire anybody! :lol: (https://thelawnforum.com/viewtopic.php?p=182573#p182573) It appears that all happened after was that the blade would very slowly spin even when disengaged, which I can live with. 
Lawnrat, you mention the "tensioner" being stuck in the loose position, could you please explain what I must look for on that particular model? 
Thanks again for your help!&#128077;


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## LawnRat (Mar 22, 2019)

IslandLife68 said:


> ....The strange thing is that if I brake and release the brake, the mower gets a wee boost and can cover a few yards before slowing down again. I managed to take it home uphill by very slightly pressing the brake which seems to have helped keeping "something" under tension to keep it going... That might make sense to some of you guys, but I'm baffled...


The brake pedal is also the clutch pedal, pressing it puts slack into the drive belt so it slips when coming to a stop. Playing with it gets the belt to catch for a second, but without enough tension it starts to slip again. That loose spring is probably for the belt tensioner.

Your link says you replaced the_ blade_ belt last year...there are also two _drive_ belts. I can't tell you where that spring goes but I can tell you it* is *important. I see at least three springs in this diagram, you'll have to figure out where it goes.

https://www.motoruf.com/n/partslists.html?id=541231

Also, if that's a 7-speed model, after playing with the drive belts you may have to help it re-adjust itself. To do this, just put it in 7th gear and release the clutch. Until this is done the lower speeds might slip.


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## IslandLife68 (Jul 1, 2019)

Hello LawnRat,
Thanks again for your suggestions. Last night, I suddenly realised that my sister in law bought the same model as mine a couple of months ago... So, because of that stupid virus, I can't take a drive to go and have a look but she sent me photos and I can see now where the cable and spring are supposed to go. Only problem, the part where the cable should be attached isn't there! Not sure how it vanished unless some unscrupulous mechanic removed it and didn't put it back... Anyway the "tensioner" I circled in red is nowhere to be seen so, it'll be an interesting little challenge to put things right. Still can't understand how I managed to cut the grass for the last couple of years, obviously without the tensioner in place! :shock: 
Thank you again for your help.


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## LawnRat (Mar 22, 2019)

That part is the blade brake. It's a safety device that quickly stops the blade when you turn off the PTO. So I take back what I said above...that spring probably isn't that important at all (unless you want the safety device). This has nothing to do with your drive problem.

That mower has two more belts for the drive wheels which is where this current problem lies.


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## IslandLife68 (Jul 1, 2019)

Ah! That confirms that after the cable broke, the only difference I noticed was that the blade kept turning (albeit very slowly, not even cutting grass) when the deck wasn't engaged.
OK, I'll inspect the other belt(s), as I think there's only one more. Thank you for your time and forgive my lack of expertise on the subject...


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## IslandLife68 (Jul 1, 2019)

Right... I've checked the tension on the drive belt (the blade belt is the one I had changed last year), checked springs and pulleys and everything seems to be ok... I managed to cut the grass on gear 3 and the mower managed to crawl and cut at the same time... However, three or four times, it simply refused to go (Forward or Reverse made no difference) and after braking and releasing the brake it eventually would start to go... Not ideal, but I'm safe for about 10 days before the next cut! In the meantime, I've ordered a new drive belt and will fit it when it comes. I'll let you know what happens...


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## LawnRat (Mar 22, 2019)

https://www.motoruf.com/n/partslists.html?id=541231

According to that diagram your mower model should have two drive belts (#55 and 56).

If the drive belts looked good and tight I'd try and "reset" the drive system by playing around with top gear, maybe it somehow got out of whack....



LawnRat said:


> ...if that's a 7-speed model, after playing with the drive belts you may have to help it re-adjust itself. To do this, just put it in 7th gear and release the clutch. Until this is done the lower speeds might slip.


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## Kallgren (Nov 10, 2018)

My Craftsman garden tractor will have belts slip; particularly if the belts get dusty or dirty, like mulching up old leaves. I've changed the seemingly good belts several times which restores performance. Past couple years have been applying belt conditioner which is less expensive and seems to work very well.


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## IslandLife68 (Jul 1, 2019)

Thanks for your input Kallgreen. I've just received my belt in the post this afternoon and I'm going to, hopefully, fit it! I'll tell you folks if it's made a difference.
"Belt conditioner"? I didn't even know it existed! Thanks for the tip!


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