[Mark / Ohio]

Welcome to the forum ARMYtango!

...I also hear what sounds like metal rubbing. I am thinking maybe the gears are stripped?....

First thought would be a sheared key on one of the wheels where they attach to the axle.

What's your model number?

 

[Mark / Ohio]

The wheel in your picture is the brake disc. The shiny spot is where the pads clamp on to it and rub when you apply the brake. The disc should turn whenever the wheels move. The lever would be what operates the brake pads.

You can find online manuals for hit here:

http://www.mtdproducts.com/webapp/w...rView?storeId=10500&catalogId=20500&langId=-1

You can also look up parts and exploded views here:

Outdoor Power Equipment Parts: Use the Part Finder Tool from MTD

I would venture to guess that if you can pin down the exact location of the metal scraping sound you'll find your problem. Another possibility would be #25 pulley in the diagram below slipping on the drive shaft of the transmission.

 

[Mark / Ohio]

Speed difference from the input to the axle is probably fine. Top pulley will be running only a little less then engine rpm. The intermittent drag could be a clue as to something going on inside or might just be the brake dragging some on the disk.

What it all boils down to is if you can lock both axles from turning and still rotate the top pulley with some effort while in gear, you have a problem inside the case.

 

[Mark / Ohio]

...If, for some reason, I have the axles locked down, and the pulley DOESN'T move, what other things should I look for?...

Then your back to a belt slipping, wheel rim slipping on axle, or drive pulley slipping on engine shaft. At least those are what i can think of off hand.

The culprit will always be the last thing you check.

 

[Mark / Ohio]

I found an exploded view of the transmission:

Parts and Diagrams for MTD 13BP605H755 (2007)

I've never had one like yours apart. But a couple thoughts come to mind, the grease might be dark in places if it is full of very fine powdery like metal shavings. Those spots would be a good place to take a second look for something worn or grinding. If it binds up when tightening the cover (worse then it was originally) that probably means something moved out of position, a bearing, gear, etc. when you opened it up. That can be a real pain to figure out what is causing it when your not experienced with working on similar models and know by heart were everything goes. Also as two gears wear the teeth can round off enough to where they try to push apart from each other instead of meshing. At some point they just start slipping and grinding and worse case loosing teeth. The bearings that hold the gears in alignment can also get sloppy enough with wear to allow the gears to slip and damage teeth.