Yardman MTD model 13A4662F129 transmission belt keeps coming off when changing from forward to reverse.Changed belt and it was worse.Sometimes it looks like idler pulley may be going out off belt too far,is there an adjustment for this or could it be a weak spring for tension? Any help greatly appreciated. Thanks theboss187

Yes the springs could be bad,but the idlers could be bad as well.
This is the diagram make sure you have it on right

Thanks DG,will get new spring and will let you know the results.It may take a bit of time though due to a health mishap that just happened.

So what was the verdict? I have the same issue

Hi,
My experience with these models is that the front transmission stay bolts have come out. The pictures have one as item #3, 710-0599 1/4"-20 x 1/2" ans two used. Arrows indicate where they go to in the housing. If stripped, there used to be a hole in the bottom of the crossbrace and in the boss forward and below the screws that took a 1/4"-28 x 1 3/4" fine thread bolt, washer, lock washer and nut(suggest a nylock)
Peace,
Clarke
PS Inspect frame at the axles for cracking.

So you are saying that replacing the springs may not be necessary? I assumed it was either a spring that is going bad allowing too much whip with the transmission belt. It started happening in the fall when I go into reverse and release the clutch the belt flies off. I replaced the back transmission belt and it still does it whenever I use reverse. I have been mowing without reverse which is a real pain! Yesterday I adjusted the speed (as covered in the manual) with the bent bar that goes to the clutch petal- basically threading it in all the way, with the cotter pin out, which lengthened the throw of the clutch petal. When I go into a speed more than 4 there is no more tension there is at 4 so I figured maybe the speed needed tweaking.
Still didn't fix it, the idler pully seems to not create enough pressure to keep the belt from shooting off the main pully. That is why I assume it must be a spring because there is nothing else I can adjust according to the manual.

I even left the cover off yesterday where the F/N/R gear shifter is below the steering wheel. I had in neutral and it was wobbling a little bit as I went all the way up to 7 speed. However, as soon as I put in reverse, dropped the speed to 2 and gradually released the clutch, the belt was vibrating violently until it slipped right off. I have to take out the battery and put the belt back on each time that happens. Occasionally it will slip off just going from neutral to forward.

Thanks so much for your help. The manual is virtually useless.

Almost forgot to say- if it matters mine is model 675
model_num=13bm675g009
serial_num=1a111b40332

Hi histreet,
Yours is a newer model. To explain your model number; 1 is mower, 3 is rider, B is year, M is something, 6 is 600 lawn tractor frame, 75 is hood, etc. sheet metal, G is 42" deck and 009 is the vendor it was made for. If you want the 770-10116c parts manual, use the link below, enter your model number, I only enter a 1 for serial(you have to enter something) and it will give you a list. Click the appropriate View Manual choice, click I Accept and download. Depending on your browser and version of Reader, you may need to go to File>Save as>pdf to save it, or you could just use the printer symbol to print. Reader will pop up a Print menu with a place to select pages(the whole thing is 41 pages and has a lot of pages that do not apply to your machine.) The pages you want are 1, 12 - 13, 22 - 31, 33 and then come the wiring and muffler listings. You will have to pick your engine - harness and muffler are engine specific. If you are on page 1, choose Current page to print it. Bring up the menu again and choose Pages and type in 12 - 13. Repeat until done. That takes longer but you do not end up with unneeded pages. Note: the picture I used of the transaxle with arrows is from a different parts manual and shows it from the front side not the back side. Those screws are #43 in your manual, same screw.
If these bolts are missing, the transaxle cocks causing a misalignment that can be seen with the cover removed. It is the torque effect.
Manual at:
PDF Manual Web Archive
Peace,
Clarke

Sounds great. I will give a look. So these screws attach the transmission to the frame? Kind of hard to picture it from the cutout. I assume these screws I can get at a hardware store? Is it worth replacing the spring while I am under there just to be sure or do those not go bad very often? Thanks!

