MTD Yard Machines 7 Speed Model 13bn771g729 HELP!

[atw22]

Hi all, 1st time post!
So I was mowing the other day everything working fine when all of a sudden the mower stopped moving like it came out of gear. It was like when you drive your truck and hit the shifter into N, just rolled to a stop. I was not doing anything crazy and was on level ground.
So I replaced the drive belt and same thing, will not go forwards or backwards.
So I took out the battery, jacked up the rear end and put it in gear. I saw the belt tighten but it is not moving the back pulleys. Front pulley spinning fine.
I shut it off, put the brake on and grabbed each rear pulley and they moved a bit back and forth (tranny belt was tight). I then put it in forward and reverse and the wheels locked.
Looked at all the levers and rods and everything seems to be moving the way it should. Not shore what else to check.
My next thought was to tighten the rod that connects to the tension pulley so it pulls the belt tighter but wanted some input on what else it could be.

 

[bertsmobile1]

Three things to check , two on this diagram
1) the, F-N-R shifter part # 2 , the spring # 22 ( might be a little different on yours ) falls off then the far end does not move the plunger on the axel which shifts the collar that engages F, R or neither
There should be polished areas to show you how far in it usually goes.
2) next is the speed controller part # 48
It limits how much tension the front belt can apply and if it falls apart or gets sticks stuck in there can end up preventing the mechanism moving which is the same as putting your foot on the clutch
3) brake clutch pedal not dissengaging , again usually a spring fallen off or a stick jambing it .

Wheels locking is usually because the brake is jambed again, look for a build up of crud around the brake or a stick stuck in the arm .

 

[atw22]

Thanks, #2 is intact and has the spring and does move as it should. I even tested it by shifting, watching the rod in the tranny and making sure the wheels lock when shifted.
The speed control does move freely and appears to operate as well. I can watch in by the pedal move and looks to function ok.
The brake\clutch also works as when it is pressed and de-pressed i can watch the belt and the pulley move back and forth.

Also when i put it in gear and if i leave it the belt will start to smoke in the front. Its almost like something is stuck but all the pulleys do move by hand (stiff) but with not a lot on hand power.
My yard is pretty flat and I have 0 sticks and the grass is always kept short.

 

[bertsmobile1]

Always hard to diagnose from words on the page
So a couple of tests
1) can you push the mower easily on flat ground when the F-N-R lever is in N ?
2) with the back wheels clear of the ground & on axel stands
Start the engine & move the speed lever to any drive position
Do the wheels
1) not move
2) move in opposite direction ?
Dose the belt smoke when you do the above

 

[atw22]

Always hard to diagnose from words on the page
So a couple of tests
1) can you push the mower easily on flat ground when the F-N-R lever is in N ?
2) with the back wheels clear of the ground & on axel stands
Start the engine & move the speed lever to any drive position
Do the wheels
1) not move
2) move in opposite direction ?
Dose the belt smoke when you do the above

#1 Yes very easy as it always has been, #2 the wheels do not move in any gear or reverse (off the ground) and the belt will eventually smoke if I leave it or rev it up.. The belt does have normal tension when the brake/clutch is off and slacks back when in park,

I did about a dozen or more tests before I posted. The only test I have not done which i will do in the morning is pull the tranny pully belt and see if the main drive belt works as it should. My 1st thought was something fell off the mower like a spring but everything appears to function as it should. 2nd thought was something bent but all the pulleys move left to right when I grab them tight. 3 rd was the tranny but i can watch the shifter mover the bar that goes to the tranny and the wheels do engage when in F or R when i turn them by hand, both settings they spin in the opposite directions but that is by hand not under power.

 

[SeniorCitizen]

This variable sheave is notorious for causing problems. As the speed control is moved from lowest to highest speeds ( without touching the clutch ) the center portion of this variable sheave should react by moving up or down to change ratios.

 

[atw22]

Thanks to everyone for input, it turned out to be the Variable Drive pulley bearings. And thanks to the engineers who designed it different parts have to be purchased. So I just said the heck with it and ordered a used one on ebay for under $30 delivered. The bearings are sealed and most of them were so bad they melted.

 

[SeniorCitizen]

You're Welcome
Just glad i could assist. Been there done that for a neighbor. The center variable sheave was stuck so bad I cut a wooden wedge to drive in to move it but also needed the torch to expand it some. Jack's had all the parts including the needle bearings. You was smart to purchase a complete assembly.

Tip - each time you mow or drive to the mail box, run the speed selector through all the 7 speeds at least once without the clutch because the clutch is not needed to change variable ratios / speeds as my neighbor was doing. That variable speed sheave needs to be rotating to operate correctly. The foot clutch needs to be engaged to operate correctly whether in neutral, forward or reverse.

Variable speed systems aren't anything new. The first I was acquainted with was in 1958 on a Gleaner combine. It was hydraulically operated and well ahead of the competition.