43 710-0599 Hex Wash. S-Tap Scr.1/4-20 x .50" Lg. That is the one(s)? I don't see where it shows two of them in there. In your picture above it clearly shows two but maybe that is different version? It also looks like these are self-tapping. You mention maybe needing a washer, nut, etc. so I'm a little confused. Thanks

Hi,
Did not read the description in your version of the manual. It does clearly state that the screw has a built-in washer as part of the head. A good hardware store will probably have them. I know that Hillman and Kimberly Midwest both offer them. Sometimes those bosses where those screws go strip out. If they do you have to resort to that second bolt and hardware. There are still supposed to still be holes in the cross brace and trans housing. Do not hold my to that because I was told they would be there 20 years ago. The man who told me that is the same one responsible for getting all those manuals online.
I have never seen a spring #63 above go bad but have seen the pivot spacer get dirty enough to bind(it looks like a washer above the idler arm, but has a shoulder on the bottom side. Part #75 is the cross brace that bolts to the inside of both sides of the frame.
Peace,
Clarke

Check the idler arm on the tension pulley , see if it wobbles when the belt is off . If so could be arm is wore out or bushing in arm .
Luck

Crigby you are a GENIUS! You were EXACTLY right. I put it on ramps and felt under there and there were two empty holes. Not a bolt securing it to the frame anymore. I went to the tractor store and they had never heard of that issue. They would have started by replacing the springs and maybe pulleys. So they had a bolt that size but not with a washer or anything special, just a hex nut. I wasn't sure if I only put one in, since the diagram shows only one. I only got it to fit in the right hole (if you were looking at the frame it screws into). I'm not sure if I should've put loctite or something so it doesn't come out again.

So I fired it up and put it in reverse and the belt stayed on! However, it wasn't catching right away. I tried forward and it won't move until I get up into the higher speed like 5-6. So at 1, 2 it won't move in either direction, it just spins. Doesn't look like the front belt is spinning and it may be slipping when it does, but it is hard to tell. I still have the top gear-shift cover off so I can see the belt action.

So now I am stuck wondering why it is still not working. I have a new front drive belt so I started getting that one off to change it. Took the deck off, and the rear belt off again, and now I can't seem to get the center nut and lock washer off to drop the front pulley. The thing spins while you turn it. Of course there is no instructions or tips on this process. The wonderful manual says- take off the nut and lock washer and drop the pulley down to slip the belt off. How in the world do you get that off?

So assuming this belt change doesn't do the trick, what do I do next? I wondered if by adjusting the speed bar, if I messed it up somehow and may need to set that back down lower?

I am done for tonight and will continue tomorrow. Oh, I also got the plug out since that hasn't been changed in the 5 years I've owned it. Very dirty but I THINK is is a RC12YC, need to confirm. Finally, I noticed that the engine was really loose (like I could spin the bolts by hand) so I tightened the bolts from below that hold it on. I don't see a nut on top of those bolts, so I'm not sure if there was intended to be nuts on top or if they just thread up in and stick out. I don't know why they make these things so all the bolts rattle loose.

Thanks again for all your help!

Hi,
Suggest that you attempt to get both in(it took five years for both to come out, how long for one?) This has been a known happenstance for over 20 years. I have on a couple of occasions seen the crossbrace break at one or both ends, but it is rare. I have never replaced the idler spring, and the idler only a couple of times. The variable speed pulley used to give problems whaen it used needle bearings with the lower one being the one that failed. Oil-impregnated silicon bronze bushings replaced them and that problem diminished.
Yes you will need to go back off the adjustment of the travel rod. There is a copy of a service manual available at: (it is 128 MB)
"K&T Parts House Lawn Mower Parts and Chain Saw & Trimmer Parts"
And pick the one marked 2000... for the one you want. You may wish to check out page 72 Figure 3 to see those screws. No place is on those machines for that other boly I spoke of..
You may have to use a wrench up top and a ratchet beneath to loose; that should be all you have to do with it is loosen.
You will need to adjust the travel as on page 17 of the owners manual.
The RC-12YC is the correct plug for an OHV engine set at 0.030" (it will come at about 1 1.2 that.)
Peace,
Clarke

I have two MTD mowers doing the same thing, mine did it so I bought another one, two weeks later it started the same thing. I also bought another transmission and put it in, same thing. I'm ready to give up but both mowers cut and run like new except for the belt flips off.